File: | src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp |
Warning: | line 738, column 24 Called C++ object pointer is null |
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1 | //===- DeadStoreElimination.cpp - MemorySSA Backed Dead Store Elimination -===// | ||||
2 | // | ||||
3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. | ||||
4 | // See https://llvm.org/LICENSE.txt for license information. | ||||
5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception | ||||
6 | // | ||||
7 | //===----------------------------------------------------------------------===// | ||||
8 | // | ||||
9 | // The code below implements dead store elimination using MemorySSA. It uses | ||||
10 | // the following general approach: given a MemoryDef, walk upwards to find | ||||
11 | // clobbering MemoryDefs that may be killed by the starting def. Then check | ||||
12 | // that there are no uses that may read the location of the original MemoryDef | ||||
13 | // in between both MemoryDefs. A bit more concretely: | ||||
14 | // | ||||
15 | // For all MemoryDefs StartDef: | ||||
16 | // 1. Get the next dominating clobbering MemoryDef (EarlierAccess) by walking | ||||
17 | // upwards. | ||||
18 | // 2. Check that there are no reads between EarlierAccess and the StartDef by | ||||
19 | // checking all uses starting at EarlierAccess and walking until we see | ||||
20 | // StartDef. | ||||
21 | // 3. For each found CurrentDef, check that: | ||||
22 | // 1. There are no barrier instructions between CurrentDef and StartDef (like | ||||
23 | // throws or stores with ordering constraints). | ||||
24 | // 2. StartDef is executed whenever CurrentDef is executed. | ||||
25 | // 3. StartDef completely overwrites CurrentDef. | ||||
26 | // 4. Erase CurrentDef from the function and MemorySSA. | ||||
27 | // | ||||
28 | //===----------------------------------------------------------------------===// | ||||
29 | |||||
30 | #include "llvm/Transforms/Scalar/DeadStoreElimination.h" | ||||
31 | #include "llvm/ADT/APInt.h" | ||||
32 | #include "llvm/ADT/DenseMap.h" | ||||
33 | #include "llvm/ADT/MapVector.h" | ||||
34 | #include "llvm/ADT/PostOrderIterator.h" | ||||
35 | #include "llvm/ADT/SetVector.h" | ||||
36 | #include "llvm/ADT/SmallPtrSet.h" | ||||
37 | #include "llvm/ADT/SmallVector.h" | ||||
38 | #include "llvm/ADT/Statistic.h" | ||||
39 | #include "llvm/ADT/StringRef.h" | ||||
40 | #include "llvm/Analysis/AliasAnalysis.h" | ||||
41 | #include "llvm/Analysis/CaptureTracking.h" | ||||
42 | #include "llvm/Analysis/GlobalsModRef.h" | ||||
43 | #include "llvm/Analysis/LoopInfo.h" | ||||
44 | #include "llvm/Analysis/MemoryBuiltins.h" | ||||
45 | #include "llvm/Analysis/MemoryLocation.h" | ||||
46 | #include "llvm/Analysis/MemorySSA.h" | ||||
47 | #include "llvm/Analysis/MemorySSAUpdater.h" | ||||
48 | #include "llvm/Analysis/MustExecute.h" | ||||
49 | #include "llvm/Analysis/PostDominators.h" | ||||
50 | #include "llvm/Analysis/TargetLibraryInfo.h" | ||||
51 | #include "llvm/Analysis/ValueTracking.h" | ||||
52 | #include "llvm/IR/Argument.h" | ||||
53 | #include "llvm/IR/BasicBlock.h" | ||||
54 | #include "llvm/IR/Constant.h" | ||||
55 | #include "llvm/IR/Constants.h" | ||||
56 | #include "llvm/IR/DataLayout.h" | ||||
57 | #include "llvm/IR/Dominators.h" | ||||
58 | #include "llvm/IR/Function.h" | ||||
59 | #include "llvm/IR/InstIterator.h" | ||||
60 | #include "llvm/IR/InstrTypes.h" | ||||
61 | #include "llvm/IR/Instruction.h" | ||||
62 | #include "llvm/IR/Instructions.h" | ||||
63 | #include "llvm/IR/IntrinsicInst.h" | ||||
64 | #include "llvm/IR/Intrinsics.h" | ||||
65 | #include "llvm/IR/LLVMContext.h" | ||||
66 | #include "llvm/IR/Module.h" | ||||
67 | #include "llvm/IR/PassManager.h" | ||||
68 | #include "llvm/IR/PatternMatch.h" | ||||
69 | #include "llvm/IR/Value.h" | ||||
70 | #include "llvm/InitializePasses.h" | ||||
71 | #include "llvm/Pass.h" | ||||
72 | #include "llvm/Support/Casting.h" | ||||
73 | #include "llvm/Support/CommandLine.h" | ||||
74 | #include "llvm/Support/Debug.h" | ||||
75 | #include "llvm/Support/DebugCounter.h" | ||||
76 | #include "llvm/Support/ErrorHandling.h" | ||||
77 | #include "llvm/Support/MathExtras.h" | ||||
78 | #include "llvm/Support/raw_ostream.h" | ||||
79 | #include "llvm/Transforms/Scalar.h" | ||||
80 | #include "llvm/Transforms/Utils/AssumeBundleBuilder.h" | ||||
81 | #include "llvm/Transforms/Utils/Local.h" | ||||
82 | #include <algorithm> | ||||
83 | #include <cassert> | ||||
84 | #include <cstddef> | ||||
85 | #include <cstdint> | ||||
86 | #include <iterator> | ||||
87 | #include <map> | ||||
88 | #include <utility> | ||||
89 | |||||
90 | using namespace llvm; | ||||
91 | using namespace PatternMatch; | ||||
92 | |||||
93 | #define DEBUG_TYPE"dse" "dse" | ||||
94 | |||||
95 | STATISTIC(NumRemainingStores, "Number of stores remaining after DSE")static llvm::Statistic NumRemainingStores = {"dse", "NumRemainingStores" , "Number of stores remaining after DSE"}; | ||||
96 | STATISTIC(NumRedundantStores, "Number of redundant stores deleted")static llvm::Statistic NumRedundantStores = {"dse", "NumRedundantStores" , "Number of redundant stores deleted"}; | ||||
97 | STATISTIC(NumFastStores, "Number of stores deleted")static llvm::Statistic NumFastStores = {"dse", "NumFastStores" , "Number of stores deleted"}; | ||||
98 | STATISTIC(NumFastOther, "Number of other instrs removed")static llvm::Statistic NumFastOther = {"dse", "NumFastOther", "Number of other instrs removed"}; | ||||
99 | STATISTIC(NumCompletePartials, "Number of stores dead by later partials")static llvm::Statistic NumCompletePartials = {"dse", "NumCompletePartials" , "Number of stores dead by later partials"}; | ||||
100 | STATISTIC(NumModifiedStores, "Number of stores modified")static llvm::Statistic NumModifiedStores = {"dse", "NumModifiedStores" , "Number of stores modified"}; | ||||
101 | STATISTIC(NumCFGChecks, "Number of stores modified")static llvm::Statistic NumCFGChecks = {"dse", "NumCFGChecks", "Number of stores modified"}; | ||||
102 | STATISTIC(NumCFGTries, "Number of stores modified")static llvm::Statistic NumCFGTries = {"dse", "NumCFGTries", "Number of stores modified" }; | ||||
103 | STATISTIC(NumCFGSuccess, "Number of stores modified")static llvm::Statistic NumCFGSuccess = {"dse", "NumCFGSuccess" , "Number of stores modified"}; | ||||
104 | STATISTIC(NumGetDomMemoryDefPassed,static llvm::Statistic NumGetDomMemoryDefPassed = {"dse", "NumGetDomMemoryDefPassed" , "Number of times a valid candidate is returned from getDomMemoryDef" } | ||||
105 | "Number of times a valid candidate is returned from getDomMemoryDef")static llvm::Statistic NumGetDomMemoryDefPassed = {"dse", "NumGetDomMemoryDefPassed" , "Number of times a valid candidate is returned from getDomMemoryDef" }; | ||||
106 | STATISTIC(NumDomMemDefChecks,static llvm::Statistic NumDomMemDefChecks = {"dse", "NumDomMemDefChecks" , "Number iterations check for reads in getDomMemoryDef"} | ||||
107 | "Number iterations check for reads in getDomMemoryDef")static llvm::Statistic NumDomMemDefChecks = {"dse", "NumDomMemDefChecks" , "Number iterations check for reads in getDomMemoryDef"}; | ||||
108 | |||||
109 | DEBUG_COUNTER(MemorySSACounter, "dse-memoryssa",static const unsigned MemorySSACounter = DebugCounter::registerCounter ("dse-memoryssa", "Controls which MemoryDefs are eliminated." ) | ||||
110 | "Controls which MemoryDefs are eliminated.")static const unsigned MemorySSACounter = DebugCounter::registerCounter ("dse-memoryssa", "Controls which MemoryDefs are eliminated." ); | ||||
111 | |||||
112 | static cl::opt<bool> | ||||
113 | EnablePartialOverwriteTracking("enable-dse-partial-overwrite-tracking", | ||||
114 | cl::init(true), cl::Hidden, | ||||
115 | cl::desc("Enable partial-overwrite tracking in DSE")); | ||||
116 | |||||
117 | static cl::opt<bool> | ||||
118 | EnablePartialStoreMerging("enable-dse-partial-store-merging", | ||||
119 | cl::init(true), cl::Hidden, | ||||
120 | cl::desc("Enable partial store merging in DSE")); | ||||
121 | |||||
122 | static cl::opt<unsigned> | ||||
123 | MemorySSAScanLimit("dse-memoryssa-scanlimit", cl::init(150), cl::Hidden, | ||||
124 | cl::desc("The number of memory instructions to scan for " | ||||
125 | "dead store elimination (default = 100)")); | ||||
126 | static cl::opt<unsigned> MemorySSAUpwardsStepLimit( | ||||
127 | "dse-memoryssa-walklimit", cl::init(90), cl::Hidden, | ||||
128 | cl::desc("The maximum number of steps while walking upwards to find " | ||||
129 | "MemoryDefs that may be killed (default = 90)")); | ||||
130 | |||||
131 | static cl::opt<unsigned> MemorySSAPartialStoreLimit( | ||||
132 | "dse-memoryssa-partial-store-limit", cl::init(5), cl::Hidden, | ||||
133 | cl::desc("The maximum number candidates that only partially overwrite the " | ||||
134 | "killing MemoryDef to consider" | ||||
135 | " (default = 5)")); | ||||
136 | |||||
137 | static cl::opt<unsigned> MemorySSADefsPerBlockLimit( | ||||
138 | "dse-memoryssa-defs-per-block-limit", cl::init(5000), cl::Hidden, | ||||
139 | cl::desc("The number of MemoryDefs we consider as candidates to eliminated " | ||||
140 | "other stores per basic block (default = 5000)")); | ||||
141 | |||||
142 | static cl::opt<unsigned> MemorySSASameBBStepCost( | ||||
143 | "dse-memoryssa-samebb-cost", cl::init(1), cl::Hidden, | ||||
144 | cl::desc( | ||||
145 | "The cost of a step in the same basic block as the killing MemoryDef" | ||||
146 | "(default = 1)")); | ||||
147 | |||||
148 | static cl::opt<unsigned> | ||||
149 | MemorySSAOtherBBStepCost("dse-memoryssa-otherbb-cost", cl::init(5), | ||||
150 | cl::Hidden, | ||||
151 | cl::desc("The cost of a step in a different basic " | ||||
152 | "block than the killing MemoryDef" | ||||
153 | "(default = 5)")); | ||||
154 | |||||
155 | static cl::opt<unsigned> MemorySSAPathCheckLimit( | ||||
156 | "dse-memoryssa-path-check-limit", cl::init(50), cl::Hidden, | ||||
157 | cl::desc("The maximum number of blocks to check when trying to prove that " | ||||
158 | "all paths to an exit go through a killing block (default = 50)")); | ||||
159 | |||||
160 | //===----------------------------------------------------------------------===// | ||||
161 | // Helper functions | ||||
162 | //===----------------------------------------------------------------------===// | ||||
163 | using OverlapIntervalsTy = std::map<int64_t, int64_t>; | ||||
164 | using InstOverlapIntervalsTy = DenseMap<Instruction *, OverlapIntervalsTy>; | ||||
165 | |||||
166 | /// Does this instruction write some memory? This only returns true for things | ||||
167 | /// that we can analyze with other helpers below. | ||||
168 | static bool hasAnalyzableMemoryWrite(Instruction *I, | ||||
169 | const TargetLibraryInfo &TLI) { | ||||
170 | if (isa<StoreInst>(I)) | ||||
171 | return true; | ||||
172 | if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { | ||||
173 | switch (II->getIntrinsicID()) { | ||||
174 | default: | ||||
175 | return false; | ||||
176 | case Intrinsic::memset: | ||||
177 | case Intrinsic::memmove: | ||||
178 | case Intrinsic::memcpy: | ||||
179 | case Intrinsic::memcpy_inline: | ||||
180 | case Intrinsic::memcpy_element_unordered_atomic: | ||||
181 | case Intrinsic::memmove_element_unordered_atomic: | ||||
182 | case Intrinsic::memset_element_unordered_atomic: | ||||
183 | case Intrinsic::init_trampoline: | ||||
184 | case Intrinsic::lifetime_end: | ||||
185 | case Intrinsic::masked_store: | ||||
186 | return true; | ||||
187 | } | ||||
188 | } | ||||
189 | if (auto *CB = dyn_cast<CallBase>(I)) { | ||||
190 | LibFunc LF; | ||||
191 | if (TLI.getLibFunc(*CB, LF) && TLI.has(LF)) { | ||||
192 | switch (LF) { | ||||
193 | case LibFunc_strcpy: | ||||
194 | case LibFunc_strncpy: | ||||
195 | case LibFunc_strcat: | ||||
196 | case LibFunc_strncat: | ||||
197 | return true; | ||||
198 | default: | ||||
199 | return false; | ||||
200 | } | ||||
201 | } | ||||
202 | } | ||||
203 | return false; | ||||
204 | } | ||||
205 | |||||
206 | /// Return a Location stored to by the specified instruction. If isRemovable | ||||
207 | /// returns true, this function and getLocForRead completely describe the memory | ||||
208 | /// operations for this instruction. | ||||
209 | static MemoryLocation getLocForWrite(Instruction *Inst, | ||||
210 | const TargetLibraryInfo &TLI) { | ||||
211 | if (StoreInst *SI
| ||||
212 | return MemoryLocation::get(SI); | ||||
213 | |||||
214 | // memcpy/memmove/memset. | ||||
215 | if (auto *MI
| ||||
216 | return MemoryLocation::getForDest(MI); | ||||
217 | |||||
218 | if (IntrinsicInst *II
| ||||
219 | switch (II->getIntrinsicID()) { | ||||
220 | default: | ||||
221 | return MemoryLocation(); // Unhandled intrinsic. | ||||
222 | case Intrinsic::init_trampoline: | ||||
223 | return MemoryLocation::getAfter(II->getArgOperand(0)); | ||||
224 | case Intrinsic::masked_store: | ||||
225 | return MemoryLocation::getForArgument(II, 1, TLI); | ||||
226 | case Intrinsic::lifetime_end: { | ||||
227 | uint64_t Len = cast<ConstantInt>(II->getArgOperand(0))->getZExtValue(); | ||||
228 | return MemoryLocation(II->getArgOperand(1), Len); | ||||
229 | } | ||||
230 | } | ||||
231 | } | ||||
232 | if (auto *CB
| ||||
233 | // All the supported TLI functions so far happen to have dest as their | ||||
234 | // first argument. | ||||
235 | return MemoryLocation::getAfter(CB->getArgOperand(0)); | ||||
236 | return MemoryLocation(); | ||||
237 | } | ||||
238 | |||||
239 | /// If the value of this instruction and the memory it writes to is unused, may | ||||
240 | /// we delete this instruction? | ||||
241 | static bool isRemovable(Instruction *I) { | ||||
242 | // Don't remove volatile/atomic stores. | ||||
243 | if (StoreInst *SI = dyn_cast<StoreInst>(I)) | ||||
244 | return SI->isUnordered(); | ||||
245 | |||||
246 | if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { | ||||
247 | switch (II->getIntrinsicID()) { | ||||
248 | default: llvm_unreachable("doesn't pass 'hasAnalyzableMemoryWrite' predicate")__builtin_unreachable(); | ||||
249 | case Intrinsic::lifetime_end: | ||||
250 | // Never remove dead lifetime_end's, e.g. because it is followed by a | ||||
251 | // free. | ||||
252 | return false; | ||||
253 | case Intrinsic::init_trampoline: | ||||
254 | // Always safe to remove init_trampoline. | ||||
255 | return true; | ||||
256 | case Intrinsic::memset: | ||||
257 | case Intrinsic::memmove: | ||||
258 | case Intrinsic::memcpy: | ||||
259 | case Intrinsic::memcpy_inline: | ||||
260 | // Don't remove volatile memory intrinsics. | ||||
261 | return !cast<MemIntrinsic>(II)->isVolatile(); | ||||
262 | case Intrinsic::memcpy_element_unordered_atomic: | ||||
263 | case Intrinsic::memmove_element_unordered_atomic: | ||||
264 | case Intrinsic::memset_element_unordered_atomic: | ||||
265 | case Intrinsic::masked_store: | ||||
266 | return true; | ||||
267 | } | ||||
268 | } | ||||
269 | |||||
270 | // note: only get here for calls with analyzable writes - i.e. libcalls | ||||
271 | if (auto *CB = dyn_cast<CallBase>(I)) | ||||
272 | return CB->use_empty(); | ||||
273 | |||||
274 | return false; | ||||
275 | } | ||||
276 | |||||
277 | /// Returns true if the end of this instruction can be safely shortened in | ||||
278 | /// length. | ||||
279 | static bool isShortenableAtTheEnd(Instruction *I) { | ||||
280 | // Don't shorten stores for now | ||||
281 | if (isa<StoreInst>(I)) | ||||
282 | return false; | ||||
283 | |||||
284 | if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { | ||||
285 | switch (II->getIntrinsicID()) { | ||||
286 | default: return false; | ||||
287 | case Intrinsic::memset: | ||||
288 | case Intrinsic::memcpy: | ||||
289 | case Intrinsic::memcpy_element_unordered_atomic: | ||||
290 | case Intrinsic::memset_element_unordered_atomic: | ||||
291 | // Do shorten memory intrinsics. | ||||
292 | // FIXME: Add memmove if it's also safe to transform. | ||||
293 | return true; | ||||
294 | } | ||||
295 | } | ||||
296 | |||||
297 | // Don't shorten libcalls calls for now. | ||||
298 | |||||
299 | return false; | ||||
300 | } | ||||
301 | |||||
302 | /// Returns true if the beginning of this instruction can be safely shortened | ||||
303 | /// in length. | ||||
304 | static bool isShortenableAtTheBeginning(Instruction *I) { | ||||
305 | // FIXME: Handle only memset for now. Supporting memcpy/memmove should be | ||||
306 | // easily done by offsetting the source address. | ||||
307 | return isa<AnyMemSetInst>(I); | ||||
308 | } | ||||
309 | |||||
310 | static uint64_t getPointerSize(const Value *V, const DataLayout &DL, | ||||
311 | const TargetLibraryInfo &TLI, | ||||
312 | const Function *F) { | ||||
313 | uint64_t Size; | ||||
314 | ObjectSizeOpts Opts; | ||||
315 | Opts.NullIsUnknownSize = NullPointerIsDefined(F); | ||||
316 | |||||
317 | if (getObjectSize(V, Size, DL, &TLI, Opts)) | ||||
318 | return Size; | ||||
319 | return MemoryLocation::UnknownSize; | ||||
320 | } | ||||
321 | |||||
322 | namespace { | ||||
323 | |||||
324 | enum OverwriteResult { | ||||
325 | OW_Begin, | ||||
326 | OW_Complete, | ||||
327 | OW_End, | ||||
328 | OW_PartialEarlierWithFullLater, | ||||
329 | OW_MaybePartial, | ||||
330 | OW_Unknown | ||||
331 | }; | ||||
332 | |||||
333 | } // end anonymous namespace | ||||
334 | |||||
335 | /// Check if two instruction are masked stores that completely | ||||
336 | /// overwrite one another. More specifically, \p Later has to | ||||
337 | /// overwrite \p Earlier. | ||||
338 | static OverwriteResult isMaskedStoreOverwrite(const Instruction *Later, | ||||
339 | const Instruction *Earlier, | ||||
340 | BatchAAResults &AA) { | ||||
341 | const auto *IIL = dyn_cast<IntrinsicInst>(Later); | ||||
342 | const auto *IIE = dyn_cast<IntrinsicInst>(Earlier); | ||||
343 | if (IIL == nullptr || IIE == nullptr) | ||||
344 | return OW_Unknown; | ||||
345 | if (IIL->getIntrinsicID() != Intrinsic::masked_store || | ||||
346 | IIE->getIntrinsicID() != Intrinsic::masked_store) | ||||
347 | return OW_Unknown; | ||||
348 | // Pointers. | ||||
349 | Value *LP = IIL->getArgOperand(1)->stripPointerCasts(); | ||||
350 | Value *EP = IIE->getArgOperand(1)->stripPointerCasts(); | ||||
351 | if (LP != EP && !AA.isMustAlias(LP, EP)) | ||||
352 | return OW_Unknown; | ||||
353 | // Masks. | ||||
354 | // TODO: check that Later's mask is a superset of the Earlier's mask. | ||||
355 | if (IIL->getArgOperand(3) != IIE->getArgOperand(3)) | ||||
356 | return OW_Unknown; | ||||
357 | return OW_Complete; | ||||
358 | } | ||||
359 | |||||
360 | /// Return 'OW_Complete' if a store to the 'Later' location completely | ||||
361 | /// overwrites a store to the 'Earlier' location, 'OW_End' if the end of the | ||||
362 | /// 'Earlier' location is completely overwritten by 'Later', 'OW_Begin' if the | ||||
363 | /// beginning of the 'Earlier' location is overwritten by 'Later'. | ||||
364 | /// 'OW_PartialEarlierWithFullLater' means that an earlier (big) store was | ||||
365 | /// overwritten by a latter (smaller) store which doesn't write outside the big | ||||
366 | /// store's memory locations. Returns 'OW_Unknown' if nothing can be determined. | ||||
367 | /// NOTE: This function must only be called if both \p Later and \p Earlier | ||||
368 | /// write to the same underlying object with valid \p EarlierOff and \p | ||||
369 | /// LaterOff. | ||||
370 | static OverwriteResult isPartialOverwrite(const MemoryLocation &Later, | ||||
371 | const MemoryLocation &Earlier, | ||||
372 | int64_t EarlierOff, int64_t LaterOff, | ||||
373 | Instruction *DepWrite, | ||||
374 | InstOverlapIntervalsTy &IOL) { | ||||
375 | const uint64_t LaterSize = Later.Size.getValue(); | ||||
376 | const uint64_t EarlierSize = Earlier.Size.getValue(); | ||||
377 | // We may now overlap, although the overlap is not complete. There might also | ||||
378 | // be other incomplete overlaps, and together, they might cover the complete | ||||
379 | // earlier write. | ||||
380 | // Note: The correctness of this logic depends on the fact that this function | ||||
381 | // is not even called providing DepWrite when there are any intervening reads. | ||||
382 | if (EnablePartialOverwriteTracking && | ||||
383 | LaterOff < int64_t(EarlierOff + EarlierSize) && | ||||
384 | int64_t(LaterOff + LaterSize) >= EarlierOff) { | ||||
385 | |||||
386 | // Insert our part of the overlap into the map. | ||||
387 | auto &IM = IOL[DepWrite]; | ||||
388 | LLVM_DEBUG(dbgs() << "DSE: Partial overwrite: Earlier [" << EarlierOffdo { } while (false) | ||||
389 | << ", " << int64_t(EarlierOff + EarlierSize)do { } while (false) | ||||
390 | << ") Later [" << LaterOff << ", "do { } while (false) | ||||
391 | << int64_t(LaterOff + LaterSize) << ")\n")do { } while (false); | ||||
392 | |||||
393 | // Make sure that we only insert non-overlapping intervals and combine | ||||
394 | // adjacent intervals. The intervals are stored in the map with the ending | ||||
395 | // offset as the key (in the half-open sense) and the starting offset as | ||||
396 | // the value. | ||||
397 | int64_t LaterIntStart = LaterOff, LaterIntEnd = LaterOff + LaterSize; | ||||
398 | |||||
399 | // Find any intervals ending at, or after, LaterIntStart which start | ||||
400 | // before LaterIntEnd. | ||||
401 | auto ILI = IM.lower_bound(LaterIntStart); | ||||
402 | if (ILI != IM.end() && ILI->second <= LaterIntEnd) { | ||||
403 | // This existing interval is overlapped with the current store somewhere | ||||
404 | // in [LaterIntStart, LaterIntEnd]. Merge them by erasing the existing | ||||
405 | // intervals and adjusting our start and end. | ||||
406 | LaterIntStart = std::min(LaterIntStart, ILI->second); | ||||
407 | LaterIntEnd = std::max(LaterIntEnd, ILI->first); | ||||
408 | ILI = IM.erase(ILI); | ||||
409 | |||||
410 | // Continue erasing and adjusting our end in case other previous | ||||
411 | // intervals are also overlapped with the current store. | ||||
412 | // | ||||
413 | // |--- ealier 1 ---| |--- ealier 2 ---| | ||||
414 | // |------- later---------| | ||||
415 | // | ||||
416 | while (ILI != IM.end() && ILI->second <= LaterIntEnd) { | ||||
417 | assert(ILI->second > LaterIntStart && "Unexpected interval")((void)0); | ||||
418 | LaterIntEnd = std::max(LaterIntEnd, ILI->first); | ||||
419 | ILI = IM.erase(ILI); | ||||
420 | } | ||||
421 | } | ||||
422 | |||||
423 | IM[LaterIntEnd] = LaterIntStart; | ||||
424 | |||||
425 | ILI = IM.begin(); | ||||
426 | if (ILI->second <= EarlierOff && | ||||
427 | ILI->first >= int64_t(EarlierOff + EarlierSize)) { | ||||
428 | LLVM_DEBUG(dbgs() << "DSE: Full overwrite from partials: Earlier ["do { } while (false) | ||||
429 | << EarlierOff << ", "do { } while (false) | ||||
430 | << int64_t(EarlierOff + EarlierSize)do { } while (false) | ||||
431 | << ") Composite Later [" << ILI->second << ", "do { } while (false) | ||||
432 | << ILI->first << ")\n")do { } while (false); | ||||
433 | ++NumCompletePartials; | ||||
434 | return OW_Complete; | ||||
435 | } | ||||
436 | } | ||||
437 | |||||
438 | // Check for an earlier store which writes to all the memory locations that | ||||
439 | // the later store writes to. | ||||
440 | if (EnablePartialStoreMerging && LaterOff >= EarlierOff && | ||||
441 | int64_t(EarlierOff + EarlierSize) > LaterOff && | ||||
442 | uint64_t(LaterOff - EarlierOff) + LaterSize <= EarlierSize) { | ||||
443 | LLVM_DEBUG(dbgs() << "DSE: Partial overwrite an earlier load ["do { } while (false) | ||||
444 | << EarlierOff << ", "do { } while (false) | ||||
445 | << int64_t(EarlierOff + EarlierSize)do { } while (false) | ||||
446 | << ") by a later store [" << LaterOff << ", "do { } while (false) | ||||
447 | << int64_t(LaterOff + LaterSize) << ")\n")do { } while (false); | ||||
448 | // TODO: Maybe come up with a better name? | ||||
449 | return OW_PartialEarlierWithFullLater; | ||||
450 | } | ||||
451 | |||||
452 | // Another interesting case is if the later store overwrites the end of the | ||||
453 | // earlier store. | ||||
454 | // | ||||
455 | // |--earlier--| | ||||
456 | // |-- later --| | ||||
457 | // | ||||
458 | // In this case we may want to trim the size of earlier to avoid generating | ||||
459 | // writes to addresses which will definitely be overwritten later | ||||
460 | if (!EnablePartialOverwriteTracking && | ||||
461 | (LaterOff > EarlierOff && LaterOff < int64_t(EarlierOff + EarlierSize) && | ||||
462 | int64_t(LaterOff + LaterSize) >= int64_t(EarlierOff + EarlierSize))) | ||||
463 | return OW_End; | ||||
464 | |||||
465 | // Finally, we also need to check if the later store overwrites the beginning | ||||
466 | // of the earlier store. | ||||
467 | // | ||||
468 | // |--earlier--| | ||||
469 | // |-- later --| | ||||
470 | // | ||||
471 | // In this case we may want to move the destination address and trim the size | ||||
472 | // of earlier to avoid generating writes to addresses which will definitely | ||||
473 | // be overwritten later. | ||||
474 | if (!EnablePartialOverwriteTracking && | ||||
475 | (LaterOff <= EarlierOff && int64_t(LaterOff + LaterSize) > EarlierOff)) { | ||||
476 | assert(int64_t(LaterOff + LaterSize) < int64_t(EarlierOff + EarlierSize) &&((void)0) | ||||
477 | "Expect to be handled as OW_Complete")((void)0); | ||||
478 | return OW_Begin; | ||||
479 | } | ||||
480 | // Otherwise, they don't completely overlap. | ||||
481 | return OW_Unknown; | ||||
482 | } | ||||
483 | |||||
484 | /// Returns true if the memory which is accessed by the second instruction is not | ||||
485 | /// modified between the first and the second instruction. | ||||
486 | /// Precondition: Second instruction must be dominated by the first | ||||
487 | /// instruction. | ||||
488 | static bool | ||||
489 | memoryIsNotModifiedBetween(Instruction *FirstI, Instruction *SecondI, | ||||
490 | BatchAAResults &AA, const DataLayout &DL, | ||||
491 | DominatorTree *DT) { | ||||
492 | // Do a backwards scan through the CFG from SecondI to FirstI. Look for | ||||
493 | // instructions which can modify the memory location accessed by SecondI. | ||||
494 | // | ||||
495 | // While doing the walk keep track of the address to check. It might be | ||||
496 | // different in different basic blocks due to PHI translation. | ||||
497 | using BlockAddressPair = std::pair<BasicBlock *, PHITransAddr>; | ||||
498 | SmallVector<BlockAddressPair, 16> WorkList; | ||||
499 | // Keep track of the address we visited each block with. Bail out if we | ||||
500 | // visit a block with different addresses. | ||||
501 | DenseMap<BasicBlock *, Value *> Visited; | ||||
502 | |||||
503 | BasicBlock::iterator FirstBBI(FirstI); | ||||
504 | ++FirstBBI; | ||||
505 | BasicBlock::iterator SecondBBI(SecondI); | ||||
506 | BasicBlock *FirstBB = FirstI->getParent(); | ||||
507 | BasicBlock *SecondBB = SecondI->getParent(); | ||||
508 | MemoryLocation MemLoc = MemoryLocation::get(SecondI); | ||||
509 | auto *MemLocPtr = const_cast<Value *>(MemLoc.Ptr); | ||||
510 | |||||
511 | // Start checking the SecondBB. | ||||
512 | WorkList.push_back( | ||||
513 | std::make_pair(SecondBB, PHITransAddr(MemLocPtr, DL, nullptr))); | ||||
514 | bool isFirstBlock = true; | ||||
515 | |||||
516 | // Check all blocks going backward until we reach the FirstBB. | ||||
517 | while (!WorkList.empty()) { | ||||
518 | BlockAddressPair Current = WorkList.pop_back_val(); | ||||
519 | BasicBlock *B = Current.first; | ||||
520 | PHITransAddr &Addr = Current.second; | ||||
521 | Value *Ptr = Addr.getAddr(); | ||||
522 | |||||
523 | // Ignore instructions before FirstI if this is the FirstBB. | ||||
524 | BasicBlock::iterator BI = (B == FirstBB ? FirstBBI : B->begin()); | ||||
525 | |||||
526 | BasicBlock::iterator EI; | ||||
527 | if (isFirstBlock) { | ||||
528 | // Ignore instructions after SecondI if this is the first visit of SecondBB. | ||||
529 | assert(B == SecondBB && "first block is not the store block")((void)0); | ||||
530 | EI = SecondBBI; | ||||
531 | isFirstBlock = false; | ||||
532 | } else { | ||||
533 | // It's not SecondBB or (in case of a loop) the second visit of SecondBB. | ||||
534 | // In this case we also have to look at instructions after SecondI. | ||||
535 | EI = B->end(); | ||||
536 | } | ||||
537 | for (; BI != EI; ++BI) { | ||||
538 | Instruction *I = &*BI; | ||||
539 | if (I->mayWriteToMemory() && I != SecondI) | ||||
540 | if (isModSet(AA.getModRefInfo(I, MemLoc.getWithNewPtr(Ptr)))) | ||||
541 | return false; | ||||
542 | } | ||||
543 | if (B != FirstBB) { | ||||
544 | assert(B != &FirstBB->getParent()->getEntryBlock() &&((void)0) | ||||
545 | "Should not hit the entry block because SI must be dominated by LI")((void)0); | ||||
546 | for (BasicBlock *Pred : predecessors(B)) { | ||||
547 | PHITransAddr PredAddr = Addr; | ||||
548 | if (PredAddr.NeedsPHITranslationFromBlock(B)) { | ||||
549 | if (!PredAddr.IsPotentiallyPHITranslatable()) | ||||
550 | return false; | ||||
551 | if (PredAddr.PHITranslateValue(B, Pred, DT, false)) | ||||
552 | return false; | ||||
553 | } | ||||
554 | Value *TranslatedPtr = PredAddr.getAddr(); | ||||
555 | auto Inserted = Visited.insert(std::make_pair(Pred, TranslatedPtr)); | ||||
556 | if (!Inserted.second) { | ||||
557 | // We already visited this block before. If it was with a different | ||||
558 | // address - bail out! | ||||
559 | if (TranslatedPtr != Inserted.first->second) | ||||
560 | return false; | ||||
561 | // ... otherwise just skip it. | ||||
562 | continue; | ||||
563 | } | ||||
564 | WorkList.push_back(std::make_pair(Pred, PredAddr)); | ||||
565 | } | ||||
566 | } | ||||
567 | } | ||||
568 | return true; | ||||
569 | } | ||||
570 | |||||
571 | static bool tryToShorten(Instruction *EarlierWrite, int64_t &EarlierStart, | ||||
572 | uint64_t &EarlierSize, int64_t LaterStart, | ||||
573 | uint64_t LaterSize, bool IsOverwriteEnd) { | ||||
574 | auto *EarlierIntrinsic = cast<AnyMemIntrinsic>(EarlierWrite); | ||||
575 | Align PrefAlign = EarlierIntrinsic->getDestAlign().valueOrOne(); | ||||
576 | |||||
577 | // We assume that memet/memcpy operates in chunks of the "largest" native | ||||
578 | // type size and aligned on the same value. That means optimal start and size | ||||
579 | // of memset/memcpy should be modulo of preferred alignment of that type. That | ||||
580 | // is it there is no any sense in trying to reduce store size any further | ||||
581 | // since any "extra" stores comes for free anyway. | ||||
582 | // On the other hand, maximum alignment we can achieve is limited by alignment | ||||
583 | // of initial store. | ||||
584 | |||||
585 | // TODO: Limit maximum alignment by preferred (or abi?) alignment of the | ||||
586 | // "largest" native type. | ||||
587 | // Note: What is the proper way to get that value? | ||||
588 | // Should TargetTransformInfo::getRegisterBitWidth be used or anything else? | ||||
589 | // PrefAlign = std::min(DL.getPrefTypeAlign(LargestType), PrefAlign); | ||||
590 | |||||
591 | int64_t ToRemoveStart = 0; | ||||
592 | uint64_t ToRemoveSize = 0; | ||||
593 | // Compute start and size of the region to remove. Make sure 'PrefAlign' is | ||||
594 | // maintained on the remaining store. | ||||
595 | if (IsOverwriteEnd) { | ||||
596 | // Calculate required adjustment for 'LaterStart'in order to keep remaining | ||||
597 | // store size aligned on 'PerfAlign'. | ||||
598 | uint64_t Off = | ||||
599 | offsetToAlignment(uint64_t(LaterStart - EarlierStart), PrefAlign); | ||||
600 | ToRemoveStart = LaterStart + Off; | ||||
601 | if (EarlierSize <= uint64_t(ToRemoveStart - EarlierStart)) | ||||
602 | return false; | ||||
603 | ToRemoveSize = EarlierSize - uint64_t(ToRemoveStart - EarlierStart); | ||||
604 | } else { | ||||
605 | ToRemoveStart = EarlierStart; | ||||
606 | assert(LaterSize >= uint64_t(EarlierStart - LaterStart) &&((void)0) | ||||
607 | "Not overlapping accesses?")((void)0); | ||||
608 | ToRemoveSize = LaterSize - uint64_t(EarlierStart - LaterStart); | ||||
609 | // Calculate required adjustment for 'ToRemoveSize'in order to keep | ||||
610 | // start of the remaining store aligned on 'PerfAlign'. | ||||
611 | uint64_t Off = offsetToAlignment(ToRemoveSize, PrefAlign); | ||||
612 | if (Off != 0) { | ||||
613 | if (ToRemoveSize <= (PrefAlign.value() - Off)) | ||||
614 | return false; | ||||
615 | ToRemoveSize -= PrefAlign.value() - Off; | ||||
616 | } | ||||
617 | assert(isAligned(PrefAlign, ToRemoveSize) &&((void)0) | ||||
618 | "Should preserve selected alignment")((void)0); | ||||
619 | } | ||||
620 | |||||
621 | assert(ToRemoveSize > 0 && "Shouldn't reach here if nothing to remove")((void)0); | ||||
622 | assert(EarlierSize > ToRemoveSize && "Can't remove more than original size")((void)0); | ||||
623 | |||||
624 | uint64_t NewSize = EarlierSize - ToRemoveSize; | ||||
625 | if (auto *AMI = dyn_cast<AtomicMemIntrinsic>(EarlierWrite)) { | ||||
626 | // When shortening an atomic memory intrinsic, the newly shortened | ||||
627 | // length must remain an integer multiple of the element size. | ||||
628 | const uint32_t ElementSize = AMI->getElementSizeInBytes(); | ||||
629 | if (0 != NewSize % ElementSize) | ||||
630 | return false; | ||||
631 | } | ||||
632 | |||||
633 | LLVM_DEBUG(dbgs() << "DSE: Remove Dead Store:\n OW "do { } while (false) | ||||
634 | << (IsOverwriteEnd ? "END" : "BEGIN") << ": "do { } while (false) | ||||
635 | << *EarlierWrite << "\n KILLER [" << ToRemoveStart << ", "do { } while (false) | ||||
636 | << int64_t(ToRemoveStart + ToRemoveSize) << ")\n")do { } while (false); | ||||
637 | |||||
638 | Value *EarlierWriteLength = EarlierIntrinsic->getLength(); | ||||
639 | Value *TrimmedLength = | ||||
640 | ConstantInt::get(EarlierWriteLength->getType(), NewSize); | ||||
641 | EarlierIntrinsic->setLength(TrimmedLength); | ||||
642 | EarlierIntrinsic->setDestAlignment(PrefAlign); | ||||
643 | |||||
644 | if (!IsOverwriteEnd) { | ||||
645 | Value *OrigDest = EarlierIntrinsic->getRawDest(); | ||||
646 | Type *Int8PtrTy = | ||||
647 | Type::getInt8PtrTy(EarlierIntrinsic->getContext(), | ||||
648 | OrigDest->getType()->getPointerAddressSpace()); | ||||
649 | Value *Dest = OrigDest; | ||||
650 | if (OrigDest->getType() != Int8PtrTy) | ||||
651 | Dest = CastInst::CreatePointerCast(OrigDest, Int8PtrTy, "", EarlierWrite); | ||||
652 | Value *Indices[1] = { | ||||
653 | ConstantInt::get(EarlierWriteLength->getType(), ToRemoveSize)}; | ||||
654 | Instruction *NewDestGEP = GetElementPtrInst::CreateInBounds( | ||||
655 | Type::getInt8Ty(EarlierIntrinsic->getContext()), | ||||
656 | Dest, Indices, "", EarlierWrite); | ||||
657 | NewDestGEP->setDebugLoc(EarlierIntrinsic->getDebugLoc()); | ||||
658 | if (NewDestGEP->getType() != OrigDest->getType()) | ||||
659 | NewDestGEP = CastInst::CreatePointerCast(NewDestGEP, OrigDest->getType(), | ||||
660 | "", EarlierWrite); | ||||
661 | EarlierIntrinsic->setDest(NewDestGEP); | ||||
662 | } | ||||
663 | |||||
664 | // Finally update start and size of earlier access. | ||||
665 | if (!IsOverwriteEnd) | ||||
666 | EarlierStart += ToRemoveSize; | ||||
667 | EarlierSize = NewSize; | ||||
668 | |||||
669 | return true; | ||||
670 | } | ||||
671 | |||||
672 | static bool tryToShortenEnd(Instruction *EarlierWrite, | ||||
673 | OverlapIntervalsTy &IntervalMap, | ||||
674 | int64_t &EarlierStart, uint64_t &EarlierSize) { | ||||
675 | if (IntervalMap.empty() || !isShortenableAtTheEnd(EarlierWrite)) | ||||
676 | return false; | ||||
677 | |||||
678 | OverlapIntervalsTy::iterator OII = --IntervalMap.end(); | ||||
679 | int64_t LaterStart = OII->second; | ||||
680 | uint64_t LaterSize = OII->first - LaterStart; | ||||
681 | |||||
682 | assert(OII->first - LaterStart >= 0 && "Size expected to be positive")((void)0); | ||||
683 | |||||
684 | if (LaterStart > EarlierStart && | ||||
685 | // Note: "LaterStart - EarlierStart" is known to be positive due to | ||||
686 | // preceding check. | ||||
687 | (uint64_t)(LaterStart - EarlierStart) < EarlierSize && | ||||
688 | // Note: "EarlierSize - (uint64_t)(LaterStart - EarlierStart)" is known to | ||||
689 | // be non negative due to preceding checks. | ||||
690 | LaterSize >= EarlierSize - (uint64_t)(LaterStart - EarlierStart)) { | ||||
691 | if (tryToShorten(EarlierWrite, EarlierStart, EarlierSize, LaterStart, | ||||
692 | LaterSize, true)) { | ||||
693 | IntervalMap.erase(OII); | ||||
694 | return true; | ||||
695 | } | ||||
696 | } | ||||
697 | return false; | ||||
698 | } | ||||
699 | |||||
700 | static bool tryToShortenBegin(Instruction *EarlierWrite, | ||||
701 | OverlapIntervalsTy &IntervalMap, | ||||
702 | int64_t &EarlierStart, uint64_t &EarlierSize) { | ||||
703 | if (IntervalMap.empty() || !isShortenableAtTheBeginning(EarlierWrite)) | ||||
704 | return false; | ||||
705 | |||||
706 | OverlapIntervalsTy::iterator OII = IntervalMap.begin(); | ||||
707 | int64_t LaterStart = OII->second; | ||||
708 | uint64_t LaterSize = OII->first - LaterStart; | ||||
709 | |||||
710 | assert(OII->first - LaterStart >= 0 && "Size expected to be positive")((void)0); | ||||
711 | |||||
712 | if (LaterStart <= EarlierStart && | ||||
713 | // Note: "EarlierStart - LaterStart" is known to be non negative due to | ||||
714 | // preceding check. | ||||
715 | LaterSize > (uint64_t)(EarlierStart - LaterStart)) { | ||||
716 | // Note: "LaterSize - (uint64_t)(EarlierStart - LaterStart)" is known to be | ||||
717 | // positive due to preceding checks. | ||||
718 | assert(LaterSize - (uint64_t)(EarlierStart - LaterStart) < EarlierSize &&((void)0) | ||||
719 | "Should have been handled as OW_Complete")((void)0); | ||||
720 | if (tryToShorten(EarlierWrite, EarlierStart, EarlierSize, LaterStart, | ||||
721 | LaterSize, false)) { | ||||
722 | IntervalMap.erase(OII); | ||||
723 | return true; | ||||
724 | } | ||||
725 | } | ||||
726 | return false; | ||||
727 | } | ||||
728 | |||||
729 | static bool removePartiallyOverlappedStores(const DataLayout &DL, | ||||
730 | InstOverlapIntervalsTy &IOL, | ||||
731 | const TargetLibraryInfo &TLI) { | ||||
732 | bool Changed = false; | ||||
733 | for (auto OI : IOL) { | ||||
734 | Instruction *EarlierWrite = OI.first; | ||||
735 | MemoryLocation Loc = getLocForWrite(EarlierWrite, TLI); | ||||
736 | assert(isRemovable(EarlierWrite) && "Expect only removable instruction")((void)0); | ||||
737 | |||||
738 | const Value *Ptr = Loc.Ptr->stripPointerCasts(); | ||||
| |||||
739 | int64_t EarlierStart = 0; | ||||
740 | uint64_t EarlierSize = Loc.Size.getValue(); | ||||
741 | GetPointerBaseWithConstantOffset(Ptr, EarlierStart, DL); | ||||
742 | OverlapIntervalsTy &IntervalMap = OI.second; | ||||
743 | Changed |= | ||||
744 | tryToShortenEnd(EarlierWrite, IntervalMap, EarlierStart, EarlierSize); | ||||
745 | if (IntervalMap.empty()) | ||||
746 | continue; | ||||
747 | Changed |= | ||||
748 | tryToShortenBegin(EarlierWrite, IntervalMap, EarlierStart, EarlierSize); | ||||
749 | } | ||||
750 | return Changed; | ||||
751 | } | ||||
752 | |||||
753 | static Constant *tryToMergePartialOverlappingStores( | ||||
754 | StoreInst *Earlier, StoreInst *Later, int64_t InstWriteOffset, | ||||
755 | int64_t DepWriteOffset, const DataLayout &DL, BatchAAResults &AA, | ||||
756 | DominatorTree *DT) { | ||||
757 | |||||
758 | if (Earlier && isa<ConstantInt>(Earlier->getValueOperand()) && | ||||
759 | DL.typeSizeEqualsStoreSize(Earlier->getValueOperand()->getType()) && | ||||
760 | Later && isa<ConstantInt>(Later->getValueOperand()) && | ||||
761 | DL.typeSizeEqualsStoreSize(Later->getValueOperand()->getType()) && | ||||
762 | memoryIsNotModifiedBetween(Earlier, Later, AA, DL, DT)) { | ||||
763 | // If the store we find is: | ||||
764 | // a) partially overwritten by the store to 'Loc' | ||||
765 | // b) the later store is fully contained in the earlier one and | ||||
766 | // c) they both have a constant value | ||||
767 | // d) none of the two stores need padding | ||||
768 | // Merge the two stores, replacing the earlier store's value with a | ||||
769 | // merge of both values. | ||||
770 | // TODO: Deal with other constant types (vectors, etc), and probably | ||||
771 | // some mem intrinsics (if needed) | ||||
772 | |||||
773 | APInt EarlierValue = | ||||
774 | cast<ConstantInt>(Earlier->getValueOperand())->getValue(); | ||||
775 | APInt LaterValue = cast<ConstantInt>(Later->getValueOperand())->getValue(); | ||||
776 | unsigned LaterBits = LaterValue.getBitWidth(); | ||||
777 | assert(EarlierValue.getBitWidth() > LaterValue.getBitWidth())((void)0); | ||||
778 | LaterValue = LaterValue.zext(EarlierValue.getBitWidth()); | ||||
779 | |||||
780 | // Offset of the smaller store inside the larger store | ||||
781 | unsigned BitOffsetDiff = (InstWriteOffset - DepWriteOffset) * 8; | ||||
782 | unsigned LShiftAmount = DL.isBigEndian() ? EarlierValue.getBitWidth() - | ||||
783 | BitOffsetDiff - LaterBits | ||||
784 | : BitOffsetDiff; | ||||
785 | APInt Mask = APInt::getBitsSet(EarlierValue.getBitWidth(), LShiftAmount, | ||||
786 | LShiftAmount + LaterBits); | ||||
787 | // Clear the bits we'll be replacing, then OR with the smaller | ||||
788 | // store, shifted appropriately. | ||||
789 | APInt Merged = (EarlierValue & ~Mask) | (LaterValue << LShiftAmount); | ||||
790 | LLVM_DEBUG(dbgs() << "DSE: Merge Stores:\n Earlier: " << *Earlierdo { } while (false) | ||||
791 | << "\n Later: " << *Laterdo { } while (false) | ||||
792 | << "\n Merged Value: " << Merged << '\n')do { } while (false); | ||||
793 | return ConstantInt::get(Earlier->getValueOperand()->getType(), Merged); | ||||
794 | } | ||||
795 | return nullptr; | ||||
796 | } | ||||
797 | |||||
798 | namespace { | ||||
799 | // Returns true if \p I is an intrisnic that does not read or write memory. | ||||
800 | bool isNoopIntrinsic(Instruction *I) { | ||||
801 | if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { | ||||
802 | switch (II->getIntrinsicID()) { | ||||
803 | case Intrinsic::lifetime_start: | ||||
804 | case Intrinsic::lifetime_end: | ||||
805 | case Intrinsic::invariant_end: | ||||
806 | case Intrinsic::launder_invariant_group: | ||||
807 | case Intrinsic::assume: | ||||
808 | return true; | ||||
809 | case Intrinsic::dbg_addr: | ||||
810 | case Intrinsic::dbg_declare: | ||||
811 | case Intrinsic::dbg_label: | ||||
812 | case Intrinsic::dbg_value: | ||||
813 | llvm_unreachable("Intrinsic should not be modeled in MemorySSA")__builtin_unreachable(); | ||||
814 | default: | ||||
815 | return false; | ||||
816 | } | ||||
817 | } | ||||
818 | return false; | ||||
819 | } | ||||
820 | |||||
821 | // Check if we can ignore \p D for DSE. | ||||
822 | bool canSkipDef(MemoryDef *D, bool DefVisibleToCaller) { | ||||
823 | Instruction *DI = D->getMemoryInst(); | ||||
824 | // Calls that only access inaccessible memory cannot read or write any memory | ||||
825 | // locations we consider for elimination. | ||||
826 | if (auto *CB = dyn_cast<CallBase>(DI)) | ||||
827 | if (CB->onlyAccessesInaccessibleMemory()) | ||||
828 | return true; | ||||
829 | |||||
830 | // We can eliminate stores to locations not visible to the caller across | ||||
831 | // throwing instructions. | ||||
832 | if (DI->mayThrow() && !DefVisibleToCaller) | ||||
833 | return true; | ||||
834 | |||||
835 | // We can remove the dead stores, irrespective of the fence and its ordering | ||||
836 | // (release/acquire/seq_cst). Fences only constraints the ordering of | ||||
837 | // already visible stores, it does not make a store visible to other | ||||
838 | // threads. So, skipping over a fence does not change a store from being | ||||
839 | // dead. | ||||
840 | if (isa<FenceInst>(DI)) | ||||
841 | return true; | ||||
842 | |||||
843 | // Skip intrinsics that do not really read or modify memory. | ||||
844 | if (isNoopIntrinsic(D->getMemoryInst())) | ||||
845 | return true; | ||||
846 | |||||
847 | return false; | ||||
848 | } | ||||
849 | |||||
850 | struct DSEState { | ||||
851 | Function &F; | ||||
852 | AliasAnalysis &AA; | ||||
853 | |||||
854 | /// The single BatchAA instance that is used to cache AA queries. It will | ||||
855 | /// not be invalidated over the whole run. This is safe, because: | ||||
856 | /// 1. Only memory writes are removed, so the alias cache for memory | ||||
857 | /// locations remains valid. | ||||
858 | /// 2. No new instructions are added (only instructions removed), so cached | ||||
859 | /// information for a deleted value cannot be accessed by a re-used new | ||||
860 | /// value pointer. | ||||
861 | BatchAAResults BatchAA; | ||||
862 | |||||
863 | MemorySSA &MSSA; | ||||
864 | DominatorTree &DT; | ||||
865 | PostDominatorTree &PDT; | ||||
866 | const TargetLibraryInfo &TLI; | ||||
867 | const DataLayout &DL; | ||||
868 | const LoopInfo &LI; | ||||
869 | |||||
870 | // Whether the function contains any irreducible control flow, useful for | ||||
871 | // being accurately able to detect loops. | ||||
872 | bool ContainsIrreducibleLoops; | ||||
873 | |||||
874 | // All MemoryDefs that potentially could kill other MemDefs. | ||||
875 | SmallVector<MemoryDef *, 64> MemDefs; | ||||
876 | // Any that should be skipped as they are already deleted | ||||
877 | SmallPtrSet<MemoryAccess *, 4> SkipStores; | ||||
878 | // Keep track of all of the objects that are invisible to the caller before | ||||
879 | // the function returns. | ||||
880 | // SmallPtrSet<const Value *, 16> InvisibleToCallerBeforeRet; | ||||
881 | DenseMap<const Value *, bool> InvisibleToCallerBeforeRet; | ||||
882 | // Keep track of all of the objects that are invisible to the caller after | ||||
883 | // the function returns. | ||||
884 | DenseMap<const Value *, bool> InvisibleToCallerAfterRet; | ||||
885 | // Keep track of blocks with throwing instructions not modeled in MemorySSA. | ||||
886 | SmallPtrSet<BasicBlock *, 16> ThrowingBlocks; | ||||
887 | // Post-order numbers for each basic block. Used to figure out if memory | ||||
888 | // accesses are executed before another access. | ||||
889 | DenseMap<BasicBlock *, unsigned> PostOrderNumbers; | ||||
890 | |||||
891 | /// Keep track of instructions (partly) overlapping with killing MemoryDefs per | ||||
892 | /// basic block. | ||||
893 | DenseMap<BasicBlock *, InstOverlapIntervalsTy> IOLs; | ||||
894 | |||||
895 | DSEState(Function &F, AliasAnalysis &AA, MemorySSA &MSSA, DominatorTree &DT, | ||||
896 | PostDominatorTree &PDT, const TargetLibraryInfo &TLI, | ||||
897 | const LoopInfo &LI) | ||||
898 | : F(F), AA(AA), BatchAA(AA), MSSA(MSSA), DT(DT), PDT(PDT), TLI(TLI), | ||||
899 | DL(F.getParent()->getDataLayout()), LI(LI) {} | ||||
900 | |||||
901 | static DSEState get(Function &F, AliasAnalysis &AA, MemorySSA &MSSA, | ||||
902 | DominatorTree &DT, PostDominatorTree &PDT, | ||||
903 | const TargetLibraryInfo &TLI, const LoopInfo &LI) { | ||||
904 | DSEState State(F, AA, MSSA, DT, PDT, TLI, LI); | ||||
905 | // Collect blocks with throwing instructions not modeled in MemorySSA and | ||||
906 | // alloc-like objects. | ||||
907 | unsigned PO = 0; | ||||
908 | for (BasicBlock *BB : post_order(&F)) { | ||||
909 | State.PostOrderNumbers[BB] = PO++; | ||||
910 | for (Instruction &I : *BB) { | ||||
911 | MemoryAccess *MA = MSSA.getMemoryAccess(&I); | ||||
912 | if (I.mayThrow() && !MA) | ||||
913 | State.ThrowingBlocks.insert(I.getParent()); | ||||
914 | |||||
915 | auto *MD = dyn_cast_or_null<MemoryDef>(MA); | ||||
916 | if (MD && State.MemDefs.size() < MemorySSADefsPerBlockLimit && | ||||
917 | (State.getLocForWriteEx(&I) || State.isMemTerminatorInst(&I))) | ||||
918 | State.MemDefs.push_back(MD); | ||||
919 | } | ||||
920 | } | ||||
921 | |||||
922 | // Treat byval or inalloca arguments the same as Allocas, stores to them are | ||||
923 | // dead at the end of the function. | ||||
924 | for (Argument &AI : F.args()) | ||||
925 | if (AI.hasPassPointeeByValueCopyAttr()) { | ||||
926 | // For byval, the caller doesn't know the address of the allocation. | ||||
927 | if (AI.hasByValAttr()) | ||||
928 | State.InvisibleToCallerBeforeRet.insert({&AI, true}); | ||||
929 | State.InvisibleToCallerAfterRet.insert({&AI, true}); | ||||
930 | } | ||||
931 | |||||
932 | // Collect whether there is any irreducible control flow in the function. | ||||
933 | State.ContainsIrreducibleLoops = mayContainIrreducibleControl(F, &LI); | ||||
934 | |||||
935 | return State; | ||||
936 | } | ||||
937 | |||||
938 | /// Return 'OW_Complete' if a store to the 'Later' location (by \p LaterI | ||||
939 | /// instruction) completely overwrites a store to the 'Earlier' location. | ||||
940 | /// (by \p EarlierI instruction). | ||||
941 | /// Return OW_MaybePartial if \p Later does not completely overwrite | ||||
942 | /// \p Earlier, but they both write to the same underlying object. In that | ||||
943 | /// case, use isPartialOverwrite to check if \p Later partially overwrites | ||||
944 | /// \p Earlier. Returns 'OW_Unknown' if nothing can be determined. | ||||
945 | OverwriteResult | ||||
946 | isOverwrite(const Instruction *LaterI, const Instruction *EarlierI, | ||||
947 | const MemoryLocation &Later, const MemoryLocation &Earlier, | ||||
948 | int64_t &EarlierOff, int64_t &LaterOff) { | ||||
949 | // AliasAnalysis does not always account for loops. Limit overwrite checks | ||||
950 | // to dependencies for which we can guarantee they are independant of any | ||||
951 | // loops they are in. | ||||
952 | if (!isGuaranteedLoopIndependent(EarlierI, LaterI, Earlier)) | ||||
953 | return OW_Unknown; | ||||
954 | |||||
955 | // FIXME: Vet that this works for size upper-bounds. Seems unlikely that we'll | ||||
956 | // get imprecise values here, though (except for unknown sizes). | ||||
957 | if (!Later.Size.isPrecise() || !Earlier.Size.isPrecise()) { | ||||
958 | // In case no constant size is known, try to an IR values for the number | ||||
959 | // of bytes written and check if they match. | ||||
960 | const auto *LaterMemI = dyn_cast<MemIntrinsic>(LaterI); | ||||
961 | const auto *EarlierMemI = dyn_cast<MemIntrinsic>(EarlierI); | ||||
962 | if (LaterMemI && EarlierMemI) { | ||||
963 | const Value *LaterV = LaterMemI->getLength(); | ||||
964 | const Value *EarlierV = EarlierMemI->getLength(); | ||||
965 | if (LaterV == EarlierV && BatchAA.isMustAlias(Earlier, Later)) | ||||
966 | return OW_Complete; | ||||
967 | } | ||||
968 | |||||
969 | // Masked stores have imprecise locations, but we can reason about them | ||||
970 | // to some extent. | ||||
971 | return isMaskedStoreOverwrite(LaterI, EarlierI, BatchAA); | ||||
972 | } | ||||
973 | |||||
974 | const uint64_t LaterSize = Later.Size.getValue(); | ||||
975 | const uint64_t EarlierSize = Earlier.Size.getValue(); | ||||
976 | |||||
977 | // Query the alias information | ||||
978 | AliasResult AAR = BatchAA.alias(Later, Earlier); | ||||
979 | |||||
980 | // If the start pointers are the same, we just have to compare sizes to see if | ||||
981 | // the later store was larger than the earlier store. | ||||
982 | if (AAR == AliasResult::MustAlias) { | ||||
983 | // Make sure that the Later size is >= the Earlier size. | ||||
984 | if (LaterSize >= EarlierSize) | ||||
985 | return OW_Complete; | ||||
986 | } | ||||
987 | |||||
988 | // If we hit a partial alias we may have a full overwrite | ||||
989 | if (AAR == AliasResult::PartialAlias && AAR.hasOffset()) { | ||||
990 | int32_t Off = AAR.getOffset(); | ||||
991 | if (Off >= 0 && (uint64_t)Off + EarlierSize <= LaterSize) | ||||
992 | return OW_Complete; | ||||
993 | } | ||||
994 | |||||
995 | // Check to see if the later store is to the entire object (either a global, | ||||
996 | // an alloca, or a byval/inalloca argument). If so, then it clearly | ||||
997 | // overwrites any other store to the same object. | ||||
998 | const Value *P1 = Earlier.Ptr->stripPointerCasts(); | ||||
999 | const Value *P2 = Later.Ptr->stripPointerCasts(); | ||||
1000 | const Value *UO1 = getUnderlyingObject(P1), *UO2 = getUnderlyingObject(P2); | ||||
1001 | |||||
1002 | // If we can't resolve the same pointers to the same object, then we can't | ||||
1003 | // analyze them at all. | ||||
1004 | if (UO1 != UO2) | ||||
1005 | return OW_Unknown; | ||||
1006 | |||||
1007 | // If the "Later" store is to a recognizable object, get its size. | ||||
1008 | uint64_t ObjectSize = getPointerSize(UO2, DL, TLI, &F); | ||||
1009 | if (ObjectSize != MemoryLocation::UnknownSize) | ||||
1010 | if (ObjectSize == LaterSize && ObjectSize >= EarlierSize) | ||||
1011 | return OW_Complete; | ||||
1012 | |||||
1013 | // Okay, we have stores to two completely different pointers. Try to | ||||
1014 | // decompose the pointer into a "base + constant_offset" form. If the base | ||||
1015 | // pointers are equal, then we can reason about the two stores. | ||||
1016 | EarlierOff = 0; | ||||
1017 | LaterOff = 0; | ||||
1018 | const Value *BP1 = GetPointerBaseWithConstantOffset(P1, EarlierOff, DL); | ||||
1019 | const Value *BP2 = GetPointerBaseWithConstantOffset(P2, LaterOff, DL); | ||||
1020 | |||||
1021 | // If the base pointers still differ, we have two completely different stores. | ||||
1022 | if (BP1 != BP2) | ||||
1023 | return OW_Unknown; | ||||
1024 | |||||
1025 | // The later access completely overlaps the earlier store if and only if | ||||
1026 | // both start and end of the earlier one is "inside" the later one: | ||||
1027 | // |<->|--earlier--|<->| | ||||
1028 | // |-------later-------| | ||||
1029 | // Accesses may overlap if and only if start of one of them is "inside" | ||||
1030 | // another one: | ||||
1031 | // |<->|--earlier--|<----->| | ||||
1032 | // |-------later-------| | ||||
1033 | // OR | ||||
1034 | // |----- earlier -----| | ||||
1035 | // |<->|---later---|<----->| | ||||
1036 | // | ||||
1037 | // We have to be careful here as *Off is signed while *.Size is unsigned. | ||||
1038 | |||||
1039 | // Check if the earlier access starts "not before" the later one. | ||||
1040 | if (EarlierOff >= LaterOff) { | ||||
1041 | // If the earlier access ends "not after" the later access then the earlier | ||||
1042 | // one is completely overwritten by the later one. | ||||
1043 | if (uint64_t(EarlierOff - LaterOff) + EarlierSize <= LaterSize) | ||||
1044 | return OW_Complete; | ||||
1045 | // If start of the earlier access is "before" end of the later access then | ||||
1046 | // accesses overlap. | ||||
1047 | else if ((uint64_t)(EarlierOff - LaterOff) < LaterSize) | ||||
1048 | return OW_MaybePartial; | ||||
1049 | } | ||||
1050 | // If start of the later access is "before" end of the earlier access then | ||||
1051 | // accesses overlap. | ||||
1052 | else if ((uint64_t)(LaterOff - EarlierOff) < EarlierSize) { | ||||
1053 | return OW_MaybePartial; | ||||
1054 | } | ||||
1055 | |||||
1056 | // Can reach here only if accesses are known not to overlap. There is no | ||||
1057 | // dedicated code to indicate no overlap so signal "unknown". | ||||
1058 | return OW_Unknown; | ||||
1059 | } | ||||
1060 | |||||
1061 | bool isInvisibleToCallerAfterRet(const Value *V) { | ||||
1062 | if (isa<AllocaInst>(V)) | ||||
1063 | return true; | ||||
1064 | auto I = InvisibleToCallerAfterRet.insert({V, false}); | ||||
1065 | if (I.second) { | ||||
1066 | if (!isInvisibleToCallerBeforeRet(V)) { | ||||
1067 | I.first->second = false; | ||||
1068 | } else { | ||||
1069 | auto *Inst = dyn_cast<Instruction>(V); | ||||
1070 | if (Inst && isAllocLikeFn(Inst, &TLI)) | ||||
1071 | I.first->second = !PointerMayBeCaptured(V, true, false); | ||||
1072 | } | ||||
1073 | } | ||||
1074 | return I.first->second; | ||||
1075 | } | ||||
1076 | |||||
1077 | bool isInvisibleToCallerBeforeRet(const Value *V) { | ||||
1078 | if (isa<AllocaInst>(V)) | ||||
1079 | return true; | ||||
1080 | auto I = InvisibleToCallerBeforeRet.insert({V, false}); | ||||
1081 | if (I.second) { | ||||
1082 | auto *Inst = dyn_cast<Instruction>(V); | ||||
1083 | if (Inst && isAllocLikeFn(Inst, &TLI)) | ||||
1084 | // NOTE: This could be made more precise by PointerMayBeCapturedBefore | ||||
1085 | // with the killing MemoryDef. But we refrain from doing so for now to | ||||
1086 | // limit compile-time and this does not cause any changes to the number | ||||
1087 | // of stores removed on a large test set in practice. | ||||
1088 | I.first->second = !PointerMayBeCaptured(V, false, true); | ||||
1089 | } | ||||
1090 | return I.first->second; | ||||
1091 | } | ||||
1092 | |||||
1093 | Optional<MemoryLocation> getLocForWriteEx(Instruction *I) const { | ||||
1094 | if (!I->mayWriteToMemory()) | ||||
1095 | return None; | ||||
1096 | |||||
1097 | if (auto *MTI = dyn_cast<AnyMemIntrinsic>(I)) | ||||
1098 | return {MemoryLocation::getForDest(MTI)}; | ||||
1099 | |||||
1100 | if (auto *CB = dyn_cast<CallBase>(I)) { | ||||
1101 | // If the functions may write to memory we do not know about, bail out. | ||||
1102 | if (!CB->onlyAccessesArgMemory() && | ||||
1103 | !CB->onlyAccessesInaccessibleMemOrArgMem()) | ||||
1104 | return None; | ||||
1105 | |||||
1106 | LibFunc LF; | ||||
1107 | if (TLI.getLibFunc(*CB, LF) && TLI.has(LF)) { | ||||
1108 | switch (LF) { | ||||
1109 | case LibFunc_strcpy: | ||||
1110 | case LibFunc_strncpy: | ||||
1111 | case LibFunc_strcat: | ||||
1112 | case LibFunc_strncat: | ||||
1113 | return {MemoryLocation::getAfter(CB->getArgOperand(0))}; | ||||
1114 | default: | ||||
1115 | break; | ||||
1116 | } | ||||
1117 | } | ||||
1118 | switch (CB->getIntrinsicID()) { | ||||
1119 | case Intrinsic::init_trampoline: | ||||
1120 | return {MemoryLocation::getAfter(CB->getArgOperand(0))}; | ||||
1121 | case Intrinsic::masked_store: | ||||
1122 | return {MemoryLocation::getForArgument(CB, 1, TLI)}; | ||||
1123 | default: | ||||
1124 | break; | ||||
1125 | } | ||||
1126 | return None; | ||||
1127 | } | ||||
1128 | |||||
1129 | return MemoryLocation::getOrNone(I); | ||||
1130 | } | ||||
1131 | |||||
1132 | /// Returns true if \p UseInst completely overwrites \p DefLoc | ||||
1133 | /// (stored by \p DefInst). | ||||
1134 | bool isCompleteOverwrite(const MemoryLocation &DefLoc, Instruction *DefInst, | ||||
1135 | Instruction *UseInst) { | ||||
1136 | // UseInst has a MemoryDef associated in MemorySSA. It's possible for a | ||||
1137 | // MemoryDef to not write to memory, e.g. a volatile load is modeled as a | ||||
1138 | // MemoryDef. | ||||
1139 | if (!UseInst->mayWriteToMemory()) | ||||
1140 | return false; | ||||
1141 | |||||
1142 | if (auto *CB = dyn_cast<CallBase>(UseInst)) | ||||
1143 | if (CB->onlyAccessesInaccessibleMemory()) | ||||
1144 | return false; | ||||
1145 | |||||
1146 | int64_t InstWriteOffset, DepWriteOffset; | ||||
1147 | if (auto CC = getLocForWriteEx(UseInst)) | ||||
1148 | return isOverwrite(UseInst, DefInst, *CC, DefLoc, DepWriteOffset, | ||||
1149 | InstWriteOffset) == OW_Complete; | ||||
1150 | return false; | ||||
1151 | } | ||||
1152 | |||||
1153 | /// Returns true if \p Def is not read before returning from the function. | ||||
1154 | bool isWriteAtEndOfFunction(MemoryDef *Def) { | ||||
1155 | LLVM_DEBUG(dbgs() << " Check if def " << *Def << " ("do { } while (false) | ||||
1156 | << *Def->getMemoryInst()do { } while (false) | ||||
1157 | << ") is at the end the function \n")do { } while (false); | ||||
1158 | |||||
1159 | auto MaybeLoc = getLocForWriteEx(Def->getMemoryInst()); | ||||
1160 | if (!MaybeLoc) { | ||||
1161 | LLVM_DEBUG(dbgs() << " ... could not get location for write.\n")do { } while (false); | ||||
1162 | return false; | ||||
1163 | } | ||||
1164 | |||||
1165 | SmallVector<MemoryAccess *, 4> WorkList; | ||||
1166 | SmallPtrSet<MemoryAccess *, 8> Visited; | ||||
1167 | auto PushMemUses = [&WorkList, &Visited](MemoryAccess *Acc) { | ||||
1168 | if (!Visited.insert(Acc).second) | ||||
1169 | return; | ||||
1170 | for (Use &U : Acc->uses()) | ||||
1171 | WorkList.push_back(cast<MemoryAccess>(U.getUser())); | ||||
1172 | }; | ||||
1173 | PushMemUses(Def); | ||||
1174 | for (unsigned I = 0; I < WorkList.size(); I++) { | ||||
1175 | if (WorkList.size() >= MemorySSAScanLimit) { | ||||
1176 | LLVM_DEBUG(dbgs() << " ... hit exploration limit.\n")do { } while (false); | ||||
1177 | return false; | ||||
1178 | } | ||||
1179 | |||||
1180 | MemoryAccess *UseAccess = WorkList[I]; | ||||
1181 | // Simply adding the users of MemoryPhi to the worklist is not enough, | ||||
1182 | // because we might miss read clobbers in different iterations of a loop, | ||||
1183 | // for example. | ||||
1184 | // TODO: Add support for phi translation to handle the loop case. | ||||
1185 | if (isa<MemoryPhi>(UseAccess)) | ||||
1186 | return false; | ||||
1187 | |||||
1188 | // TODO: Checking for aliasing is expensive. Consider reducing the amount | ||||
1189 | // of times this is called and/or caching it. | ||||
1190 | Instruction *UseInst = cast<MemoryUseOrDef>(UseAccess)->getMemoryInst(); | ||||
1191 | if (isReadClobber(*MaybeLoc, UseInst)) { | ||||
1192 | LLVM_DEBUG(dbgs() << " ... hit read clobber " << *UseInst << ".\n")do { } while (false); | ||||
1193 | return false; | ||||
1194 | } | ||||
1195 | |||||
1196 | if (MemoryDef *UseDef = dyn_cast<MemoryDef>(UseAccess)) | ||||
1197 | PushMemUses(UseDef); | ||||
1198 | } | ||||
1199 | return true; | ||||
1200 | } | ||||
1201 | |||||
1202 | /// If \p I is a memory terminator like llvm.lifetime.end or free, return a | ||||
1203 | /// pair with the MemoryLocation terminated by \p I and a boolean flag | ||||
1204 | /// indicating whether \p I is a free-like call. | ||||
1205 | Optional<std::pair<MemoryLocation, bool>> | ||||
1206 | getLocForTerminator(Instruction *I) const { | ||||
1207 | uint64_t Len; | ||||
1208 | Value *Ptr; | ||||
1209 | if (match(I, m_Intrinsic<Intrinsic::lifetime_end>(m_ConstantInt(Len), | ||||
1210 | m_Value(Ptr)))) | ||||
1211 | return {std::make_pair(MemoryLocation(Ptr, Len), false)}; | ||||
1212 | |||||
1213 | if (auto *CB = dyn_cast<CallBase>(I)) { | ||||
1214 | if (isFreeCall(I, &TLI)) | ||||
1215 | return {std::make_pair(MemoryLocation::getAfter(CB->getArgOperand(0)), | ||||
1216 | true)}; | ||||
1217 | } | ||||
1218 | |||||
1219 | return None; | ||||
1220 | } | ||||
1221 | |||||
1222 | /// Returns true if \p I is a memory terminator instruction like | ||||
1223 | /// llvm.lifetime.end or free. | ||||
1224 | bool isMemTerminatorInst(Instruction *I) const { | ||||
1225 | IntrinsicInst *II = dyn_cast<IntrinsicInst>(I); | ||||
1226 | return (II && II->getIntrinsicID() == Intrinsic::lifetime_end) || | ||||
1227 | isFreeCall(I, &TLI); | ||||
1228 | } | ||||
1229 | |||||
1230 | /// Returns true if \p MaybeTerm is a memory terminator for \p Loc from | ||||
1231 | /// instruction \p AccessI. | ||||
1232 | bool isMemTerminator(const MemoryLocation &Loc, Instruction *AccessI, | ||||
1233 | Instruction *MaybeTerm) { | ||||
1234 | Optional<std::pair<MemoryLocation, bool>> MaybeTermLoc = | ||||
1235 | getLocForTerminator(MaybeTerm); | ||||
1236 | |||||
1237 | if (!MaybeTermLoc) | ||||
1238 | return false; | ||||
1239 | |||||
1240 | // If the terminator is a free-like call, all accesses to the underlying | ||||
1241 | // object can be considered terminated. | ||||
1242 | if (getUnderlyingObject(Loc.Ptr) != | ||||
1243 | getUnderlyingObject(MaybeTermLoc->first.Ptr)) | ||||
1244 | return false; | ||||
1245 | |||||
1246 | auto TermLoc = MaybeTermLoc->first; | ||||
1247 | if (MaybeTermLoc->second) { | ||||
1248 | const Value *LocUO = getUnderlyingObject(Loc.Ptr); | ||||
1249 | return BatchAA.isMustAlias(TermLoc.Ptr, LocUO); | ||||
1250 | } | ||||
1251 | int64_t InstWriteOffset, DepWriteOffset; | ||||
1252 | return isOverwrite(MaybeTerm, AccessI, TermLoc, Loc, DepWriteOffset, | ||||
1253 | InstWriteOffset) == OW_Complete; | ||||
1254 | } | ||||
1255 | |||||
1256 | // Returns true if \p Use may read from \p DefLoc. | ||||
1257 | bool isReadClobber(const MemoryLocation &DefLoc, Instruction *UseInst) { | ||||
1258 | if (isNoopIntrinsic(UseInst)) | ||||
1259 | return false; | ||||
1260 | |||||
1261 | // Monotonic or weaker atomic stores can be re-ordered and do not need to be | ||||
1262 | // treated as read clobber. | ||||
1263 | if (auto SI = dyn_cast<StoreInst>(UseInst)) | ||||
1264 | return isStrongerThan(SI->getOrdering(), AtomicOrdering::Monotonic); | ||||
1265 | |||||
1266 | if (!UseInst->mayReadFromMemory()) | ||||
1267 | return false; | ||||
1268 | |||||
1269 | if (auto *CB = dyn_cast<CallBase>(UseInst)) | ||||
1270 | if (CB->onlyAccessesInaccessibleMemory()) | ||||
1271 | return false; | ||||
1272 | |||||
1273 | // NOTE: For calls, the number of stores removed could be slightly improved | ||||
1274 | // by using AA.callCapturesBefore(UseInst, DefLoc, &DT), but that showed to | ||||
1275 | // be expensive compared to the benefits in practice. For now, avoid more | ||||
1276 | // expensive analysis to limit compile-time. | ||||
1277 | return isRefSet(BatchAA.getModRefInfo(UseInst, DefLoc)); | ||||
1278 | } | ||||
1279 | |||||
1280 | /// Returns true if a dependency between \p Current and \p KillingDef is | ||||
1281 | /// guaranteed to be loop invariant for the loops that they are in. Either | ||||
1282 | /// because they are known to be in the same block, in the same loop level or | ||||
1283 | /// by guaranteeing that \p CurrentLoc only references a single MemoryLocation | ||||
1284 | /// during execution of the containing function. | ||||
1285 | bool isGuaranteedLoopIndependent(const Instruction *Current, | ||||
1286 | const Instruction *KillingDef, | ||||
1287 | const MemoryLocation &CurrentLoc) { | ||||
1288 | // If the dependency is within the same block or loop level (being careful | ||||
1289 | // of irreducible loops), we know that AA will return a valid result for the | ||||
1290 | // memory dependency. (Both at the function level, outside of any loop, | ||||
1291 | // would also be valid but we currently disable that to limit compile time). | ||||
1292 | if (Current->getParent() == KillingDef->getParent()) | ||||
1293 | return true; | ||||
1294 | const Loop *CurrentLI = LI.getLoopFor(Current->getParent()); | ||||
1295 | if (!ContainsIrreducibleLoops && CurrentLI && | ||||
1296 | CurrentLI == LI.getLoopFor(KillingDef->getParent())) | ||||
1297 | return true; | ||||
1298 | // Otherwise check the memory location is invariant to any loops. | ||||
1299 | return isGuaranteedLoopInvariant(CurrentLoc.Ptr); | ||||
1300 | } | ||||
1301 | |||||
1302 | /// Returns true if \p Ptr is guaranteed to be loop invariant for any possible | ||||
1303 | /// loop. In particular, this guarantees that it only references a single | ||||
1304 | /// MemoryLocation during execution of the containing function. | ||||
1305 | bool isGuaranteedLoopInvariant(const Value *Ptr) { | ||||
1306 | auto IsGuaranteedLoopInvariantBase = [this](const Value *Ptr) { | ||||
1307 | Ptr = Ptr->stripPointerCasts(); | ||||
1308 | if (auto *I = dyn_cast<Instruction>(Ptr)) { | ||||
1309 | if (isa<AllocaInst>(Ptr)) | ||||
1310 | return true; | ||||
1311 | |||||
1312 | if (isAllocLikeFn(I, &TLI)) | ||||
1313 | return true; | ||||
1314 | |||||
1315 | return false; | ||||
1316 | } | ||||
1317 | return true; | ||||
1318 | }; | ||||
1319 | |||||
1320 | Ptr = Ptr->stripPointerCasts(); | ||||
1321 | if (auto *I = dyn_cast<Instruction>(Ptr)) { | ||||
1322 | if (I->getParent()->isEntryBlock()) | ||||
1323 | return true; | ||||
1324 | } | ||||
1325 | if (auto *GEP = dyn_cast<GEPOperator>(Ptr)) { | ||||
1326 | return IsGuaranteedLoopInvariantBase(GEP->getPointerOperand()) && | ||||
1327 | GEP->hasAllConstantIndices(); | ||||
1328 | } | ||||
1329 | return IsGuaranteedLoopInvariantBase(Ptr); | ||||
1330 | } | ||||
1331 | |||||
1332 | // Find a MemoryDef writing to \p DefLoc and dominating \p StartAccess, with | ||||
1333 | // no read access between them or on any other path to a function exit block | ||||
1334 | // if \p DefLoc is not accessible after the function returns. If there is no | ||||
1335 | // such MemoryDef, return None. The returned value may not (completely) | ||||
1336 | // overwrite \p DefLoc. Currently we bail out when we encounter an aliasing | ||||
1337 | // MemoryUse (read). | ||||
1338 | Optional<MemoryAccess *> | ||||
1339 | getDomMemoryDef(MemoryDef *KillingDef, MemoryAccess *StartAccess, | ||||
1340 | const MemoryLocation &DefLoc, const Value *DefUO, | ||||
1341 | unsigned &ScanLimit, unsigned &WalkerStepLimit, | ||||
1342 | bool IsMemTerm, unsigned &PartialLimit) { | ||||
1343 | if (ScanLimit == 0 || WalkerStepLimit == 0) { | ||||
1344 | LLVM_DEBUG(dbgs() << "\n ... hit scan limit\n")do { } while (false); | ||||
1345 | return None; | ||||
1346 | } | ||||
1347 | |||||
1348 | MemoryAccess *Current = StartAccess; | ||||
1349 | Instruction *KillingI = KillingDef->getMemoryInst(); | ||||
1350 | LLVM_DEBUG(dbgs() << " trying to get dominating access\n")do { } while (false); | ||||
1351 | |||||
1352 | // Find the next clobbering Mod access for DefLoc, starting at StartAccess. | ||||
1353 | Optional<MemoryLocation> CurrentLoc; | ||||
1354 | for (;; Current = cast<MemoryDef>(Current)->getDefiningAccess()) { | ||||
1355 | LLVM_DEBUG({do { } while (false) | ||||
1356 | dbgs() << " visiting " << *Current;do { } while (false) | ||||
1357 | if (!MSSA.isLiveOnEntryDef(Current) && isa<MemoryUseOrDef>(Current))do { } while (false) | ||||
1358 | dbgs() << " (" << *cast<MemoryUseOrDef>(Current)->getMemoryInst()do { } while (false) | ||||
1359 | << ")";do { } while (false) | ||||
1360 | dbgs() << "\n";do { } while (false) | ||||
1361 | })do { } while (false); | ||||
1362 | |||||
1363 | // Reached TOP. | ||||
1364 | if (MSSA.isLiveOnEntryDef(Current)) { | ||||
1365 | LLVM_DEBUG(dbgs() << " ... found LiveOnEntryDef\n")do { } while (false); | ||||
1366 | return None; | ||||
1367 | } | ||||
1368 | |||||
1369 | // Cost of a step. Accesses in the same block are more likely to be valid | ||||
1370 | // candidates for elimination, hence consider them cheaper. | ||||
1371 | unsigned StepCost = KillingDef->getBlock() == Current->getBlock() | ||||
1372 | ? MemorySSASameBBStepCost | ||||
1373 | : MemorySSAOtherBBStepCost; | ||||
1374 | if (WalkerStepLimit <= StepCost) { | ||||
1375 | LLVM_DEBUG(dbgs() << " ... hit walker step limit\n")do { } while (false); | ||||
1376 | return None; | ||||
1377 | } | ||||
1378 | WalkerStepLimit -= StepCost; | ||||
1379 | |||||
1380 | // Return for MemoryPhis. They cannot be eliminated directly and the | ||||
1381 | // caller is responsible for traversing them. | ||||
1382 | if (isa<MemoryPhi>(Current)) { | ||||
1383 | LLVM_DEBUG(dbgs() << " ... found MemoryPhi\n")do { } while (false); | ||||
1384 | return Current; | ||||
1385 | } | ||||
1386 | |||||
1387 | // Below, check if CurrentDef is a valid candidate to be eliminated by | ||||
1388 | // KillingDef. If it is not, check the next candidate. | ||||
1389 | MemoryDef *CurrentDef = cast<MemoryDef>(Current); | ||||
1390 | Instruction *CurrentI = CurrentDef->getMemoryInst(); | ||||
1391 | |||||
1392 | if (canSkipDef(CurrentDef, !isInvisibleToCallerBeforeRet(DefUO))) | ||||
1393 | continue; | ||||
1394 | |||||
1395 | // Before we try to remove anything, check for any extra throwing | ||||
1396 | // instructions that block us from DSEing | ||||
1397 | if (mayThrowBetween(KillingI, CurrentI, DefUO)) { | ||||
1398 | LLVM_DEBUG(dbgs() << " ... skip, may throw!\n")do { } while (false); | ||||
1399 | return None; | ||||
1400 | } | ||||
1401 | |||||
1402 | // Check for anything that looks like it will be a barrier to further | ||||
1403 | // removal | ||||
1404 | if (isDSEBarrier(DefUO, CurrentI)) { | ||||
1405 | LLVM_DEBUG(dbgs() << " ... skip, barrier\n")do { } while (false); | ||||
1406 | return None; | ||||
1407 | } | ||||
1408 | |||||
1409 | // If Current is known to be on path that reads DefLoc or is a read | ||||
1410 | // clobber, bail out, as the path is not profitable. We skip this check | ||||
1411 | // for intrinsic calls, because the code knows how to handle memcpy | ||||
1412 | // intrinsics. | ||||
1413 | if (!isa<IntrinsicInst>(CurrentI) && isReadClobber(DefLoc, CurrentI)) | ||||
1414 | return None; | ||||
1415 | |||||
1416 | // Quick check if there are direct uses that are read-clobbers. | ||||
1417 | if (any_of(Current->uses(), [this, &DefLoc, StartAccess](Use &U) { | ||||
1418 | if (auto *UseOrDef = dyn_cast<MemoryUseOrDef>(U.getUser())) | ||||
1419 | return !MSSA.dominates(StartAccess, UseOrDef) && | ||||
1420 | isReadClobber(DefLoc, UseOrDef->getMemoryInst()); | ||||
1421 | return false; | ||||
1422 | })) { | ||||
1423 | LLVM_DEBUG(dbgs() << " ... found a read clobber\n")do { } while (false); | ||||
1424 | return None; | ||||
1425 | } | ||||
1426 | |||||
1427 | // If Current cannot be analyzed or is not removable, check the next | ||||
1428 | // candidate. | ||||
1429 | if (!hasAnalyzableMemoryWrite(CurrentI, TLI) || !isRemovable(CurrentI)) | ||||
1430 | continue; | ||||
1431 | |||||
1432 | // If Current does not have an analyzable write location, skip it | ||||
1433 | CurrentLoc = getLocForWriteEx(CurrentI); | ||||
1434 | if (!CurrentLoc) | ||||
1435 | continue; | ||||
1436 | |||||
1437 | // AliasAnalysis does not account for loops. Limit elimination to | ||||
1438 | // candidates for which we can guarantee they always store to the same | ||||
1439 | // memory location and not located in different loops. | ||||
1440 | if (!isGuaranteedLoopIndependent(CurrentI, KillingI, *CurrentLoc)) { | ||||
1441 | LLVM_DEBUG(dbgs() << " ... not guaranteed loop independent\n")do { } while (false); | ||||
1442 | WalkerStepLimit -= 1; | ||||
1443 | continue; | ||||
1444 | } | ||||
1445 | |||||
1446 | if (IsMemTerm) { | ||||
1447 | // If the killing def is a memory terminator (e.g. lifetime.end), check | ||||
1448 | // the next candidate if the current Current does not write the same | ||||
1449 | // underlying object as the terminator. | ||||
1450 | if (!isMemTerminator(*CurrentLoc, CurrentI, KillingI)) | ||||
1451 | continue; | ||||
1452 | } else { | ||||
1453 | int64_t InstWriteOffset, DepWriteOffset; | ||||
1454 | auto OR = isOverwrite(KillingI, CurrentI, DefLoc, *CurrentLoc, | ||||
1455 | DepWriteOffset, InstWriteOffset); | ||||
1456 | // If Current does not write to the same object as KillingDef, check | ||||
1457 | // the next candidate. | ||||
1458 | if (OR == OW_Unknown) | ||||
1459 | continue; | ||||
1460 | else if (OR == OW_MaybePartial) { | ||||
1461 | // If KillingDef only partially overwrites Current, check the next | ||||
1462 | // candidate if the partial step limit is exceeded. This aggressively | ||||
1463 | // limits the number of candidates for partial store elimination, | ||||
1464 | // which are less likely to be removable in the end. | ||||
1465 | if (PartialLimit <= 1) { | ||||
1466 | WalkerStepLimit -= 1; | ||||
1467 | continue; | ||||
1468 | } | ||||
1469 | PartialLimit -= 1; | ||||
1470 | } | ||||
1471 | } | ||||
1472 | break; | ||||
1473 | }; | ||||
1474 | |||||
1475 | // Accesses to objects accessible after the function returns can only be | ||||
1476 | // eliminated if the access is killed along all paths to the exit. Collect | ||||
1477 | // the blocks with killing (=completely overwriting MemoryDefs) and check if | ||||
1478 | // they cover all paths from EarlierAccess to any function exit. | ||||
1479 | SmallPtrSet<Instruction *, 16> KillingDefs; | ||||
1480 | KillingDefs.insert(KillingDef->getMemoryInst()); | ||||
1481 | MemoryAccess *EarlierAccess = Current; | ||||
1482 | Instruction *EarlierMemInst = | ||||
1483 | cast<MemoryDef>(EarlierAccess)->getMemoryInst(); | ||||
1484 | LLVM_DEBUG(dbgs() << " Checking for reads of " << *EarlierAccess << " ("do { } while (false) | ||||
1485 | << *EarlierMemInst << ")\n")do { } while (false); | ||||
1486 | |||||
1487 | SmallSetVector<MemoryAccess *, 32> WorkList; | ||||
1488 | auto PushMemUses = [&WorkList](MemoryAccess *Acc) { | ||||
1489 | for (Use &U : Acc->uses()) | ||||
1490 | WorkList.insert(cast<MemoryAccess>(U.getUser())); | ||||
1491 | }; | ||||
1492 | PushMemUses(EarlierAccess); | ||||
1493 | |||||
1494 | // Optimistically collect all accesses for reads. If we do not find any | ||||
1495 | // read clobbers, add them to the cache. | ||||
1496 | SmallPtrSet<MemoryAccess *, 16> KnownNoReads; | ||||
1497 | if (!EarlierMemInst->mayReadFromMemory()) | ||||
1498 | KnownNoReads.insert(EarlierAccess); | ||||
1499 | // Check if EarlierDef may be read. | ||||
1500 | for (unsigned I = 0; I < WorkList.size(); I++) { | ||||
1501 | MemoryAccess *UseAccess = WorkList[I]; | ||||
1502 | |||||
1503 | LLVM_DEBUG(dbgs() << " " << *UseAccess)do { } while (false); | ||||
1504 | // Bail out if the number of accesses to check exceeds the scan limit. | ||||
1505 | if (ScanLimit < (WorkList.size() - I)) { | ||||
1506 | LLVM_DEBUG(dbgs() << "\n ... hit scan limit\n")do { } while (false); | ||||
1507 | return None; | ||||
1508 | } | ||||
1509 | --ScanLimit; | ||||
1510 | NumDomMemDefChecks++; | ||||
1511 | KnownNoReads.insert(UseAccess); | ||||
1512 | |||||
1513 | if (isa<MemoryPhi>(UseAccess)) { | ||||
1514 | if (any_of(KillingDefs, [this, UseAccess](Instruction *KI) { | ||||
1515 | return DT.properlyDominates(KI->getParent(), | ||||
1516 | UseAccess->getBlock()); | ||||
1517 | })) { | ||||
1518 | LLVM_DEBUG(dbgs() << " ... skipping, dominated by killing block\n")do { } while (false); | ||||
1519 | continue; | ||||
1520 | } | ||||
1521 | LLVM_DEBUG(dbgs() << "\n ... adding PHI uses\n")do { } while (false); | ||||
1522 | PushMemUses(UseAccess); | ||||
1523 | continue; | ||||
1524 | } | ||||
1525 | |||||
1526 | Instruction *UseInst = cast<MemoryUseOrDef>(UseAccess)->getMemoryInst(); | ||||
1527 | LLVM_DEBUG(dbgs() << " (" << *UseInst << ")\n")do { } while (false); | ||||
1528 | |||||
1529 | if (any_of(KillingDefs, [this, UseInst](Instruction *KI) { | ||||
1530 | return DT.dominates(KI, UseInst); | ||||
1531 | })) { | ||||
1532 | LLVM_DEBUG(dbgs() << " ... skipping, dominated by killing def\n")do { } while (false); | ||||
1533 | continue; | ||||
1534 | } | ||||
1535 | |||||
1536 | // A memory terminator kills all preceeding MemoryDefs and all succeeding | ||||
1537 | // MemoryAccesses. We do not have to check it's users. | ||||
1538 | if (isMemTerminator(*CurrentLoc, EarlierMemInst, UseInst)) { | ||||
1539 | LLVM_DEBUG(do { } while (false) | ||||
1540 | dbgs()do { } while (false) | ||||
1541 | << " ... skipping, memterminator invalidates following accesses\n")do { } while (false); | ||||
1542 | continue; | ||||
1543 | } | ||||
1544 | |||||
1545 | if (isNoopIntrinsic(cast<MemoryUseOrDef>(UseAccess)->getMemoryInst())) { | ||||
1546 | LLVM_DEBUG(dbgs() << " ... adding uses of intrinsic\n")do { } while (false); | ||||
1547 | PushMemUses(UseAccess); | ||||
1548 | continue; | ||||
1549 | } | ||||
1550 | |||||
1551 | if (UseInst->mayThrow() && !isInvisibleToCallerBeforeRet(DefUO)) { | ||||
1552 | LLVM_DEBUG(dbgs() << " ... found throwing instruction\n")do { } while (false); | ||||
1553 | return None; | ||||
1554 | } | ||||
1555 | |||||
1556 | // Uses which may read the original MemoryDef mean we cannot eliminate the | ||||
1557 | // original MD. Stop walk. | ||||
1558 | if (isReadClobber(*CurrentLoc, UseInst)) { | ||||
1559 | LLVM_DEBUG(dbgs() << " ... found read clobber\n")do { } while (false); | ||||
1560 | return None; | ||||
1561 | } | ||||
1562 | |||||
1563 | // If this worklist walks back to the original memory access (and the | ||||
1564 | // pointer is not guarenteed loop invariant) then we cannot assume that a | ||||
1565 | // store kills itself. | ||||
1566 | if (EarlierAccess == UseAccess && | ||||
1567 | !isGuaranteedLoopInvariant(CurrentLoc->Ptr)) { | ||||
1568 | LLVM_DEBUG(dbgs() << " ... found not loop invariant self access\n")do { } while (false); | ||||
1569 | return None; | ||||
1570 | } | ||||
1571 | // Otherwise, for the KillingDef and EarlierAccess we only have to check | ||||
1572 | // if it reads the memory location. | ||||
1573 | // TODO: It would probably be better to check for self-reads before | ||||
1574 | // calling the function. | ||||
1575 | if (KillingDef == UseAccess || EarlierAccess == UseAccess) { | ||||
1576 | LLVM_DEBUG(dbgs() << " ... skipping killing def/dom access\n")do { } while (false); | ||||
1577 | continue; | ||||
1578 | } | ||||
1579 | |||||
1580 | // Check all uses for MemoryDefs, except for defs completely overwriting | ||||
1581 | // the original location. Otherwise we have to check uses of *all* | ||||
1582 | // MemoryDefs we discover, including non-aliasing ones. Otherwise we might | ||||
1583 | // miss cases like the following | ||||
1584 | // 1 = Def(LoE) ; <----- EarlierDef stores [0,1] | ||||
1585 | // 2 = Def(1) ; (2, 1) = NoAlias, stores [2,3] | ||||
1586 | // Use(2) ; MayAlias 2 *and* 1, loads [0, 3]. | ||||
1587 | // (The Use points to the *first* Def it may alias) | ||||
1588 | // 3 = Def(1) ; <---- Current (3, 2) = NoAlias, (3,1) = MayAlias, | ||||
1589 | // stores [0,1] | ||||
1590 | if (MemoryDef *UseDef = dyn_cast<MemoryDef>(UseAccess)) { | ||||
1591 | if (isCompleteOverwrite(*CurrentLoc, EarlierMemInst, UseInst)) { | ||||
1592 | BasicBlock *MaybeKillingBlock = UseInst->getParent(); | ||||
1593 | if (PostOrderNumbers.find(MaybeKillingBlock)->second < | ||||
1594 | PostOrderNumbers.find(EarlierAccess->getBlock())->second) { | ||||
1595 | if (!isInvisibleToCallerAfterRet(DefUO)) { | ||||
1596 | LLVM_DEBUG(dbgs()do { } while (false) | ||||
1597 | << " ... found killing def " << *UseInst << "\n")do { } while (false); | ||||
1598 | KillingDefs.insert(UseInst); | ||||
1599 | } | ||||
1600 | } else { | ||||
1601 | LLVM_DEBUG(dbgs()do { } while (false) | ||||
1602 | << " ... found preceeding def " << *UseInst << "\n")do { } while (false); | ||||
1603 | return None; | ||||
1604 | } | ||||
1605 | } else | ||||
1606 | PushMemUses(UseDef); | ||||
1607 | } | ||||
1608 | } | ||||
1609 | |||||
1610 | // For accesses to locations visible after the function returns, make sure | ||||
1611 | // that the location is killed (=overwritten) along all paths from | ||||
1612 | // EarlierAccess to the exit. | ||||
1613 | if (!isInvisibleToCallerAfterRet(DefUO)) { | ||||
1614 | SmallPtrSet<BasicBlock *, 16> KillingBlocks; | ||||
1615 | for (Instruction *KD : KillingDefs) | ||||
1616 | KillingBlocks.insert(KD->getParent()); | ||||
1617 | assert(!KillingBlocks.empty() &&((void)0) | ||||
1618 | "Expected at least a single killing block")((void)0); | ||||
1619 | |||||
1620 | // Find the common post-dominator of all killing blocks. | ||||
1621 | BasicBlock *CommonPred = *KillingBlocks.begin(); | ||||
1622 | for (auto I = std::next(KillingBlocks.begin()), E = KillingBlocks.end(); | ||||
1623 | I != E; I++) { | ||||
1624 | if (!CommonPred) | ||||
1625 | break; | ||||
1626 | CommonPred = PDT.findNearestCommonDominator(CommonPred, *I); | ||||
1627 | } | ||||
1628 | |||||
1629 | // If CommonPred is in the set of killing blocks, just check if it | ||||
1630 | // post-dominates EarlierAccess. | ||||
1631 | if (KillingBlocks.count(CommonPred)) { | ||||
1632 | if (PDT.dominates(CommonPred, EarlierAccess->getBlock())) | ||||
1633 | return {EarlierAccess}; | ||||
1634 | return None; | ||||
1635 | } | ||||
1636 | |||||
1637 | // If the common post-dominator does not post-dominate EarlierAccess, | ||||
1638 | // there is a path from EarlierAccess to an exit not going through a | ||||
1639 | // killing block. | ||||
1640 | if (PDT.dominates(CommonPred, EarlierAccess->getBlock())) { | ||||
1641 | SetVector<BasicBlock *> WorkList; | ||||
1642 | |||||
1643 | // If CommonPred is null, there are multiple exits from the function. | ||||
1644 | // They all have to be added to the worklist. | ||||
1645 | if (CommonPred) | ||||
1646 | WorkList.insert(CommonPred); | ||||
1647 | else | ||||
1648 | for (BasicBlock *R : PDT.roots()) | ||||
1649 | WorkList.insert(R); | ||||
1650 | |||||
1651 | NumCFGTries++; | ||||
1652 | // Check if all paths starting from an exit node go through one of the | ||||
1653 | // killing blocks before reaching EarlierAccess. | ||||
1654 | for (unsigned I = 0; I < WorkList.size(); I++) { | ||||
1655 | NumCFGChecks++; | ||||
1656 | BasicBlock *Current = WorkList[I]; | ||||
1657 | if (KillingBlocks.count(Current)) | ||||
1658 | continue; | ||||
1659 | if (Current == EarlierAccess->getBlock()) | ||||
1660 | return None; | ||||
1661 | |||||
1662 | // EarlierAccess is reachable from the entry, so we don't have to | ||||
1663 | // explore unreachable blocks further. | ||||
1664 | if (!DT.isReachableFromEntry(Current)) | ||||
1665 | continue; | ||||
1666 | |||||
1667 | for (BasicBlock *Pred : predecessors(Current)) | ||||
1668 | WorkList.insert(Pred); | ||||
1669 | |||||
1670 | if (WorkList.size() >= MemorySSAPathCheckLimit) | ||||
1671 | return None; | ||||
1672 | } | ||||
1673 | NumCFGSuccess++; | ||||
1674 | return {EarlierAccess}; | ||||
1675 | } | ||||
1676 | return None; | ||||
1677 | } | ||||
1678 | |||||
1679 | // No aliasing MemoryUses of EarlierAccess found, EarlierAccess is | ||||
1680 | // potentially dead. | ||||
1681 | return {EarlierAccess}; | ||||
1682 | } | ||||
1683 | |||||
1684 | // Delete dead memory defs | ||||
1685 | void deleteDeadInstruction(Instruction *SI) { | ||||
1686 | MemorySSAUpdater Updater(&MSSA); | ||||
1687 | SmallVector<Instruction *, 32> NowDeadInsts; | ||||
1688 | NowDeadInsts.push_back(SI); | ||||
1689 | --NumFastOther; | ||||
1690 | |||||
1691 | while (!NowDeadInsts.empty()) { | ||||
1692 | Instruction *DeadInst = NowDeadInsts.pop_back_val(); | ||||
1693 | ++NumFastOther; | ||||
1694 | |||||
1695 | // Try to preserve debug information attached to the dead instruction. | ||||
1696 | salvageDebugInfo(*DeadInst); | ||||
1697 | salvageKnowledge(DeadInst); | ||||
1698 | |||||
1699 | // Remove the Instruction from MSSA. | ||||
1700 | if (MemoryAccess *MA = MSSA.getMemoryAccess(DeadInst)) { | ||||
1701 | if (MemoryDef *MD = dyn_cast<MemoryDef>(MA)) { | ||||
1702 | SkipStores.insert(MD); | ||||
1703 | } | ||||
1704 | Updater.removeMemoryAccess(MA); | ||||
1705 | } | ||||
1706 | |||||
1707 | auto I = IOLs.find(DeadInst->getParent()); | ||||
1708 | if (I != IOLs.end()) | ||||
1709 | I->second.erase(DeadInst); | ||||
1710 | // Remove its operands | ||||
1711 | for (Use &O : DeadInst->operands()) | ||||
1712 | if (Instruction *OpI = dyn_cast<Instruction>(O)) { | ||||
1713 | O = nullptr; | ||||
1714 | if (isInstructionTriviallyDead(OpI, &TLI)) | ||||
1715 | NowDeadInsts.push_back(OpI); | ||||
1716 | } | ||||
1717 | |||||
1718 | DeadInst->eraseFromParent(); | ||||
1719 | } | ||||
1720 | } | ||||
1721 | |||||
1722 | // Check for any extra throws between SI and NI that block DSE. This only | ||||
1723 | // checks extra maythrows (those that aren't MemoryDef's). MemoryDef that may | ||||
1724 | // throw are handled during the walk from one def to the next. | ||||
1725 | bool mayThrowBetween(Instruction *SI, Instruction *NI, | ||||
1726 | const Value *SILocUnd) { | ||||
1727 | // First see if we can ignore it by using the fact that SI is an | ||||
1728 | // alloca/alloca like object that is not visible to the caller during | ||||
1729 | // execution of the function. | ||||
1730 | if (SILocUnd && isInvisibleToCallerBeforeRet(SILocUnd)) | ||||
1731 | return false; | ||||
1732 | |||||
1733 | if (SI->getParent() == NI->getParent()) | ||||
1734 | return ThrowingBlocks.count(SI->getParent()); | ||||
1735 | return !ThrowingBlocks.empty(); | ||||
1736 | } | ||||
1737 | |||||
1738 | // Check if \p NI acts as a DSE barrier for \p SI. The following instructions | ||||
1739 | // act as barriers: | ||||
1740 | // * A memory instruction that may throw and \p SI accesses a non-stack | ||||
1741 | // object. | ||||
1742 | // * Atomic stores stronger that monotonic. | ||||
1743 | bool isDSEBarrier(const Value *SILocUnd, Instruction *NI) { | ||||
1744 | // If NI may throw it acts as a barrier, unless we are to an alloca/alloca | ||||
1745 | // like object that does not escape. | ||||
1746 | if (NI->mayThrow() && !isInvisibleToCallerBeforeRet(SILocUnd)) | ||||
1747 | return true; | ||||
1748 | |||||
1749 | // If NI is an atomic load/store stronger than monotonic, do not try to | ||||
1750 | // eliminate/reorder it. | ||||
1751 | if (NI->isAtomic()) { | ||||
1752 | if (auto *LI = dyn_cast<LoadInst>(NI)) | ||||
1753 | return isStrongerThanMonotonic(LI->getOrdering()); | ||||
1754 | if (auto *SI = dyn_cast<StoreInst>(NI)) | ||||
1755 | return isStrongerThanMonotonic(SI->getOrdering()); | ||||
1756 | if (auto *ARMW = dyn_cast<AtomicRMWInst>(NI)) | ||||
1757 | return isStrongerThanMonotonic(ARMW->getOrdering()); | ||||
1758 | if (auto *CmpXchg = dyn_cast<AtomicCmpXchgInst>(NI)) | ||||
1759 | return isStrongerThanMonotonic(CmpXchg->getSuccessOrdering()) || | ||||
1760 | isStrongerThanMonotonic(CmpXchg->getFailureOrdering()); | ||||
1761 | llvm_unreachable("other instructions should be skipped in MemorySSA")__builtin_unreachable(); | ||||
1762 | } | ||||
1763 | return false; | ||||
1764 | } | ||||
1765 | |||||
1766 | /// Eliminate writes to objects that are not visible in the caller and are not | ||||
1767 | /// accessed before returning from the function. | ||||
1768 | bool eliminateDeadWritesAtEndOfFunction() { | ||||
1769 | bool MadeChange = false; | ||||
1770 | LLVM_DEBUG(do { } while (false) | ||||
1771 | dbgs()do { } while (false) | ||||
1772 | << "Trying to eliminate MemoryDefs at the end of the function\n")do { } while (false); | ||||
1773 | for (int I = MemDefs.size() - 1; I >= 0; I--) { | ||||
1774 | MemoryDef *Def = MemDefs[I]; | ||||
1775 | if (SkipStores.contains(Def) || !isRemovable(Def->getMemoryInst())) | ||||
1776 | continue; | ||||
1777 | |||||
1778 | Instruction *DefI = Def->getMemoryInst(); | ||||
1779 | SmallVector<const Value *, 4> Pointers; | ||||
1780 | auto DefLoc = getLocForWriteEx(DefI); | ||||
1781 | if (!DefLoc) | ||||
1782 | continue; | ||||
1783 | |||||
1784 | // NOTE: Currently eliminating writes at the end of a function is limited | ||||
1785 | // to MemoryDefs with a single underlying object, to save compile-time. In | ||||
1786 | // practice it appears the case with multiple underlying objects is very | ||||
1787 | // uncommon. If it turns out to be important, we can use | ||||
1788 | // getUnderlyingObjects here instead. | ||||
1789 | const Value *UO = getUnderlyingObject(DefLoc->Ptr); | ||||
1790 | if (!UO || !isInvisibleToCallerAfterRet(UO)) | ||||
1791 | continue; | ||||
1792 | |||||
1793 | if (isWriteAtEndOfFunction(Def)) { | ||||
1794 | // See through pointer-to-pointer bitcasts | ||||
1795 | LLVM_DEBUG(dbgs() << " ... MemoryDef is not accessed until the end "do { } while (false) | ||||
1796 | "of the function\n")do { } while (false); | ||||
1797 | deleteDeadInstruction(DefI); | ||||
1798 | ++NumFastStores; | ||||
1799 | MadeChange = true; | ||||
1800 | } | ||||
1801 | } | ||||
1802 | return MadeChange; | ||||
1803 | } | ||||
1804 | |||||
1805 | /// \returns true if \p Def is a no-op store, either because it | ||||
1806 | /// directly stores back a loaded value or stores zero to a calloced object. | ||||
1807 | bool storeIsNoop(MemoryDef *Def, const MemoryLocation &DefLoc, | ||||
1808 | const Value *DefUO) { | ||||
1809 | StoreInst *Store = dyn_cast<StoreInst>(Def->getMemoryInst()); | ||||
1810 | MemSetInst *MemSet = dyn_cast<MemSetInst>(Def->getMemoryInst()); | ||||
1811 | Constant *StoredConstant = nullptr; | ||||
1812 | if (Store) | ||||
1813 | StoredConstant = dyn_cast<Constant>(Store->getOperand(0)); | ||||
1814 | if (MemSet) | ||||
1815 | StoredConstant = dyn_cast<Constant>(MemSet->getValue()); | ||||
1816 | |||||
1817 | if (StoredConstant && StoredConstant->isNullValue()) { | ||||
1818 | auto *DefUOInst = dyn_cast<Instruction>(DefUO); | ||||
1819 | if (DefUOInst && isCallocLikeFn(DefUOInst, &TLI)) { | ||||
1820 | auto *UnderlyingDef = cast<MemoryDef>(MSSA.getMemoryAccess(DefUOInst)); | ||||
1821 | // If UnderlyingDef is the clobbering access of Def, no instructions | ||||
1822 | // between them can modify the memory location. | ||||
1823 | auto *ClobberDef = | ||||
1824 | MSSA.getSkipSelfWalker()->getClobberingMemoryAccess(Def); | ||||
1825 | return UnderlyingDef == ClobberDef; | ||||
1826 | } | ||||
1827 | } | ||||
1828 | |||||
1829 | if (!Store) | ||||
1830 | return false; | ||||
1831 | |||||
1832 | if (auto *LoadI = dyn_cast<LoadInst>(Store->getOperand(0))) { | ||||
1833 | if (LoadI->getPointerOperand() == Store->getOperand(1)) { | ||||
1834 | // Get the defining access for the load. | ||||
1835 | auto *LoadAccess = MSSA.getMemoryAccess(LoadI)->getDefiningAccess(); | ||||
1836 | // Fast path: the defining accesses are the same. | ||||
1837 | if (LoadAccess == Def->getDefiningAccess()) | ||||
1838 | return true; | ||||
1839 | |||||
1840 | // Look through phi accesses. Recursively scan all phi accesses by | ||||
1841 | // adding them to a worklist. Bail when we run into a memory def that | ||||
1842 | // does not match LoadAccess. | ||||
1843 | SetVector<MemoryAccess *> ToCheck; | ||||
1844 | MemoryAccess *Current = | ||||
1845 | MSSA.getWalker()->getClobberingMemoryAccess(Def); | ||||
1846 | // We don't want to bail when we run into the store memory def. But, | ||||
1847 | // the phi access may point to it. So, pretend like we've already | ||||
1848 | // checked it. | ||||
1849 | ToCheck.insert(Def); | ||||
1850 | ToCheck.insert(Current); | ||||
1851 | // Start at current (1) to simulate already having checked Def. | ||||
1852 | for (unsigned I = 1; I < ToCheck.size(); ++I) { | ||||
1853 | Current = ToCheck[I]; | ||||
1854 | if (auto PhiAccess = dyn_cast<MemoryPhi>(Current)) { | ||||
1855 | // Check all the operands. | ||||
1856 | for (auto &Use : PhiAccess->incoming_values()) | ||||
1857 | ToCheck.insert(cast<MemoryAccess>(&Use)); | ||||
1858 | continue; | ||||
1859 | } | ||||
1860 | |||||
1861 | // If we found a memory def, bail. This happens when we have an | ||||
1862 | // unrelated write in between an otherwise noop store. | ||||
1863 | assert(isa<MemoryDef>(Current) &&((void)0) | ||||
1864 | "Only MemoryDefs should reach here.")((void)0); | ||||
1865 | // TODO: Skip no alias MemoryDefs that have no aliasing reads. | ||||
1866 | // We are searching for the definition of the store's destination. | ||||
1867 | // So, if that is the same definition as the load, then this is a | ||||
1868 | // noop. Otherwise, fail. | ||||
1869 | if (LoadAccess != Current) | ||||
1870 | return false; | ||||
1871 | } | ||||
1872 | return true; | ||||
1873 | } | ||||
1874 | } | ||||
1875 | |||||
1876 | return false; | ||||
1877 | } | ||||
1878 | }; | ||||
1879 | |||||
1880 | static bool eliminateDeadStores(Function &F, AliasAnalysis &AA, MemorySSA &MSSA, | ||||
1881 | DominatorTree &DT, PostDominatorTree &PDT, | ||||
1882 | const TargetLibraryInfo &TLI, | ||||
1883 | const LoopInfo &LI) { | ||||
1884 | bool MadeChange = false; | ||||
1885 | |||||
1886 | DSEState State = DSEState::get(F, AA, MSSA, DT, PDT, TLI, LI); | ||||
1887 | // For each store: | ||||
1888 | for (unsigned I = 0; I < State.MemDefs.size(); I++) { | ||||
1889 | MemoryDef *KillingDef = State.MemDefs[I]; | ||||
1890 | if (State.SkipStores.count(KillingDef)) | ||||
1891 | continue; | ||||
1892 | Instruction *SI = KillingDef->getMemoryInst(); | ||||
1893 | |||||
1894 | Optional<MemoryLocation> MaybeSILoc; | ||||
1895 | if (State.isMemTerminatorInst(SI)) | ||||
1896 | MaybeSILoc = State.getLocForTerminator(SI).map( | ||||
1897 | [](const std::pair<MemoryLocation, bool> &P) { return P.first; }); | ||||
1898 | else | ||||
1899 | MaybeSILoc = State.getLocForWriteEx(SI); | ||||
1900 | |||||
1901 | if (!MaybeSILoc) { | ||||
1902 | LLVM_DEBUG(dbgs() << "Failed to find analyzable write location for "do { } while (false) | ||||
1903 | << *SI << "\n")do { } while (false); | ||||
1904 | continue; | ||||
1905 | } | ||||
1906 | MemoryLocation SILoc = *MaybeSILoc; | ||||
1907 | assert(SILoc.Ptr && "SILoc should not be null")((void)0); | ||||
1908 | const Value *SILocUnd = getUnderlyingObject(SILoc.Ptr); | ||||
1909 | |||||
1910 | MemoryAccess *Current = KillingDef; | ||||
1911 | LLVM_DEBUG(dbgs() << "Trying to eliminate MemoryDefs killed by "do { } while (false) | ||||
1912 | << *Current << " (" << *SI << ")\n")do { } while (false); | ||||
1913 | |||||
1914 | unsigned ScanLimit = MemorySSAScanLimit; | ||||
1915 | unsigned WalkerStepLimit = MemorySSAUpwardsStepLimit; | ||||
1916 | unsigned PartialLimit = MemorySSAPartialStoreLimit; | ||||
1917 | // Worklist of MemoryAccesses that may be killed by KillingDef. | ||||
1918 | SetVector<MemoryAccess *> ToCheck; | ||||
1919 | |||||
1920 | if (SILocUnd) | ||||
1921 | ToCheck.insert(KillingDef->getDefiningAccess()); | ||||
1922 | |||||
1923 | bool Shortend = false; | ||||
1924 | bool IsMemTerm = State.isMemTerminatorInst(SI); | ||||
1925 | // Check if MemoryAccesses in the worklist are killed by KillingDef. | ||||
1926 | for (unsigned I = 0; I < ToCheck.size(); I++) { | ||||
1927 | Current = ToCheck[I]; | ||||
1928 | if (State.SkipStores.count(Current)) | ||||
1929 | continue; | ||||
1930 | |||||
1931 | Optional<MemoryAccess *> Next = State.getDomMemoryDef( | ||||
1932 | KillingDef, Current, SILoc, SILocUnd, ScanLimit, WalkerStepLimit, | ||||
1933 | IsMemTerm, PartialLimit); | ||||
1934 | |||||
1935 | if (!Next) { | ||||
1936 | LLVM_DEBUG(dbgs() << " finished walk\n")do { } while (false); | ||||
1937 | continue; | ||||
1938 | } | ||||
1939 | |||||
1940 | MemoryAccess *EarlierAccess = *Next; | ||||
1941 | LLVM_DEBUG(dbgs() << " Checking if we can kill " << *EarlierAccess)do { } while (false); | ||||
1942 | if (isa<MemoryPhi>(EarlierAccess)) { | ||||
1943 | LLVM_DEBUG(dbgs() << "\n ... adding incoming values to worklist\n")do { } while (false); | ||||
1944 | for (Value *V : cast<MemoryPhi>(EarlierAccess)->incoming_values()) { | ||||
1945 | MemoryAccess *IncomingAccess = cast<MemoryAccess>(V); | ||||
1946 | BasicBlock *IncomingBlock = IncomingAccess->getBlock(); | ||||
1947 | BasicBlock *PhiBlock = EarlierAccess->getBlock(); | ||||
1948 | |||||
1949 | // We only consider incoming MemoryAccesses that come before the | ||||
1950 | // MemoryPhi. Otherwise we could discover candidates that do not | ||||
1951 | // strictly dominate our starting def. | ||||
1952 | if (State.PostOrderNumbers[IncomingBlock] > | ||||
1953 | State.PostOrderNumbers[PhiBlock]) | ||||
1954 | ToCheck.insert(IncomingAccess); | ||||
1955 | } | ||||
1956 | continue; | ||||
1957 | } | ||||
1958 | auto *NextDef = cast<MemoryDef>(EarlierAccess); | ||||
1959 | Instruction *NI = NextDef->getMemoryInst(); | ||||
1960 | LLVM_DEBUG(dbgs() << " (" << *NI << ")\n")do { } while (false); | ||||
1961 | ToCheck.insert(NextDef->getDefiningAccess()); | ||||
1962 | NumGetDomMemoryDefPassed++; | ||||
1963 | |||||
1964 | if (!DebugCounter::shouldExecute(MemorySSACounter)) | ||||
1965 | continue; | ||||
1966 | |||||
1967 | MemoryLocation NILoc = *State.getLocForWriteEx(NI); | ||||
1968 | |||||
1969 | if (IsMemTerm) { | ||||
1970 | const Value *NIUnd = getUnderlyingObject(NILoc.Ptr); | ||||
1971 | if (SILocUnd != NIUnd) | ||||
1972 | continue; | ||||
1973 | LLVM_DEBUG(dbgs() << "DSE: Remove Dead Store:\n DEAD: " << *NIdo { } while (false) | ||||
1974 | << "\n KILLER: " << *SI << '\n')do { } while (false); | ||||
1975 | State.deleteDeadInstruction(NI); | ||||
1976 | ++NumFastStores; | ||||
1977 | MadeChange = true; | ||||
1978 | } else { | ||||
1979 | // Check if NI overwrites SI. | ||||
1980 | int64_t InstWriteOffset, DepWriteOffset; | ||||
1981 | OverwriteResult OR = State.isOverwrite(SI, NI, SILoc, NILoc, | ||||
1982 | DepWriteOffset, InstWriteOffset); | ||||
1983 | if (OR == OW_MaybePartial) { | ||||
1984 | auto Iter = State.IOLs.insert( | ||||
1985 | std::make_pair<BasicBlock *, InstOverlapIntervalsTy>( | ||||
1986 | NI->getParent(), InstOverlapIntervalsTy())); | ||||
1987 | auto &IOL = Iter.first->second; | ||||
1988 | OR = isPartialOverwrite(SILoc, NILoc, DepWriteOffset, InstWriteOffset, | ||||
1989 | NI, IOL); | ||||
1990 | } | ||||
1991 | |||||
1992 | if (EnablePartialStoreMerging && OR == OW_PartialEarlierWithFullLater) { | ||||
1993 | auto *Earlier = dyn_cast<StoreInst>(NI); | ||||
1994 | auto *Later = dyn_cast<StoreInst>(SI); | ||||
1995 | // We are re-using tryToMergePartialOverlappingStores, which requires | ||||
1996 | // Earlier to domiante Later. | ||||
1997 | // TODO: implement tryToMergeParialOverlappingStores using MemorySSA. | ||||
1998 | if (Earlier && Later && DT.dominates(Earlier, Later)) { | ||||
1999 | if (Constant *Merged = tryToMergePartialOverlappingStores( | ||||
2000 | Earlier, Later, InstWriteOffset, DepWriteOffset, State.DL, | ||||
2001 | State.BatchAA, &DT)) { | ||||
2002 | |||||
2003 | // Update stored value of earlier store to merged constant. | ||||
2004 | Earlier->setOperand(0, Merged); | ||||
2005 | ++NumModifiedStores; | ||||
2006 | MadeChange = true; | ||||
2007 | |||||
2008 | Shortend = true; | ||||
2009 | // Remove later store and remove any outstanding overlap intervals | ||||
2010 | // for the updated store. | ||||
2011 | State.deleteDeadInstruction(Later); | ||||
2012 | auto I = State.IOLs.find(Earlier->getParent()); | ||||
2013 | if (I != State.IOLs.end()) | ||||
2014 | I->second.erase(Earlier); | ||||
2015 | break; | ||||
2016 | } | ||||
2017 | } | ||||
2018 | } | ||||
2019 | |||||
2020 | if (OR == OW_Complete) { | ||||
2021 | LLVM_DEBUG(dbgs() << "DSE: Remove Dead Store:\n DEAD: " << *NIdo { } while (false) | ||||
2022 | << "\n KILLER: " << *SI << '\n')do { } while (false); | ||||
2023 | State.deleteDeadInstruction(NI); | ||||
2024 | ++NumFastStores; | ||||
2025 | MadeChange = true; | ||||
2026 | } | ||||
2027 | } | ||||
2028 | } | ||||
2029 | |||||
2030 | // Check if the store is a no-op. | ||||
2031 | if (!Shortend && isRemovable(SI) && | ||||
2032 | State.storeIsNoop(KillingDef, SILoc, SILocUnd)) { | ||||
2033 | LLVM_DEBUG(dbgs() << "DSE: Remove No-Op Store:\n DEAD: " << *SI << '\n')do { } while (false); | ||||
2034 | State.deleteDeadInstruction(SI); | ||||
2035 | NumRedundantStores++; | ||||
2036 | MadeChange = true; | ||||
2037 | continue; | ||||
2038 | } | ||||
2039 | } | ||||
2040 | |||||
2041 | if (EnablePartialOverwriteTracking) | ||||
2042 | for (auto &KV : State.IOLs) | ||||
2043 | MadeChange |= removePartiallyOverlappedStores(State.DL, KV.second, TLI); | ||||
2044 | |||||
2045 | MadeChange |= State.eliminateDeadWritesAtEndOfFunction(); | ||||
2046 | return MadeChange; | ||||
2047 | } | ||||
2048 | } // end anonymous namespace | ||||
2049 | |||||
2050 | //===----------------------------------------------------------------------===// | ||||
2051 | // DSE Pass | ||||
2052 | //===----------------------------------------------------------------------===// | ||||
2053 | PreservedAnalyses DSEPass::run(Function &F, FunctionAnalysisManager &AM) { | ||||
2054 | AliasAnalysis &AA = AM.getResult<AAManager>(F); | ||||
2055 | const TargetLibraryInfo &TLI = AM.getResult<TargetLibraryAnalysis>(F); | ||||
2056 | DominatorTree &DT = AM.getResult<DominatorTreeAnalysis>(F); | ||||
2057 | MemorySSA &MSSA = AM.getResult<MemorySSAAnalysis>(F).getMSSA(); | ||||
2058 | PostDominatorTree &PDT = AM.getResult<PostDominatorTreeAnalysis>(F); | ||||
2059 | LoopInfo &LI = AM.getResult<LoopAnalysis>(F); | ||||
2060 | |||||
2061 | bool Changed = eliminateDeadStores(F, AA, MSSA, DT, PDT, TLI, LI); | ||||
| |||||
2062 | |||||
2063 | #ifdef LLVM_ENABLE_STATS0 | ||||
2064 | if (AreStatisticsEnabled()) | ||||
2065 | for (auto &I : instructions(F)) | ||||
2066 | NumRemainingStores += isa<StoreInst>(&I); | ||||
2067 | #endif | ||||
2068 | |||||
2069 | if (!Changed) | ||||
2070 | return PreservedAnalyses::all(); | ||||
2071 | |||||
2072 | PreservedAnalyses PA; | ||||
2073 | PA.preserveSet<CFGAnalyses>(); | ||||
2074 | PA.preserve<MemorySSAAnalysis>(); | ||||
2075 | PA.preserve<LoopAnalysis>(); | ||||
2076 | return PA; | ||||
2077 | } | ||||
2078 | |||||
2079 | namespace { | ||||
2080 | |||||
2081 | /// A legacy pass for the legacy pass manager that wraps \c DSEPass. | ||||
2082 | class DSELegacyPass : public FunctionPass { | ||||
2083 | public: | ||||
2084 | static char ID; // Pass identification, replacement for typeid | ||||
2085 | |||||
2086 | DSELegacyPass() : FunctionPass(ID) { | ||||
2087 | initializeDSELegacyPassPass(*PassRegistry::getPassRegistry()); | ||||
2088 | } | ||||
2089 | |||||
2090 | bool runOnFunction(Function &F) override { | ||||
2091 | if (skipFunction(F)) | ||||
2092 | return false; | ||||
2093 | |||||
2094 | AliasAnalysis &AA = getAnalysis<AAResultsWrapperPass>().getAAResults(); | ||||
2095 | DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree(); | ||||
2096 | const TargetLibraryInfo &TLI = | ||||
2097 | getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F); | ||||
2098 | MemorySSA &MSSA = getAnalysis<MemorySSAWrapperPass>().getMSSA(); | ||||
2099 | PostDominatorTree &PDT = | ||||
2100 | getAnalysis<PostDominatorTreeWrapperPass>().getPostDomTree(); | ||||
2101 | LoopInfo &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo(); | ||||
2102 | |||||
2103 | bool Changed = eliminateDeadStores(F, AA, MSSA, DT, PDT, TLI, LI); | ||||
2104 | |||||
2105 | #ifdef LLVM_ENABLE_STATS0 | ||||
2106 | if (AreStatisticsEnabled()) | ||||
2107 | for (auto &I : instructions(F)) | ||||
2108 | NumRemainingStores += isa<StoreInst>(&I); | ||||
2109 | #endif | ||||
2110 | |||||
2111 | return Changed; | ||||
2112 | } | ||||
2113 | |||||
2114 | void getAnalysisUsage(AnalysisUsage &AU) const override { | ||||
2115 | AU.setPreservesCFG(); | ||||
2116 | AU.addRequired<AAResultsWrapperPass>(); | ||||
2117 | AU.addRequired<TargetLibraryInfoWrapperPass>(); | ||||
2118 | AU.addPreserved<GlobalsAAWrapperPass>(); | ||||
2119 | AU.addRequired<DominatorTreeWrapperPass>(); | ||||
2120 | AU.addPreserved<DominatorTreeWrapperPass>(); | ||||
2121 | AU.addRequired<PostDominatorTreeWrapperPass>(); | ||||
2122 | AU.addRequired<MemorySSAWrapperPass>(); | ||||
2123 | AU.addPreserved<PostDominatorTreeWrapperPass>(); | ||||
2124 | AU.addPreserved<MemorySSAWrapperPass>(); | ||||
2125 | AU.addRequired<LoopInfoWrapperPass>(); | ||||
2126 | AU.addPreserved<LoopInfoWrapperPass>(); | ||||
2127 | } | ||||
2128 | }; | ||||
2129 | |||||
2130 | } // end anonymous namespace | ||||
2131 | |||||
2132 | char DSELegacyPass::ID = 0; | ||||
2133 | |||||
2134 | INITIALIZE_PASS_BEGIN(DSELegacyPass, "dse", "Dead Store Elimination", false,static void *initializeDSELegacyPassPassOnce(PassRegistry & Registry) { | ||||
2135 | false)static void *initializeDSELegacyPassPassOnce(PassRegistry & Registry) { | ||||
2136 | INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)initializeDominatorTreeWrapperPassPass(Registry); | ||||
2137 | INITIALIZE_PASS_DEPENDENCY(PostDominatorTreeWrapperPass)initializePostDominatorTreeWrapperPassPass(Registry); | ||||
2138 | INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)initializeAAResultsWrapperPassPass(Registry); | ||||
2139 | INITIALIZE_PASS_DEPENDENCY(GlobalsAAWrapperPass)initializeGlobalsAAWrapperPassPass(Registry); | ||||
2140 | INITIALIZE_PASS_DEPENDENCY(MemorySSAWrapperPass)initializeMemorySSAWrapperPassPass(Registry); | ||||
2141 | INITIALIZE_PASS_DEPENDENCY(MemoryDependenceWrapperPass)initializeMemoryDependenceWrapperPassPass(Registry); | ||||
2142 | INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)initializeTargetLibraryInfoWrapperPassPass(Registry); | ||||
2143 | INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)initializeLoopInfoWrapperPassPass(Registry); | ||||
2144 | INITIALIZE_PASS_END(DSELegacyPass, "dse", "Dead Store Elimination", false,PassInfo *PI = new PassInfo( "Dead Store Elimination", "dse", &DSELegacyPass::ID, PassInfo::NormalCtor_t(callDefaultCtor <DSELegacyPass>), false, false); Registry.registerPass( *PI, true); return PI; } static llvm::once_flag InitializeDSELegacyPassPassFlag ; void llvm::initializeDSELegacyPassPass(PassRegistry &Registry ) { llvm::call_once(InitializeDSELegacyPassPassFlag, initializeDSELegacyPassPassOnce , std::ref(Registry)); } | ||||
2145 | false)PassInfo *PI = new PassInfo( "Dead Store Elimination", "dse", &DSELegacyPass::ID, PassInfo::NormalCtor_t(callDefaultCtor <DSELegacyPass>), false, false); Registry.registerPass( *PI, true); return PI; } static llvm::once_flag InitializeDSELegacyPassPassFlag ; void llvm::initializeDSELegacyPassPass(PassRegistry &Registry ) { llvm::call_once(InitializeDSELegacyPassPassFlag, initializeDSELegacyPassPassOnce , std::ref(Registry)); } | ||||
2146 | |||||
2147 | FunctionPass *llvm::createDeadStoreEliminationPass() { | ||||
2148 | return new DSELegacyPass(); | ||||
2149 | } |
1 | //===- MemoryLocation.h - Memory location descriptions ----------*- C++ -*-===// |
2 | // |
3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
4 | // See https://llvm.org/LICENSE.txt for license information. |
5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
6 | // |
7 | //===----------------------------------------------------------------------===// |
8 | /// \file |
9 | /// This file provides utility analysis objects describing memory locations. |
10 | /// These are used both by the Alias Analysis infrastructure and more |
11 | /// specialized memory analysis layers. |
12 | /// |
13 | //===----------------------------------------------------------------------===// |
14 | |
15 | #ifndef LLVM_ANALYSIS_MEMORYLOCATION_H |
16 | #define LLVM_ANALYSIS_MEMORYLOCATION_H |
17 | |
18 | #include "llvm/ADT/DenseMapInfo.h" |
19 | #include "llvm/ADT/Optional.h" |
20 | #include "llvm/IR/Metadata.h" |
21 | #include "llvm/Support/TypeSize.h" |
22 | |
23 | namespace llvm { |
24 | |
25 | class CallBase; |
26 | class Instruction; |
27 | class LoadInst; |
28 | class StoreInst; |
29 | class MemTransferInst; |
30 | class MemIntrinsic; |
31 | class AtomicCmpXchgInst; |
32 | class AtomicMemTransferInst; |
33 | class AtomicMemIntrinsic; |
34 | class AtomicRMWInst; |
35 | class AnyMemTransferInst; |
36 | class AnyMemIntrinsic; |
37 | class TargetLibraryInfo; |
38 | class VAArgInst; |
39 | |
40 | // Represents the size of a MemoryLocation. Logically, it's an |
41 | // Optional<uint63_t> that also carries a bit to represent whether the integer |
42 | // it contains, N, is 'precise'. Precise, in this context, means that we know |
43 | // that the area of storage referenced by the given MemoryLocation must be |
44 | // precisely N bytes. An imprecise value is formed as the union of two or more |
45 | // precise values, and can conservatively represent all of the values unioned |
46 | // into it. Importantly, imprecise values are an *upper-bound* on the size of a |
47 | // MemoryLocation. |
48 | // |
49 | // Concretely, a precise MemoryLocation is (%p, 4) in |
50 | // store i32 0, i32* %p |
51 | // |
52 | // Since we know that %p must be at least 4 bytes large at this point. |
53 | // Otherwise, we have UB. An example of an imprecise MemoryLocation is (%p, 4) |
54 | // at the memcpy in |
55 | // |
56 | // %n = select i1 %foo, i64 1, i64 4 |
57 | // call void @llvm.memcpy.p0i8.p0i8.i64(i8* %p, i8* %baz, i64 %n, i32 1, |
58 | // i1 false) |
59 | // |
60 | // ...Since we'll copy *up to* 4 bytes into %p, but we can't guarantee that |
61 | // we'll ever actually do so. |
62 | // |
63 | // If asked to represent a pathologically large value, this will degrade to |
64 | // None. |
65 | class LocationSize { |
66 | enum : uint64_t { |
67 | BeforeOrAfterPointer = ~uint64_t(0), |
68 | AfterPointer = BeforeOrAfterPointer - 1, |
69 | MapEmpty = BeforeOrAfterPointer - 2, |
70 | MapTombstone = BeforeOrAfterPointer - 3, |
71 | ImpreciseBit = uint64_t(1) << 63, |
72 | |
73 | // The maximum value we can represent without falling back to 'unknown'. |
74 | MaxValue = (MapTombstone - 1) & ~ImpreciseBit, |
75 | }; |
76 | |
77 | uint64_t Value; |
78 | |
79 | // Hack to support implicit construction. This should disappear when the |
80 | // public LocationSize ctor goes away. |
81 | enum DirectConstruction { Direct }; |
82 | |
83 | constexpr LocationSize(uint64_t Raw, DirectConstruction): Value(Raw) {} |
84 | |
85 | static_assert(AfterPointer & ImpreciseBit, |
86 | "AfterPointer is imprecise by definition."); |
87 | static_assert(BeforeOrAfterPointer & ImpreciseBit, |
88 | "BeforeOrAfterPointer is imprecise by definition."); |
89 | |
90 | public: |
91 | // FIXME: Migrate all users to construct via either `precise` or `upperBound`, |
92 | // to make it more obvious at the callsite the kind of size that they're |
93 | // providing. |
94 | // |
95 | // Since the overwhelming majority of users of this provide precise values, |
96 | // this assumes the provided value is precise. |
97 | constexpr LocationSize(uint64_t Raw) |
98 | : Value(Raw > MaxValue ? AfterPointer : Raw) {} |
99 | |
100 | static LocationSize precise(uint64_t Value) { return LocationSize(Value); } |
101 | static LocationSize precise(TypeSize Value) { |
102 | if (Value.isScalable()) |
103 | return afterPointer(); |
104 | return precise(Value.getFixedSize()); |
105 | } |
106 | |
107 | static LocationSize upperBound(uint64_t Value) { |
108 | // You can't go lower than 0, so give a precise result. |
109 | if (LLVM_UNLIKELY(Value == 0)__builtin_expect((bool)(Value == 0), false)) |
110 | return precise(0); |
111 | if (LLVM_UNLIKELY(Value > MaxValue)__builtin_expect((bool)(Value > MaxValue), false)) |
112 | return afterPointer(); |
113 | return LocationSize(Value | ImpreciseBit, Direct); |
114 | } |
115 | static LocationSize upperBound(TypeSize Value) { |
116 | if (Value.isScalable()) |
117 | return afterPointer(); |
118 | return upperBound(Value.getFixedSize()); |
119 | } |
120 | |
121 | /// Any location after the base pointer (but still within the underlying |
122 | /// object). |
123 | constexpr static LocationSize afterPointer() { |
124 | return LocationSize(AfterPointer, Direct); |
125 | } |
126 | |
127 | /// Any location before or after the base pointer (but still within the |
128 | /// underlying object). |
129 | constexpr static LocationSize beforeOrAfterPointer() { |
130 | return LocationSize(BeforeOrAfterPointer, Direct); |
131 | } |
132 | |
133 | // Sentinel values, generally used for maps. |
134 | constexpr static LocationSize mapTombstone() { |
135 | return LocationSize(MapTombstone, Direct); |
136 | } |
137 | constexpr static LocationSize mapEmpty() { |
138 | return LocationSize(MapEmpty, Direct); |
139 | } |
140 | |
141 | // Returns a LocationSize that can correctly represent either `*this` or |
142 | // `Other`. |
143 | LocationSize unionWith(LocationSize Other) const { |
144 | if (Other == *this) |
145 | return *this; |
146 | |
147 | if (Value == BeforeOrAfterPointer || Other.Value == BeforeOrAfterPointer) |
148 | return beforeOrAfterPointer(); |
149 | if (Value == AfterPointer || Other.Value == AfterPointer) |
150 | return afterPointer(); |
151 | |
152 | return upperBound(std::max(getValue(), Other.getValue())); |
153 | } |
154 | |
155 | bool hasValue() const { |
156 | return Value != AfterPointer && Value != BeforeOrAfterPointer; |
157 | } |
158 | uint64_t getValue() const { |
159 | assert(hasValue() && "Getting value from an unknown LocationSize!")((void)0); |
160 | return Value & ~ImpreciseBit; |
161 | } |
162 | |
163 | // Returns whether or not this value is precise. Note that if a value is |
164 | // precise, it's guaranteed to not be unknown. |
165 | bool isPrecise() const { |
166 | return (Value & ImpreciseBit) == 0; |
167 | } |
168 | |
169 | // Convenience method to check if this LocationSize's value is 0. |
170 | bool isZero() const { return hasValue() && getValue() == 0; } |
171 | |
172 | /// Whether accesses before the base pointer are possible. |
173 | bool mayBeBeforePointer() const { return Value == BeforeOrAfterPointer; } |
174 | |
175 | bool operator==(const LocationSize &Other) const { |
176 | return Value == Other.Value; |
177 | } |
178 | |
179 | bool operator!=(const LocationSize &Other) const { |
180 | return !(*this == Other); |
181 | } |
182 | |
183 | // Ordering operators are not provided, since it's unclear if there's only one |
184 | // reasonable way to compare: |
185 | // - values that don't exist against values that do, and |
186 | // - precise values to imprecise values |
187 | |
188 | void print(raw_ostream &OS) const; |
189 | |
190 | // Returns an opaque value that represents this LocationSize. Cannot be |
191 | // reliably converted back into a LocationSize. |
192 | uint64_t toRaw() const { return Value; } |
193 | }; |
194 | |
195 | inline raw_ostream &operator<<(raw_ostream &OS, LocationSize Size) { |
196 | Size.print(OS); |
197 | return OS; |
198 | } |
199 | |
200 | /// Representation for a specific memory location. |
201 | /// |
202 | /// This abstraction can be used to represent a specific location in memory. |
203 | /// The goal of the location is to represent enough information to describe |
204 | /// abstract aliasing, modification, and reference behaviors of whatever |
205 | /// value(s) are stored in memory at the particular location. |
206 | /// |
207 | /// The primary user of this interface is LLVM's Alias Analysis, but other |
208 | /// memory analyses such as MemoryDependence can use it as well. |
209 | class MemoryLocation { |
210 | public: |
211 | /// UnknownSize - This is a special value which can be used with the |
212 | /// size arguments in alias queries to indicate that the caller does not |
213 | /// know the sizes of the potential memory references. |
214 | enum : uint64_t { UnknownSize = ~UINT64_C(0)0ULL }; |
215 | |
216 | /// The address of the start of the location. |
217 | const Value *Ptr; |
218 | |
219 | /// The maximum size of the location, in address-units, or |
220 | /// UnknownSize if the size is not known. |
221 | /// |
222 | /// Note that an unknown size does not mean the pointer aliases the entire |
223 | /// virtual address space, because there are restrictions on stepping out of |
224 | /// one object and into another. See |
225 | /// http://llvm.org/docs/LangRef.html#pointeraliasing |
226 | LocationSize Size; |
227 | |
228 | /// The metadata nodes which describes the aliasing of the location (each |
229 | /// member is null if that kind of information is unavailable). |
230 | AAMDNodes AATags; |
231 | |
232 | void print(raw_ostream &OS) const { OS << *Ptr << " " << Size << "\n"; } |
233 | |
234 | /// Return a location with information about the memory reference by the given |
235 | /// instruction. |
236 | static MemoryLocation get(const LoadInst *LI); |
237 | static MemoryLocation get(const StoreInst *SI); |
238 | static MemoryLocation get(const VAArgInst *VI); |
239 | static MemoryLocation get(const AtomicCmpXchgInst *CXI); |
240 | static MemoryLocation get(const AtomicRMWInst *RMWI); |
241 | static MemoryLocation get(const Instruction *Inst) { |
242 | return *MemoryLocation::getOrNone(Inst); |
243 | } |
244 | static Optional<MemoryLocation> getOrNone(const Instruction *Inst); |
245 | |
246 | /// Return a location representing the source of a memory transfer. |
247 | static MemoryLocation getForSource(const MemTransferInst *MTI); |
248 | static MemoryLocation getForSource(const AtomicMemTransferInst *MTI); |
249 | static MemoryLocation getForSource(const AnyMemTransferInst *MTI); |
250 | |
251 | /// Return a location representing the destination of a memory set or |
252 | /// transfer. |
253 | static MemoryLocation getForDest(const MemIntrinsic *MI); |
254 | static MemoryLocation getForDest(const AtomicMemIntrinsic *MI); |
255 | static MemoryLocation getForDest(const AnyMemIntrinsic *MI); |
256 | |
257 | /// Return a location representing a particular argument of a call. |
258 | static MemoryLocation getForArgument(const CallBase *Call, unsigned ArgIdx, |
259 | const TargetLibraryInfo *TLI); |
260 | static MemoryLocation getForArgument(const CallBase *Call, unsigned ArgIdx, |
261 | const TargetLibraryInfo &TLI) { |
262 | return getForArgument(Call, ArgIdx, &TLI); |
263 | } |
264 | |
265 | /// Return a location that may access any location after Ptr, while remaining |
266 | /// within the underlying object. |
267 | static MemoryLocation getAfter(const Value *Ptr, |
268 | const AAMDNodes &AATags = AAMDNodes()) { |
269 | return MemoryLocation(Ptr, LocationSize::afterPointer(), AATags); |
270 | } |
271 | |
272 | /// Return a location that may access any location before or after Ptr, while |
273 | /// remaining within the underlying object. |
274 | static MemoryLocation |
275 | getBeforeOrAfter(const Value *Ptr, const AAMDNodes &AATags = AAMDNodes()) { |
276 | return MemoryLocation(Ptr, LocationSize::beforeOrAfterPointer(), AATags); |
277 | } |
278 | |
279 | // Return the exact size if the exact size is known at compiletime, |
280 | // otherwise return MemoryLocation::UnknownSize. |
281 | static uint64_t getSizeOrUnknown(const TypeSize &T) { |
282 | return T.isScalable() ? UnknownSize : T.getFixedSize(); |
283 | } |
284 | |
285 | MemoryLocation() |
286 | : Ptr(nullptr), Size(LocationSize::beforeOrAfterPointer()), AATags() {} |
287 | |
288 | explicit MemoryLocation(const Value *Ptr, LocationSize Size, |
289 | const AAMDNodes &AATags = AAMDNodes()) |
290 | : Ptr(Ptr), Size(Size), AATags(AATags) {} |
291 | |
292 | MemoryLocation getWithNewPtr(const Value *NewPtr) const { |
293 | MemoryLocation Copy(*this); |
294 | Copy.Ptr = NewPtr; |
295 | return Copy; |
296 | } |
297 | |
298 | MemoryLocation getWithNewSize(LocationSize NewSize) const { |
299 | MemoryLocation Copy(*this); |
300 | Copy.Size = NewSize; |
301 | return Copy; |
302 | } |
303 | |
304 | MemoryLocation getWithoutAATags() const { |
305 | MemoryLocation Copy(*this); |
306 | Copy.AATags = AAMDNodes(); |
307 | return Copy; |
308 | } |
309 | |
310 | bool operator==(const MemoryLocation &Other) const { |
311 | return Ptr == Other.Ptr && Size == Other.Size && AATags == Other.AATags; |
312 | } |
313 | }; |
314 | |
315 | // Specialize DenseMapInfo. |
316 | template <> struct DenseMapInfo<LocationSize> { |
317 | static inline LocationSize getEmptyKey() { |
318 | return LocationSize::mapEmpty(); |
319 | } |
320 | static inline LocationSize getTombstoneKey() { |
321 | return LocationSize::mapTombstone(); |
322 | } |
323 | static unsigned getHashValue(const LocationSize &Val) { |
324 | return DenseMapInfo<uint64_t>::getHashValue(Val.toRaw()); |
325 | } |
326 | static bool isEqual(const LocationSize &LHS, const LocationSize &RHS) { |
327 | return LHS == RHS; |
328 | } |
329 | }; |
330 | |
331 | template <> struct DenseMapInfo<MemoryLocation> { |
332 | static inline MemoryLocation getEmptyKey() { |
333 | return MemoryLocation(DenseMapInfo<const Value *>::getEmptyKey(), |
334 | DenseMapInfo<LocationSize>::getEmptyKey()); |
335 | } |
336 | static inline MemoryLocation getTombstoneKey() { |
337 | return MemoryLocation(DenseMapInfo<const Value *>::getTombstoneKey(), |
338 | DenseMapInfo<LocationSize>::getTombstoneKey()); |
339 | } |
340 | static unsigned getHashValue(const MemoryLocation &Val) { |
341 | return DenseMapInfo<const Value *>::getHashValue(Val.Ptr) ^ |
342 | DenseMapInfo<LocationSize>::getHashValue(Val.Size) ^ |
343 | DenseMapInfo<AAMDNodes>::getHashValue(Val.AATags); |
344 | } |
345 | static bool isEqual(const MemoryLocation &LHS, const MemoryLocation &RHS) { |
346 | return LHS == RHS; |
347 | } |
348 | }; |
349 | } |
350 | |
351 | #endif |