File: | src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Analysis/LoopAccessAnalysis.cpp |
Warning: | line 211, column 15 Called C++ object pointer is null |
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1 | //===- LoopAccessAnalysis.cpp - Loop Access Analysis Implementation --------==// | ||||
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 implementation for the loop memory dependence that was originally | ||||
10 | // developed for the loop vectorizer. | ||||
11 | // | ||||
12 | //===----------------------------------------------------------------------===// | ||||
13 | |||||
14 | #include "llvm/Analysis/LoopAccessAnalysis.h" | ||||
15 | #include "llvm/ADT/APInt.h" | ||||
16 | #include "llvm/ADT/DenseMap.h" | ||||
17 | #include "llvm/ADT/DepthFirstIterator.h" | ||||
18 | #include "llvm/ADT/EquivalenceClasses.h" | ||||
19 | #include "llvm/ADT/PointerIntPair.h" | ||||
20 | #include "llvm/ADT/STLExtras.h" | ||||
21 | #include "llvm/ADT/SetVector.h" | ||||
22 | #include "llvm/ADT/SmallPtrSet.h" | ||||
23 | #include "llvm/ADT/SmallSet.h" | ||||
24 | #include "llvm/ADT/SmallVector.h" | ||||
25 | #include "llvm/ADT/iterator_range.h" | ||||
26 | #include "llvm/Analysis/AliasAnalysis.h" | ||||
27 | #include "llvm/Analysis/AliasSetTracker.h" | ||||
28 | #include "llvm/Analysis/LoopAnalysisManager.h" | ||||
29 | #include "llvm/Analysis/LoopInfo.h" | ||||
30 | #include "llvm/Analysis/MemoryLocation.h" | ||||
31 | #include "llvm/Analysis/OptimizationRemarkEmitter.h" | ||||
32 | #include "llvm/Analysis/ScalarEvolution.h" | ||||
33 | #include "llvm/Analysis/ScalarEvolutionExpressions.h" | ||||
34 | #include "llvm/Analysis/TargetLibraryInfo.h" | ||||
35 | #include "llvm/Analysis/ValueTracking.h" | ||||
36 | #include "llvm/Analysis/VectorUtils.h" | ||||
37 | #include "llvm/IR/BasicBlock.h" | ||||
38 | #include "llvm/IR/Constants.h" | ||||
39 | #include "llvm/IR/DataLayout.h" | ||||
40 | #include "llvm/IR/DebugLoc.h" | ||||
41 | #include "llvm/IR/DerivedTypes.h" | ||||
42 | #include "llvm/IR/DiagnosticInfo.h" | ||||
43 | #include "llvm/IR/Dominators.h" | ||||
44 | #include "llvm/IR/Function.h" | ||||
45 | #include "llvm/IR/InstrTypes.h" | ||||
46 | #include "llvm/IR/Instruction.h" | ||||
47 | #include "llvm/IR/Instructions.h" | ||||
48 | #include "llvm/IR/Operator.h" | ||||
49 | #include "llvm/IR/PassManager.h" | ||||
50 | #include "llvm/IR/Type.h" | ||||
51 | #include "llvm/IR/Value.h" | ||||
52 | #include "llvm/IR/ValueHandle.h" | ||||
53 | #include "llvm/InitializePasses.h" | ||||
54 | #include "llvm/Pass.h" | ||||
55 | #include "llvm/Support/Casting.h" | ||||
56 | #include "llvm/Support/CommandLine.h" | ||||
57 | #include "llvm/Support/Debug.h" | ||||
58 | #include "llvm/Support/ErrorHandling.h" | ||||
59 | #include "llvm/Support/raw_ostream.h" | ||||
60 | #include <algorithm> | ||||
61 | #include <cassert> | ||||
62 | #include <cstdint> | ||||
63 | #include <cstdlib> | ||||
64 | #include <iterator> | ||||
65 | #include <utility> | ||||
66 | #include <vector> | ||||
67 | |||||
68 | using namespace llvm; | ||||
69 | |||||
70 | #define DEBUG_TYPE"loop-accesses" "loop-accesses" | ||||
71 | |||||
72 | static cl::opt<unsigned, true> | ||||
73 | VectorizationFactor("force-vector-width", cl::Hidden, | ||||
74 | cl::desc("Sets the SIMD width. Zero is autoselect."), | ||||
75 | cl::location(VectorizerParams::VectorizationFactor)); | ||||
76 | unsigned VectorizerParams::VectorizationFactor; | ||||
77 | |||||
78 | static cl::opt<unsigned, true> | ||||
79 | VectorizationInterleave("force-vector-interleave", cl::Hidden, | ||||
80 | cl::desc("Sets the vectorization interleave count. " | ||||
81 | "Zero is autoselect."), | ||||
82 | cl::location( | ||||
83 | VectorizerParams::VectorizationInterleave)); | ||||
84 | unsigned VectorizerParams::VectorizationInterleave; | ||||
85 | |||||
86 | static cl::opt<unsigned, true> RuntimeMemoryCheckThreshold( | ||||
87 | "runtime-memory-check-threshold", cl::Hidden, | ||||
88 | cl::desc("When performing memory disambiguation checks at runtime do not " | ||||
89 | "generate more than this number of comparisons (default = 8)."), | ||||
90 | cl::location(VectorizerParams::RuntimeMemoryCheckThreshold), cl::init(8)); | ||||
91 | unsigned VectorizerParams::RuntimeMemoryCheckThreshold; | ||||
92 | |||||
93 | /// The maximum iterations used to merge memory checks | ||||
94 | static cl::opt<unsigned> MemoryCheckMergeThreshold( | ||||
95 | "memory-check-merge-threshold", cl::Hidden, | ||||
96 | cl::desc("Maximum number of comparisons done when trying to merge " | ||||
97 | "runtime memory checks. (default = 100)"), | ||||
98 | cl::init(100)); | ||||
99 | |||||
100 | /// Maximum SIMD width. | ||||
101 | const unsigned VectorizerParams::MaxVectorWidth = 64; | ||||
102 | |||||
103 | /// We collect dependences up to this threshold. | ||||
104 | static cl::opt<unsigned> | ||||
105 | MaxDependences("max-dependences", cl::Hidden, | ||||
106 | cl::desc("Maximum number of dependences collected by " | ||||
107 | "loop-access analysis (default = 100)"), | ||||
108 | cl::init(100)); | ||||
109 | |||||
110 | /// This enables versioning on the strides of symbolically striding memory | ||||
111 | /// accesses in code like the following. | ||||
112 | /// for (i = 0; i < N; ++i) | ||||
113 | /// A[i * Stride1] += B[i * Stride2] ... | ||||
114 | /// | ||||
115 | /// Will be roughly translated to | ||||
116 | /// if (Stride1 == 1 && Stride2 == 1) { | ||||
117 | /// for (i = 0; i < N; i+=4) | ||||
118 | /// A[i:i+3] += ... | ||||
119 | /// } else | ||||
120 | /// ... | ||||
121 | static cl::opt<bool> EnableMemAccessVersioning( | ||||
122 | "enable-mem-access-versioning", cl::init(true), cl::Hidden, | ||||
123 | cl::desc("Enable symbolic stride memory access versioning")); | ||||
124 | |||||
125 | /// Enable store-to-load forwarding conflict detection. This option can | ||||
126 | /// be disabled for correctness testing. | ||||
127 | static cl::opt<bool> EnableForwardingConflictDetection( | ||||
128 | "store-to-load-forwarding-conflict-detection", cl::Hidden, | ||||
129 | cl::desc("Enable conflict detection in loop-access analysis"), | ||||
130 | cl::init(true)); | ||||
131 | |||||
132 | bool VectorizerParams::isInterleaveForced() { | ||||
133 | return ::VectorizationInterleave.getNumOccurrences() > 0; | ||||
134 | } | ||||
135 | |||||
136 | Value *llvm::stripIntegerCast(Value *V) { | ||||
137 | if (auto *CI = dyn_cast<CastInst>(V)) | ||||
138 | if (CI->getOperand(0)->getType()->isIntegerTy()) | ||||
139 | return CI->getOperand(0); | ||||
140 | return V; | ||||
141 | } | ||||
142 | |||||
143 | const SCEV *llvm::replaceSymbolicStrideSCEV(PredicatedScalarEvolution &PSE, | ||||
144 | const ValueToValueMap &PtrToStride, | ||||
145 | Value *Ptr, Value *OrigPtr) { | ||||
146 | const SCEV *OrigSCEV = PSE.getSCEV(Ptr); | ||||
147 | |||||
148 | // If there is an entry in the map return the SCEV of the pointer with the | ||||
149 | // symbolic stride replaced by one. | ||||
150 | ValueToValueMap::const_iterator SI = | ||||
151 | PtrToStride.find(OrigPtr ? OrigPtr : Ptr); | ||||
152 | if (SI == PtrToStride.end()) | ||||
153 | // For a non-symbolic stride, just return the original expression. | ||||
154 | return OrigSCEV; | ||||
155 | |||||
156 | Value *StrideVal = stripIntegerCast(SI->second); | ||||
157 | |||||
158 | ScalarEvolution *SE = PSE.getSE(); | ||||
159 | const auto *U = cast<SCEVUnknown>(SE->getSCEV(StrideVal)); | ||||
160 | const auto *CT = | ||||
161 | static_cast<const SCEVConstant *>(SE->getOne(StrideVal->getType())); | ||||
162 | |||||
163 | PSE.addPredicate(*SE->getEqualPredicate(U, CT)); | ||||
164 | auto *Expr = PSE.getSCEV(Ptr); | ||||
165 | |||||
166 | LLVM_DEBUG(dbgs() << "LAA: Replacing SCEV: " << *OrigSCEVdo { } while (false) | ||||
167 | << " by: " << *Expr << "\n")do { } while (false); | ||||
168 | return Expr; | ||||
169 | } | ||||
170 | |||||
171 | RuntimeCheckingPtrGroup::RuntimeCheckingPtrGroup( | ||||
172 | unsigned Index, RuntimePointerChecking &RtCheck) | ||||
173 | : High(RtCheck.Pointers[Index].End), Low(RtCheck.Pointers[Index].Start), | ||||
174 | AddressSpace(RtCheck.Pointers[Index] | ||||
175 | .PointerValue->getType() | ||||
176 | ->getPointerAddressSpace()) { | ||||
177 | Members.push_back(Index); | ||||
178 | } | ||||
179 | |||||
180 | /// Calculate Start and End points of memory access. | ||||
181 | /// Let's assume A is the first access and B is a memory access on N-th loop | ||||
182 | /// iteration. Then B is calculated as: | ||||
183 | /// B = A + Step*N . | ||||
184 | /// Step value may be positive or negative. | ||||
185 | /// N is a calculated back-edge taken count: | ||||
186 | /// N = (TripCount > 0) ? RoundDown(TripCount -1 , VF) : 0 | ||||
187 | /// Start and End points are calculated in the following way: | ||||
188 | /// Start = UMIN(A, B) ; End = UMAX(A, B) + SizeOfElt, | ||||
189 | /// where SizeOfElt is the size of single memory access in bytes. | ||||
190 | /// | ||||
191 | /// There is no conflict when the intervals are disjoint: | ||||
192 | /// NoConflict = (P2.Start >= P1.End) || (P1.Start >= P2.End) | ||||
193 | void RuntimePointerChecking::insert(Loop *Lp, Value *Ptr, bool WritePtr, | ||||
194 | unsigned DepSetId, unsigned ASId, | ||||
195 | const ValueToValueMap &Strides, | ||||
196 | PredicatedScalarEvolution &PSE) { | ||||
197 | // Get the stride replaced scev. | ||||
198 | const SCEV *Sc = replaceSymbolicStrideSCEV(PSE, Strides, Ptr); | ||||
199 | ScalarEvolution *SE = PSE.getSE(); | ||||
200 | |||||
201 | const SCEV *ScStart; | ||||
202 | const SCEV *ScEnd; | ||||
203 | |||||
204 | if (SE->isLoopInvariant(Sc, Lp)) { | ||||
205 | ScStart = ScEnd = Sc; | ||||
206 | } else { | ||||
207 | const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(Sc); | ||||
208 | assert(AR && "Invalid addrec expression")((void)0); | ||||
209 | const SCEV *Ex = PSE.getBackedgeTakenCount(); | ||||
210 | |||||
211 | ScStart = AR->getStart(); | ||||
| |||||
212 | ScEnd = AR->evaluateAtIteration(Ex, *SE); | ||||
213 | const SCEV *Step = AR->getStepRecurrence(*SE); | ||||
214 | |||||
215 | // For expressions with negative step, the upper bound is ScStart and the | ||||
216 | // lower bound is ScEnd. | ||||
217 | if (const auto *CStep = dyn_cast<SCEVConstant>(Step)) { | ||||
218 | if (CStep->getValue()->isNegative()) | ||||
219 | std::swap(ScStart, ScEnd); | ||||
220 | } else { | ||||
221 | // Fallback case: the step is not constant, but we can still | ||||
222 | // get the upper and lower bounds of the interval by using min/max | ||||
223 | // expressions. | ||||
224 | ScStart = SE->getUMinExpr(ScStart, ScEnd); | ||||
225 | ScEnd = SE->getUMaxExpr(AR->getStart(), ScEnd); | ||||
226 | } | ||||
227 | } | ||||
228 | // Add the size of the pointed element to ScEnd. | ||||
229 | auto &DL = Lp->getHeader()->getModule()->getDataLayout(); | ||||
230 | Type *IdxTy = DL.getIndexType(Ptr->getType()); | ||||
231 | const SCEV *EltSizeSCEV = | ||||
232 | SE->getStoreSizeOfExpr(IdxTy, Ptr->getType()->getPointerElementType()); | ||||
233 | ScEnd = SE->getAddExpr(ScEnd, EltSizeSCEV); | ||||
234 | |||||
235 | Pointers.emplace_back(Ptr, ScStart, ScEnd, WritePtr, DepSetId, ASId, Sc); | ||||
236 | } | ||||
237 | |||||
238 | SmallVector<RuntimePointerCheck, 4> | ||||
239 | RuntimePointerChecking::generateChecks() const { | ||||
240 | SmallVector<RuntimePointerCheck, 4> Checks; | ||||
241 | |||||
242 | for (unsigned I = 0; I < CheckingGroups.size(); ++I) { | ||||
243 | for (unsigned J = I + 1; J < CheckingGroups.size(); ++J) { | ||||
244 | const RuntimeCheckingPtrGroup &CGI = CheckingGroups[I]; | ||||
245 | const RuntimeCheckingPtrGroup &CGJ = CheckingGroups[J]; | ||||
246 | |||||
247 | if (needsChecking(CGI, CGJ)) | ||||
248 | Checks.push_back(std::make_pair(&CGI, &CGJ)); | ||||
249 | } | ||||
250 | } | ||||
251 | return Checks; | ||||
252 | } | ||||
253 | |||||
254 | void RuntimePointerChecking::generateChecks( | ||||
255 | MemoryDepChecker::DepCandidates &DepCands, bool UseDependencies) { | ||||
256 | assert(Checks.empty() && "Checks is not empty")((void)0); | ||||
257 | groupChecks(DepCands, UseDependencies); | ||||
258 | Checks = generateChecks(); | ||||
259 | } | ||||
260 | |||||
261 | bool RuntimePointerChecking::needsChecking( | ||||
262 | const RuntimeCheckingPtrGroup &M, const RuntimeCheckingPtrGroup &N) const { | ||||
263 | for (unsigned I = 0, EI = M.Members.size(); EI != I; ++I) | ||||
264 | for (unsigned J = 0, EJ = N.Members.size(); EJ != J; ++J) | ||||
265 | if (needsChecking(M.Members[I], N.Members[J])) | ||||
266 | return true; | ||||
267 | return false; | ||||
268 | } | ||||
269 | |||||
270 | /// Compare \p I and \p J and return the minimum. | ||||
271 | /// Return nullptr in case we couldn't find an answer. | ||||
272 | static const SCEV *getMinFromExprs(const SCEV *I, const SCEV *J, | ||||
273 | ScalarEvolution *SE) { | ||||
274 | const SCEV *Diff = SE->getMinusSCEV(J, I); | ||||
275 | const SCEVConstant *C = dyn_cast<const SCEVConstant>(Diff); | ||||
276 | |||||
277 | if (!C) | ||||
278 | return nullptr; | ||||
279 | if (C->getValue()->isNegative()) | ||||
280 | return J; | ||||
281 | return I; | ||||
282 | } | ||||
283 | |||||
284 | bool RuntimeCheckingPtrGroup::addPointer(unsigned Index, | ||||
285 | RuntimePointerChecking &RtCheck) { | ||||
286 | return addPointer( | ||||
287 | Index, RtCheck.Pointers[Index].Start, RtCheck.Pointers[Index].End, | ||||
288 | RtCheck.Pointers[Index].PointerValue->getType()->getPointerAddressSpace(), | ||||
289 | *RtCheck.SE); | ||||
290 | } | ||||
291 | |||||
292 | bool RuntimeCheckingPtrGroup::addPointer(unsigned Index, const SCEV *Start, | ||||
293 | const SCEV *End, unsigned AS, | ||||
294 | ScalarEvolution &SE) { | ||||
295 | assert(AddressSpace == AS &&((void)0) | ||||
296 | "all pointers in a checking group must be in the same address space")((void)0); | ||||
297 | |||||
298 | // Compare the starts and ends with the known minimum and maximum | ||||
299 | // of this set. We need to know how we compare against the min/max | ||||
300 | // of the set in order to be able to emit memchecks. | ||||
301 | const SCEV *Min0 = getMinFromExprs(Start, Low, &SE); | ||||
302 | if (!Min0) | ||||
303 | return false; | ||||
304 | |||||
305 | const SCEV *Min1 = getMinFromExprs(End, High, &SE); | ||||
306 | if (!Min1) | ||||
307 | return false; | ||||
308 | |||||
309 | // Update the low bound expression if we've found a new min value. | ||||
310 | if (Min0 == Start) | ||||
311 | Low = Start; | ||||
312 | |||||
313 | // Update the high bound expression if we've found a new max value. | ||||
314 | if (Min1 != End) | ||||
315 | High = End; | ||||
316 | |||||
317 | Members.push_back(Index); | ||||
318 | return true; | ||||
319 | } | ||||
320 | |||||
321 | void RuntimePointerChecking::groupChecks( | ||||
322 | MemoryDepChecker::DepCandidates &DepCands, bool UseDependencies) { | ||||
323 | // We build the groups from dependency candidates equivalence classes | ||||
324 | // because: | ||||
325 | // - We know that pointers in the same equivalence class share | ||||
326 | // the same underlying object and therefore there is a chance | ||||
327 | // that we can compare pointers | ||||
328 | // - We wouldn't be able to merge two pointers for which we need | ||||
329 | // to emit a memcheck. The classes in DepCands are already | ||||
330 | // conveniently built such that no two pointers in the same | ||||
331 | // class need checking against each other. | ||||
332 | |||||
333 | // We use the following (greedy) algorithm to construct the groups | ||||
334 | // For every pointer in the equivalence class: | ||||
335 | // For each existing group: | ||||
336 | // - if the difference between this pointer and the min/max bounds | ||||
337 | // of the group is a constant, then make the pointer part of the | ||||
338 | // group and update the min/max bounds of that group as required. | ||||
339 | |||||
340 | CheckingGroups.clear(); | ||||
341 | |||||
342 | // If we need to check two pointers to the same underlying object | ||||
343 | // with a non-constant difference, we shouldn't perform any pointer | ||||
344 | // grouping with those pointers. This is because we can easily get | ||||
345 | // into cases where the resulting check would return false, even when | ||||
346 | // the accesses are safe. | ||||
347 | // | ||||
348 | // The following example shows this: | ||||
349 | // for (i = 0; i < 1000; ++i) | ||||
350 | // a[5000 + i * m] = a[i] + a[i + 9000] | ||||
351 | // | ||||
352 | // Here grouping gives a check of (5000, 5000 + 1000 * m) against | ||||
353 | // (0, 10000) which is always false. However, if m is 1, there is no | ||||
354 | // dependence. Not grouping the checks for a[i] and a[i + 9000] allows | ||||
355 | // us to perform an accurate check in this case. | ||||
356 | // | ||||
357 | // The above case requires that we have an UnknownDependence between | ||||
358 | // accesses to the same underlying object. This cannot happen unless | ||||
359 | // FoundNonConstantDistanceDependence is set, and therefore UseDependencies | ||||
360 | // is also false. In this case we will use the fallback path and create | ||||
361 | // separate checking groups for all pointers. | ||||
362 | |||||
363 | // If we don't have the dependency partitions, construct a new | ||||
364 | // checking pointer group for each pointer. This is also required | ||||
365 | // for correctness, because in this case we can have checking between | ||||
366 | // pointers to the same underlying object. | ||||
367 | if (!UseDependencies) { | ||||
368 | for (unsigned I = 0; I < Pointers.size(); ++I) | ||||
369 | CheckingGroups.push_back(RuntimeCheckingPtrGroup(I, *this)); | ||||
370 | return; | ||||
371 | } | ||||
372 | |||||
373 | unsigned TotalComparisons = 0; | ||||
374 | |||||
375 | DenseMap<Value *, unsigned> PositionMap; | ||||
376 | for (unsigned Index = 0; Index < Pointers.size(); ++Index) | ||||
377 | PositionMap[Pointers[Index].PointerValue] = Index; | ||||
378 | |||||
379 | // We need to keep track of what pointers we've already seen so we | ||||
380 | // don't process them twice. | ||||
381 | SmallSet<unsigned, 2> Seen; | ||||
382 | |||||
383 | // Go through all equivalence classes, get the "pointer check groups" | ||||
384 | // and add them to the overall solution. We use the order in which accesses | ||||
385 | // appear in 'Pointers' to enforce determinism. | ||||
386 | for (unsigned I = 0; I < Pointers.size(); ++I) { | ||||
387 | // We've seen this pointer before, and therefore already processed | ||||
388 | // its equivalence class. | ||||
389 | if (Seen.count(I)) | ||||
390 | continue; | ||||
391 | |||||
392 | MemoryDepChecker::MemAccessInfo Access(Pointers[I].PointerValue, | ||||
393 | Pointers[I].IsWritePtr); | ||||
394 | |||||
395 | SmallVector<RuntimeCheckingPtrGroup, 2> Groups; | ||||
396 | auto LeaderI = DepCands.findValue(DepCands.getLeaderValue(Access)); | ||||
397 | |||||
398 | // Because DepCands is constructed by visiting accesses in the order in | ||||
399 | // which they appear in alias sets (which is deterministic) and the | ||||
400 | // iteration order within an equivalence class member is only dependent on | ||||
401 | // the order in which unions and insertions are performed on the | ||||
402 | // equivalence class, the iteration order is deterministic. | ||||
403 | for (auto MI = DepCands.member_begin(LeaderI), ME = DepCands.member_end(); | ||||
404 | MI != ME; ++MI) { | ||||
405 | auto PointerI = PositionMap.find(MI->getPointer()); | ||||
406 | assert(PointerI != PositionMap.end() &&((void)0) | ||||
407 | "pointer in equivalence class not found in PositionMap")((void)0); | ||||
408 | unsigned Pointer = PointerI->second; | ||||
409 | bool Merged = false; | ||||
410 | // Mark this pointer as seen. | ||||
411 | Seen.insert(Pointer); | ||||
412 | |||||
413 | // Go through all the existing sets and see if we can find one | ||||
414 | // which can include this pointer. | ||||
415 | for (RuntimeCheckingPtrGroup &Group : Groups) { | ||||
416 | // Don't perform more than a certain amount of comparisons. | ||||
417 | // This should limit the cost of grouping the pointers to something | ||||
418 | // reasonable. If we do end up hitting this threshold, the algorithm | ||||
419 | // will create separate groups for all remaining pointers. | ||||
420 | if (TotalComparisons > MemoryCheckMergeThreshold) | ||||
421 | break; | ||||
422 | |||||
423 | TotalComparisons++; | ||||
424 | |||||
425 | if (Group.addPointer(Pointer, *this)) { | ||||
426 | Merged = true; | ||||
427 | break; | ||||
428 | } | ||||
429 | } | ||||
430 | |||||
431 | if (!Merged) | ||||
432 | // We couldn't add this pointer to any existing set or the threshold | ||||
433 | // for the number of comparisons has been reached. Create a new group | ||||
434 | // to hold the current pointer. | ||||
435 | Groups.push_back(RuntimeCheckingPtrGroup(Pointer, *this)); | ||||
436 | } | ||||
437 | |||||
438 | // We've computed the grouped checks for this partition. | ||||
439 | // Save the results and continue with the next one. | ||||
440 | llvm::copy(Groups, std::back_inserter(CheckingGroups)); | ||||
441 | } | ||||
442 | } | ||||
443 | |||||
444 | bool RuntimePointerChecking::arePointersInSamePartition( | ||||
445 | const SmallVectorImpl<int> &PtrToPartition, unsigned PtrIdx1, | ||||
446 | unsigned PtrIdx2) { | ||||
447 | return (PtrToPartition[PtrIdx1] != -1 && | ||||
448 | PtrToPartition[PtrIdx1] == PtrToPartition[PtrIdx2]); | ||||
449 | } | ||||
450 | |||||
451 | bool RuntimePointerChecking::needsChecking(unsigned I, unsigned J) const { | ||||
452 | const PointerInfo &PointerI = Pointers[I]; | ||||
453 | const PointerInfo &PointerJ = Pointers[J]; | ||||
454 | |||||
455 | // No need to check if two readonly pointers intersect. | ||||
456 | if (!PointerI.IsWritePtr && !PointerJ.IsWritePtr) | ||||
457 | return false; | ||||
458 | |||||
459 | // Only need to check pointers between two different dependency sets. | ||||
460 | if (PointerI.DependencySetId == PointerJ.DependencySetId) | ||||
461 | return false; | ||||
462 | |||||
463 | // Only need to check pointers in the same alias set. | ||||
464 | if (PointerI.AliasSetId != PointerJ.AliasSetId) | ||||
465 | return false; | ||||
466 | |||||
467 | return true; | ||||
468 | } | ||||
469 | |||||
470 | void RuntimePointerChecking::printChecks( | ||||
471 | raw_ostream &OS, const SmallVectorImpl<RuntimePointerCheck> &Checks, | ||||
472 | unsigned Depth) const { | ||||
473 | unsigned N = 0; | ||||
474 | for (const auto &Check : Checks) { | ||||
475 | const auto &First = Check.first->Members, &Second = Check.second->Members; | ||||
476 | |||||
477 | OS.indent(Depth) << "Check " << N++ << ":\n"; | ||||
478 | |||||
479 | OS.indent(Depth + 2) << "Comparing group (" << Check.first << "):\n"; | ||||
480 | for (unsigned K = 0; K < First.size(); ++K) | ||||
481 | OS.indent(Depth + 2) << *Pointers[First[K]].PointerValue << "\n"; | ||||
482 | |||||
483 | OS.indent(Depth + 2) << "Against group (" << Check.second << "):\n"; | ||||
484 | for (unsigned K = 0; K < Second.size(); ++K) | ||||
485 | OS.indent(Depth + 2) << *Pointers[Second[K]].PointerValue << "\n"; | ||||
486 | } | ||||
487 | } | ||||
488 | |||||
489 | void RuntimePointerChecking::print(raw_ostream &OS, unsigned Depth) const { | ||||
490 | |||||
491 | OS.indent(Depth) << "Run-time memory checks:\n"; | ||||
492 | printChecks(OS, Checks, Depth); | ||||
493 | |||||
494 | OS.indent(Depth) << "Grouped accesses:\n"; | ||||
495 | for (unsigned I = 0; I < CheckingGroups.size(); ++I) { | ||||
496 | const auto &CG = CheckingGroups[I]; | ||||
497 | |||||
498 | OS.indent(Depth + 2) << "Group " << &CG << ":\n"; | ||||
499 | OS.indent(Depth + 4) << "(Low: " << *CG.Low << " High: " << *CG.High | ||||
500 | << ")\n"; | ||||
501 | for (unsigned J = 0; J < CG.Members.size(); ++J) { | ||||
502 | OS.indent(Depth + 6) << "Member: " << *Pointers[CG.Members[J]].Expr | ||||
503 | << "\n"; | ||||
504 | } | ||||
505 | } | ||||
506 | } | ||||
507 | |||||
508 | namespace { | ||||
509 | |||||
510 | /// Analyses memory accesses in a loop. | ||||
511 | /// | ||||
512 | /// Checks whether run time pointer checks are needed and builds sets for data | ||||
513 | /// dependence checking. | ||||
514 | class AccessAnalysis { | ||||
515 | public: | ||||
516 | /// Read or write access location. | ||||
517 | typedef PointerIntPair<Value *, 1, bool> MemAccessInfo; | ||||
518 | typedef SmallVector<MemAccessInfo, 8> MemAccessInfoList; | ||||
519 | |||||
520 | AccessAnalysis(Loop *TheLoop, AAResults *AA, LoopInfo *LI, | ||||
521 | MemoryDepChecker::DepCandidates &DA, | ||||
522 | PredicatedScalarEvolution &PSE) | ||||
523 | : TheLoop(TheLoop), AST(*AA), LI(LI), DepCands(DA), | ||||
524 | IsRTCheckAnalysisNeeded(false), PSE(PSE) {} | ||||
525 | |||||
526 | /// Register a load and whether it is only read from. | ||||
527 | void addLoad(MemoryLocation &Loc, bool IsReadOnly) { | ||||
528 | Value *Ptr = const_cast<Value*>(Loc.Ptr); | ||||
529 | AST.add(Ptr, LocationSize::beforeOrAfterPointer(), Loc.AATags); | ||||
530 | Accesses.insert(MemAccessInfo(Ptr, false)); | ||||
531 | if (IsReadOnly) | ||||
532 | ReadOnlyPtr.insert(Ptr); | ||||
533 | } | ||||
534 | |||||
535 | /// Register a store. | ||||
536 | void addStore(MemoryLocation &Loc) { | ||||
537 | Value *Ptr = const_cast<Value*>(Loc.Ptr); | ||||
538 | AST.add(Ptr, LocationSize::beforeOrAfterPointer(), Loc.AATags); | ||||
539 | Accesses.insert(MemAccessInfo(Ptr, true)); | ||||
540 | } | ||||
541 | |||||
542 | /// Check if we can emit a run-time no-alias check for \p Access. | ||||
543 | /// | ||||
544 | /// Returns true if we can emit a run-time no alias check for \p Access. | ||||
545 | /// If we can check this access, this also adds it to a dependence set and | ||||
546 | /// adds a run-time to check for it to \p RtCheck. If \p Assume is true, | ||||
547 | /// we will attempt to use additional run-time checks in order to get | ||||
548 | /// the bounds of the pointer. | ||||
549 | bool createCheckForAccess(RuntimePointerChecking &RtCheck, | ||||
550 | MemAccessInfo Access, | ||||
551 | const ValueToValueMap &Strides, | ||||
552 | DenseMap<Value *, unsigned> &DepSetId, | ||||
553 | Loop *TheLoop, unsigned &RunningDepId, | ||||
554 | unsigned ASId, bool ShouldCheckStride, | ||||
555 | bool Assume); | ||||
556 | |||||
557 | /// Check whether we can check the pointers at runtime for | ||||
558 | /// non-intersection. | ||||
559 | /// | ||||
560 | /// Returns true if we need no check or if we do and we can generate them | ||||
561 | /// (i.e. the pointers have computable bounds). | ||||
562 | bool canCheckPtrAtRT(RuntimePointerChecking &RtCheck, ScalarEvolution *SE, | ||||
563 | Loop *TheLoop, const ValueToValueMap &Strides, | ||||
564 | bool ShouldCheckWrap = false); | ||||
565 | |||||
566 | /// Goes over all memory accesses, checks whether a RT check is needed | ||||
567 | /// and builds sets of dependent accesses. | ||||
568 | void buildDependenceSets() { | ||||
569 | processMemAccesses(); | ||||
570 | } | ||||
571 | |||||
572 | /// Initial processing of memory accesses determined that we need to | ||||
573 | /// perform dependency checking. | ||||
574 | /// | ||||
575 | /// Note that this can later be cleared if we retry memcheck analysis without | ||||
576 | /// dependency checking (i.e. FoundNonConstantDistanceDependence). | ||||
577 | bool isDependencyCheckNeeded() { return !CheckDeps.empty(); } | ||||
578 | |||||
579 | /// We decided that no dependence analysis would be used. Reset the state. | ||||
580 | void resetDepChecks(MemoryDepChecker &DepChecker) { | ||||
581 | CheckDeps.clear(); | ||||
582 | DepChecker.clearDependences(); | ||||
583 | } | ||||
584 | |||||
585 | MemAccessInfoList &getDependenciesToCheck() { return CheckDeps; } | ||||
586 | |||||
587 | private: | ||||
588 | typedef SetVector<MemAccessInfo> PtrAccessSet; | ||||
589 | |||||
590 | /// Go over all memory access and check whether runtime pointer checks | ||||
591 | /// are needed and build sets of dependency check candidates. | ||||
592 | void processMemAccesses(); | ||||
593 | |||||
594 | /// Set of all accesses. | ||||
595 | PtrAccessSet Accesses; | ||||
596 | |||||
597 | /// The loop being checked. | ||||
598 | const Loop *TheLoop; | ||||
599 | |||||
600 | /// List of accesses that need a further dependence check. | ||||
601 | MemAccessInfoList CheckDeps; | ||||
602 | |||||
603 | /// Set of pointers that are read only. | ||||
604 | SmallPtrSet<Value*, 16> ReadOnlyPtr; | ||||
605 | |||||
606 | /// An alias set tracker to partition the access set by underlying object and | ||||
607 | //intrinsic property (such as TBAA metadata). | ||||
608 | AliasSetTracker AST; | ||||
609 | |||||
610 | LoopInfo *LI; | ||||
611 | |||||
612 | /// Sets of potentially dependent accesses - members of one set share an | ||||
613 | /// underlying pointer. The set "CheckDeps" identfies which sets really need a | ||||
614 | /// dependence check. | ||||
615 | MemoryDepChecker::DepCandidates &DepCands; | ||||
616 | |||||
617 | /// Initial processing of memory accesses determined that we may need | ||||
618 | /// to add memchecks. Perform the analysis to determine the necessary checks. | ||||
619 | /// | ||||
620 | /// Note that, this is different from isDependencyCheckNeeded. When we retry | ||||
621 | /// memcheck analysis without dependency checking | ||||
622 | /// (i.e. FoundNonConstantDistanceDependence), isDependencyCheckNeeded is | ||||
623 | /// cleared while this remains set if we have potentially dependent accesses. | ||||
624 | bool IsRTCheckAnalysisNeeded; | ||||
625 | |||||
626 | /// The SCEV predicate containing all the SCEV-related assumptions. | ||||
627 | PredicatedScalarEvolution &PSE; | ||||
628 | }; | ||||
629 | |||||
630 | } // end anonymous namespace | ||||
631 | |||||
632 | /// Check whether a pointer can participate in a runtime bounds check. | ||||
633 | /// If \p Assume, try harder to prove that we can compute the bounds of \p Ptr | ||||
634 | /// by adding run-time checks (overflow checks) if necessary. | ||||
635 | static bool hasComputableBounds(PredicatedScalarEvolution &PSE, | ||||
636 | const ValueToValueMap &Strides, Value *Ptr, | ||||
637 | Loop *L, bool Assume) { | ||||
638 | const SCEV *PtrScev = replaceSymbolicStrideSCEV(PSE, Strides, Ptr); | ||||
639 | |||||
640 | // The bounds for loop-invariant pointer is trivial. | ||||
641 | if (PSE.getSE()->isLoopInvariant(PtrScev, L)) | ||||
642 | return true; | ||||
643 | |||||
644 | const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(PtrScev); | ||||
645 | |||||
646 | if (!AR && Assume) | ||||
647 | AR = PSE.getAsAddRec(Ptr); | ||||
648 | |||||
649 | if (!AR) | ||||
650 | return false; | ||||
651 | |||||
652 | return AR->isAffine(); | ||||
653 | } | ||||
654 | |||||
655 | /// Check whether a pointer address cannot wrap. | ||||
656 | static bool isNoWrap(PredicatedScalarEvolution &PSE, | ||||
657 | const ValueToValueMap &Strides, Value *Ptr, Loop *L) { | ||||
658 | const SCEV *PtrScev = PSE.getSCEV(Ptr); | ||||
659 | if (PSE.getSE()->isLoopInvariant(PtrScev, L)) | ||||
660 | return true; | ||||
661 | |||||
662 | int64_t Stride = getPtrStride(PSE, Ptr, L, Strides); | ||||
663 | if (Stride == 1 || PSE.hasNoOverflow(Ptr, SCEVWrapPredicate::IncrementNUSW)) | ||||
664 | return true; | ||||
665 | |||||
666 | return false; | ||||
667 | } | ||||
668 | |||||
669 | bool AccessAnalysis::createCheckForAccess(RuntimePointerChecking &RtCheck, | ||||
670 | MemAccessInfo Access, | ||||
671 | const ValueToValueMap &StridesMap, | ||||
672 | DenseMap<Value *, unsigned> &DepSetId, | ||||
673 | Loop *TheLoop, unsigned &RunningDepId, | ||||
674 | unsigned ASId, bool ShouldCheckWrap, | ||||
675 | bool Assume) { | ||||
676 | Value *Ptr = Access.getPointer(); | ||||
677 | |||||
678 | if (!hasComputableBounds(PSE, StridesMap, Ptr, TheLoop, Assume)) | ||||
679 | return false; | ||||
680 | |||||
681 | // When we run after a failing dependency check we have to make sure | ||||
682 | // we don't have wrapping pointers. | ||||
683 | if (ShouldCheckWrap
| ||||
684 | auto *Expr = PSE.getSCEV(Ptr); | ||||
685 | if (!Assume || !isa<SCEVAddRecExpr>(Expr)) | ||||
686 | return false; | ||||
687 | PSE.setNoOverflow(Ptr, SCEVWrapPredicate::IncrementNUSW); | ||||
688 | } | ||||
689 | |||||
690 | // The id of the dependence set. | ||||
691 | unsigned DepId; | ||||
692 | |||||
693 | if (isDependencyCheckNeeded()) { | ||||
694 | Value *Leader = DepCands.getLeaderValue(Access).getPointer(); | ||||
695 | unsigned &LeaderId = DepSetId[Leader]; | ||||
696 | if (!LeaderId) | ||||
697 | LeaderId = RunningDepId++; | ||||
698 | DepId = LeaderId; | ||||
699 | } else | ||||
700 | // Each access has its own dependence set. | ||||
701 | DepId = RunningDepId++; | ||||
702 | |||||
703 | bool IsWrite = Access.getInt(); | ||||
704 | RtCheck.insert(TheLoop, Ptr, IsWrite, DepId, ASId, StridesMap, PSE); | ||||
705 | LLVM_DEBUG(dbgs() << "LAA: Found a runtime check ptr:" << *Ptr << '\n')do { } while (false); | ||||
706 | |||||
707 | return true; | ||||
708 | } | ||||
709 | |||||
710 | bool AccessAnalysis::canCheckPtrAtRT(RuntimePointerChecking &RtCheck, | ||||
711 | ScalarEvolution *SE, Loop *TheLoop, | ||||
712 | const ValueToValueMap &StridesMap, | ||||
713 | bool ShouldCheckWrap) { | ||||
714 | // Find pointers with computable bounds. We are going to use this information | ||||
715 | // to place a runtime bound check. | ||||
716 | bool CanDoRT = true; | ||||
717 | |||||
718 | bool MayNeedRTCheck = false; | ||||
719 | if (!IsRTCheckAnalysisNeeded) return true; | ||||
720 | |||||
721 | bool IsDepCheckNeeded = isDependencyCheckNeeded(); | ||||
722 | |||||
723 | // We assign a consecutive id to access from different alias sets. | ||||
724 | // Accesses between different groups doesn't need to be checked. | ||||
725 | unsigned ASId = 0; | ||||
726 | for (auto &AS : AST) { | ||||
727 | int NumReadPtrChecks = 0; | ||||
728 | int NumWritePtrChecks = 0; | ||||
729 | bool CanDoAliasSetRT = true; | ||||
730 | ++ASId; | ||||
731 | |||||
732 | // We assign consecutive id to access from different dependence sets. | ||||
733 | // Accesses within the same set don't need a runtime check. | ||||
734 | unsigned RunningDepId = 1; | ||||
735 | DenseMap<Value *, unsigned> DepSetId; | ||||
736 | |||||
737 | SmallVector<MemAccessInfo, 4> Retries; | ||||
738 | |||||
739 | // First, count how many write and read accesses are in the alias set. Also | ||||
740 | // collect MemAccessInfos for later. | ||||
741 | SmallVector<MemAccessInfo, 4> AccessInfos; | ||||
742 | for (const auto &A : AS) { | ||||
743 | Value *Ptr = A.getValue(); | ||||
744 | bool IsWrite = Accesses.count(MemAccessInfo(Ptr, true)); | ||||
745 | |||||
746 | if (IsWrite) | ||||
747 | ++NumWritePtrChecks; | ||||
748 | else | ||||
749 | ++NumReadPtrChecks; | ||||
750 | AccessInfos.emplace_back(Ptr, IsWrite); | ||||
751 | } | ||||
752 | |||||
753 | // We do not need runtime checks for this alias set, if there are no writes | ||||
754 | // or a single write and no reads. | ||||
755 | if (NumWritePtrChecks
| ||||
756 | (NumWritePtrChecks
| ||||
757 | assert((AS.size() <= 1 ||((void)0) | ||||
758 | all_of(AS,((void)0) | ||||
759 | [this](auto AC) {((void)0) | ||||
760 | MemAccessInfo AccessWrite(AC.getValue(), true);((void)0) | ||||
761 | return DepCands.findValue(AccessWrite) == DepCands.end();((void)0) | ||||
762 | })) &&((void)0) | ||||
763 | "Can only skip updating CanDoRT below, if all entries in AS "((void)0) | ||||
764 | "are reads or there is at most 1 entry")((void)0); | ||||
765 | continue; | ||||
766 | } | ||||
767 | |||||
768 | for (auto &Access : AccessInfos) { | ||||
769 | if (!createCheckForAccess(RtCheck, Access, StridesMap, DepSetId, TheLoop, | ||||
770 | RunningDepId, ASId, ShouldCheckWrap, false)) { | ||||
771 | LLVM_DEBUG(dbgs() << "LAA: Can't find bounds for ptr:"do { } while (false) | ||||
772 | << *Access.getPointer() << '\n')do { } while (false); | ||||
773 | Retries.push_back(Access); | ||||
774 | CanDoAliasSetRT = false; | ||||
775 | } | ||||
776 | } | ||||
777 | |||||
778 | // Note that this function computes CanDoRT and MayNeedRTCheck | ||||
779 | // independently. For example CanDoRT=false, MayNeedRTCheck=false means that | ||||
780 | // we have a pointer for which we couldn't find the bounds but we don't | ||||
781 | // actually need to emit any checks so it does not matter. | ||||
782 | // | ||||
783 | // We need runtime checks for this alias set, if there are at least 2 | ||||
784 | // dependence sets (in which case RunningDepId > 2) or if we need to re-try | ||||
785 | // any bound checks (because in that case the number of dependence sets is | ||||
786 | // incomplete). | ||||
787 | bool NeedsAliasSetRTCheck = RunningDepId > 2 || !Retries.empty(); | ||||
788 | |||||
789 | // We need to perform run-time alias checks, but some pointers had bounds | ||||
790 | // that couldn't be checked. | ||||
791 | if (NeedsAliasSetRTCheck && !CanDoAliasSetRT) { | ||||
792 | // Reset the CanDoSetRt flag and retry all accesses that have failed. | ||||
793 | // We know that we need these checks, so we can now be more aggressive | ||||
794 | // and add further checks if required (overflow checks). | ||||
795 | CanDoAliasSetRT = true; | ||||
796 | for (auto Access : Retries) | ||||
797 | if (!createCheckForAccess(RtCheck, Access, StridesMap, DepSetId, | ||||
798 | TheLoop, RunningDepId, ASId, | ||||
799 | ShouldCheckWrap, /*Assume=*/true)) { | ||||
800 | CanDoAliasSetRT = false; | ||||
801 | break; | ||||
802 | } | ||||
803 | } | ||||
804 | |||||
805 | CanDoRT &= CanDoAliasSetRT; | ||||
806 | MayNeedRTCheck |= NeedsAliasSetRTCheck; | ||||
807 | ++ASId; | ||||
808 | } | ||||
809 | |||||
810 | // If the pointers that we would use for the bounds comparison have different | ||||
811 | // address spaces, assume the values aren't directly comparable, so we can't | ||||
812 | // use them for the runtime check. We also have to assume they could | ||||
813 | // overlap. In the future there should be metadata for whether address spaces | ||||
814 | // are disjoint. | ||||
815 | unsigned NumPointers = RtCheck.Pointers.size(); | ||||
816 | for (unsigned i = 0; i < NumPointers; ++i) { | ||||
817 | for (unsigned j = i + 1; j < NumPointers; ++j) { | ||||
818 | // Only need to check pointers between two different dependency sets. | ||||
819 | if (RtCheck.Pointers[i].DependencySetId == | ||||
820 | RtCheck.Pointers[j].DependencySetId) | ||||
821 | continue; | ||||
822 | // Only need to check pointers in the same alias set. | ||||
823 | if (RtCheck.Pointers[i].AliasSetId != RtCheck.Pointers[j].AliasSetId) | ||||
824 | continue; | ||||
825 | |||||
826 | Value *PtrI = RtCheck.Pointers[i].PointerValue; | ||||
827 | Value *PtrJ = RtCheck.Pointers[j].PointerValue; | ||||
828 | |||||
829 | unsigned ASi = PtrI->getType()->getPointerAddressSpace(); | ||||
830 | unsigned ASj = PtrJ->getType()->getPointerAddressSpace(); | ||||
831 | if (ASi != ASj) { | ||||
832 | LLVM_DEBUG(do { } while (false) | ||||
833 | dbgs() << "LAA: Runtime check would require comparison between"do { } while (false) | ||||
834 | " different address spaces\n")do { } while (false); | ||||
835 | return false; | ||||
836 | } | ||||
837 | } | ||||
838 | } | ||||
839 | |||||
840 | if (MayNeedRTCheck && CanDoRT) | ||||
841 | RtCheck.generateChecks(DepCands, IsDepCheckNeeded); | ||||
842 | |||||
843 | LLVM_DEBUG(dbgs() << "LAA: We need to do " << RtCheck.getNumberOfChecks()do { } while (false) | ||||
844 | << " pointer comparisons.\n")do { } while (false); | ||||
845 | |||||
846 | // If we can do run-time checks, but there are no checks, no runtime checks | ||||
847 | // are needed. This can happen when all pointers point to the same underlying | ||||
848 | // object for example. | ||||
849 | RtCheck.Need = CanDoRT ? RtCheck.getNumberOfChecks() != 0 : MayNeedRTCheck; | ||||
850 | |||||
851 | bool CanDoRTIfNeeded = !RtCheck.Need || CanDoRT; | ||||
852 | if (!CanDoRTIfNeeded) | ||||
853 | RtCheck.reset(); | ||||
854 | return CanDoRTIfNeeded; | ||||
855 | } | ||||
856 | |||||
857 | void AccessAnalysis::processMemAccesses() { | ||||
858 | // We process the set twice: first we process read-write pointers, last we | ||||
859 | // process read-only pointers. This allows us to skip dependence tests for | ||||
860 | // read-only pointers. | ||||
861 | |||||
862 | LLVM_DEBUG(dbgs() << "LAA: Processing memory accesses...\n")do { } while (false); | ||||
863 | LLVM_DEBUG(dbgs() << " AST: "; AST.dump())do { } while (false); | ||||
864 | LLVM_DEBUG(dbgs() << "LAA: Accesses(" << Accesses.size() << "):\n")do { } while (false); | ||||
865 | LLVM_DEBUG({do { } while (false) | ||||
866 | for (auto A : Accesses)do { } while (false) | ||||
867 | dbgs() << "\t" << *A.getPointer() << " (" <<do { } while (false) | ||||
868 | (A.getInt() ? "write" : (ReadOnlyPtr.count(A.getPointer()) ?do { } while (false) | ||||
869 | "read-only" : "read")) << ")\n";do { } while (false) | ||||
870 | })do { } while (false); | ||||
871 | |||||
872 | // The AliasSetTracker has nicely partitioned our pointers by metadata | ||||
873 | // compatibility and potential for underlying-object overlap. As a result, we | ||||
874 | // only need to check for potential pointer dependencies within each alias | ||||
875 | // set. | ||||
876 | for (const auto &AS : AST) { | ||||
877 | // Note that both the alias-set tracker and the alias sets themselves used | ||||
878 | // linked lists internally and so the iteration order here is deterministic | ||||
879 | // (matching the original instruction order within each set). | ||||
880 | |||||
881 | bool SetHasWrite = false; | ||||
882 | |||||
883 | // Map of pointers to last access encountered. | ||||
884 | typedef DenseMap<const Value*, MemAccessInfo> UnderlyingObjToAccessMap; | ||||
885 | UnderlyingObjToAccessMap ObjToLastAccess; | ||||
886 | |||||
887 | // Set of access to check after all writes have been processed. | ||||
888 | PtrAccessSet DeferredAccesses; | ||||
889 | |||||
890 | // Iterate over each alias set twice, once to process read/write pointers, | ||||
891 | // and then to process read-only pointers. | ||||
892 | for (int SetIteration = 0; SetIteration < 2; ++SetIteration) { | ||||
893 | bool UseDeferred = SetIteration > 0; | ||||
894 | PtrAccessSet &S = UseDeferred ? DeferredAccesses : Accesses; | ||||
895 | |||||
896 | for (const auto &AV : AS) { | ||||
897 | Value *Ptr = AV.getValue(); | ||||
898 | |||||
899 | // For a single memory access in AliasSetTracker, Accesses may contain | ||||
900 | // both read and write, and they both need to be handled for CheckDeps. | ||||
901 | for (const auto &AC : S) { | ||||
902 | if (AC.getPointer() != Ptr) | ||||
903 | continue; | ||||
904 | |||||
905 | bool IsWrite = AC.getInt(); | ||||
906 | |||||
907 | // If we're using the deferred access set, then it contains only | ||||
908 | // reads. | ||||
909 | bool IsReadOnlyPtr = ReadOnlyPtr.count(Ptr) && !IsWrite; | ||||
910 | if (UseDeferred && !IsReadOnlyPtr) | ||||
911 | continue; | ||||
912 | // Otherwise, the pointer must be in the PtrAccessSet, either as a | ||||
913 | // read or a write. | ||||
914 | assert(((IsReadOnlyPtr && UseDeferred) || IsWrite ||((void)0) | ||||
915 | S.count(MemAccessInfo(Ptr, false))) &&((void)0) | ||||
916 | "Alias-set pointer not in the access set?")((void)0); | ||||
917 | |||||
918 | MemAccessInfo Access(Ptr, IsWrite); | ||||
919 | DepCands.insert(Access); | ||||
920 | |||||
921 | // Memorize read-only pointers for later processing and skip them in | ||||
922 | // the first round (they need to be checked after we have seen all | ||||
923 | // write pointers). Note: we also mark pointer that are not | ||||
924 | // consecutive as "read-only" pointers (so that we check | ||||
925 | // "a[b[i]] +="). Hence, we need the second check for "!IsWrite". | ||||
926 | if (!UseDeferred && IsReadOnlyPtr) { | ||||
927 | DeferredAccesses.insert(Access); | ||||
928 | continue; | ||||
929 | } | ||||
930 | |||||
931 | // If this is a write - check other reads and writes for conflicts. If | ||||
932 | // this is a read only check other writes for conflicts (but only if | ||||
933 | // there is no other write to the ptr - this is an optimization to | ||||
934 | // catch "a[i] = a[i] + " without having to do a dependence check). | ||||
935 | if ((IsWrite || IsReadOnlyPtr) && SetHasWrite) { | ||||
936 | CheckDeps.push_back(Access); | ||||
937 | IsRTCheckAnalysisNeeded = true; | ||||
938 | } | ||||
939 | |||||
940 | if (IsWrite) | ||||
941 | SetHasWrite = true; | ||||
942 | |||||
943 | // Create sets of pointers connected by a shared alias set and | ||||
944 | // underlying object. | ||||
945 | typedef SmallVector<const Value *, 16> ValueVector; | ||||
946 | ValueVector TempObjects; | ||||
947 | |||||
948 | getUnderlyingObjects(Ptr, TempObjects, LI); | ||||
949 | LLVM_DEBUG(dbgs()do { } while (false) | ||||
950 | << "Underlying objects for pointer " << *Ptr << "\n")do { } while (false); | ||||
951 | for (const Value *UnderlyingObj : TempObjects) { | ||||
952 | // nullptr never alias, don't join sets for pointer that have "null" | ||||
953 | // in their UnderlyingObjects list. | ||||
954 | if (isa<ConstantPointerNull>(UnderlyingObj) && | ||||
955 | !NullPointerIsDefined( | ||||
956 | TheLoop->getHeader()->getParent(), | ||||
957 | UnderlyingObj->getType()->getPointerAddressSpace())) | ||||
958 | continue; | ||||
959 | |||||
960 | UnderlyingObjToAccessMap::iterator Prev = | ||||
961 | ObjToLastAccess.find(UnderlyingObj); | ||||
962 | if (Prev != ObjToLastAccess.end()) | ||||
963 | DepCands.unionSets(Access, Prev->second); | ||||
964 | |||||
965 | ObjToLastAccess[UnderlyingObj] = Access; | ||||
966 | LLVM_DEBUG(dbgs() << " " << *UnderlyingObj << "\n")do { } while (false); | ||||
967 | } | ||||
968 | } | ||||
969 | } | ||||
970 | } | ||||
971 | } | ||||
972 | } | ||||
973 | |||||
974 | static bool isInBoundsGep(Value *Ptr) { | ||||
975 | if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Ptr)) | ||||
976 | return GEP->isInBounds(); | ||||
977 | return false; | ||||
978 | } | ||||
979 | |||||
980 | /// Return true if an AddRec pointer \p Ptr is unsigned non-wrapping, | ||||
981 | /// i.e. monotonically increasing/decreasing. | ||||
982 | static bool isNoWrapAddRec(Value *Ptr, const SCEVAddRecExpr *AR, | ||||
983 | PredicatedScalarEvolution &PSE, const Loop *L) { | ||||
984 | // FIXME: This should probably only return true for NUW. | ||||
985 | if (AR->getNoWrapFlags(SCEV::NoWrapMask)) | ||||
986 | return true; | ||||
987 | |||||
988 | // Scalar evolution does not propagate the non-wrapping flags to values that | ||||
989 | // are derived from a non-wrapping induction variable because non-wrapping | ||||
990 | // could be flow-sensitive. | ||||
991 | // | ||||
992 | // Look through the potentially overflowing instruction to try to prove | ||||
993 | // non-wrapping for the *specific* value of Ptr. | ||||
994 | |||||
995 | // The arithmetic implied by an inbounds GEP can't overflow. | ||||
996 | auto *GEP = dyn_cast<GetElementPtrInst>(Ptr); | ||||
997 | if (!GEP || !GEP->isInBounds()) | ||||
998 | return false; | ||||
999 | |||||
1000 | // Make sure there is only one non-const index and analyze that. | ||||
1001 | Value *NonConstIndex = nullptr; | ||||
1002 | for (Value *Index : GEP->indices()) | ||||
1003 | if (!isa<ConstantInt>(Index)) { | ||||
1004 | if (NonConstIndex) | ||||
1005 | return false; | ||||
1006 | NonConstIndex = Index; | ||||
1007 | } | ||||
1008 | if (!NonConstIndex) | ||||
1009 | // The recurrence is on the pointer, ignore for now. | ||||
1010 | return false; | ||||
1011 | |||||
1012 | // The index in GEP is signed. It is non-wrapping if it's derived from a NSW | ||||
1013 | // AddRec using a NSW operation. | ||||
1014 | if (auto *OBO = dyn_cast<OverflowingBinaryOperator>(NonConstIndex)) | ||||
1015 | if (OBO->hasNoSignedWrap() && | ||||
1016 | // Assume constant for other the operand so that the AddRec can be | ||||
1017 | // easily found. | ||||
1018 | isa<ConstantInt>(OBO->getOperand(1))) { | ||||
1019 | auto *OpScev = PSE.getSCEV(OBO->getOperand(0)); | ||||
1020 | |||||
1021 | if (auto *OpAR = dyn_cast<SCEVAddRecExpr>(OpScev)) | ||||
1022 | return OpAR->getLoop() == L && OpAR->getNoWrapFlags(SCEV::FlagNSW); | ||||
1023 | } | ||||
1024 | |||||
1025 | return false; | ||||
1026 | } | ||||
1027 | |||||
1028 | /// Check whether the access through \p Ptr has a constant stride. | ||||
1029 | int64_t llvm::getPtrStride(PredicatedScalarEvolution &PSE, Value *Ptr, | ||||
1030 | const Loop *Lp, const ValueToValueMap &StridesMap, | ||||
1031 | bool Assume, bool ShouldCheckWrap) { | ||||
1032 | Type *Ty = Ptr->getType(); | ||||
1033 | assert(Ty->isPointerTy() && "Unexpected non-ptr")((void)0); | ||||
1034 | |||||
1035 | // Make sure that the pointer does not point to aggregate types. | ||||
1036 | auto *PtrTy = cast<PointerType>(Ty); | ||||
1037 | if (PtrTy->getElementType()->isAggregateType()) { | ||||
1038 | LLVM_DEBUG(dbgs() << "LAA: Bad stride - Not a pointer to a scalar type"do { } while (false) | ||||
1039 | << *Ptr << "\n")do { } while (false); | ||||
1040 | return 0; | ||||
1041 | } | ||||
1042 | |||||
1043 | const SCEV *PtrScev = replaceSymbolicStrideSCEV(PSE, StridesMap, Ptr); | ||||
1044 | |||||
1045 | const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(PtrScev); | ||||
1046 | if (Assume && !AR) | ||||
1047 | AR = PSE.getAsAddRec(Ptr); | ||||
1048 | |||||
1049 | if (!AR) { | ||||
1050 | LLVM_DEBUG(dbgs() << "LAA: Bad stride - Not an AddRecExpr pointer " << *Ptrdo { } while (false) | ||||
1051 | << " SCEV: " << *PtrScev << "\n")do { } while (false); | ||||
1052 | return 0; | ||||
1053 | } | ||||
1054 | |||||
1055 | // The access function must stride over the innermost loop. | ||||
1056 | if (Lp != AR->getLoop()) { | ||||
1057 | LLVM_DEBUG(dbgs() << "LAA: Bad stride - Not striding over innermost loop "do { } while (false) | ||||
1058 | << *Ptr << " SCEV: " << *AR << "\n")do { } while (false); | ||||
1059 | return 0; | ||||
1060 | } | ||||
1061 | |||||
1062 | // The address calculation must not wrap. Otherwise, a dependence could be | ||||
1063 | // inverted. | ||||
1064 | // An inbounds getelementptr that is a AddRec with a unit stride | ||||
1065 | // cannot wrap per definition. The unit stride requirement is checked later. | ||||
1066 | // An getelementptr without an inbounds attribute and unit stride would have | ||||
1067 | // to access the pointer value "0" which is undefined behavior in address | ||||
1068 | // space 0, therefore we can also vectorize this case. | ||||
1069 | bool IsInBoundsGEP = isInBoundsGep(Ptr); | ||||
1070 | bool IsNoWrapAddRec = !ShouldCheckWrap || | ||||
1071 | PSE.hasNoOverflow(Ptr, SCEVWrapPredicate::IncrementNUSW) || | ||||
1072 | isNoWrapAddRec(Ptr, AR, PSE, Lp); | ||||
1073 | if (!IsNoWrapAddRec && !IsInBoundsGEP && | ||||
1074 | NullPointerIsDefined(Lp->getHeader()->getParent(), | ||||
1075 | PtrTy->getAddressSpace())) { | ||||
1076 | if (Assume) { | ||||
1077 | PSE.setNoOverflow(Ptr, SCEVWrapPredicate::IncrementNUSW); | ||||
1078 | IsNoWrapAddRec = true; | ||||
1079 | LLVM_DEBUG(dbgs() << "LAA: Pointer may wrap in the address space:\n"do { } while (false) | ||||
1080 | << "LAA: Pointer: " << *Ptr << "\n"do { } while (false) | ||||
1081 | << "LAA: SCEV: " << *AR << "\n"do { } while (false) | ||||
1082 | << "LAA: Added an overflow assumption\n")do { } while (false); | ||||
1083 | } else { | ||||
1084 | LLVM_DEBUG(do { } while (false) | ||||
1085 | dbgs() << "LAA: Bad stride - Pointer may wrap in the address space "do { } while (false) | ||||
1086 | << *Ptr << " SCEV: " << *AR << "\n")do { } while (false); | ||||
1087 | return 0; | ||||
1088 | } | ||||
1089 | } | ||||
1090 | |||||
1091 | // Check the step is constant. | ||||
1092 | const SCEV *Step = AR->getStepRecurrence(*PSE.getSE()); | ||||
1093 | |||||
1094 | // Calculate the pointer stride and check if it is constant. | ||||
1095 | const SCEVConstant *C = dyn_cast<SCEVConstant>(Step); | ||||
1096 | if (!C) { | ||||
1097 | LLVM_DEBUG(dbgs() << "LAA: Bad stride - Not a constant strided " << *Ptrdo { } while (false) | ||||
1098 | << " SCEV: " << *AR << "\n")do { } while (false); | ||||
1099 | return 0; | ||||
1100 | } | ||||
1101 | |||||
1102 | auto &DL = Lp->getHeader()->getModule()->getDataLayout(); | ||||
1103 | int64_t Size = DL.getTypeAllocSize(PtrTy->getElementType()); | ||||
1104 | const APInt &APStepVal = C->getAPInt(); | ||||
1105 | |||||
1106 | // Huge step value - give up. | ||||
1107 | if (APStepVal.getBitWidth() > 64) | ||||
1108 | return 0; | ||||
1109 | |||||
1110 | int64_t StepVal = APStepVal.getSExtValue(); | ||||
1111 | |||||
1112 | // Strided access. | ||||
1113 | int64_t Stride = StepVal / Size; | ||||
1114 | int64_t Rem = StepVal % Size; | ||||
1115 | if (Rem) | ||||
1116 | return 0; | ||||
1117 | |||||
1118 | // If the SCEV could wrap but we have an inbounds gep with a unit stride we | ||||
1119 | // know we can't "wrap around the address space". In case of address space | ||||
1120 | // zero we know that this won't happen without triggering undefined behavior. | ||||
1121 | if (!IsNoWrapAddRec && Stride != 1 && Stride != -1 && | ||||
1122 | (IsInBoundsGEP || !NullPointerIsDefined(Lp->getHeader()->getParent(), | ||||
1123 | PtrTy->getAddressSpace()))) { | ||||
1124 | if (Assume) { | ||||
1125 | // We can avoid this case by adding a run-time check. | ||||
1126 | LLVM_DEBUG(dbgs() << "LAA: Non unit strided pointer which is not either "do { } while (false) | ||||
1127 | << "inbounds or in address space 0 may wrap:\n"do { } while (false) | ||||
1128 | << "LAA: Pointer: " << *Ptr << "\n"do { } while (false) | ||||
1129 | << "LAA: SCEV: " << *AR << "\n"do { } while (false) | ||||
1130 | << "LAA: Added an overflow assumption\n")do { } while (false); | ||||
1131 | PSE.setNoOverflow(Ptr, SCEVWrapPredicate::IncrementNUSW); | ||||
1132 | } else | ||||
1133 | return 0; | ||||
1134 | } | ||||
1135 | |||||
1136 | return Stride; | ||||
1137 | } | ||||
1138 | |||||
1139 | Optional<int> llvm::getPointersDiff(Type *ElemTyA, Value *PtrA, Type *ElemTyB, | ||||
1140 | Value *PtrB, const DataLayout &DL, | ||||
1141 | ScalarEvolution &SE, bool StrictCheck, | ||||
1142 | bool CheckType) { | ||||
1143 | assert(PtrA && PtrB && "Expected non-nullptr pointers.")((void)0); | ||||
1144 | assert(cast<PointerType>(PtrA->getType())((void)0) | ||||
1145 | ->isOpaqueOrPointeeTypeMatches(ElemTyA) && "Wrong PtrA type")((void)0); | ||||
1146 | assert(cast<PointerType>(PtrB->getType())((void)0) | ||||
1147 | ->isOpaqueOrPointeeTypeMatches(ElemTyB) && "Wrong PtrB type")((void)0); | ||||
1148 | |||||
1149 | // Make sure that A and B are different pointers. | ||||
1150 | if (PtrA == PtrB) | ||||
1151 | return 0; | ||||
1152 | |||||
1153 | // Make sure that the element types are the same if required. | ||||
1154 | if (CheckType && ElemTyA != ElemTyB) | ||||
1155 | return None; | ||||
1156 | |||||
1157 | unsigned ASA = PtrA->getType()->getPointerAddressSpace(); | ||||
1158 | unsigned ASB = PtrB->getType()->getPointerAddressSpace(); | ||||
1159 | |||||
1160 | // Check that the address spaces match. | ||||
1161 | if (ASA != ASB) | ||||
1162 | return None; | ||||
1163 | unsigned IdxWidth = DL.getIndexSizeInBits(ASA); | ||||
1164 | |||||
1165 | APInt OffsetA(IdxWidth, 0), OffsetB(IdxWidth, 0); | ||||
1166 | Value *PtrA1 = PtrA->stripAndAccumulateInBoundsConstantOffsets(DL, OffsetA); | ||||
1167 | Value *PtrB1 = PtrB->stripAndAccumulateInBoundsConstantOffsets(DL, OffsetB); | ||||
1168 | |||||
1169 | int Val; | ||||
1170 | if (PtrA1 == PtrB1) { | ||||
1171 | // Retrieve the address space again as pointer stripping now tracks through | ||||
1172 | // `addrspacecast`. | ||||
1173 | ASA = cast<PointerType>(PtrA1->getType())->getAddressSpace(); | ||||
1174 | ASB = cast<PointerType>(PtrB1->getType())->getAddressSpace(); | ||||
1175 | // Check that the address spaces match and that the pointers are valid. | ||||
1176 | if (ASA != ASB) | ||||
1177 | return None; | ||||
1178 | |||||
1179 | IdxWidth = DL.getIndexSizeInBits(ASA); | ||||
1180 | OffsetA = OffsetA.sextOrTrunc(IdxWidth); | ||||
1181 | OffsetB = OffsetB.sextOrTrunc(IdxWidth); | ||||
1182 | |||||
1183 | OffsetB -= OffsetA; | ||||
1184 | Val = OffsetB.getSExtValue(); | ||||
1185 | } else { | ||||
1186 | // Otherwise compute the distance with SCEV between the base pointers. | ||||
1187 | const SCEV *PtrSCEVA = SE.getSCEV(PtrA); | ||||
1188 | const SCEV *PtrSCEVB = SE.getSCEV(PtrB); | ||||
1189 | const auto *Diff = | ||||
1190 | dyn_cast<SCEVConstant>(SE.getMinusSCEV(PtrSCEVB, PtrSCEVA)); | ||||
1191 | if (!Diff) | ||||
1192 | return None; | ||||
1193 | Val = Diff->getAPInt().getSExtValue(); | ||||
1194 | } | ||||
1195 | int Size = DL.getTypeStoreSize(ElemTyA); | ||||
1196 | int Dist = Val / Size; | ||||
1197 | |||||
1198 | // Ensure that the calculated distance matches the type-based one after all | ||||
1199 | // the bitcasts removal in the provided pointers. | ||||
1200 | if (!StrictCheck || Dist * Size == Val) | ||||
1201 | return Dist; | ||||
1202 | return None; | ||||
1203 | } | ||||
1204 | |||||
1205 | bool llvm::sortPtrAccesses(ArrayRef<Value *> VL, Type *ElemTy, | ||||
1206 | const DataLayout &DL, ScalarEvolution &SE, | ||||
1207 | SmallVectorImpl<unsigned> &SortedIndices) { | ||||
1208 | assert(llvm::all_of(((void)0) | ||||
1209 | VL, [](const Value *V) { return V->getType()->isPointerTy(); }) &&((void)0) | ||||
1210 | "Expected list of pointer operands.")((void)0); | ||||
1211 | // Walk over the pointers, and map each of them to an offset relative to | ||||
1212 | // first pointer in the array. | ||||
1213 | Value *Ptr0 = VL[0]; | ||||
1214 | |||||
1215 | using DistOrdPair = std::pair<int64_t, int>; | ||||
1216 | auto Compare = [](const DistOrdPair &L, const DistOrdPair &R) { | ||||
1217 | return L.first < R.first; | ||||
1218 | }; | ||||
1219 | std::set<DistOrdPair, decltype(Compare)> Offsets(Compare); | ||||
1220 | Offsets.emplace(0, 0); | ||||
1221 | int Cnt = 1; | ||||
1222 | bool IsConsecutive = true; | ||||
1223 | for (auto *Ptr : VL.drop_front()) { | ||||
1224 | Optional<int> Diff = getPointersDiff(ElemTy, Ptr0, ElemTy, Ptr, DL, SE, | ||||
1225 | /*StrictCheck=*/true); | ||||
1226 | if (!Diff) | ||||
1227 | return false; | ||||
1228 | |||||
1229 | // Check if the pointer with the same offset is found. | ||||
1230 | int64_t Offset = *Diff; | ||||
1231 | auto Res = Offsets.emplace(Offset, Cnt); | ||||
1232 | if (!Res.second) | ||||
1233 | return false; | ||||
1234 | // Consecutive order if the inserted element is the last one. | ||||
1235 | IsConsecutive = IsConsecutive && std::next(Res.first) == Offsets.end(); | ||||
1236 | ++Cnt; | ||||
1237 | } | ||||
1238 | SortedIndices.clear(); | ||||
1239 | if (!IsConsecutive) { | ||||
1240 | // Fill SortedIndices array only if it is non-consecutive. | ||||
1241 | SortedIndices.resize(VL.size()); | ||||
1242 | Cnt = 0; | ||||
1243 | for (const std::pair<int64_t, int> &Pair : Offsets) { | ||||
1244 | SortedIndices[Cnt] = Pair.second; | ||||
1245 | ++Cnt; | ||||
1246 | } | ||||
1247 | } | ||||
1248 | return true; | ||||
1249 | } | ||||
1250 | |||||
1251 | /// Returns true if the memory operations \p A and \p B are consecutive. | ||||
1252 | bool llvm::isConsecutiveAccess(Value *A, Value *B, const DataLayout &DL, | ||||
1253 | ScalarEvolution &SE, bool CheckType) { | ||||
1254 | Value *PtrA = getLoadStorePointerOperand(A); | ||||
1255 | Value *PtrB = getLoadStorePointerOperand(B); | ||||
1256 | if (!PtrA || !PtrB) | ||||
1257 | return false; | ||||
1258 | Type *ElemTyA = getLoadStoreType(A); | ||||
1259 | Type *ElemTyB = getLoadStoreType(B); | ||||
1260 | Optional<int> Diff = getPointersDiff(ElemTyA, PtrA, ElemTyB, PtrB, DL, SE, | ||||
1261 | /*StrictCheck=*/true, CheckType); | ||||
1262 | return Diff && *Diff == 1; | ||||
1263 | } | ||||
1264 | |||||
1265 | MemoryDepChecker::VectorizationSafetyStatus | ||||
1266 | MemoryDepChecker::Dependence::isSafeForVectorization(DepType Type) { | ||||
1267 | switch (Type) { | ||||
1268 | case NoDep: | ||||
1269 | case Forward: | ||||
1270 | case BackwardVectorizable: | ||||
1271 | return VectorizationSafetyStatus::Safe; | ||||
1272 | |||||
1273 | case Unknown: | ||||
1274 | return VectorizationSafetyStatus::PossiblySafeWithRtChecks; | ||||
1275 | case ForwardButPreventsForwarding: | ||||
1276 | case Backward: | ||||
1277 | case BackwardVectorizableButPreventsForwarding: | ||||
1278 | return VectorizationSafetyStatus::Unsafe; | ||||
1279 | } | ||||
1280 | llvm_unreachable("unexpected DepType!")__builtin_unreachable(); | ||||
1281 | } | ||||
1282 | |||||
1283 | bool MemoryDepChecker::Dependence::isBackward() const { | ||||
1284 | switch (Type) { | ||||
1285 | case NoDep: | ||||
1286 | case Forward: | ||||
1287 | case ForwardButPreventsForwarding: | ||||
1288 | case Unknown: | ||||
1289 | return false; | ||||
1290 | |||||
1291 | case BackwardVectorizable: | ||||
1292 | case Backward: | ||||
1293 | case BackwardVectorizableButPreventsForwarding: | ||||
1294 | return true; | ||||
1295 | } | ||||
1296 | llvm_unreachable("unexpected DepType!")__builtin_unreachable(); | ||||
1297 | } | ||||
1298 | |||||
1299 | bool MemoryDepChecker::Dependence::isPossiblyBackward() const { | ||||
1300 | return isBackward() || Type == Unknown; | ||||
1301 | } | ||||
1302 | |||||
1303 | bool MemoryDepChecker::Dependence::isForward() const { | ||||
1304 | switch (Type) { | ||||
1305 | case Forward: | ||||
1306 | case ForwardButPreventsForwarding: | ||||
1307 | return true; | ||||
1308 | |||||
1309 | case NoDep: | ||||
1310 | case Unknown: | ||||
1311 | case BackwardVectorizable: | ||||
1312 | case Backward: | ||||
1313 | case BackwardVectorizableButPreventsForwarding: | ||||
1314 | return false; | ||||
1315 | } | ||||
1316 | llvm_unreachable("unexpected DepType!")__builtin_unreachable(); | ||||
1317 | } | ||||
1318 | |||||
1319 | bool MemoryDepChecker::couldPreventStoreLoadForward(uint64_t Distance, | ||||
1320 | uint64_t TypeByteSize) { | ||||
1321 | // If loads occur at a distance that is not a multiple of a feasible vector | ||||
1322 | // factor store-load forwarding does not take place. | ||||
1323 | // Positive dependences might cause troubles because vectorizing them might | ||||
1324 | // prevent store-load forwarding making vectorized code run a lot slower. | ||||
1325 | // a[i] = a[i-3] ^ a[i-8]; | ||||
1326 | // The stores to a[i:i+1] don't align with the stores to a[i-3:i-2] and | ||||
1327 | // hence on your typical architecture store-load forwarding does not take | ||||
1328 | // place. Vectorizing in such cases does not make sense. | ||||
1329 | // Store-load forwarding distance. | ||||
1330 | |||||
1331 | // After this many iterations store-to-load forwarding conflicts should not | ||||
1332 | // cause any slowdowns. | ||||
1333 | const uint64_t NumItersForStoreLoadThroughMemory = 8 * TypeByteSize; | ||||
1334 | // Maximum vector factor. | ||||
1335 | uint64_t MaxVFWithoutSLForwardIssues = std::min( | ||||
1336 | VectorizerParams::MaxVectorWidth * TypeByteSize, MaxSafeDepDistBytes); | ||||
1337 | |||||
1338 | // Compute the smallest VF at which the store and load would be misaligned. | ||||
1339 | for (uint64_t VF = 2 * TypeByteSize; VF <= MaxVFWithoutSLForwardIssues; | ||||
1340 | VF *= 2) { | ||||
1341 | // If the number of vector iteration between the store and the load are | ||||
1342 | // small we could incur conflicts. | ||||
1343 | if (Distance % VF && Distance / VF < NumItersForStoreLoadThroughMemory) { | ||||
1344 | MaxVFWithoutSLForwardIssues = (VF >> 1); | ||||
1345 | break; | ||||
1346 | } | ||||
1347 | } | ||||
1348 | |||||
1349 | if (MaxVFWithoutSLForwardIssues < 2 * TypeByteSize) { | ||||
1350 | LLVM_DEBUG(do { } while (false) | ||||
1351 | dbgs() << "LAA: Distance " << Distancedo { } while (false) | ||||
1352 | << " that could cause a store-load forwarding conflict\n")do { } while (false); | ||||
1353 | return true; | ||||
1354 | } | ||||
1355 | |||||
1356 | if (MaxVFWithoutSLForwardIssues < MaxSafeDepDistBytes && | ||||
1357 | MaxVFWithoutSLForwardIssues != | ||||
1358 | VectorizerParams::MaxVectorWidth * TypeByteSize) | ||||
1359 | MaxSafeDepDistBytes = MaxVFWithoutSLForwardIssues; | ||||
1360 | return false; | ||||
1361 | } | ||||
1362 | |||||
1363 | void MemoryDepChecker::mergeInStatus(VectorizationSafetyStatus S) { | ||||
1364 | if (Status < S) | ||||
1365 | Status = S; | ||||
1366 | } | ||||
1367 | |||||
1368 | /// Given a non-constant (unknown) dependence-distance \p Dist between two | ||||
1369 | /// memory accesses, that have the same stride whose absolute value is given | ||||
1370 | /// in \p Stride, and that have the same type size \p TypeByteSize, | ||||
1371 | /// in a loop whose takenCount is \p BackedgeTakenCount, check if it is | ||||
1372 | /// possible to prove statically that the dependence distance is larger | ||||
1373 | /// than the range that the accesses will travel through the execution of | ||||
1374 | /// the loop. If so, return true; false otherwise. This is useful for | ||||
1375 | /// example in loops such as the following (PR31098): | ||||
1376 | /// for (i = 0; i < D; ++i) { | ||||
1377 | /// = out[i]; | ||||
1378 | /// out[i+D] = | ||||
1379 | /// } | ||||
1380 | static bool isSafeDependenceDistance(const DataLayout &DL, ScalarEvolution &SE, | ||||
1381 | const SCEV &BackedgeTakenCount, | ||||
1382 | const SCEV &Dist, uint64_t Stride, | ||||
1383 | uint64_t TypeByteSize) { | ||||
1384 | |||||
1385 | // If we can prove that | ||||
1386 | // (**) |Dist| > BackedgeTakenCount * Step | ||||
1387 | // where Step is the absolute stride of the memory accesses in bytes, | ||||
1388 | // then there is no dependence. | ||||
1389 | // | ||||
1390 | // Rationale: | ||||
1391 | // We basically want to check if the absolute distance (|Dist/Step|) | ||||
1392 | // is >= the loop iteration count (or > BackedgeTakenCount). | ||||
1393 | // This is equivalent to the Strong SIV Test (Practical Dependence Testing, | ||||
1394 | // Section 4.2.1); Note, that for vectorization it is sufficient to prove | ||||
1395 | // that the dependence distance is >= VF; This is checked elsewhere. | ||||
1396 | // But in some cases we can prune unknown dependence distances early, and | ||||
1397 | // even before selecting the VF, and without a runtime test, by comparing | ||||
1398 | // the distance against the loop iteration count. Since the vectorized code | ||||
1399 | // will be executed only if LoopCount >= VF, proving distance >= LoopCount | ||||
1400 | // also guarantees that distance >= VF. | ||||
1401 | // | ||||
1402 | const uint64_t ByteStride = Stride * TypeByteSize; | ||||
1403 | const SCEV *Step = SE.getConstant(BackedgeTakenCount.getType(), ByteStride); | ||||
1404 | const SCEV *Product = SE.getMulExpr(&BackedgeTakenCount, Step); | ||||
1405 | |||||
1406 | const SCEV *CastedDist = &Dist; | ||||
1407 | const SCEV *CastedProduct = Product; | ||||
1408 | uint64_t DistTypeSize = DL.getTypeAllocSize(Dist.getType()); | ||||
1409 | uint64_t ProductTypeSize = DL.getTypeAllocSize(Product->getType()); | ||||
1410 | |||||
1411 | // The dependence distance can be positive/negative, so we sign extend Dist; | ||||
1412 | // The multiplication of the absolute stride in bytes and the | ||||
1413 | // backedgeTakenCount is non-negative, so we zero extend Product. | ||||
1414 | if (DistTypeSize > ProductTypeSize) | ||||
1415 | CastedProduct = SE.getZeroExtendExpr(Product, Dist.getType()); | ||||
1416 | else | ||||
1417 | CastedDist = SE.getNoopOrSignExtend(&Dist, Product->getType()); | ||||
1418 | |||||
1419 | // Is Dist - (BackedgeTakenCount * Step) > 0 ? | ||||
1420 | // (If so, then we have proven (**) because |Dist| >= Dist) | ||||
1421 | const SCEV *Minus = SE.getMinusSCEV(CastedDist, CastedProduct); | ||||
1422 | if (SE.isKnownPositive(Minus)) | ||||
1423 | return true; | ||||
1424 | |||||
1425 | // Second try: Is -Dist - (BackedgeTakenCount * Step) > 0 ? | ||||
1426 | // (If so, then we have proven (**) because |Dist| >= -1*Dist) | ||||
1427 | const SCEV *NegDist = SE.getNegativeSCEV(CastedDist); | ||||
1428 | Minus = SE.getMinusSCEV(NegDist, CastedProduct); | ||||
1429 | if (SE.isKnownPositive(Minus)) | ||||
1430 | return true; | ||||
1431 | |||||
1432 | return false; | ||||
1433 | } | ||||
1434 | |||||
1435 | /// Check the dependence for two accesses with the same stride \p Stride. | ||||
1436 | /// \p Distance is the positive distance and \p TypeByteSize is type size in | ||||
1437 | /// bytes. | ||||
1438 | /// | ||||
1439 | /// \returns true if they are independent. | ||||
1440 | static bool areStridedAccessesIndependent(uint64_t Distance, uint64_t Stride, | ||||
1441 | uint64_t TypeByteSize) { | ||||
1442 | assert(Stride > 1 && "The stride must be greater than 1")((void)0); | ||||
1443 | assert(TypeByteSize > 0 && "The type size in byte must be non-zero")((void)0); | ||||
1444 | assert(Distance > 0 && "The distance must be non-zero")((void)0); | ||||
1445 | |||||
1446 | // Skip if the distance is not multiple of type byte size. | ||||
1447 | if (Distance % TypeByteSize) | ||||
1448 | return false; | ||||
1449 | |||||
1450 | uint64_t ScaledDist = Distance / TypeByteSize; | ||||
1451 | |||||
1452 | // No dependence if the scaled distance is not multiple of the stride. | ||||
1453 | // E.g. | ||||
1454 | // for (i = 0; i < 1024 ; i += 4) | ||||
1455 | // A[i+2] = A[i] + 1; | ||||
1456 | // | ||||
1457 | // Two accesses in memory (scaled distance is 2, stride is 4): | ||||
1458 | // | A[0] | | | | A[4] | | | | | ||||
1459 | // | | | A[2] | | | | A[6] | | | ||||
1460 | // | ||||
1461 | // E.g. | ||||
1462 | // for (i = 0; i < 1024 ; i += 3) | ||||
1463 | // A[i+4] = A[i] + 1; | ||||
1464 | // | ||||
1465 | // Two accesses in memory (scaled distance is 4, stride is 3): | ||||
1466 | // | A[0] | | | A[3] | | | A[6] | | | | ||||
1467 | // | | | | | A[4] | | | A[7] | | | ||||
1468 | return ScaledDist % Stride; | ||||
1469 | } | ||||
1470 | |||||
1471 | MemoryDepChecker::Dependence::DepType | ||||
1472 | MemoryDepChecker::isDependent(const MemAccessInfo &A, unsigned AIdx, | ||||
1473 | const MemAccessInfo &B, unsigned BIdx, | ||||
1474 | const ValueToValueMap &Strides) { | ||||
1475 | assert (AIdx < BIdx && "Must pass arguments in program order")((void)0); | ||||
1476 | |||||
1477 | Value *APtr = A.getPointer(); | ||||
1478 | Value *BPtr = B.getPointer(); | ||||
1479 | bool AIsWrite = A.getInt(); | ||||
1480 | bool BIsWrite = B.getInt(); | ||||
1481 | |||||
1482 | // Two reads are independent. | ||||
1483 | if (!AIsWrite && !BIsWrite) | ||||
1484 | return Dependence::NoDep; | ||||
1485 | |||||
1486 | // We cannot check pointers in different address spaces. | ||||
1487 | if (APtr->getType()->getPointerAddressSpace() != | ||||
1488 | BPtr->getType()->getPointerAddressSpace()) | ||||
1489 | return Dependence::Unknown; | ||||
1490 | |||||
1491 | int64_t StrideAPtr = getPtrStride(PSE, APtr, InnermostLoop, Strides, true); | ||||
1492 | int64_t StrideBPtr = getPtrStride(PSE, BPtr, InnermostLoop, Strides, true); | ||||
1493 | |||||
1494 | const SCEV *Src = PSE.getSCEV(APtr); | ||||
1495 | const SCEV *Sink = PSE.getSCEV(BPtr); | ||||
1496 | |||||
1497 | // If the induction step is negative we have to invert source and sink of the | ||||
1498 | // dependence. | ||||
1499 | if (StrideAPtr < 0) { | ||||
1500 | std::swap(APtr, BPtr); | ||||
1501 | std::swap(Src, Sink); | ||||
1502 | std::swap(AIsWrite, BIsWrite); | ||||
1503 | std::swap(AIdx, BIdx); | ||||
1504 | std::swap(StrideAPtr, StrideBPtr); | ||||
1505 | } | ||||
1506 | |||||
1507 | const SCEV *Dist = PSE.getSE()->getMinusSCEV(Sink, Src); | ||||
1508 | |||||
1509 | LLVM_DEBUG(dbgs() << "LAA: Src Scev: " << *Src << "Sink Scev: " << *Sinkdo { } while (false) | ||||
1510 | << "(Induction step: " << StrideAPtr << ")\n")do { } while (false); | ||||
1511 | LLVM_DEBUG(dbgs() << "LAA: Distance for " << *InstMap[AIdx] << " to "do { } while (false) | ||||
1512 | << *InstMap[BIdx] << ": " << *Dist << "\n")do { } while (false); | ||||
1513 | |||||
1514 | // Need accesses with constant stride. We don't want to vectorize | ||||
1515 | // "A[B[i]] += ..." and similar code or pointer arithmetic that could wrap in | ||||
1516 | // the address space. | ||||
1517 | if (!StrideAPtr || !StrideBPtr || StrideAPtr != StrideBPtr){ | ||||
1518 | LLVM_DEBUG(dbgs() << "Pointer access with non-constant stride\n")do { } while (false); | ||||
1519 | return Dependence::Unknown; | ||||
1520 | } | ||||
1521 | |||||
1522 | Type *ATy = APtr->getType()->getPointerElementType(); | ||||
1523 | Type *BTy = BPtr->getType()->getPointerElementType(); | ||||
1524 | auto &DL = InnermostLoop->getHeader()->getModule()->getDataLayout(); | ||||
1525 | uint64_t TypeByteSize = DL.getTypeAllocSize(ATy); | ||||
1526 | uint64_t Stride = std::abs(StrideAPtr); | ||||
1527 | const SCEVConstant *C = dyn_cast<SCEVConstant>(Dist); | ||||
1528 | if (!C) { | ||||
1529 | if (!isa<SCEVCouldNotCompute>(Dist) && | ||||
1530 | TypeByteSize == DL.getTypeAllocSize(BTy) && | ||||
1531 | isSafeDependenceDistance(DL, *(PSE.getSE()), | ||||
1532 | *(PSE.getBackedgeTakenCount()), *Dist, Stride, | ||||
1533 | TypeByteSize)) | ||||
1534 | return Dependence::NoDep; | ||||
1535 | |||||
1536 | LLVM_DEBUG(dbgs() << "LAA: Dependence because of non-constant distance\n")do { } while (false); | ||||
1537 | FoundNonConstantDistanceDependence = true; | ||||
1538 | return Dependence::Unknown; | ||||
1539 | } | ||||
1540 | |||||
1541 | const APInt &Val = C->getAPInt(); | ||||
1542 | int64_t Distance = Val.getSExtValue(); | ||||
1543 | |||||
1544 | // Attempt to prove strided accesses independent. | ||||
1545 | if (std::abs(Distance) > 0 && Stride > 1 && ATy == BTy && | ||||
1546 | areStridedAccessesIndependent(std::abs(Distance), Stride, TypeByteSize)) { | ||||
1547 | LLVM_DEBUG(dbgs() << "LAA: Strided accesses are independent\n")do { } while (false); | ||||
1548 | return Dependence::NoDep; | ||||
1549 | } | ||||
1550 | |||||
1551 | // Negative distances are not plausible dependencies. | ||||
1552 | if (Val.isNegative()) { | ||||
1553 | bool IsTrueDataDependence = (AIsWrite && !BIsWrite); | ||||
1554 | if (IsTrueDataDependence && EnableForwardingConflictDetection && | ||||
1555 | (couldPreventStoreLoadForward(Val.abs().getZExtValue(), TypeByteSize) || | ||||
1556 | ATy != BTy)) { | ||||
1557 | LLVM_DEBUG(dbgs() << "LAA: Forward but may prevent st->ld forwarding\n")do { } while (false); | ||||
1558 | return Dependence::ForwardButPreventsForwarding; | ||||
1559 | } | ||||
1560 | |||||
1561 | LLVM_DEBUG(dbgs() << "LAA: Dependence is negative\n")do { } while (false); | ||||
1562 | return Dependence::Forward; | ||||
1563 | } | ||||
1564 | |||||
1565 | // Write to the same location with the same size. | ||||
1566 | // Could be improved to assert type sizes are the same (i32 == float, etc). | ||||
1567 | if (Val == 0) { | ||||
1568 | if (ATy == BTy) | ||||
1569 | return Dependence::Forward; | ||||
1570 | LLVM_DEBUG(do { } while (false) | ||||
1571 | dbgs() << "LAA: Zero dependence difference but different types\n")do { } while (false); | ||||
1572 | return Dependence::Unknown; | ||||
1573 | } | ||||
1574 | |||||
1575 | assert(Val.isStrictlyPositive() && "Expect a positive value")((void)0); | ||||
1576 | |||||
1577 | if (ATy != BTy) { | ||||
1578 | LLVM_DEBUG(do { } while (false) | ||||
1579 | dbgs()do { } while (false) | ||||
1580 | << "LAA: ReadWrite-Write positive dependency with different types\n")do { } while (false); | ||||
1581 | return Dependence::Unknown; | ||||
1582 | } | ||||
1583 | |||||
1584 | // Bail out early if passed-in parameters make vectorization not feasible. | ||||
1585 | unsigned ForcedFactor = (VectorizerParams::VectorizationFactor ? | ||||
1586 | VectorizerParams::VectorizationFactor : 1); | ||||
1587 | unsigned ForcedUnroll = (VectorizerParams::VectorizationInterleave ? | ||||
1588 | VectorizerParams::VectorizationInterleave : 1); | ||||
1589 | // The minimum number of iterations for a vectorized/unrolled version. | ||||
1590 | unsigned MinNumIter = std::max(ForcedFactor * ForcedUnroll, 2U); | ||||
1591 | |||||
1592 | // It's not vectorizable if the distance is smaller than the minimum distance | ||||
1593 | // needed for a vectroized/unrolled version. Vectorizing one iteration in | ||||
1594 | // front needs TypeByteSize * Stride. Vectorizing the last iteration needs | ||||
1595 | // TypeByteSize (No need to plus the last gap distance). | ||||
1596 | // | ||||
1597 | // E.g. Assume one char is 1 byte in memory and one int is 4 bytes. | ||||
1598 | // foo(int *A) { | ||||
1599 | // int *B = (int *)((char *)A + 14); | ||||
1600 | // for (i = 0 ; i < 1024 ; i += 2) | ||||
1601 | // B[i] = A[i] + 1; | ||||
1602 | // } | ||||
1603 | // | ||||
1604 | // Two accesses in memory (stride is 2): | ||||
1605 | // | A[0] | | A[2] | | A[4] | | A[6] | | | ||||
1606 | // | B[0] | | B[2] | | B[4] | | ||||
1607 | // | ||||
1608 | // Distance needs for vectorizing iterations except the last iteration: | ||||
1609 | // 4 * 2 * (MinNumIter - 1). Distance needs for the last iteration: 4. | ||||
1610 | // So the minimum distance needed is: 4 * 2 * (MinNumIter - 1) + 4. | ||||
1611 | // | ||||
1612 | // If MinNumIter is 2, it is vectorizable as the minimum distance needed is | ||||
1613 | // 12, which is less than distance. | ||||
1614 | // | ||||
1615 | // If MinNumIter is 4 (Say if a user forces the vectorization factor to be 4), | ||||
1616 | // the minimum distance needed is 28, which is greater than distance. It is | ||||
1617 | // not safe to do vectorization. | ||||
1618 | uint64_t MinDistanceNeeded = | ||||
1619 | TypeByteSize * Stride * (MinNumIter - 1) + TypeByteSize; | ||||
1620 | if (MinDistanceNeeded > static_cast<uint64_t>(Distance)) { | ||||
1621 | LLVM_DEBUG(dbgs() << "LAA: Failure because of positive distance "do { } while (false) | ||||
1622 | << Distance << '\n')do { } while (false); | ||||
1623 | return Dependence::Backward; | ||||
1624 | } | ||||
1625 | |||||
1626 | // Unsafe if the minimum distance needed is greater than max safe distance. | ||||
1627 | if (MinDistanceNeeded > MaxSafeDepDistBytes) { | ||||
1628 | LLVM_DEBUG(dbgs() << "LAA: Failure because it needs at least "do { } while (false) | ||||
1629 | << MinDistanceNeeded << " size in bytes")do { } while (false); | ||||
1630 | return Dependence::Backward; | ||||
1631 | } | ||||
1632 | |||||
1633 | // Positive distance bigger than max vectorization factor. | ||||
1634 | // FIXME: Should use max factor instead of max distance in bytes, which could | ||||
1635 | // not handle different types. | ||||
1636 | // E.g. Assume one char is 1 byte in memory and one int is 4 bytes. | ||||
1637 | // void foo (int *A, char *B) { | ||||
1638 | // for (unsigned i = 0; i < 1024; i++) { | ||||
1639 | // A[i+2] = A[i] + 1; | ||||
1640 | // B[i+2] = B[i] + 1; | ||||
1641 | // } | ||||
1642 | // } | ||||
1643 | // | ||||
1644 | // This case is currently unsafe according to the max safe distance. If we | ||||
1645 | // analyze the two accesses on array B, the max safe dependence distance | ||||
1646 | // is 2. Then we analyze the accesses on array A, the minimum distance needed | ||||
1647 | // is 8, which is less than 2 and forbidden vectorization, But actually | ||||
1648 | // both A and B could be vectorized by 2 iterations. | ||||
1649 | MaxSafeDepDistBytes = | ||||
1650 | std::min(static_cast<uint64_t>(Distance), MaxSafeDepDistBytes); | ||||
1651 | |||||
1652 | bool IsTrueDataDependence = (!AIsWrite && BIsWrite); | ||||
1653 | if (IsTrueDataDependence && EnableForwardingConflictDetection && | ||||
1654 | couldPreventStoreLoadForward(Distance, TypeByteSize)) | ||||
1655 | return Dependence::BackwardVectorizableButPreventsForwarding; | ||||
1656 | |||||
1657 | uint64_t MaxVF = MaxSafeDepDistBytes / (TypeByteSize * Stride); | ||||
1658 | LLVM_DEBUG(dbgs() << "LAA: Positive distance " << Val.getSExtValue()do { } while (false) | ||||
1659 | << " with max VF = " << MaxVF << '\n')do { } while (false); | ||||
1660 | uint64_t MaxVFInBits = MaxVF * TypeByteSize * 8; | ||||
1661 | MaxSafeVectorWidthInBits = std::min(MaxSafeVectorWidthInBits, MaxVFInBits); | ||||
1662 | return Dependence::BackwardVectorizable; | ||||
1663 | } | ||||
1664 | |||||
1665 | bool MemoryDepChecker::areDepsSafe(DepCandidates &AccessSets, | ||||
1666 | MemAccessInfoList &CheckDeps, | ||||
1667 | const ValueToValueMap &Strides) { | ||||
1668 | |||||
1669 | MaxSafeDepDistBytes = -1; | ||||
1670 | SmallPtrSet<MemAccessInfo, 8> Visited; | ||||
1671 | for (MemAccessInfo CurAccess : CheckDeps) { | ||||
1672 | if (Visited.count(CurAccess)) | ||||
1673 | continue; | ||||
1674 | |||||
1675 | // Get the relevant memory access set. | ||||
1676 | EquivalenceClasses<MemAccessInfo>::iterator I = | ||||
1677 | AccessSets.findValue(AccessSets.getLeaderValue(CurAccess)); | ||||
1678 | |||||
1679 | // Check accesses within this set. | ||||
1680 | EquivalenceClasses<MemAccessInfo>::member_iterator AI = | ||||
1681 | AccessSets.member_begin(I); | ||||
1682 | EquivalenceClasses<MemAccessInfo>::member_iterator AE = | ||||
1683 | AccessSets.member_end(); | ||||
1684 | |||||
1685 | // Check every access pair. | ||||
1686 | while (AI != AE) { | ||||
1687 | Visited.insert(*AI); | ||||
1688 | bool AIIsWrite = AI->getInt(); | ||||
1689 | // Check loads only against next equivalent class, but stores also against | ||||
1690 | // other stores in the same equivalence class - to the same address. | ||||
1691 | EquivalenceClasses<MemAccessInfo>::member_iterator OI = | ||||
1692 | (AIIsWrite ? AI : std::next(AI)); | ||||
1693 | while (OI != AE) { | ||||
1694 | // Check every accessing instruction pair in program order. | ||||
1695 | for (std::vector<unsigned>::iterator I1 = Accesses[*AI].begin(), | ||||
1696 | I1E = Accesses[*AI].end(); I1 != I1E; ++I1) | ||||
1697 | // Scan all accesses of another equivalence class, but only the next | ||||
1698 | // accesses of the same equivalent class. | ||||
1699 | for (std::vector<unsigned>::iterator | ||||
1700 | I2 = (OI == AI ? std::next(I1) : Accesses[*OI].begin()), | ||||
1701 | I2E = (OI == AI ? I1E : Accesses[*OI].end()); | ||||
1702 | I2 != I2E; ++I2) { | ||||
1703 | auto A = std::make_pair(&*AI, *I1); | ||||
1704 | auto B = std::make_pair(&*OI, *I2); | ||||
1705 | |||||
1706 | assert(*I1 != *I2)((void)0); | ||||
1707 | if (*I1 > *I2) | ||||
1708 | std::swap(A, B); | ||||
1709 | |||||
1710 | Dependence::DepType Type = | ||||
1711 | isDependent(*A.first, A.second, *B.first, B.second, Strides); | ||||
1712 | mergeInStatus(Dependence::isSafeForVectorization(Type)); | ||||
1713 | |||||
1714 | // Gather dependences unless we accumulated MaxDependences | ||||
1715 | // dependences. In that case return as soon as we find the first | ||||
1716 | // unsafe dependence. This puts a limit on this quadratic | ||||
1717 | // algorithm. | ||||
1718 | if (RecordDependences) { | ||||
1719 | if (Type != Dependence::NoDep) | ||||
1720 | Dependences.push_back(Dependence(A.second, B.second, Type)); | ||||
1721 | |||||
1722 | if (Dependences.size() >= MaxDependences) { | ||||
1723 | RecordDependences = false; | ||||
1724 | Dependences.clear(); | ||||
1725 | LLVM_DEBUG(dbgs()do { } while (false) | ||||
1726 | << "Too many dependences, stopped recording\n")do { } while (false); | ||||
1727 | } | ||||
1728 | } | ||||
1729 | if (!RecordDependences && !isSafeForVectorization()) | ||||
1730 | return false; | ||||
1731 | } | ||||
1732 | ++OI; | ||||
1733 | } | ||||
1734 | AI++; | ||||
1735 | } | ||||
1736 | } | ||||
1737 | |||||
1738 | LLVM_DEBUG(dbgs() << "Total Dependences: " << Dependences.size() << "\n")do { } while (false); | ||||
1739 | return isSafeForVectorization(); | ||||
1740 | } | ||||
1741 | |||||
1742 | SmallVector<Instruction *, 4> | ||||
1743 | MemoryDepChecker::getInstructionsForAccess(Value *Ptr, bool isWrite) const { | ||||
1744 | MemAccessInfo Access(Ptr, isWrite); | ||||
1745 | auto &IndexVector = Accesses.find(Access)->second; | ||||
1746 | |||||
1747 | SmallVector<Instruction *, 4> Insts; | ||||
1748 | transform(IndexVector, | ||||
1749 | std::back_inserter(Insts), | ||||
1750 | [&](unsigned Idx) { return this->InstMap[Idx]; }); | ||||
1751 | return Insts; | ||||
1752 | } | ||||
1753 | |||||
1754 | const char *MemoryDepChecker::Dependence::DepName[] = { | ||||
1755 | "NoDep", "Unknown", "Forward", "ForwardButPreventsForwarding", "Backward", | ||||
1756 | "BackwardVectorizable", "BackwardVectorizableButPreventsForwarding"}; | ||||
1757 | |||||
1758 | void MemoryDepChecker::Dependence::print( | ||||
1759 | raw_ostream &OS, unsigned Depth, | ||||
1760 | const SmallVectorImpl<Instruction *> &Instrs) const { | ||||
1761 | OS.indent(Depth) << DepName[Type] << ":\n"; | ||||
1762 | OS.indent(Depth + 2) << *Instrs[Source] << " -> \n"; | ||||
1763 | OS.indent(Depth + 2) << *Instrs[Destination] << "\n"; | ||||
1764 | } | ||||
1765 | |||||
1766 | bool LoopAccessInfo::canAnalyzeLoop() { | ||||
1767 | // We need to have a loop header. | ||||
1768 | LLVM_DEBUG(dbgs() << "LAA: Found a loop in "do { } while (false) | ||||
1769 | << TheLoop->getHeader()->getParent()->getName() << ": "do { } while (false) | ||||
1770 | << TheLoop->getHeader()->getName() << '\n')do { } while (false); | ||||
1771 | |||||
1772 | // We can only analyze innermost loops. | ||||
1773 | if (!TheLoop->isInnermost()) { | ||||
1774 | LLVM_DEBUG(dbgs() << "LAA: loop is not the innermost loop\n")do { } while (false); | ||||
1775 | recordAnalysis("NotInnerMostLoop") << "loop is not the innermost loop"; | ||||
1776 | return false; | ||||
1777 | } | ||||
1778 | |||||
1779 | // We must have a single backedge. | ||||
1780 | if (TheLoop->getNumBackEdges() != 1) { | ||||
1781 | LLVM_DEBUG(do { } while (false) | ||||
1782 | dbgs() << "LAA: loop control flow is not understood by analyzer\n")do { } while (false); | ||||
1783 | recordAnalysis("CFGNotUnderstood") | ||||
1784 | << "loop control flow is not understood by analyzer"; | ||||
1785 | return false; | ||||
1786 | } | ||||
1787 | |||||
1788 | // ScalarEvolution needs to be able to find the exit count. | ||||
1789 | const SCEV *ExitCount = PSE->getBackedgeTakenCount(); | ||||
1790 | if (isa<SCEVCouldNotCompute>(ExitCount)) { | ||||
1791 | recordAnalysis("CantComputeNumberOfIterations") | ||||
1792 | << "could not determine number of loop iterations"; | ||||
1793 | LLVM_DEBUG(dbgs() << "LAA: SCEV could not compute the loop exit count.\n")do { } while (false); | ||||
1794 | return false; | ||||
1795 | } | ||||
1796 | |||||
1797 | return true; | ||||
1798 | } | ||||
1799 | |||||
1800 | void LoopAccessInfo::analyzeLoop(AAResults *AA, LoopInfo *LI, | ||||
1801 | const TargetLibraryInfo *TLI, | ||||
1802 | DominatorTree *DT) { | ||||
1803 | typedef SmallPtrSet<Value*, 16> ValueSet; | ||||
1804 | |||||
1805 | // Holds the Load and Store instructions. | ||||
1806 | SmallVector<LoadInst *, 16> Loads; | ||||
1807 | SmallVector<StoreInst *, 16> Stores; | ||||
1808 | |||||
1809 | // Holds all the different accesses in the loop. | ||||
1810 | unsigned NumReads = 0; | ||||
1811 | unsigned NumReadWrites = 0; | ||||
1812 | |||||
1813 | bool HasComplexMemInst = false; | ||||
1814 | |||||
1815 | // A runtime check is only legal to insert if there are no convergent calls. | ||||
1816 | HasConvergentOp = false; | ||||
1817 | |||||
1818 | PtrRtChecking->Pointers.clear(); | ||||
1819 | PtrRtChecking->Need = false; | ||||
1820 | |||||
1821 | const bool IsAnnotatedParallel = TheLoop->isAnnotatedParallel(); | ||||
1822 | |||||
1823 | const bool EnableMemAccessVersioningOfLoop = | ||||
1824 | EnableMemAccessVersioning && | ||||
| |||||
1825 | !TheLoop->getHeader()->getParent()->hasOptSize(); | ||||
1826 | |||||
1827 | // For each block. | ||||
1828 | for (BasicBlock *BB : TheLoop->blocks()) { | ||||
1829 | // Scan the BB and collect legal loads and stores. Also detect any | ||||
1830 | // convergent instructions. | ||||
1831 | for (Instruction &I : *BB) { | ||||
1832 | if (auto *Call = dyn_cast<CallBase>(&I)) { | ||||
1833 | if (Call->isConvergent()) | ||||
1834 | HasConvergentOp = true; | ||||
1835 | } | ||||
1836 | |||||
1837 | // With both a non-vectorizable memory instruction and a convergent | ||||
1838 | // operation, found in this loop, no reason to continue the search. | ||||
1839 | if (HasComplexMemInst && HasConvergentOp) { | ||||
1840 | CanVecMem = false; | ||||
1841 | return; | ||||
1842 | } | ||||
1843 | |||||
1844 | // Avoid hitting recordAnalysis multiple times. | ||||
1845 | if (HasComplexMemInst) | ||||
1846 | continue; | ||||
1847 | |||||
1848 | // If this is a load, save it. If this instruction can read from memory | ||||
1849 | // but is not a load, then we quit. Notice that we don't handle function | ||||
1850 | // calls that read or write. | ||||
1851 | if (I.mayReadFromMemory()) { | ||||
1852 | // Many math library functions read the rounding mode. We will only | ||||
1853 | // vectorize a loop if it contains known function calls that don't set | ||||
1854 | // the flag. Therefore, it is safe to ignore this read from memory. | ||||
1855 | auto *Call = dyn_cast<CallInst>(&I); | ||||
1856 | if (Call && getVectorIntrinsicIDForCall(Call, TLI)) | ||||
1857 | continue; | ||||
1858 | |||||
1859 | // If the function has an explicit vectorized counterpart, we can safely | ||||
1860 | // assume that it can be vectorized. | ||||
1861 | if (Call && !Call->isNoBuiltin() && Call->getCalledFunction() && | ||||
1862 | !VFDatabase::getMappings(*Call).empty()) | ||||
1863 | continue; | ||||
1864 | |||||
1865 | auto *Ld = dyn_cast<LoadInst>(&I); | ||||
1866 | if (!Ld) { | ||||
1867 | recordAnalysis("CantVectorizeInstruction", Ld) | ||||
1868 | << "instruction cannot be vectorized"; | ||||
1869 | HasComplexMemInst = true; | ||||
1870 | continue; | ||||
1871 | } | ||||
1872 | if (!Ld->isSimple() && !IsAnnotatedParallel) { | ||||
1873 | recordAnalysis("NonSimpleLoad", Ld) | ||||
1874 | << "read with atomic ordering or volatile read"; | ||||
1875 | LLVM_DEBUG(dbgs() << "LAA: Found a non-simple load.\n")do { } while (false); | ||||
1876 | HasComplexMemInst = true; | ||||
1877 | continue; | ||||
1878 | } | ||||
1879 | NumLoads++; | ||||
1880 | Loads.push_back(Ld); | ||||
1881 | DepChecker->addAccess(Ld); | ||||
1882 | if (EnableMemAccessVersioningOfLoop) | ||||
1883 | collectStridedAccess(Ld); | ||||
1884 | continue; | ||||
1885 | } | ||||
1886 | |||||
1887 | // Save 'store' instructions. Abort if other instructions write to memory. | ||||
1888 | if (I.mayWriteToMemory()) { | ||||
1889 | auto *St = dyn_cast<StoreInst>(&I); | ||||
1890 | if (!St) { | ||||
1891 | recordAnalysis("CantVectorizeInstruction", St) | ||||
1892 | << "instruction cannot be vectorized"; | ||||
1893 | HasComplexMemInst = true; | ||||
1894 | continue; | ||||
1895 | } | ||||
1896 | if (!St->isSimple() && !IsAnnotatedParallel) { | ||||
1897 | recordAnalysis("NonSimpleStore", St) | ||||
1898 | << "write with atomic ordering or volatile write"; | ||||
1899 | LLVM_DEBUG(dbgs() << "LAA: Found a non-simple store.\n")do { } while (false); | ||||
1900 | HasComplexMemInst = true; | ||||
1901 | continue; | ||||
1902 | } | ||||
1903 | NumStores++; | ||||
1904 | Stores.push_back(St); | ||||
1905 | DepChecker->addAccess(St); | ||||
1906 | if (EnableMemAccessVersioningOfLoop) | ||||
1907 | collectStridedAccess(St); | ||||
1908 | } | ||||
1909 | } // Next instr. | ||||
1910 | } // Next block. | ||||
1911 | |||||
1912 | if (HasComplexMemInst
| ||||
1913 | CanVecMem = false; | ||||
1914 | return; | ||||
1915 | } | ||||
1916 | |||||
1917 | // Now we have two lists that hold the loads and the stores. | ||||
1918 | // Next, we find the pointers that they use. | ||||
1919 | |||||
1920 | // Check if we see any stores. If there are no stores, then we don't | ||||
1921 | // care if the pointers are *restrict*. | ||||
1922 | if (!Stores.size()) { | ||||
1923 | LLVM_DEBUG(dbgs() << "LAA: Found a read-only loop!\n")do { } while (false); | ||||
1924 | CanVecMem = true; | ||||
1925 | return; | ||||
1926 | } | ||||
1927 | |||||
1928 | MemoryDepChecker::DepCandidates DependentAccesses; | ||||
1929 | AccessAnalysis Accesses(TheLoop, AA, LI, DependentAccesses, *PSE); | ||||
1930 | |||||
1931 | // Holds the analyzed pointers. We don't want to call getUnderlyingObjects | ||||
1932 | // multiple times on the same object. If the ptr is accessed twice, once | ||||
1933 | // for read and once for write, it will only appear once (on the write | ||||
1934 | // list). This is okay, since we are going to check for conflicts between | ||||
1935 | // writes and between reads and writes, but not between reads and reads. | ||||
1936 | ValueSet Seen; | ||||
1937 | |||||
1938 | // Record uniform store addresses to identify if we have multiple stores | ||||
1939 | // to the same address. | ||||
1940 | ValueSet UniformStores; | ||||
1941 | |||||
1942 | for (StoreInst *ST : Stores) { | ||||
1943 | Value *Ptr = ST->getPointerOperand(); | ||||
1944 | |||||
1945 | if (isUniform(Ptr)) | ||||
1946 | HasDependenceInvolvingLoopInvariantAddress |= | ||||
1947 | !UniformStores.insert(Ptr).second; | ||||
1948 | |||||
1949 | // If we did *not* see this pointer before, insert it to the read-write | ||||
1950 | // list. At this phase it is only a 'write' list. | ||||
1951 | if (Seen.insert(Ptr).second) { | ||||
1952 | ++NumReadWrites; | ||||
1953 | |||||
1954 | MemoryLocation Loc = MemoryLocation::get(ST); | ||||
1955 | // The TBAA metadata could have a control dependency on the predication | ||||
1956 | // condition, so we cannot rely on it when determining whether or not we | ||||
1957 | // need runtime pointer checks. | ||||
1958 | if (blockNeedsPredication(ST->getParent(), TheLoop, DT)) | ||||
1959 | Loc.AATags.TBAA = nullptr; | ||||
1960 | |||||
1961 | Accesses.addStore(Loc); | ||||
1962 | } | ||||
1963 | } | ||||
1964 | |||||
1965 | if (IsAnnotatedParallel) { | ||||
1966 | LLVM_DEBUG(do { } while (false) | ||||
1967 | dbgs() << "LAA: A loop annotated parallel, ignore memory dependency "do { } while (false) | ||||
1968 | << "checks.\n")do { } while (false); | ||||
1969 | CanVecMem = true; | ||||
1970 | return; | ||||
1971 | } | ||||
1972 | |||||
1973 | for (LoadInst *LD : Loads) { | ||||
1974 | Value *Ptr = LD->getPointerOperand(); | ||||
1975 | // If we did *not* see this pointer before, insert it to the | ||||
1976 | // read list. If we *did* see it before, then it is already in | ||||
1977 | // the read-write list. This allows us to vectorize expressions | ||||
1978 | // such as A[i] += x; Because the address of A[i] is a read-write | ||||
1979 | // pointer. This only works if the index of A[i] is consecutive. | ||||
1980 | // If the address of i is unknown (for example A[B[i]]) then we may | ||||
1981 | // read a few words, modify, and write a few words, and some of the | ||||
1982 | // words may be written to the same address. | ||||
1983 | bool IsReadOnlyPtr = false; | ||||
1984 | if (Seen.insert(Ptr).second || | ||||
1985 | !getPtrStride(*PSE, Ptr, TheLoop, SymbolicStrides)) { | ||||
1986 | ++NumReads; | ||||
1987 | IsReadOnlyPtr = true; | ||||
1988 | } | ||||
1989 | |||||
1990 | // See if there is an unsafe dependency between a load to a uniform address and | ||||
1991 | // store to the same uniform address. | ||||
1992 | if (UniformStores.count(Ptr)) { | ||||
1993 | LLVM_DEBUG(dbgs() << "LAA: Found an unsafe dependency between a uniform "do { } while (false) | ||||
1994 | "load and uniform store to the same address!\n")do { } while (false); | ||||
1995 | HasDependenceInvolvingLoopInvariantAddress = true; | ||||
1996 | } | ||||
1997 | |||||
1998 | MemoryLocation Loc = MemoryLocation::get(LD); | ||||
1999 | // The TBAA metadata could have a control dependency on the predication | ||||
2000 | // condition, so we cannot rely on it when determining whether or not we | ||||
2001 | // need runtime pointer checks. | ||||
2002 | if (blockNeedsPredication(LD->getParent(), TheLoop, DT)) | ||||
2003 | Loc.AATags.TBAA = nullptr; | ||||
2004 | |||||
2005 | Accesses.addLoad(Loc, IsReadOnlyPtr); | ||||
2006 | } | ||||
2007 | |||||
2008 | // If we write (or read-write) to a single destination and there are no | ||||
2009 | // other reads in this loop then is it safe to vectorize. | ||||
2010 | if (NumReadWrites
| ||||
2011 | LLVM_DEBUG(dbgs() << "LAA: Found a write-only loop!\n")do { } while (false); | ||||
2012 | CanVecMem = true; | ||||
2013 | return; | ||||
2014 | } | ||||
2015 | |||||
2016 | // Build dependence sets and check whether we need a runtime pointer bounds | ||||
2017 | // check. | ||||
2018 | Accesses.buildDependenceSets(); | ||||
2019 | |||||
2020 | // Find pointers with computable bounds. We are going to use this information | ||||
2021 | // to place a runtime bound check. | ||||
2022 | bool CanDoRTIfNeeded = Accesses.canCheckPtrAtRT(*PtrRtChecking, PSE->getSE(), | ||||
2023 | TheLoop, SymbolicStrides); | ||||
2024 | if (!CanDoRTIfNeeded) { | ||||
2025 | recordAnalysis("CantIdentifyArrayBounds") << "cannot identify array bounds"; | ||||
2026 | LLVM_DEBUG(dbgs() << "LAA: We can't vectorize because we can't find "do { } while (false) | ||||
2027 | << "the array bounds.\n")do { } while (false); | ||||
2028 | CanVecMem = false; | ||||
2029 | return; | ||||
2030 | } | ||||
2031 | |||||
2032 | LLVM_DEBUG(do { } while (false) | ||||
2033 | dbgs() << "LAA: May be able to perform a memory runtime check if needed.\n")do { } while (false); | ||||
2034 | |||||
2035 | CanVecMem = true; | ||||
2036 | if (Accesses.isDependencyCheckNeeded()) { | ||||
2037 | LLVM_DEBUG(dbgs() << "LAA: Checking memory dependencies\n")do { } while (false); | ||||
2038 | CanVecMem = DepChecker->areDepsSafe( | ||||
2039 | DependentAccesses, Accesses.getDependenciesToCheck(), SymbolicStrides); | ||||
2040 | MaxSafeDepDistBytes = DepChecker->getMaxSafeDepDistBytes(); | ||||
2041 | |||||
2042 | if (!CanVecMem && DepChecker->shouldRetryWithRuntimeCheck()) { | ||||
2043 | LLVM_DEBUG(dbgs() << "LAA: Retrying with memory checks\n")do { } while (false); | ||||
2044 | |||||
2045 | // Clear the dependency checks. We assume they are not needed. | ||||
2046 | Accesses.resetDepChecks(*DepChecker); | ||||
2047 | |||||
2048 | PtrRtChecking->reset(); | ||||
2049 | PtrRtChecking->Need = true; | ||||
2050 | |||||
2051 | auto *SE = PSE->getSE(); | ||||
2052 | CanDoRTIfNeeded = Accesses.canCheckPtrAtRT(*PtrRtChecking, SE, TheLoop, | ||||
2053 | SymbolicStrides, true); | ||||
2054 | |||||
2055 | // Check that we found the bounds for the pointer. | ||||
2056 | if (!CanDoRTIfNeeded) { | ||||
2057 | recordAnalysis("CantCheckMemDepsAtRunTime") | ||||
2058 | << "cannot check memory dependencies at runtime"; | ||||
2059 | LLVM_DEBUG(dbgs() << "LAA: Can't vectorize with memory checks\n")do { } while (false); | ||||
2060 | CanVecMem = false; | ||||
2061 | return; | ||||
2062 | } | ||||
2063 | |||||
2064 | CanVecMem = true; | ||||
2065 | } | ||||
2066 | } | ||||
2067 | |||||
2068 | if (HasConvergentOp) { | ||||
2069 | recordAnalysis("CantInsertRuntimeCheckWithConvergent") | ||||
2070 | << "cannot add control dependency to convergent operation"; | ||||
2071 | LLVM_DEBUG(dbgs() << "LAA: We can't vectorize because a runtime check "do { } while (false) | ||||
2072 | "would be needed with a convergent operation\n")do { } while (false); | ||||
2073 | CanVecMem = false; | ||||
2074 | return; | ||||
2075 | } | ||||
2076 | |||||
2077 | if (CanVecMem) | ||||
2078 | LLVM_DEBUG(do { } while (false) | ||||
2079 | dbgs() << "LAA: No unsafe dependent memory operations in loop. We"do { } while (false) | ||||
2080 | << (PtrRtChecking->Need ? "" : " don't")do { } while (false) | ||||
2081 | << " need runtime memory checks.\n")do { } while (false); | ||||
2082 | else { | ||||
2083 | recordAnalysis("UnsafeMemDep") | ||||
2084 | << "unsafe dependent memory operations in loop. Use " | ||||
2085 | "#pragma loop distribute(enable) to allow loop distribution " | ||||
2086 | "to attempt to isolate the offending operations into a separate " | ||||
2087 | "loop"; | ||||
2088 | LLVM_DEBUG(dbgs() << "LAA: unsafe dependent memory operations in loop\n")do { } while (false); | ||||
2089 | } | ||||
2090 | } | ||||
2091 | |||||
2092 | bool LoopAccessInfo::blockNeedsPredication(BasicBlock *BB, Loop *TheLoop, | ||||
2093 | DominatorTree *DT) { | ||||
2094 | assert(TheLoop->contains(BB) && "Unknown block used")((void)0); | ||||
2095 | |||||
2096 | // Blocks that do not dominate the latch need predication. | ||||
2097 | BasicBlock* Latch = TheLoop->getLoopLatch(); | ||||
2098 | return !DT->dominates(BB, Latch); | ||||
2099 | } | ||||
2100 | |||||
2101 | OptimizationRemarkAnalysis &LoopAccessInfo::recordAnalysis(StringRef RemarkName, | ||||
2102 | Instruction *I) { | ||||
2103 | assert(!Report && "Multiple reports generated")((void)0); | ||||
2104 | |||||
2105 | Value *CodeRegion = TheLoop->getHeader(); | ||||
2106 | DebugLoc DL = TheLoop->getStartLoc(); | ||||
2107 | |||||
2108 | if (I) { | ||||
2109 | CodeRegion = I->getParent(); | ||||
2110 | // If there is no debug location attached to the instruction, revert back to | ||||
2111 | // using the loop's. | ||||
2112 | if (I->getDebugLoc()) | ||||
2113 | DL = I->getDebugLoc(); | ||||
2114 | } | ||||
2115 | |||||
2116 | Report = std::make_unique<OptimizationRemarkAnalysis>(DEBUG_TYPE"loop-accesses", RemarkName, DL, | ||||
2117 | CodeRegion); | ||||
2118 | return *Report; | ||||
2119 | } | ||||
2120 | |||||
2121 | bool LoopAccessInfo::isUniform(Value *V) const { | ||||
2122 | auto *SE = PSE->getSE(); | ||||
2123 | // Since we rely on SCEV for uniformity, if the type is not SCEVable, it is | ||||
2124 | // never considered uniform. | ||||
2125 | // TODO: Is this really what we want? Even without FP SCEV, we may want some | ||||
2126 | // trivially loop-invariant FP values to be considered uniform. | ||||
2127 | if (!SE->isSCEVable(V->getType())) | ||||
2128 | return false; | ||||
2129 | return (SE->isLoopInvariant(SE->getSCEV(V), TheLoop)); | ||||
2130 | } | ||||
2131 | |||||
2132 | void LoopAccessInfo::collectStridedAccess(Value *MemAccess) { | ||||
2133 | Value *Ptr = getLoadStorePointerOperand(MemAccess); | ||||
2134 | if (!Ptr) | ||||
2135 | return; | ||||
2136 | |||||
2137 | Value *Stride = getStrideFromPointer(Ptr, PSE->getSE(), TheLoop); | ||||
2138 | if (!Stride) | ||||
2139 | return; | ||||
2140 | |||||
2141 | LLVM_DEBUG(dbgs() << "LAA: Found a strided access that is a candidate for "do { } while (false) | ||||
2142 | "versioning:")do { } while (false); | ||||
2143 | LLVM_DEBUG(dbgs() << " Ptr: " << *Ptr << " Stride: " << *Stride << "\n")do { } while (false); | ||||
2144 | |||||
2145 | // Avoid adding the "Stride == 1" predicate when we know that | ||||
2146 | // Stride >= Trip-Count. Such a predicate will effectively optimize a single | ||||
2147 | // or zero iteration loop, as Trip-Count <= Stride == 1. | ||||
2148 | // | ||||
2149 | // TODO: We are currently not making a very informed decision on when it is | ||||
2150 | // beneficial to apply stride versioning. It might make more sense that the | ||||
2151 | // users of this analysis (such as the vectorizer) will trigger it, based on | ||||
2152 | // their specific cost considerations; For example, in cases where stride | ||||
2153 | // versioning does not help resolving memory accesses/dependences, the | ||||
2154 | // vectorizer should evaluate the cost of the runtime test, and the benefit | ||||
2155 | // of various possible stride specializations, considering the alternatives | ||||
2156 | // of using gather/scatters (if available). | ||||
2157 | |||||
2158 | const SCEV *StrideExpr = PSE->getSCEV(Stride); | ||||
2159 | const SCEV *BETakenCount = PSE->getBackedgeTakenCount(); | ||||
2160 | |||||
2161 | // Match the types so we can compare the stride and the BETakenCount. | ||||
2162 | // The Stride can be positive/negative, so we sign extend Stride; | ||||
2163 | // The backedgeTakenCount is non-negative, so we zero extend BETakenCount. | ||||
2164 | const DataLayout &DL = TheLoop->getHeader()->getModule()->getDataLayout(); | ||||
2165 | uint64_t StrideTypeSize = DL.getTypeAllocSize(StrideExpr->getType()); | ||||
2166 | uint64_t BETypeSize = DL.getTypeAllocSize(BETakenCount->getType()); | ||||
2167 | const SCEV *CastedStride = StrideExpr; | ||||
2168 | const SCEV *CastedBECount = BETakenCount; | ||||
2169 | ScalarEvolution *SE = PSE->getSE(); | ||||
2170 | if (BETypeSize >= StrideTypeSize) | ||||
2171 | CastedStride = SE->getNoopOrSignExtend(StrideExpr, BETakenCount->getType()); | ||||
2172 | else | ||||
2173 | CastedBECount = SE->getZeroExtendExpr(BETakenCount, StrideExpr->getType()); | ||||
2174 | const SCEV *StrideMinusBETaken = SE->getMinusSCEV(CastedStride, CastedBECount); | ||||
2175 | // Since TripCount == BackEdgeTakenCount + 1, checking: | ||||
2176 | // "Stride >= TripCount" is equivalent to checking: | ||||
2177 | // Stride - BETakenCount > 0 | ||||
2178 | if (SE->isKnownPositive(StrideMinusBETaken)) { | ||||
2179 | LLVM_DEBUG(do { } while (false) | ||||
2180 | dbgs() << "LAA: Stride>=TripCount; No point in versioning as the "do { } while (false) | ||||
2181 | "Stride==1 predicate will imply that the loop executes "do { } while (false) | ||||
2182 | "at most once.\n")do { } while (false); | ||||
2183 | return; | ||||
2184 | } | ||||
2185 | LLVM_DEBUG(dbgs() << "LAA: Found a strided access that we can version.")do { } while (false); | ||||
2186 | |||||
2187 | SymbolicStrides[Ptr] = Stride; | ||||
2188 | StrideSet.insert(Stride); | ||||
2189 | } | ||||
2190 | |||||
2191 | LoopAccessInfo::LoopAccessInfo(Loop *L, ScalarEvolution *SE, | ||||
2192 | const TargetLibraryInfo *TLI, AAResults *AA, | ||||
2193 | DominatorTree *DT, LoopInfo *LI) | ||||
2194 | : PSE(std::make_unique<PredicatedScalarEvolution>(*SE, *L)), | ||||
2195 | PtrRtChecking(std::make_unique<RuntimePointerChecking>(SE)), | ||||
2196 | DepChecker(std::make_unique<MemoryDepChecker>(*PSE, L)), TheLoop(L), | ||||
2197 | NumLoads(0), NumStores(0), MaxSafeDepDistBytes(-1), CanVecMem(false), | ||||
2198 | HasConvergentOp(false), | ||||
2199 | HasDependenceInvolvingLoopInvariantAddress(false) { | ||||
2200 | if (canAnalyzeLoop()) | ||||
2201 | analyzeLoop(AA, LI, TLI, DT); | ||||
2202 | } | ||||
2203 | |||||
2204 | void LoopAccessInfo::print(raw_ostream &OS, unsigned Depth) const { | ||||
2205 | if (CanVecMem) { | ||||
2206 | OS.indent(Depth) << "Memory dependences are safe"; | ||||
2207 | if (MaxSafeDepDistBytes != -1ULL) | ||||
2208 | OS << " with a maximum dependence distance of " << MaxSafeDepDistBytes | ||||
2209 | << " bytes"; | ||||
2210 | if (PtrRtChecking->Need) | ||||
2211 | OS << " with run-time checks"; | ||||
2212 | OS << "\n"; | ||||
2213 | } | ||||
2214 | |||||
2215 | if (HasConvergentOp) | ||||
2216 | OS.indent(Depth) << "Has convergent operation in loop\n"; | ||||
2217 | |||||
2218 | if (Report) | ||||
2219 | OS.indent(Depth) << "Report: " << Report->getMsg() << "\n"; | ||||
2220 | |||||
2221 | if (auto *Dependences = DepChecker->getDependences()) { | ||||
2222 | OS.indent(Depth) << "Dependences:\n"; | ||||
2223 | for (auto &Dep : *Dependences) { | ||||
2224 | Dep.print(OS, Depth + 2, DepChecker->getMemoryInstructions()); | ||||
2225 | OS << "\n"; | ||||
2226 | } | ||||
2227 | } else | ||||
2228 | OS.indent(Depth) << "Too many dependences, not recorded\n"; | ||||
2229 | |||||
2230 | // List the pair of accesses need run-time checks to prove independence. | ||||
2231 | PtrRtChecking->print(OS, Depth); | ||||
2232 | OS << "\n"; | ||||
2233 | |||||
2234 | OS.indent(Depth) << "Non vectorizable stores to invariant address were " | ||||
2235 | << (HasDependenceInvolvingLoopInvariantAddress ? "" : "not ") | ||||
2236 | << "found in loop.\n"; | ||||
2237 | |||||
2238 | OS.indent(Depth) << "SCEV assumptions:\n"; | ||||
2239 | PSE->getUnionPredicate().print(OS, Depth); | ||||
2240 | |||||
2241 | OS << "\n"; | ||||
2242 | |||||
2243 | OS.indent(Depth) << "Expressions re-written:\n"; | ||||
2244 | PSE->print(OS, Depth); | ||||
2245 | } | ||||
2246 | |||||
2247 | LoopAccessLegacyAnalysis::LoopAccessLegacyAnalysis() : FunctionPass(ID) { | ||||
2248 | initializeLoopAccessLegacyAnalysisPass(*PassRegistry::getPassRegistry()); | ||||
2249 | } | ||||
2250 | |||||
2251 | const LoopAccessInfo &LoopAccessLegacyAnalysis::getInfo(Loop *L) { | ||||
2252 | auto &LAI = LoopAccessInfoMap[L]; | ||||
2253 | |||||
2254 | if (!LAI) | ||||
2255 | LAI = std::make_unique<LoopAccessInfo>(L, SE, TLI, AA, DT, LI); | ||||
2256 | |||||
2257 | return *LAI.get(); | ||||
2258 | } | ||||
2259 | |||||
2260 | void LoopAccessLegacyAnalysis::print(raw_ostream &OS, const Module *M) const { | ||||
2261 | LoopAccessLegacyAnalysis &LAA = *const_cast<LoopAccessLegacyAnalysis *>(this); | ||||
2262 | |||||
2263 | for (Loop *TopLevelLoop : *LI) | ||||
2264 | for (Loop *L : depth_first(TopLevelLoop)) { | ||||
2265 | OS.indent(2) << L->getHeader()->getName() << ":\n"; | ||||
2266 | auto &LAI = LAA.getInfo(L); | ||||
2267 | LAI.print(OS, 4); | ||||
2268 | } | ||||
2269 | } | ||||
2270 | |||||
2271 | bool LoopAccessLegacyAnalysis::runOnFunction(Function &F) { | ||||
2272 | SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE(); | ||||
2273 | auto *TLIP = getAnalysisIfAvailable<TargetLibraryInfoWrapperPass>(); | ||||
2274 | TLI = TLIP ? &TLIP->getTLI(F) : nullptr; | ||||
2275 | AA = &getAnalysis<AAResultsWrapperPass>().getAAResults(); | ||||
2276 | DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree(); | ||||
2277 | LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo(); | ||||
2278 | |||||
2279 | return false; | ||||
2280 | } | ||||
2281 | |||||
2282 | void LoopAccessLegacyAnalysis::getAnalysisUsage(AnalysisUsage &AU) const { | ||||
2283 | AU.addRequiredTransitive<ScalarEvolutionWrapperPass>(); | ||||
2284 | AU.addRequiredTransitive<AAResultsWrapperPass>(); | ||||
2285 | AU.addRequiredTransitive<DominatorTreeWrapperPass>(); | ||||
2286 | AU.addRequiredTransitive<LoopInfoWrapperPass>(); | ||||
2287 | |||||
2288 | AU.setPreservesAll(); | ||||
2289 | } | ||||
2290 | |||||
2291 | char LoopAccessLegacyAnalysis::ID = 0; | ||||
2292 | static const char laa_name[] = "Loop Access Analysis"; | ||||
2293 | #define LAA_NAME"loop-accesses" "loop-accesses" | ||||
2294 | |||||
2295 | INITIALIZE_PASS_BEGIN(LoopAccessLegacyAnalysis, LAA_NAME, laa_name, false, true)static void *initializeLoopAccessLegacyAnalysisPassOnce(PassRegistry &Registry) { | ||||
2296 | INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)initializeAAResultsWrapperPassPass(Registry); | ||||
2297 | INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)initializeScalarEvolutionWrapperPassPass(Registry); | ||||
2298 | INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)initializeDominatorTreeWrapperPassPass(Registry); | ||||
2299 | INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)initializeLoopInfoWrapperPassPass(Registry); | ||||
2300 | INITIALIZE_PASS_END(LoopAccessLegacyAnalysis, LAA_NAME, laa_name, false, true)PassInfo *PI = new PassInfo( laa_name, "loop-accesses", & LoopAccessLegacyAnalysis::ID, PassInfo::NormalCtor_t(callDefaultCtor <LoopAccessLegacyAnalysis>), false, true); Registry.registerPass (*PI, true); return PI; } static llvm::once_flag InitializeLoopAccessLegacyAnalysisPassFlag ; void llvm::initializeLoopAccessLegacyAnalysisPass(PassRegistry &Registry) { llvm::call_once(InitializeLoopAccessLegacyAnalysisPassFlag , initializeLoopAccessLegacyAnalysisPassOnce, std::ref(Registry )); } | ||||
2301 | |||||
2302 | AnalysisKey LoopAccessAnalysis::Key; | ||||
2303 | |||||
2304 | LoopAccessInfo LoopAccessAnalysis::run(Loop &L, LoopAnalysisManager &AM, | ||||
2305 | LoopStandardAnalysisResults &AR) { | ||||
2306 | return LoopAccessInfo(&L, &AR.SE, &AR.TLI, &AR.AA, &AR.DT, &AR.LI); | ||||
2307 | } | ||||
2308 | |||||
2309 | namespace llvm { | ||||
2310 | |||||
2311 | Pass *createLAAPass() { | ||||
2312 | return new LoopAccessLegacyAnalysis(); | ||||
2313 | } | ||||
2314 | |||||
2315 | } // end namespace llvm |