Bug Summary

File:src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
Warning:line 738, column 24
Called C++ object pointer is null

Annotated Source Code

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clang -cc1 -cc1 -triple amd64-unknown-openbsd7.0 -analyze -disable-free -disable-llvm-verifier -discard-value-names -main-file-name DeadStoreElimination.cpp -analyzer-store=region -analyzer-opt-analyze-nested-blocks -analyzer-checker=core -analyzer-checker=apiModeling -analyzer-checker=unix -analyzer-checker=deadcode -analyzer-checker=cplusplus -analyzer-checker=security.insecureAPI.UncheckedReturn -analyzer-checker=security.insecureAPI.getpw -analyzer-checker=security.insecureAPI.gets -analyzer-checker=security.insecureAPI.mktemp -analyzer-checker=security.insecureAPI.mkstemp -analyzer-checker=security.insecureAPI.vfork -analyzer-checker=nullability.NullPassedToNonnull -analyzer-checker=nullability.NullReturnedFromNonnull -analyzer-output plist -w -setup-static-analyzer -mrelocation-model pic -pic-level 1 -fhalf-no-semantic-interposition -mframe-pointer=all -relaxed-aliasing -fno-rounding-math -mconstructor-aliases -munwind-tables -target-cpu x86-64 -tune-cpu generic -debugger-tuning=gdb -fcoverage-compilation-dir=/usr/src/gnu/usr.bin/clang/libLLVM/obj -resource-dir /usr/local/lib/clang/13.0.0 -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/AMDGPU -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Target/AMDGPU -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/AMDGPU -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Target/AMDGPU -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/AMDGPU -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Target/AMDGPU -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/AMDGPU -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Target/AMDGPU -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/AMDGPU -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Target/AMDGPU -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/AMDGPU -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Target/AMDGPU -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Analysis -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/ASMParser -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/BinaryFormat -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Bitcode -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Bitcode -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Bitstream -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms -I /include/llvm/CodeGen -I /include/llvm/CodeGen/PBQP -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/IR -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/IR -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms/Coroutines -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/ProfileData/Coverage -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/DebugInfo/CodeView -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/DebugInfo/DWARF -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/DebugInfo -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/DebugInfo/MSF -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/DebugInfo/PDB -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Demangle -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/ExecutionEngine -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/ExecutionEngine/JITLink -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/ExecutionEngine/Orc -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Frontend -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Frontend/OpenACC -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Frontend -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Frontend/OpenMP -I /include/llvm/CodeGen/GlobalISel -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/IRReader -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms/InstCombine -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/Transforms/InstCombine -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/LTO -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Linker -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/MC -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/MC/MCParser -I /include/llvm/CodeGen/MIRParser -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Object -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Option -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Passes -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/ -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/ProfileData -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms/Scalar -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/ADT -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Support -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/DebugInfo/Symbolize -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Target -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms/Utils -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms/Vectorize -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/X86 -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Target/X86 -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/X86 -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Target/X86 -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/X86 -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Target/X86 -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/X86 -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Target/X86 -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/X86 -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Target/X86 -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms/IPO -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include -I /usr/src/gnu/usr.bin/clang/libLLVM/../include -I /usr/src/gnu/usr.bin/clang/libLLVM/obj -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include -D NDEBUG -D __STDC_LIMIT_MACROS -D __STDC_CONSTANT_MACROS -D __STDC_FORMAT_MACROS -D LLVM_PREFIX="/usr" -D PIC -internal-isystem /usr/include/c++/v1 -internal-isystem /usr/local/lib/clang/13.0.0/include -internal-externc-isystem /usr/include -O2 -Wno-unused-parameter -Wwrite-strings -Wno-missing-field-initializers -Wno-long-long -Wno-comment -std=c++14 -fdeprecated-macro -fdebug-compilation-dir=/usr/src/gnu/usr.bin/clang/libLLVM/obj -ferror-limit 19 -fvisibility-inlines-hidden -fwrapv -D_RET_PROTECTOR -ret-protector -fno-rtti -fgnuc-version=4.2.1 -vectorize-loops -vectorize-slp -fno-builtin-malloc -fno-builtin-calloc -fno-builtin-realloc -fno-builtin-valloc -fno-builtin-free -fno-builtin-strdup -fno-builtin-strndup -analyzer-output=html -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -o /home/ben/Projects/vmm/scan-build/2022-01-12-194120-40624-1 -x c++ /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp

/usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp

1//===- DeadStoreElimination.cpp - MemorySSA Backed Dead Store Elimination -===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// The code below implements dead store elimination using MemorySSA. It uses
10// the following general approach: given a MemoryDef, walk upwards to find
11// clobbering MemoryDefs that may be killed by the starting def. Then check
12// that there are no uses that may read the location of the original MemoryDef
13// in between both MemoryDefs. A bit more concretely:
14//
15// For all MemoryDefs StartDef:
16// 1. Get the next dominating clobbering MemoryDef (EarlierAccess) by walking
17// upwards.
18// 2. Check that there are no reads between EarlierAccess and the StartDef by
19// checking all uses starting at EarlierAccess and walking until we see
20// StartDef.
21// 3. For each found CurrentDef, check that:
22// 1. There are no barrier instructions between CurrentDef and StartDef (like
23// throws or stores with ordering constraints).
24// 2. StartDef is executed whenever CurrentDef is executed.
25// 3. StartDef completely overwrites CurrentDef.
26// 4. Erase CurrentDef from the function and MemorySSA.
27//
28//===----------------------------------------------------------------------===//
29
30#include "llvm/Transforms/Scalar/DeadStoreElimination.h"
31#include "llvm/ADT/APInt.h"
32#include "llvm/ADT/DenseMap.h"
33#include "llvm/ADT/MapVector.h"
34#include "llvm/ADT/PostOrderIterator.h"
35#include "llvm/ADT/SetVector.h"
36#include "llvm/ADT/SmallPtrSet.h"
37#include "llvm/ADT/SmallVector.h"
38#include "llvm/ADT/Statistic.h"
39#include "llvm/ADT/StringRef.h"
40#include "llvm/Analysis/AliasAnalysis.h"
41#include "llvm/Analysis/CaptureTracking.h"
42#include "llvm/Analysis/GlobalsModRef.h"
43#include "llvm/Analysis/LoopInfo.h"
44#include "llvm/Analysis/MemoryBuiltins.h"
45#include "llvm/Analysis/MemoryLocation.h"
46#include "llvm/Analysis/MemorySSA.h"
47#include "llvm/Analysis/MemorySSAUpdater.h"
48#include "llvm/Analysis/MustExecute.h"
49#include "llvm/Analysis/PostDominators.h"
50#include "llvm/Analysis/TargetLibraryInfo.h"
51#include "llvm/Analysis/ValueTracking.h"
52#include "llvm/IR/Argument.h"
53#include "llvm/IR/BasicBlock.h"
54#include "llvm/IR/Constant.h"
55#include "llvm/IR/Constants.h"
56#include "llvm/IR/DataLayout.h"
57#include "llvm/IR/Dominators.h"
58#include "llvm/IR/Function.h"
59#include "llvm/IR/InstIterator.h"
60#include "llvm/IR/InstrTypes.h"
61#include "llvm/IR/Instruction.h"
62#include "llvm/IR/Instructions.h"
63#include "llvm/IR/IntrinsicInst.h"
64#include "llvm/IR/Intrinsics.h"
65#include "llvm/IR/LLVMContext.h"
66#include "llvm/IR/Module.h"
67#include "llvm/IR/PassManager.h"
68#include "llvm/IR/PatternMatch.h"
69#include "llvm/IR/Value.h"
70#include "llvm/InitializePasses.h"
71#include "llvm/Pass.h"
72#include "llvm/Support/Casting.h"
73#include "llvm/Support/CommandLine.h"
74#include "llvm/Support/Debug.h"
75#include "llvm/Support/DebugCounter.h"
76#include "llvm/Support/ErrorHandling.h"
77#include "llvm/Support/MathExtras.h"
78#include "llvm/Support/raw_ostream.h"
79#include "llvm/Transforms/Scalar.h"
80#include "llvm/Transforms/Utils/AssumeBundleBuilder.h"
81#include "llvm/Transforms/Utils/Local.h"
82#include <algorithm>
83#include <cassert>
84#include <cstddef>
85#include <cstdint>
86#include <iterator>
87#include <map>
88#include <utility>
89
90using namespace llvm;
91using namespace PatternMatch;
92
93#define DEBUG_TYPE"dse" "dse"
94
95STATISTIC(NumRemainingStores, "Number of stores remaining after DSE")static llvm::Statistic NumRemainingStores = {"dse", "NumRemainingStores"
, "Number of stores remaining after DSE"}
;
96STATISTIC(NumRedundantStores, "Number of redundant stores deleted")static llvm::Statistic NumRedundantStores = {"dse", "NumRedundantStores"
, "Number of redundant stores deleted"}
;
97STATISTIC(NumFastStores, "Number of stores deleted")static llvm::Statistic NumFastStores = {"dse", "NumFastStores"
, "Number of stores deleted"}
;
98STATISTIC(NumFastOther, "Number of other instrs removed")static llvm::Statistic NumFastOther = {"dse", "NumFastOther",
"Number of other instrs removed"}
;
99STATISTIC(NumCompletePartials, "Number of stores dead by later partials")static llvm::Statistic NumCompletePartials = {"dse", "NumCompletePartials"
, "Number of stores dead by later partials"}
;
100STATISTIC(NumModifiedStores, "Number of stores modified")static llvm::Statistic NumModifiedStores = {"dse", "NumModifiedStores"
, "Number of stores modified"}
;
101STATISTIC(NumCFGChecks, "Number of stores modified")static llvm::Statistic NumCFGChecks = {"dse", "NumCFGChecks",
"Number of stores modified"}
;
102STATISTIC(NumCFGTries, "Number of stores modified")static llvm::Statistic NumCFGTries = {"dse", "NumCFGTries", "Number of stores modified"
}
;
103STATISTIC(NumCFGSuccess, "Number of stores modified")static llvm::Statistic NumCFGSuccess = {"dse", "NumCFGSuccess"
, "Number of stores modified"}
;
104STATISTIC(NumGetDomMemoryDefPassed,static llvm::Statistic NumGetDomMemoryDefPassed = {"dse", "NumGetDomMemoryDefPassed"
, "Number of times a valid candidate is returned from getDomMemoryDef"
}
105 "Number of times a valid candidate is returned from getDomMemoryDef")static llvm::Statistic NumGetDomMemoryDefPassed = {"dse", "NumGetDomMemoryDefPassed"
, "Number of times a valid candidate is returned from getDomMemoryDef"
}
;
106STATISTIC(NumDomMemDefChecks,static llvm::Statistic NumDomMemDefChecks = {"dse", "NumDomMemDefChecks"
, "Number iterations check for reads in getDomMemoryDef"}
107 "Number iterations check for reads in getDomMemoryDef")static llvm::Statistic NumDomMemDefChecks = {"dse", "NumDomMemDefChecks"
, "Number iterations check for reads in getDomMemoryDef"}
;
108
109DEBUG_COUNTER(MemorySSACounter, "dse-memoryssa",static const unsigned MemorySSACounter = DebugCounter::registerCounter
("dse-memoryssa", "Controls which MemoryDefs are eliminated."
)
110 "Controls which MemoryDefs are eliminated.")static const unsigned MemorySSACounter = DebugCounter::registerCounter
("dse-memoryssa", "Controls which MemoryDefs are eliminated."
)
;
111
112static cl::opt<bool>
113EnablePartialOverwriteTracking("enable-dse-partial-overwrite-tracking",
114 cl::init(true), cl::Hidden,
115 cl::desc("Enable partial-overwrite tracking in DSE"));
116
117static cl::opt<bool>
118EnablePartialStoreMerging("enable-dse-partial-store-merging",
119 cl::init(true), cl::Hidden,
120 cl::desc("Enable partial store merging in DSE"));
121
122static cl::opt<unsigned>
123 MemorySSAScanLimit("dse-memoryssa-scanlimit", cl::init(150), cl::Hidden,
124 cl::desc("The number of memory instructions to scan for "
125 "dead store elimination (default = 100)"));
126static cl::opt<unsigned> MemorySSAUpwardsStepLimit(
127 "dse-memoryssa-walklimit", cl::init(90), cl::Hidden,
128 cl::desc("The maximum number of steps while walking upwards to find "
129 "MemoryDefs that may be killed (default = 90)"));
130
131static cl::opt<unsigned> MemorySSAPartialStoreLimit(
132 "dse-memoryssa-partial-store-limit", cl::init(5), cl::Hidden,
133 cl::desc("The maximum number candidates that only partially overwrite the "
134 "killing MemoryDef to consider"
135 " (default = 5)"));
136
137static cl::opt<unsigned> MemorySSADefsPerBlockLimit(
138 "dse-memoryssa-defs-per-block-limit", cl::init(5000), cl::Hidden,
139 cl::desc("The number of MemoryDefs we consider as candidates to eliminated "
140 "other stores per basic block (default = 5000)"));
141
142static cl::opt<unsigned> MemorySSASameBBStepCost(
143 "dse-memoryssa-samebb-cost", cl::init(1), cl::Hidden,
144 cl::desc(
145 "The cost of a step in the same basic block as the killing MemoryDef"
146 "(default = 1)"));
147
148static cl::opt<unsigned>
149 MemorySSAOtherBBStepCost("dse-memoryssa-otherbb-cost", cl::init(5),
150 cl::Hidden,
151 cl::desc("The cost of a step in a different basic "
152 "block than the killing MemoryDef"
153 "(default = 5)"));
154
155static cl::opt<unsigned> MemorySSAPathCheckLimit(
156 "dse-memoryssa-path-check-limit", cl::init(50), cl::Hidden,
157 cl::desc("The maximum number of blocks to check when trying to prove that "
158 "all paths to an exit go through a killing block (default = 50)"));
159
160//===----------------------------------------------------------------------===//
161// Helper functions
162//===----------------------------------------------------------------------===//
163using OverlapIntervalsTy = std::map<int64_t, int64_t>;
164using InstOverlapIntervalsTy = DenseMap<Instruction *, OverlapIntervalsTy>;
165
166/// Does this instruction write some memory? This only returns true for things
167/// that we can analyze with other helpers below.
168static bool hasAnalyzableMemoryWrite(Instruction *I,
169 const TargetLibraryInfo &TLI) {
170 if (isa<StoreInst>(I))
171 return true;
172 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
173 switch (II->getIntrinsicID()) {
174 default:
175 return false;
176 case Intrinsic::memset:
177 case Intrinsic::memmove:
178 case Intrinsic::memcpy:
179 case Intrinsic::memcpy_inline:
180 case Intrinsic::memcpy_element_unordered_atomic:
181 case Intrinsic::memmove_element_unordered_atomic:
182 case Intrinsic::memset_element_unordered_atomic:
183 case Intrinsic::init_trampoline:
184 case Intrinsic::lifetime_end:
185 case Intrinsic::masked_store:
186 return true;
187 }
188 }
189 if (auto *CB = dyn_cast<CallBase>(I)) {
190 LibFunc LF;
191 if (TLI.getLibFunc(*CB, LF) && TLI.has(LF)) {
192 switch (LF) {
193 case LibFunc_strcpy:
194 case LibFunc_strncpy:
195 case LibFunc_strcat:
196 case LibFunc_strncat:
197 return true;
198 default:
199 return false;
200 }
201 }
202 }
203 return false;
204}
205
206/// Return a Location stored to by the specified instruction. If isRemovable
207/// returns true, this function and getLocForRead completely describe the memory
208/// operations for this instruction.
209static MemoryLocation getLocForWrite(Instruction *Inst,
210 const TargetLibraryInfo &TLI) {
211 if (StoreInst *SI
8.1
'SI' is null
8.1
'SI' is null
= dyn_cast<StoreInst>(Inst))
8
Assuming 'Inst' is not a 'StoreInst'
9
Taking false branch
212 return MemoryLocation::get(SI);
213
214 // memcpy/memmove/memset.
215 if (auto *MI
10.1
'MI' is null
10.1
'MI' is null
= dyn_cast<AnyMemIntrinsic>(Inst))
10
Assuming 'Inst' is not a 'AnyMemIntrinsic'
11
Taking false branch
216 return MemoryLocation::getForDest(MI);
217
218 if (IntrinsicInst *II
12.1
'II' is null
12.1
'II' is null
= dyn_cast<IntrinsicInst>(Inst)) {
12
Assuming 'Inst' is not a 'IntrinsicInst'
13
Taking false branch
219 switch (II->getIntrinsicID()) {
220 default:
221 return MemoryLocation(); // Unhandled intrinsic.
222 case Intrinsic::init_trampoline:
223 return MemoryLocation::getAfter(II->getArgOperand(0));
224 case Intrinsic::masked_store:
225 return MemoryLocation::getForArgument(II, 1, TLI);
226 case Intrinsic::lifetime_end: {
227 uint64_t Len = cast<ConstantInt>(II->getArgOperand(0))->getZExtValue();
228 return MemoryLocation(II->getArgOperand(1), Len);
229 }
230 }
231 }
232 if (auto *CB
14.1
'CB' is null
14.1
'CB' is null
= dyn_cast<CallBase>(Inst))
14
Assuming 'Inst' is not a 'CallBase'
15
Taking false branch
233 // All the supported TLI functions so far happen to have dest as their
234 // first argument.
235 return MemoryLocation::getAfter(CB->getArgOperand(0));
236 return MemoryLocation();
16
Calling default constructor for 'MemoryLocation'
18
Returning from default constructor for 'MemoryLocation'
237}
238
239/// If the value of this instruction and the memory it writes to is unused, may
240/// we delete this instruction?
241static bool isRemovable(Instruction *I) {
242 // Don't remove volatile/atomic stores.
243 if (StoreInst *SI = dyn_cast<StoreInst>(I))
244 return SI->isUnordered();
245
246 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
247 switch (II->getIntrinsicID()) {
248 default: llvm_unreachable("doesn't pass 'hasAnalyzableMemoryWrite' predicate")__builtin_unreachable();
249 case Intrinsic::lifetime_end:
250 // Never remove dead lifetime_end's, e.g. because it is followed by a
251 // free.
252 return false;
253 case Intrinsic::init_trampoline:
254 // Always safe to remove init_trampoline.
255 return true;
256 case Intrinsic::memset:
257 case Intrinsic::memmove:
258 case Intrinsic::memcpy:
259 case Intrinsic::memcpy_inline:
260 // Don't remove volatile memory intrinsics.
261 return !cast<MemIntrinsic>(II)->isVolatile();
262 case Intrinsic::memcpy_element_unordered_atomic:
263 case Intrinsic::memmove_element_unordered_atomic:
264 case Intrinsic::memset_element_unordered_atomic:
265 case Intrinsic::masked_store:
266 return true;
267 }
268 }
269
270 // note: only get here for calls with analyzable writes - i.e. libcalls
271 if (auto *CB = dyn_cast<CallBase>(I))
272 return CB->use_empty();
273
274 return false;
275}
276
277/// Returns true if the end of this instruction can be safely shortened in
278/// length.
279static bool isShortenableAtTheEnd(Instruction *I) {
280 // Don't shorten stores for now
281 if (isa<StoreInst>(I))
282 return false;
283
284 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
285 switch (II->getIntrinsicID()) {
286 default: return false;
287 case Intrinsic::memset:
288 case Intrinsic::memcpy:
289 case Intrinsic::memcpy_element_unordered_atomic:
290 case Intrinsic::memset_element_unordered_atomic:
291 // Do shorten memory intrinsics.
292 // FIXME: Add memmove if it's also safe to transform.
293 return true;
294 }
295 }
296
297 // Don't shorten libcalls calls for now.
298
299 return false;
300}
301
302/// Returns true if the beginning of this instruction can be safely shortened
303/// in length.
304static bool isShortenableAtTheBeginning(Instruction *I) {
305 // FIXME: Handle only memset for now. Supporting memcpy/memmove should be
306 // easily done by offsetting the source address.
307 return isa<AnyMemSetInst>(I);
308}
309
310static uint64_t getPointerSize(const Value *V, const DataLayout &DL,
311 const TargetLibraryInfo &TLI,
312 const Function *F) {
313 uint64_t Size;
314 ObjectSizeOpts Opts;
315 Opts.NullIsUnknownSize = NullPointerIsDefined(F);
316
317 if (getObjectSize(V, Size, DL, &TLI, Opts))
318 return Size;
319 return MemoryLocation::UnknownSize;
320}
321
322namespace {
323
324enum OverwriteResult {
325 OW_Begin,
326 OW_Complete,
327 OW_End,
328 OW_PartialEarlierWithFullLater,
329 OW_MaybePartial,
330 OW_Unknown
331};
332
333} // end anonymous namespace
334
335/// Check if two instruction are masked stores that completely
336/// overwrite one another. More specifically, \p Later has to
337/// overwrite \p Earlier.
338static OverwriteResult isMaskedStoreOverwrite(const Instruction *Later,
339 const Instruction *Earlier,
340 BatchAAResults &AA) {
341 const auto *IIL = dyn_cast<IntrinsicInst>(Later);
342 const auto *IIE = dyn_cast<IntrinsicInst>(Earlier);
343 if (IIL == nullptr || IIE == nullptr)
344 return OW_Unknown;
345 if (IIL->getIntrinsicID() != Intrinsic::masked_store ||
346 IIE->getIntrinsicID() != Intrinsic::masked_store)
347 return OW_Unknown;
348 // Pointers.
349 Value *LP = IIL->getArgOperand(1)->stripPointerCasts();
350 Value *EP = IIE->getArgOperand(1)->stripPointerCasts();
351 if (LP != EP && !AA.isMustAlias(LP, EP))
352 return OW_Unknown;
353 // Masks.
354 // TODO: check that Later's mask is a superset of the Earlier's mask.
355 if (IIL->getArgOperand(3) != IIE->getArgOperand(3))
356 return OW_Unknown;
357 return OW_Complete;
358}
359
360/// Return 'OW_Complete' if a store to the 'Later' location completely
361/// overwrites a store to the 'Earlier' location, 'OW_End' if the end of the
362/// 'Earlier' location is completely overwritten by 'Later', 'OW_Begin' if the
363/// beginning of the 'Earlier' location is overwritten by 'Later'.
364/// 'OW_PartialEarlierWithFullLater' means that an earlier (big) store was
365/// overwritten by a latter (smaller) store which doesn't write outside the big
366/// store's memory locations. Returns 'OW_Unknown' if nothing can be determined.
367/// NOTE: This function must only be called if both \p Later and \p Earlier
368/// write to the same underlying object with valid \p EarlierOff and \p
369/// LaterOff.
370static OverwriteResult isPartialOverwrite(const MemoryLocation &Later,
371 const MemoryLocation &Earlier,
372 int64_t EarlierOff, int64_t LaterOff,
373 Instruction *DepWrite,
374 InstOverlapIntervalsTy &IOL) {
375 const uint64_t LaterSize = Later.Size.getValue();
376 const uint64_t EarlierSize = Earlier.Size.getValue();
377 // We may now overlap, although the overlap is not complete. There might also
378 // be other incomplete overlaps, and together, they might cover the complete
379 // earlier write.
380 // Note: The correctness of this logic depends on the fact that this function
381 // is not even called providing DepWrite when there are any intervening reads.
382 if (EnablePartialOverwriteTracking &&
383 LaterOff < int64_t(EarlierOff + EarlierSize) &&
384 int64_t(LaterOff + LaterSize) >= EarlierOff) {
385
386 // Insert our part of the overlap into the map.
387 auto &IM = IOL[DepWrite];
388 LLVM_DEBUG(dbgs() << "DSE: Partial overwrite: Earlier [" << EarlierOffdo { } while (false)
389 << ", " << int64_t(EarlierOff + EarlierSize)do { } while (false)
390 << ") Later [" << LaterOff << ", "do { } while (false)
391 << int64_t(LaterOff + LaterSize) << ")\n")do { } while (false);
392
393 // Make sure that we only insert non-overlapping intervals and combine
394 // adjacent intervals. The intervals are stored in the map with the ending
395 // offset as the key (in the half-open sense) and the starting offset as
396 // the value.
397 int64_t LaterIntStart = LaterOff, LaterIntEnd = LaterOff + LaterSize;
398
399 // Find any intervals ending at, or after, LaterIntStart which start
400 // before LaterIntEnd.
401 auto ILI = IM.lower_bound(LaterIntStart);
402 if (ILI != IM.end() && ILI->second <= LaterIntEnd) {
403 // This existing interval is overlapped with the current store somewhere
404 // in [LaterIntStart, LaterIntEnd]. Merge them by erasing the existing
405 // intervals and adjusting our start and end.
406 LaterIntStart = std::min(LaterIntStart, ILI->second);
407 LaterIntEnd = std::max(LaterIntEnd, ILI->first);
408 ILI = IM.erase(ILI);
409
410 // Continue erasing and adjusting our end in case other previous
411 // intervals are also overlapped with the current store.
412 //
413 // |--- ealier 1 ---| |--- ealier 2 ---|
414 // |------- later---------|
415 //
416 while (ILI != IM.end() && ILI->second <= LaterIntEnd) {
417 assert(ILI->second > LaterIntStart && "Unexpected interval")((void)0);
418 LaterIntEnd = std::max(LaterIntEnd, ILI->first);
419 ILI = IM.erase(ILI);
420 }
421 }
422
423 IM[LaterIntEnd] = LaterIntStart;
424
425 ILI = IM.begin();
426 if (ILI->second <= EarlierOff &&
427 ILI->first >= int64_t(EarlierOff + EarlierSize)) {
428 LLVM_DEBUG(dbgs() << "DSE: Full overwrite from partials: Earlier ["do { } while (false)
429 << EarlierOff << ", "do { } while (false)
430 << int64_t(EarlierOff + EarlierSize)do { } while (false)
431 << ") Composite Later [" << ILI->second << ", "do { } while (false)
432 << ILI->first << ")\n")do { } while (false);
433 ++NumCompletePartials;
434 return OW_Complete;
435 }
436 }
437
438 // Check for an earlier store which writes to all the memory locations that
439 // the later store writes to.
440 if (EnablePartialStoreMerging && LaterOff >= EarlierOff &&
441 int64_t(EarlierOff + EarlierSize) > LaterOff &&
442 uint64_t(LaterOff - EarlierOff) + LaterSize <= EarlierSize) {
443 LLVM_DEBUG(dbgs() << "DSE: Partial overwrite an earlier load ["do { } while (false)
444 << EarlierOff << ", "do { } while (false)
445 << int64_t(EarlierOff + EarlierSize)do { } while (false)
446 << ") by a later store [" << LaterOff << ", "do { } while (false)
447 << int64_t(LaterOff + LaterSize) << ")\n")do { } while (false);
448 // TODO: Maybe come up with a better name?
449 return OW_PartialEarlierWithFullLater;
450 }
451
452 // Another interesting case is if the later store overwrites the end of the
453 // earlier store.
454 //
455 // |--earlier--|
456 // |-- later --|
457 //
458 // In this case we may want to trim the size of earlier to avoid generating
459 // writes to addresses which will definitely be overwritten later
460 if (!EnablePartialOverwriteTracking &&
461 (LaterOff > EarlierOff && LaterOff < int64_t(EarlierOff + EarlierSize) &&
462 int64_t(LaterOff + LaterSize) >= int64_t(EarlierOff + EarlierSize)))
463 return OW_End;
464
465 // Finally, we also need to check if the later store overwrites the beginning
466 // of the earlier store.
467 //
468 // |--earlier--|
469 // |-- later --|
470 //
471 // In this case we may want to move the destination address and trim the size
472 // of earlier to avoid generating writes to addresses which will definitely
473 // be overwritten later.
474 if (!EnablePartialOverwriteTracking &&
475 (LaterOff <= EarlierOff && int64_t(LaterOff + LaterSize) > EarlierOff)) {
476 assert(int64_t(LaterOff + LaterSize) < int64_t(EarlierOff + EarlierSize) &&((void)0)
477 "Expect to be handled as OW_Complete")((void)0);
478 return OW_Begin;
479 }
480 // Otherwise, they don't completely overlap.
481 return OW_Unknown;
482}
483
484/// Returns true if the memory which is accessed by the second instruction is not
485/// modified between the first and the second instruction.
486/// Precondition: Second instruction must be dominated by the first
487/// instruction.
488static bool
489memoryIsNotModifiedBetween(Instruction *FirstI, Instruction *SecondI,
490 BatchAAResults &AA, const DataLayout &DL,
491 DominatorTree *DT) {
492 // Do a backwards scan through the CFG from SecondI to FirstI. Look for
493 // instructions which can modify the memory location accessed by SecondI.
494 //
495 // While doing the walk keep track of the address to check. It might be
496 // different in different basic blocks due to PHI translation.
497 using BlockAddressPair = std::pair<BasicBlock *, PHITransAddr>;
498 SmallVector<BlockAddressPair, 16> WorkList;
499 // Keep track of the address we visited each block with. Bail out if we
500 // visit a block with different addresses.
501 DenseMap<BasicBlock *, Value *> Visited;
502
503 BasicBlock::iterator FirstBBI(FirstI);
504 ++FirstBBI;
505 BasicBlock::iterator SecondBBI(SecondI);
506 BasicBlock *FirstBB = FirstI->getParent();
507 BasicBlock *SecondBB = SecondI->getParent();
508 MemoryLocation MemLoc = MemoryLocation::get(SecondI);
509 auto *MemLocPtr = const_cast<Value *>(MemLoc.Ptr);
510
511 // Start checking the SecondBB.
512 WorkList.push_back(
513 std::make_pair(SecondBB, PHITransAddr(MemLocPtr, DL, nullptr)));
514 bool isFirstBlock = true;
515
516 // Check all blocks going backward until we reach the FirstBB.
517 while (!WorkList.empty()) {
518 BlockAddressPair Current = WorkList.pop_back_val();
519 BasicBlock *B = Current.first;
520 PHITransAddr &Addr = Current.second;
521 Value *Ptr = Addr.getAddr();
522
523 // Ignore instructions before FirstI if this is the FirstBB.
524 BasicBlock::iterator BI = (B == FirstBB ? FirstBBI : B->begin());
525
526 BasicBlock::iterator EI;
527 if (isFirstBlock) {
528 // Ignore instructions after SecondI if this is the first visit of SecondBB.
529 assert(B == SecondBB && "first block is not the store block")((void)0);
530 EI = SecondBBI;
531 isFirstBlock = false;
532 } else {
533 // It's not SecondBB or (in case of a loop) the second visit of SecondBB.
534 // In this case we also have to look at instructions after SecondI.
535 EI = B->end();
536 }
537 for (; BI != EI; ++BI) {
538 Instruction *I = &*BI;
539 if (I->mayWriteToMemory() && I != SecondI)
540 if (isModSet(AA.getModRefInfo(I, MemLoc.getWithNewPtr(Ptr))))
541 return false;
542 }
543 if (B != FirstBB) {
544 assert(B != &FirstBB->getParent()->getEntryBlock() &&((void)0)
545 "Should not hit the entry block because SI must be dominated by LI")((void)0);
546 for (BasicBlock *Pred : predecessors(B)) {
547 PHITransAddr PredAddr = Addr;
548 if (PredAddr.NeedsPHITranslationFromBlock(B)) {
549 if (!PredAddr.IsPotentiallyPHITranslatable())
550 return false;
551 if (PredAddr.PHITranslateValue(B, Pred, DT, false))
552 return false;
553 }
554 Value *TranslatedPtr = PredAddr.getAddr();
555 auto Inserted = Visited.insert(std::make_pair(Pred, TranslatedPtr));
556 if (!Inserted.second) {
557 // We already visited this block before. If it was with a different
558 // address - bail out!
559 if (TranslatedPtr != Inserted.first->second)
560 return false;
561 // ... otherwise just skip it.
562 continue;
563 }
564 WorkList.push_back(std::make_pair(Pred, PredAddr));
565 }
566 }
567 }
568 return true;
569}
570
571static bool tryToShorten(Instruction *EarlierWrite, int64_t &EarlierStart,
572 uint64_t &EarlierSize, int64_t LaterStart,
573 uint64_t LaterSize, bool IsOverwriteEnd) {
574 auto *EarlierIntrinsic = cast<AnyMemIntrinsic>(EarlierWrite);
575 Align PrefAlign = EarlierIntrinsic->getDestAlign().valueOrOne();
576
577 // We assume that memet/memcpy operates in chunks of the "largest" native
578 // type size and aligned on the same value. That means optimal start and size
579 // of memset/memcpy should be modulo of preferred alignment of that type. That
580 // is it there is no any sense in trying to reduce store size any further
581 // since any "extra" stores comes for free anyway.
582 // On the other hand, maximum alignment we can achieve is limited by alignment
583 // of initial store.
584
585 // TODO: Limit maximum alignment by preferred (or abi?) alignment of the
586 // "largest" native type.
587 // Note: What is the proper way to get that value?
588 // Should TargetTransformInfo::getRegisterBitWidth be used or anything else?
589 // PrefAlign = std::min(DL.getPrefTypeAlign(LargestType), PrefAlign);
590
591 int64_t ToRemoveStart = 0;
592 uint64_t ToRemoveSize = 0;
593 // Compute start and size of the region to remove. Make sure 'PrefAlign' is
594 // maintained on the remaining store.
595 if (IsOverwriteEnd) {
596 // Calculate required adjustment for 'LaterStart'in order to keep remaining
597 // store size aligned on 'PerfAlign'.
598 uint64_t Off =
599 offsetToAlignment(uint64_t(LaterStart - EarlierStart), PrefAlign);
600 ToRemoveStart = LaterStart + Off;
601 if (EarlierSize <= uint64_t(ToRemoveStart - EarlierStart))
602 return false;
603 ToRemoveSize = EarlierSize - uint64_t(ToRemoveStart - EarlierStart);
604 } else {
605 ToRemoveStart = EarlierStart;
606 assert(LaterSize >= uint64_t(EarlierStart - LaterStart) &&((void)0)
607 "Not overlapping accesses?")((void)0);
608 ToRemoveSize = LaterSize - uint64_t(EarlierStart - LaterStart);
609 // Calculate required adjustment for 'ToRemoveSize'in order to keep
610 // start of the remaining store aligned on 'PerfAlign'.
611 uint64_t Off = offsetToAlignment(ToRemoveSize, PrefAlign);
612 if (Off != 0) {
613 if (ToRemoveSize <= (PrefAlign.value() - Off))
614 return false;
615 ToRemoveSize -= PrefAlign.value() - Off;
616 }
617 assert(isAligned(PrefAlign, ToRemoveSize) &&((void)0)
618 "Should preserve selected alignment")((void)0);
619 }
620
621 assert(ToRemoveSize > 0 && "Shouldn't reach here if nothing to remove")((void)0);
622 assert(EarlierSize > ToRemoveSize && "Can't remove more than original size")((void)0);
623
624 uint64_t NewSize = EarlierSize - ToRemoveSize;
625 if (auto *AMI = dyn_cast<AtomicMemIntrinsic>(EarlierWrite)) {
626 // When shortening an atomic memory intrinsic, the newly shortened
627 // length must remain an integer multiple of the element size.
628 const uint32_t ElementSize = AMI->getElementSizeInBytes();
629 if (0 != NewSize % ElementSize)
630 return false;
631 }
632
633 LLVM_DEBUG(dbgs() << "DSE: Remove Dead Store:\n OW "do { } while (false)
634 << (IsOverwriteEnd ? "END" : "BEGIN") << ": "do { } while (false)
635 << *EarlierWrite << "\n KILLER [" << ToRemoveStart << ", "do { } while (false)
636 << int64_t(ToRemoveStart + ToRemoveSize) << ")\n")do { } while (false);
637
638 Value *EarlierWriteLength = EarlierIntrinsic->getLength();
639 Value *TrimmedLength =
640 ConstantInt::get(EarlierWriteLength->getType(), NewSize);
641 EarlierIntrinsic->setLength(TrimmedLength);
642 EarlierIntrinsic->setDestAlignment(PrefAlign);
643
644 if (!IsOverwriteEnd) {
645 Value *OrigDest = EarlierIntrinsic->getRawDest();
646 Type *Int8PtrTy =
647 Type::getInt8PtrTy(EarlierIntrinsic->getContext(),
648 OrigDest->getType()->getPointerAddressSpace());
649 Value *Dest = OrigDest;
650 if (OrigDest->getType() != Int8PtrTy)
651 Dest = CastInst::CreatePointerCast(OrigDest, Int8PtrTy, "", EarlierWrite);
652 Value *Indices[1] = {
653 ConstantInt::get(EarlierWriteLength->getType(), ToRemoveSize)};
654 Instruction *NewDestGEP = GetElementPtrInst::CreateInBounds(
655 Type::getInt8Ty(EarlierIntrinsic->getContext()),
656 Dest, Indices, "", EarlierWrite);
657 NewDestGEP->setDebugLoc(EarlierIntrinsic->getDebugLoc());
658 if (NewDestGEP->getType() != OrigDest->getType())
659 NewDestGEP = CastInst::CreatePointerCast(NewDestGEP, OrigDest->getType(),
660 "", EarlierWrite);
661 EarlierIntrinsic->setDest(NewDestGEP);
662 }
663
664 // Finally update start and size of earlier access.
665 if (!IsOverwriteEnd)
666 EarlierStart += ToRemoveSize;
667 EarlierSize = NewSize;
668
669 return true;
670}
671
672static bool tryToShortenEnd(Instruction *EarlierWrite,
673 OverlapIntervalsTy &IntervalMap,
674 int64_t &EarlierStart, uint64_t &EarlierSize) {
675 if (IntervalMap.empty() || !isShortenableAtTheEnd(EarlierWrite))
676 return false;
677
678 OverlapIntervalsTy::iterator OII = --IntervalMap.end();
679 int64_t LaterStart = OII->second;
680 uint64_t LaterSize = OII->first - LaterStart;
681
682 assert(OII->first - LaterStart >= 0 && "Size expected to be positive")((void)0);
683
684 if (LaterStart > EarlierStart &&
685 // Note: "LaterStart - EarlierStart" is known to be positive due to
686 // preceding check.
687 (uint64_t)(LaterStart - EarlierStart) < EarlierSize &&
688 // Note: "EarlierSize - (uint64_t)(LaterStart - EarlierStart)" is known to
689 // be non negative due to preceding checks.
690 LaterSize >= EarlierSize - (uint64_t)(LaterStart - EarlierStart)) {
691 if (tryToShorten(EarlierWrite, EarlierStart, EarlierSize, LaterStart,
692 LaterSize, true)) {
693 IntervalMap.erase(OII);
694 return true;
695 }
696 }
697 return false;
698}
699
700static bool tryToShortenBegin(Instruction *EarlierWrite,
701 OverlapIntervalsTy &IntervalMap,
702 int64_t &EarlierStart, uint64_t &EarlierSize) {
703 if (IntervalMap.empty() || !isShortenableAtTheBeginning(EarlierWrite))
704 return false;
705
706 OverlapIntervalsTy::iterator OII = IntervalMap.begin();
707 int64_t LaterStart = OII->second;
708 uint64_t LaterSize = OII->first - LaterStart;
709
710 assert(OII->first - LaterStart >= 0 && "Size expected to be positive")((void)0);
711
712 if (LaterStart <= EarlierStart &&
713 // Note: "EarlierStart - LaterStart" is known to be non negative due to
714 // preceding check.
715 LaterSize > (uint64_t)(EarlierStart - LaterStart)) {
716 // Note: "LaterSize - (uint64_t)(EarlierStart - LaterStart)" is known to be
717 // positive due to preceding checks.
718 assert(LaterSize - (uint64_t)(EarlierStart - LaterStart) < EarlierSize &&((void)0)
719 "Should have been handled as OW_Complete")((void)0);
720 if (tryToShorten(EarlierWrite, EarlierStart, EarlierSize, LaterStart,
721 LaterSize, false)) {
722 IntervalMap.erase(OII);
723 return true;
724 }
725 }
726 return false;
727}
728
729static bool removePartiallyOverlappedStores(const DataLayout &DL,
730 InstOverlapIntervalsTy &IOL,
731 const TargetLibraryInfo &TLI) {
732 bool Changed = false;
733 for (auto OI : IOL) {
734 Instruction *EarlierWrite = OI.first;
735 MemoryLocation Loc = getLocForWrite(EarlierWrite, TLI);
7
Calling 'getLocForWrite'
19
Returning from 'getLocForWrite'
736 assert(isRemovable(EarlierWrite) && "Expect only removable instruction")((void)0);
737
738 const Value *Ptr = Loc.Ptr->stripPointerCasts();
20
Called C++ object pointer is null
739 int64_t EarlierStart = 0;
740 uint64_t EarlierSize = Loc.Size.getValue();
741 GetPointerBaseWithConstantOffset(Ptr, EarlierStart, DL);
742 OverlapIntervalsTy &IntervalMap = OI.second;
743 Changed |=
744 tryToShortenEnd(EarlierWrite, IntervalMap, EarlierStart, EarlierSize);
745 if (IntervalMap.empty())
746 continue;
747 Changed |=
748 tryToShortenBegin(EarlierWrite, IntervalMap, EarlierStart, EarlierSize);
749 }
750 return Changed;
751}
752
753static Constant *tryToMergePartialOverlappingStores(
754 StoreInst *Earlier, StoreInst *Later, int64_t InstWriteOffset,
755 int64_t DepWriteOffset, const DataLayout &DL, BatchAAResults &AA,
756 DominatorTree *DT) {
757
758 if (Earlier && isa<ConstantInt>(Earlier->getValueOperand()) &&
759 DL.typeSizeEqualsStoreSize(Earlier->getValueOperand()->getType()) &&
760 Later && isa<ConstantInt>(Later->getValueOperand()) &&
761 DL.typeSizeEqualsStoreSize(Later->getValueOperand()->getType()) &&
762 memoryIsNotModifiedBetween(Earlier, Later, AA, DL, DT)) {
763 // If the store we find is:
764 // a) partially overwritten by the store to 'Loc'
765 // b) the later store is fully contained in the earlier one and
766 // c) they both have a constant value
767 // d) none of the two stores need padding
768 // Merge the two stores, replacing the earlier store's value with a
769 // merge of both values.
770 // TODO: Deal with other constant types (vectors, etc), and probably
771 // some mem intrinsics (if needed)
772
773 APInt EarlierValue =
774 cast<ConstantInt>(Earlier->getValueOperand())->getValue();
775 APInt LaterValue = cast<ConstantInt>(Later->getValueOperand())->getValue();
776 unsigned LaterBits = LaterValue.getBitWidth();
777 assert(EarlierValue.getBitWidth() > LaterValue.getBitWidth())((void)0);
778 LaterValue = LaterValue.zext(EarlierValue.getBitWidth());
779
780 // Offset of the smaller store inside the larger store
781 unsigned BitOffsetDiff = (InstWriteOffset - DepWriteOffset) * 8;
782 unsigned LShiftAmount = DL.isBigEndian() ? EarlierValue.getBitWidth() -
783 BitOffsetDiff - LaterBits
784 : BitOffsetDiff;
785 APInt Mask = APInt::getBitsSet(EarlierValue.getBitWidth(), LShiftAmount,
786 LShiftAmount + LaterBits);
787 // Clear the bits we'll be replacing, then OR with the smaller
788 // store, shifted appropriately.
789 APInt Merged = (EarlierValue & ~Mask) | (LaterValue << LShiftAmount);
790 LLVM_DEBUG(dbgs() << "DSE: Merge Stores:\n Earlier: " << *Earlierdo { } while (false)
791 << "\n Later: " << *Laterdo { } while (false)
792 << "\n Merged Value: " << Merged << '\n')do { } while (false);
793 return ConstantInt::get(Earlier->getValueOperand()->getType(), Merged);
794 }
795 return nullptr;
796}
797
798namespace {
799// Returns true if \p I is an intrisnic that does not read or write memory.
800bool isNoopIntrinsic(Instruction *I) {
801 if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
802 switch (II->getIntrinsicID()) {
803 case Intrinsic::lifetime_start:
804 case Intrinsic::lifetime_end:
805 case Intrinsic::invariant_end:
806 case Intrinsic::launder_invariant_group:
807 case Intrinsic::assume:
808 return true;
809 case Intrinsic::dbg_addr:
810 case Intrinsic::dbg_declare:
811 case Intrinsic::dbg_label:
812 case Intrinsic::dbg_value:
813 llvm_unreachable("Intrinsic should not be modeled in MemorySSA")__builtin_unreachable();
814 default:
815 return false;
816 }
817 }
818 return false;
819}
820
821// Check if we can ignore \p D for DSE.
822bool canSkipDef(MemoryDef *D, bool DefVisibleToCaller) {
823 Instruction *DI = D->getMemoryInst();
824 // Calls that only access inaccessible memory cannot read or write any memory
825 // locations we consider for elimination.
826 if (auto *CB = dyn_cast<CallBase>(DI))
827 if (CB->onlyAccessesInaccessibleMemory())
828 return true;
829
830 // We can eliminate stores to locations not visible to the caller across
831 // throwing instructions.
832 if (DI->mayThrow() && !DefVisibleToCaller)
833 return true;
834
835 // We can remove the dead stores, irrespective of the fence and its ordering
836 // (release/acquire/seq_cst). Fences only constraints the ordering of
837 // already visible stores, it does not make a store visible to other
838 // threads. So, skipping over a fence does not change a store from being
839 // dead.
840 if (isa<FenceInst>(DI))
841 return true;
842
843 // Skip intrinsics that do not really read or modify memory.
844 if (isNoopIntrinsic(D->getMemoryInst()))
845 return true;
846
847 return false;
848}
849
850struct DSEState {
851 Function &F;
852 AliasAnalysis &AA;
853
854 /// The single BatchAA instance that is used to cache AA queries. It will
855 /// not be invalidated over the whole run. This is safe, because:
856 /// 1. Only memory writes are removed, so the alias cache for memory
857 /// locations remains valid.
858 /// 2. No new instructions are added (only instructions removed), so cached
859 /// information for a deleted value cannot be accessed by a re-used new
860 /// value pointer.
861 BatchAAResults BatchAA;
862
863 MemorySSA &MSSA;
864 DominatorTree &DT;
865 PostDominatorTree &PDT;
866 const TargetLibraryInfo &TLI;
867 const DataLayout &DL;
868 const LoopInfo &LI;
869
870 // Whether the function contains any irreducible control flow, useful for
871 // being accurately able to detect loops.
872 bool ContainsIrreducibleLoops;
873
874 // All MemoryDefs that potentially could kill other MemDefs.
875 SmallVector<MemoryDef *, 64> MemDefs;
876 // Any that should be skipped as they are already deleted
877 SmallPtrSet<MemoryAccess *, 4> SkipStores;
878 // Keep track of all of the objects that are invisible to the caller before
879 // the function returns.
880 // SmallPtrSet<const Value *, 16> InvisibleToCallerBeforeRet;
881 DenseMap<const Value *, bool> InvisibleToCallerBeforeRet;
882 // Keep track of all of the objects that are invisible to the caller after
883 // the function returns.
884 DenseMap<const Value *, bool> InvisibleToCallerAfterRet;
885 // Keep track of blocks with throwing instructions not modeled in MemorySSA.
886 SmallPtrSet<BasicBlock *, 16> ThrowingBlocks;
887 // Post-order numbers for each basic block. Used to figure out if memory
888 // accesses are executed before another access.
889 DenseMap<BasicBlock *, unsigned> PostOrderNumbers;
890
891 /// Keep track of instructions (partly) overlapping with killing MemoryDefs per
892 /// basic block.
893 DenseMap<BasicBlock *, InstOverlapIntervalsTy> IOLs;
894
895 DSEState(Function &F, AliasAnalysis &AA, MemorySSA &MSSA, DominatorTree &DT,
896 PostDominatorTree &PDT, const TargetLibraryInfo &TLI,
897 const LoopInfo &LI)
898 : F(F), AA(AA), BatchAA(AA), MSSA(MSSA), DT(DT), PDT(PDT), TLI(TLI),
899 DL(F.getParent()->getDataLayout()), LI(LI) {}
900
901 static DSEState get(Function &F, AliasAnalysis &AA, MemorySSA &MSSA,
902 DominatorTree &DT, PostDominatorTree &PDT,
903 const TargetLibraryInfo &TLI, const LoopInfo &LI) {
904 DSEState State(F, AA, MSSA, DT, PDT, TLI, LI);
905 // Collect blocks with throwing instructions not modeled in MemorySSA and
906 // alloc-like objects.
907 unsigned PO = 0;
908 for (BasicBlock *BB : post_order(&F)) {
909 State.PostOrderNumbers[BB] = PO++;
910 for (Instruction &I : *BB) {
911 MemoryAccess *MA = MSSA.getMemoryAccess(&I);
912 if (I.mayThrow() && !MA)
913 State.ThrowingBlocks.insert(I.getParent());
914
915 auto *MD = dyn_cast_or_null<MemoryDef>(MA);
916 if (MD && State.MemDefs.size() < MemorySSADefsPerBlockLimit &&
917 (State.getLocForWriteEx(&I) || State.isMemTerminatorInst(&I)))
918 State.MemDefs.push_back(MD);
919 }
920 }
921
922 // Treat byval or inalloca arguments the same as Allocas, stores to them are
923 // dead at the end of the function.
924 for (Argument &AI : F.args())
925 if (AI.hasPassPointeeByValueCopyAttr()) {
926 // For byval, the caller doesn't know the address of the allocation.
927 if (AI.hasByValAttr())
928 State.InvisibleToCallerBeforeRet.insert({&AI, true});
929 State.InvisibleToCallerAfterRet.insert({&AI, true});
930 }
931
932 // Collect whether there is any irreducible control flow in the function.
933 State.ContainsIrreducibleLoops = mayContainIrreducibleControl(F, &LI);
934
935 return State;
936 }
937
938 /// Return 'OW_Complete' if a store to the 'Later' location (by \p LaterI
939 /// instruction) completely overwrites a store to the 'Earlier' location.
940 /// (by \p EarlierI instruction).
941 /// Return OW_MaybePartial if \p Later does not completely overwrite
942 /// \p Earlier, but they both write to the same underlying object. In that
943 /// case, use isPartialOverwrite to check if \p Later partially overwrites
944 /// \p Earlier. Returns 'OW_Unknown' if nothing can be determined.
945 OverwriteResult
946 isOverwrite(const Instruction *LaterI, const Instruction *EarlierI,
947 const MemoryLocation &Later, const MemoryLocation &Earlier,
948 int64_t &EarlierOff, int64_t &LaterOff) {
949 // AliasAnalysis does not always account for loops. Limit overwrite checks
950 // to dependencies for which we can guarantee they are independant of any
951 // loops they are in.
952 if (!isGuaranteedLoopIndependent(EarlierI, LaterI, Earlier))
953 return OW_Unknown;
954
955 // FIXME: Vet that this works for size upper-bounds. Seems unlikely that we'll
956 // get imprecise values here, though (except for unknown sizes).
957 if (!Later.Size.isPrecise() || !Earlier.Size.isPrecise()) {
958 // In case no constant size is known, try to an IR values for the number
959 // of bytes written and check if they match.
960 const auto *LaterMemI = dyn_cast<MemIntrinsic>(LaterI);
961 const auto *EarlierMemI = dyn_cast<MemIntrinsic>(EarlierI);
962 if (LaterMemI && EarlierMemI) {
963 const Value *LaterV = LaterMemI->getLength();
964 const Value *EarlierV = EarlierMemI->getLength();
965 if (LaterV == EarlierV && BatchAA.isMustAlias(Earlier, Later))
966 return OW_Complete;
967 }
968
969 // Masked stores have imprecise locations, but we can reason about them
970 // to some extent.
971 return isMaskedStoreOverwrite(LaterI, EarlierI, BatchAA);
972 }
973
974 const uint64_t LaterSize = Later.Size.getValue();
975 const uint64_t EarlierSize = Earlier.Size.getValue();
976
977 // Query the alias information
978 AliasResult AAR = BatchAA.alias(Later, Earlier);
979
980 // If the start pointers are the same, we just have to compare sizes to see if
981 // the later store was larger than the earlier store.
982 if (AAR == AliasResult::MustAlias) {
983 // Make sure that the Later size is >= the Earlier size.
984 if (LaterSize >= EarlierSize)
985 return OW_Complete;
986 }
987
988 // If we hit a partial alias we may have a full overwrite
989 if (AAR == AliasResult::PartialAlias && AAR.hasOffset()) {
990 int32_t Off = AAR.getOffset();
991 if (Off >= 0 && (uint64_t)Off + EarlierSize <= LaterSize)
992 return OW_Complete;
993 }
994
995 // Check to see if the later store is to the entire object (either a global,
996 // an alloca, or a byval/inalloca argument). If so, then it clearly
997 // overwrites any other store to the same object.
998 const Value *P1 = Earlier.Ptr->stripPointerCasts();
999 const Value *P2 = Later.Ptr->stripPointerCasts();
1000 const Value *UO1 = getUnderlyingObject(P1), *UO2 = getUnderlyingObject(P2);
1001
1002 // If we can't resolve the same pointers to the same object, then we can't
1003 // analyze them at all.
1004 if (UO1 != UO2)
1005 return OW_Unknown;
1006
1007 // If the "Later" store is to a recognizable object, get its size.
1008 uint64_t ObjectSize = getPointerSize(UO2, DL, TLI, &F);
1009 if (ObjectSize != MemoryLocation::UnknownSize)
1010 if (ObjectSize == LaterSize && ObjectSize >= EarlierSize)
1011 return OW_Complete;
1012
1013 // Okay, we have stores to two completely different pointers. Try to
1014 // decompose the pointer into a "base + constant_offset" form. If the base
1015 // pointers are equal, then we can reason about the two stores.
1016 EarlierOff = 0;
1017 LaterOff = 0;
1018 const Value *BP1 = GetPointerBaseWithConstantOffset(P1, EarlierOff, DL);
1019 const Value *BP2 = GetPointerBaseWithConstantOffset(P2, LaterOff, DL);
1020
1021 // If the base pointers still differ, we have two completely different stores.
1022 if (BP1 != BP2)
1023 return OW_Unknown;
1024
1025 // The later access completely overlaps the earlier store if and only if
1026 // both start and end of the earlier one is "inside" the later one:
1027 // |<->|--earlier--|<->|
1028 // |-------later-------|
1029 // Accesses may overlap if and only if start of one of them is "inside"
1030 // another one:
1031 // |<->|--earlier--|<----->|
1032 // |-------later-------|
1033 // OR
1034 // |----- earlier -----|
1035 // |<->|---later---|<----->|
1036 //
1037 // We have to be careful here as *Off is signed while *.Size is unsigned.
1038
1039 // Check if the earlier access starts "not before" the later one.
1040 if (EarlierOff >= LaterOff) {
1041 // If the earlier access ends "not after" the later access then the earlier
1042 // one is completely overwritten by the later one.
1043 if (uint64_t(EarlierOff - LaterOff) + EarlierSize <= LaterSize)
1044 return OW_Complete;
1045 // If start of the earlier access is "before" end of the later access then
1046 // accesses overlap.
1047 else if ((uint64_t)(EarlierOff - LaterOff) < LaterSize)
1048 return OW_MaybePartial;
1049 }
1050 // If start of the later access is "before" end of the earlier access then
1051 // accesses overlap.
1052 else if ((uint64_t)(LaterOff - EarlierOff) < EarlierSize) {
1053 return OW_MaybePartial;
1054 }
1055
1056 // Can reach here only if accesses are known not to overlap. There is no
1057 // dedicated code to indicate no overlap so signal "unknown".
1058 return OW_Unknown;
1059 }
1060
1061 bool isInvisibleToCallerAfterRet(const Value *V) {
1062 if (isa<AllocaInst>(V))
1063 return true;
1064 auto I = InvisibleToCallerAfterRet.insert({V, false});
1065 if (I.second) {
1066 if (!isInvisibleToCallerBeforeRet(V)) {
1067 I.first->second = false;
1068 } else {
1069 auto *Inst = dyn_cast<Instruction>(V);
1070 if (Inst && isAllocLikeFn(Inst, &TLI))
1071 I.first->second = !PointerMayBeCaptured(V, true, false);
1072 }
1073 }
1074 return I.first->second;
1075 }
1076
1077 bool isInvisibleToCallerBeforeRet(const Value *V) {
1078 if (isa<AllocaInst>(V))
1079 return true;
1080 auto I = InvisibleToCallerBeforeRet.insert({V, false});
1081 if (I.second) {
1082 auto *Inst = dyn_cast<Instruction>(V);
1083 if (Inst && isAllocLikeFn(Inst, &TLI))
1084 // NOTE: This could be made more precise by PointerMayBeCapturedBefore
1085 // with the killing MemoryDef. But we refrain from doing so for now to
1086 // limit compile-time and this does not cause any changes to the number
1087 // of stores removed on a large test set in practice.
1088 I.first->second = !PointerMayBeCaptured(V, false, true);
1089 }
1090 return I.first->second;
1091 }
1092
1093 Optional<MemoryLocation> getLocForWriteEx(Instruction *I) const {
1094 if (!I->mayWriteToMemory())
1095 return None;
1096
1097 if (auto *MTI = dyn_cast<AnyMemIntrinsic>(I))
1098 return {MemoryLocation::getForDest(MTI)};
1099
1100 if (auto *CB = dyn_cast<CallBase>(I)) {
1101 // If the functions may write to memory we do not know about, bail out.
1102 if (!CB->onlyAccessesArgMemory() &&
1103 !CB->onlyAccessesInaccessibleMemOrArgMem())
1104 return None;
1105
1106 LibFunc LF;
1107 if (TLI.getLibFunc(*CB, LF) && TLI.has(LF)) {
1108 switch (LF) {
1109 case LibFunc_strcpy:
1110 case LibFunc_strncpy:
1111 case LibFunc_strcat:
1112 case LibFunc_strncat:
1113 return {MemoryLocation::getAfter(CB->getArgOperand(0))};
1114 default:
1115 break;
1116 }
1117 }
1118 switch (CB->getIntrinsicID()) {
1119 case Intrinsic::init_trampoline:
1120 return {MemoryLocation::getAfter(CB->getArgOperand(0))};
1121 case Intrinsic::masked_store:
1122 return {MemoryLocation::getForArgument(CB, 1, TLI)};
1123 default:
1124 break;
1125 }
1126 return None;
1127 }
1128
1129 return MemoryLocation::getOrNone(I);
1130 }
1131
1132 /// Returns true if \p UseInst completely overwrites \p DefLoc
1133 /// (stored by \p DefInst).
1134 bool isCompleteOverwrite(const MemoryLocation &DefLoc, Instruction *DefInst,
1135 Instruction *UseInst) {
1136 // UseInst has a MemoryDef associated in MemorySSA. It's possible for a
1137 // MemoryDef to not write to memory, e.g. a volatile load is modeled as a
1138 // MemoryDef.
1139 if (!UseInst->mayWriteToMemory())
1140 return false;
1141
1142 if (auto *CB = dyn_cast<CallBase>(UseInst))
1143 if (CB->onlyAccessesInaccessibleMemory())
1144 return false;
1145
1146 int64_t InstWriteOffset, DepWriteOffset;
1147 if (auto CC = getLocForWriteEx(UseInst))
1148 return isOverwrite(UseInst, DefInst, *CC, DefLoc, DepWriteOffset,
1149 InstWriteOffset) == OW_Complete;
1150 return false;
1151 }
1152
1153 /// Returns true if \p Def is not read before returning from the function.
1154 bool isWriteAtEndOfFunction(MemoryDef *Def) {
1155 LLVM_DEBUG(dbgs() << " Check if def " << *Def << " ("do { } while (false)
1156 << *Def->getMemoryInst()do { } while (false)
1157 << ") is at the end the function \n")do { } while (false);
1158
1159 auto MaybeLoc = getLocForWriteEx(Def->getMemoryInst());
1160 if (!MaybeLoc) {
1161 LLVM_DEBUG(dbgs() << " ... could not get location for write.\n")do { } while (false);
1162 return false;
1163 }
1164
1165 SmallVector<MemoryAccess *, 4> WorkList;
1166 SmallPtrSet<MemoryAccess *, 8> Visited;
1167 auto PushMemUses = [&WorkList, &Visited](MemoryAccess *Acc) {
1168 if (!Visited.insert(Acc).second)
1169 return;
1170 for (Use &U : Acc->uses())
1171 WorkList.push_back(cast<MemoryAccess>(U.getUser()));
1172 };
1173 PushMemUses(Def);
1174 for (unsigned I = 0; I < WorkList.size(); I++) {
1175 if (WorkList.size() >= MemorySSAScanLimit) {
1176 LLVM_DEBUG(dbgs() << " ... hit exploration limit.\n")do { } while (false);
1177 return false;
1178 }
1179
1180 MemoryAccess *UseAccess = WorkList[I];
1181 // Simply adding the users of MemoryPhi to the worklist is not enough,
1182 // because we might miss read clobbers in different iterations of a loop,
1183 // for example.
1184 // TODO: Add support for phi translation to handle the loop case.
1185 if (isa<MemoryPhi>(UseAccess))
1186 return false;
1187
1188 // TODO: Checking for aliasing is expensive. Consider reducing the amount
1189 // of times this is called and/or caching it.
1190 Instruction *UseInst = cast<MemoryUseOrDef>(UseAccess)->getMemoryInst();
1191 if (isReadClobber(*MaybeLoc, UseInst)) {
1192 LLVM_DEBUG(dbgs() << " ... hit read clobber " << *UseInst << ".\n")do { } while (false);
1193 return false;
1194 }
1195
1196 if (MemoryDef *UseDef = dyn_cast<MemoryDef>(UseAccess))
1197 PushMemUses(UseDef);
1198 }
1199 return true;
1200 }
1201
1202 /// If \p I is a memory terminator like llvm.lifetime.end or free, return a
1203 /// pair with the MemoryLocation terminated by \p I and a boolean flag
1204 /// indicating whether \p I is a free-like call.
1205 Optional<std::pair<MemoryLocation, bool>>
1206 getLocForTerminator(Instruction *I) const {
1207 uint64_t Len;
1208 Value *Ptr;
1209 if (match(I, m_Intrinsic<Intrinsic::lifetime_end>(m_ConstantInt(Len),
1210 m_Value(Ptr))))
1211 return {std::make_pair(MemoryLocation(Ptr, Len), false)};
1212
1213 if (auto *CB = dyn_cast<CallBase>(I)) {
1214 if (isFreeCall(I, &TLI))
1215 return {std::make_pair(MemoryLocation::getAfter(CB->getArgOperand(0)),
1216 true)};
1217 }
1218
1219 return None;
1220 }
1221
1222 /// Returns true if \p I is a memory terminator instruction like
1223 /// llvm.lifetime.end or free.
1224 bool isMemTerminatorInst(Instruction *I) const {
1225 IntrinsicInst *II = dyn_cast<IntrinsicInst>(I);
1226 return (II && II->getIntrinsicID() == Intrinsic::lifetime_end) ||
1227 isFreeCall(I, &TLI);
1228 }
1229
1230 /// Returns true if \p MaybeTerm is a memory terminator for \p Loc from
1231 /// instruction \p AccessI.
1232 bool isMemTerminator(const MemoryLocation &Loc, Instruction *AccessI,
1233 Instruction *MaybeTerm) {
1234 Optional<std::pair<MemoryLocation, bool>> MaybeTermLoc =
1235 getLocForTerminator(MaybeTerm);
1236
1237 if (!MaybeTermLoc)
1238 return false;
1239
1240 // If the terminator is a free-like call, all accesses to the underlying
1241 // object can be considered terminated.
1242 if (getUnderlyingObject(Loc.Ptr) !=
1243 getUnderlyingObject(MaybeTermLoc->first.Ptr))
1244 return false;
1245
1246 auto TermLoc = MaybeTermLoc->first;
1247 if (MaybeTermLoc->second) {
1248 const Value *LocUO = getUnderlyingObject(Loc.Ptr);
1249 return BatchAA.isMustAlias(TermLoc.Ptr, LocUO);
1250 }
1251 int64_t InstWriteOffset, DepWriteOffset;
1252 return isOverwrite(MaybeTerm, AccessI, TermLoc, Loc, DepWriteOffset,
1253 InstWriteOffset) == OW_Complete;
1254 }
1255
1256 // Returns true if \p Use may read from \p DefLoc.
1257 bool isReadClobber(const MemoryLocation &DefLoc, Instruction *UseInst) {
1258 if (isNoopIntrinsic(UseInst))
1259 return false;
1260
1261 // Monotonic or weaker atomic stores can be re-ordered and do not need to be
1262 // treated as read clobber.
1263 if (auto SI = dyn_cast<StoreInst>(UseInst))
1264 return isStrongerThan(SI->getOrdering(), AtomicOrdering::Monotonic);
1265
1266 if (!UseInst->mayReadFromMemory())
1267 return false;
1268
1269 if (auto *CB = dyn_cast<CallBase>(UseInst))
1270 if (CB->onlyAccessesInaccessibleMemory())
1271 return false;
1272
1273 // NOTE: For calls, the number of stores removed could be slightly improved
1274 // by using AA.callCapturesBefore(UseInst, DefLoc, &DT), but that showed to
1275 // be expensive compared to the benefits in practice. For now, avoid more
1276 // expensive analysis to limit compile-time.
1277 return isRefSet(BatchAA.getModRefInfo(UseInst, DefLoc));
1278 }
1279
1280 /// Returns true if a dependency between \p Current and \p KillingDef is
1281 /// guaranteed to be loop invariant for the loops that they are in. Either
1282 /// because they are known to be in the same block, in the same loop level or
1283 /// by guaranteeing that \p CurrentLoc only references a single MemoryLocation
1284 /// during execution of the containing function.
1285 bool isGuaranteedLoopIndependent(const Instruction *Current,
1286 const Instruction *KillingDef,
1287 const MemoryLocation &CurrentLoc) {
1288 // If the dependency is within the same block or loop level (being careful
1289 // of irreducible loops), we know that AA will return a valid result for the
1290 // memory dependency. (Both at the function level, outside of any loop,
1291 // would also be valid but we currently disable that to limit compile time).
1292 if (Current->getParent() == KillingDef->getParent())
1293 return true;
1294 const Loop *CurrentLI = LI.getLoopFor(Current->getParent());
1295 if (!ContainsIrreducibleLoops && CurrentLI &&
1296 CurrentLI == LI.getLoopFor(KillingDef->getParent()))
1297 return true;
1298 // Otherwise check the memory location is invariant to any loops.
1299 return isGuaranteedLoopInvariant(CurrentLoc.Ptr);
1300 }
1301
1302 /// Returns true if \p Ptr is guaranteed to be loop invariant for any possible
1303 /// loop. In particular, this guarantees that it only references a single
1304 /// MemoryLocation during execution of the containing function.
1305 bool isGuaranteedLoopInvariant(const Value *Ptr) {
1306 auto IsGuaranteedLoopInvariantBase = [this](const Value *Ptr) {
1307 Ptr = Ptr->stripPointerCasts();
1308 if (auto *I = dyn_cast<Instruction>(Ptr)) {
1309 if (isa<AllocaInst>(Ptr))
1310 return true;
1311
1312 if (isAllocLikeFn(I, &TLI))
1313 return true;
1314
1315 return false;
1316 }
1317 return true;
1318 };
1319
1320 Ptr = Ptr->stripPointerCasts();
1321 if (auto *I = dyn_cast<Instruction>(Ptr)) {
1322 if (I->getParent()->isEntryBlock())
1323 return true;
1324 }
1325 if (auto *GEP = dyn_cast<GEPOperator>(Ptr)) {
1326 return IsGuaranteedLoopInvariantBase(GEP->getPointerOperand()) &&
1327 GEP->hasAllConstantIndices();
1328 }
1329 return IsGuaranteedLoopInvariantBase(Ptr);
1330 }
1331
1332 // Find a MemoryDef writing to \p DefLoc and dominating \p StartAccess, with
1333 // no read access between them or on any other path to a function exit block
1334 // if \p DefLoc is not accessible after the function returns. If there is no
1335 // such MemoryDef, return None. The returned value may not (completely)
1336 // overwrite \p DefLoc. Currently we bail out when we encounter an aliasing
1337 // MemoryUse (read).
1338 Optional<MemoryAccess *>
1339 getDomMemoryDef(MemoryDef *KillingDef, MemoryAccess *StartAccess,
1340 const MemoryLocation &DefLoc, const Value *DefUO,
1341 unsigned &ScanLimit, unsigned &WalkerStepLimit,
1342 bool IsMemTerm, unsigned &PartialLimit) {
1343 if (ScanLimit == 0 || WalkerStepLimit == 0) {
1344 LLVM_DEBUG(dbgs() << "\n ... hit scan limit\n")do { } while (false);
1345 return None;
1346 }
1347
1348 MemoryAccess *Current = StartAccess;
1349 Instruction *KillingI = KillingDef->getMemoryInst();
1350 LLVM_DEBUG(dbgs() << " trying to get dominating access\n")do { } while (false);
1351
1352 // Find the next clobbering Mod access for DefLoc, starting at StartAccess.
1353 Optional<MemoryLocation> CurrentLoc;
1354 for (;; Current = cast<MemoryDef>(Current)->getDefiningAccess()) {
1355 LLVM_DEBUG({do { } while (false)
1356 dbgs() << " visiting " << *Current;do { } while (false)
1357 if (!MSSA.isLiveOnEntryDef(Current) && isa<MemoryUseOrDef>(Current))do { } while (false)
1358 dbgs() << " (" << *cast<MemoryUseOrDef>(Current)->getMemoryInst()do { } while (false)
1359 << ")";do { } while (false)
1360 dbgs() << "\n";do { } while (false)
1361 })do { } while (false);
1362
1363 // Reached TOP.
1364 if (MSSA.isLiveOnEntryDef(Current)) {
1365 LLVM_DEBUG(dbgs() << " ... found LiveOnEntryDef\n")do { } while (false);
1366 return None;
1367 }
1368
1369 // Cost of a step. Accesses in the same block are more likely to be valid
1370 // candidates for elimination, hence consider them cheaper.
1371 unsigned StepCost = KillingDef->getBlock() == Current->getBlock()
1372 ? MemorySSASameBBStepCost
1373 : MemorySSAOtherBBStepCost;
1374 if (WalkerStepLimit <= StepCost) {
1375 LLVM_DEBUG(dbgs() << " ... hit walker step limit\n")do { } while (false);
1376 return None;
1377 }
1378 WalkerStepLimit -= StepCost;
1379
1380 // Return for MemoryPhis. They cannot be eliminated directly and the
1381 // caller is responsible for traversing them.
1382 if (isa<MemoryPhi>(Current)) {
1383 LLVM_DEBUG(dbgs() << " ... found MemoryPhi\n")do { } while (false);
1384 return Current;
1385 }
1386
1387 // Below, check if CurrentDef is a valid candidate to be eliminated by
1388 // KillingDef. If it is not, check the next candidate.
1389 MemoryDef *CurrentDef = cast<MemoryDef>(Current);
1390 Instruction *CurrentI = CurrentDef->getMemoryInst();
1391
1392 if (canSkipDef(CurrentDef, !isInvisibleToCallerBeforeRet(DefUO)))
1393 continue;
1394
1395 // Before we try to remove anything, check for any extra throwing
1396 // instructions that block us from DSEing
1397 if (mayThrowBetween(KillingI, CurrentI, DefUO)) {
1398 LLVM_DEBUG(dbgs() << " ... skip, may throw!\n")do { } while (false);
1399 return None;
1400 }
1401
1402 // Check for anything that looks like it will be a barrier to further
1403 // removal
1404 if (isDSEBarrier(DefUO, CurrentI)) {
1405 LLVM_DEBUG(dbgs() << " ... skip, barrier\n")do { } while (false);
1406 return None;
1407 }
1408
1409 // If Current is known to be on path that reads DefLoc or is a read
1410 // clobber, bail out, as the path is not profitable. We skip this check
1411 // for intrinsic calls, because the code knows how to handle memcpy
1412 // intrinsics.
1413 if (!isa<IntrinsicInst>(CurrentI) && isReadClobber(DefLoc, CurrentI))
1414 return None;
1415
1416 // Quick check if there are direct uses that are read-clobbers.
1417 if (any_of(Current->uses(), [this, &DefLoc, StartAccess](Use &U) {
1418 if (auto *UseOrDef = dyn_cast<MemoryUseOrDef>(U.getUser()))
1419 return !MSSA.dominates(StartAccess, UseOrDef) &&
1420 isReadClobber(DefLoc, UseOrDef->getMemoryInst());
1421 return false;
1422 })) {
1423 LLVM_DEBUG(dbgs() << " ... found a read clobber\n")do { } while (false);
1424 return None;
1425 }
1426
1427 // If Current cannot be analyzed or is not removable, check the next
1428 // candidate.
1429 if (!hasAnalyzableMemoryWrite(CurrentI, TLI) || !isRemovable(CurrentI))
1430 continue;
1431
1432 // If Current does not have an analyzable write location, skip it
1433 CurrentLoc = getLocForWriteEx(CurrentI);
1434 if (!CurrentLoc)
1435 continue;
1436
1437 // AliasAnalysis does not account for loops. Limit elimination to
1438 // candidates for which we can guarantee they always store to the same
1439 // memory location and not located in different loops.
1440 if (!isGuaranteedLoopIndependent(CurrentI, KillingI, *CurrentLoc)) {
1441 LLVM_DEBUG(dbgs() << " ... not guaranteed loop independent\n")do { } while (false);
1442 WalkerStepLimit -= 1;
1443 continue;
1444 }
1445
1446 if (IsMemTerm) {
1447 // If the killing def is a memory terminator (e.g. lifetime.end), check
1448 // the next candidate if the current Current does not write the same
1449 // underlying object as the terminator.
1450 if (!isMemTerminator(*CurrentLoc, CurrentI, KillingI))
1451 continue;
1452 } else {
1453 int64_t InstWriteOffset, DepWriteOffset;
1454 auto OR = isOverwrite(KillingI, CurrentI, DefLoc, *CurrentLoc,
1455 DepWriteOffset, InstWriteOffset);
1456 // If Current does not write to the same object as KillingDef, check
1457 // the next candidate.
1458 if (OR == OW_Unknown)
1459 continue;
1460 else if (OR == OW_MaybePartial) {
1461 // If KillingDef only partially overwrites Current, check the next
1462 // candidate if the partial step limit is exceeded. This aggressively
1463 // limits the number of candidates for partial store elimination,
1464 // which are less likely to be removable in the end.
1465 if (PartialLimit <= 1) {
1466 WalkerStepLimit -= 1;
1467 continue;
1468 }
1469 PartialLimit -= 1;
1470 }
1471 }
1472 break;
1473 };
1474
1475 // Accesses to objects accessible after the function returns can only be
1476 // eliminated if the access is killed along all paths to the exit. Collect
1477 // the blocks with killing (=completely overwriting MemoryDefs) and check if
1478 // they cover all paths from EarlierAccess to any function exit.
1479 SmallPtrSet<Instruction *, 16> KillingDefs;
1480 KillingDefs.insert(KillingDef->getMemoryInst());
1481 MemoryAccess *EarlierAccess = Current;
1482 Instruction *EarlierMemInst =
1483 cast<MemoryDef>(EarlierAccess)->getMemoryInst();
1484 LLVM_DEBUG(dbgs() << " Checking for reads of " << *EarlierAccess << " ("do { } while (false)
1485 << *EarlierMemInst << ")\n")do { } while (false);
1486
1487 SmallSetVector<MemoryAccess *, 32> WorkList;
1488 auto PushMemUses = [&WorkList](MemoryAccess *Acc) {
1489 for (Use &U : Acc->uses())
1490 WorkList.insert(cast<MemoryAccess>(U.getUser()));
1491 };
1492 PushMemUses(EarlierAccess);
1493
1494 // Optimistically collect all accesses for reads. If we do not find any
1495 // read clobbers, add them to the cache.
1496 SmallPtrSet<MemoryAccess *, 16> KnownNoReads;
1497 if (!EarlierMemInst->mayReadFromMemory())
1498 KnownNoReads.insert(EarlierAccess);
1499 // Check if EarlierDef may be read.
1500 for (unsigned I = 0; I < WorkList.size(); I++) {
1501 MemoryAccess *UseAccess = WorkList[I];
1502
1503 LLVM_DEBUG(dbgs() << " " << *UseAccess)do { } while (false);
1504 // Bail out if the number of accesses to check exceeds the scan limit.
1505 if (ScanLimit < (WorkList.size() - I)) {
1506 LLVM_DEBUG(dbgs() << "\n ... hit scan limit\n")do { } while (false);
1507 return None;
1508 }
1509 --ScanLimit;
1510 NumDomMemDefChecks++;
1511 KnownNoReads.insert(UseAccess);
1512
1513 if (isa<MemoryPhi>(UseAccess)) {
1514 if (any_of(KillingDefs, [this, UseAccess](Instruction *KI) {
1515 return DT.properlyDominates(KI->getParent(),
1516 UseAccess->getBlock());
1517 })) {
1518 LLVM_DEBUG(dbgs() << " ... skipping, dominated by killing block\n")do { } while (false);
1519 continue;
1520 }
1521 LLVM_DEBUG(dbgs() << "\n ... adding PHI uses\n")do { } while (false);
1522 PushMemUses(UseAccess);
1523 continue;
1524 }
1525
1526 Instruction *UseInst = cast<MemoryUseOrDef>(UseAccess)->getMemoryInst();
1527 LLVM_DEBUG(dbgs() << " (" << *UseInst << ")\n")do { } while (false);
1528
1529 if (any_of(KillingDefs, [this, UseInst](Instruction *KI) {
1530 return DT.dominates(KI, UseInst);
1531 })) {
1532 LLVM_DEBUG(dbgs() << " ... skipping, dominated by killing def\n")do { } while (false);
1533 continue;
1534 }
1535
1536 // A memory terminator kills all preceeding MemoryDefs and all succeeding
1537 // MemoryAccesses. We do not have to check it's users.
1538 if (isMemTerminator(*CurrentLoc, EarlierMemInst, UseInst)) {
1539 LLVM_DEBUG(do { } while (false)
1540 dbgs()do { } while (false)
1541 << " ... skipping, memterminator invalidates following accesses\n")do { } while (false);
1542 continue;
1543 }
1544
1545 if (isNoopIntrinsic(cast<MemoryUseOrDef>(UseAccess)->getMemoryInst())) {
1546 LLVM_DEBUG(dbgs() << " ... adding uses of intrinsic\n")do { } while (false);
1547 PushMemUses(UseAccess);
1548 continue;
1549 }
1550
1551 if (UseInst->mayThrow() && !isInvisibleToCallerBeforeRet(DefUO)) {
1552 LLVM_DEBUG(dbgs() << " ... found throwing instruction\n")do { } while (false);
1553 return None;
1554 }
1555
1556 // Uses which may read the original MemoryDef mean we cannot eliminate the
1557 // original MD. Stop walk.
1558 if (isReadClobber(*CurrentLoc, UseInst)) {
1559 LLVM_DEBUG(dbgs() << " ... found read clobber\n")do { } while (false);
1560 return None;
1561 }
1562
1563 // If this worklist walks back to the original memory access (and the
1564 // pointer is not guarenteed loop invariant) then we cannot assume that a
1565 // store kills itself.
1566 if (EarlierAccess == UseAccess &&
1567 !isGuaranteedLoopInvariant(CurrentLoc->Ptr)) {
1568 LLVM_DEBUG(dbgs() << " ... found not loop invariant self access\n")do { } while (false);
1569 return None;
1570 }
1571 // Otherwise, for the KillingDef and EarlierAccess we only have to check
1572 // if it reads the memory location.
1573 // TODO: It would probably be better to check for self-reads before
1574 // calling the function.
1575 if (KillingDef == UseAccess || EarlierAccess == UseAccess) {
1576 LLVM_DEBUG(dbgs() << " ... skipping killing def/dom access\n")do { } while (false);
1577 continue;
1578 }
1579
1580 // Check all uses for MemoryDefs, except for defs completely overwriting
1581 // the original location. Otherwise we have to check uses of *all*
1582 // MemoryDefs we discover, including non-aliasing ones. Otherwise we might
1583 // miss cases like the following
1584 // 1 = Def(LoE) ; <----- EarlierDef stores [0,1]
1585 // 2 = Def(1) ; (2, 1) = NoAlias, stores [2,3]
1586 // Use(2) ; MayAlias 2 *and* 1, loads [0, 3].
1587 // (The Use points to the *first* Def it may alias)
1588 // 3 = Def(1) ; <---- Current (3, 2) = NoAlias, (3,1) = MayAlias,
1589 // stores [0,1]
1590 if (MemoryDef *UseDef = dyn_cast<MemoryDef>(UseAccess)) {
1591 if (isCompleteOverwrite(*CurrentLoc, EarlierMemInst, UseInst)) {
1592 BasicBlock *MaybeKillingBlock = UseInst->getParent();
1593 if (PostOrderNumbers.find(MaybeKillingBlock)->second <
1594 PostOrderNumbers.find(EarlierAccess->getBlock())->second) {
1595 if (!isInvisibleToCallerAfterRet(DefUO)) {
1596 LLVM_DEBUG(dbgs()do { } while (false)
1597 << " ... found killing def " << *UseInst << "\n")do { } while (false);
1598 KillingDefs.insert(UseInst);
1599 }
1600 } else {
1601 LLVM_DEBUG(dbgs()do { } while (false)
1602 << " ... found preceeding def " << *UseInst << "\n")do { } while (false);
1603 return None;
1604 }
1605 } else
1606 PushMemUses(UseDef);
1607 }
1608 }
1609
1610 // For accesses to locations visible after the function returns, make sure
1611 // that the location is killed (=overwritten) along all paths from
1612 // EarlierAccess to the exit.
1613 if (!isInvisibleToCallerAfterRet(DefUO)) {
1614 SmallPtrSet<BasicBlock *, 16> KillingBlocks;
1615 for (Instruction *KD : KillingDefs)
1616 KillingBlocks.insert(KD->getParent());
1617 assert(!KillingBlocks.empty() &&((void)0)
1618 "Expected at least a single killing block")((void)0);
1619
1620 // Find the common post-dominator of all killing blocks.
1621 BasicBlock *CommonPred = *KillingBlocks.begin();
1622 for (auto I = std::next(KillingBlocks.begin()), E = KillingBlocks.end();
1623 I != E; I++) {
1624 if (!CommonPred)
1625 break;
1626 CommonPred = PDT.findNearestCommonDominator(CommonPred, *I);
1627 }
1628
1629 // If CommonPred is in the set of killing blocks, just check if it
1630 // post-dominates EarlierAccess.
1631 if (KillingBlocks.count(CommonPred)) {
1632 if (PDT.dominates(CommonPred, EarlierAccess->getBlock()))
1633 return {EarlierAccess};
1634 return None;
1635 }
1636
1637 // If the common post-dominator does not post-dominate EarlierAccess,
1638 // there is a path from EarlierAccess to an exit not going through a
1639 // killing block.
1640 if (PDT.dominates(CommonPred, EarlierAccess->getBlock())) {
1641 SetVector<BasicBlock *> WorkList;
1642
1643 // If CommonPred is null, there are multiple exits from the function.
1644 // They all have to be added to the worklist.
1645 if (CommonPred)
1646 WorkList.insert(CommonPred);
1647 else
1648 for (BasicBlock *R : PDT.roots())
1649 WorkList.insert(R);
1650
1651 NumCFGTries++;
1652 // Check if all paths starting from an exit node go through one of the
1653 // killing blocks before reaching EarlierAccess.
1654 for (unsigned I = 0; I < WorkList.size(); I++) {
1655 NumCFGChecks++;
1656 BasicBlock *Current = WorkList[I];
1657 if (KillingBlocks.count(Current))
1658 continue;
1659 if (Current == EarlierAccess->getBlock())
1660 return None;
1661
1662 // EarlierAccess is reachable from the entry, so we don't have to
1663 // explore unreachable blocks further.
1664 if (!DT.isReachableFromEntry(Current))
1665 continue;
1666
1667 for (BasicBlock *Pred : predecessors(Current))
1668 WorkList.insert(Pred);
1669
1670 if (WorkList.size() >= MemorySSAPathCheckLimit)
1671 return None;
1672 }
1673 NumCFGSuccess++;
1674 return {EarlierAccess};
1675 }
1676 return None;
1677 }
1678
1679 // No aliasing MemoryUses of EarlierAccess found, EarlierAccess is
1680 // potentially dead.
1681 return {EarlierAccess};
1682 }
1683
1684 // Delete dead memory defs
1685 void deleteDeadInstruction(Instruction *SI) {
1686 MemorySSAUpdater Updater(&MSSA);
1687 SmallVector<Instruction *, 32> NowDeadInsts;
1688 NowDeadInsts.push_back(SI);
1689 --NumFastOther;
1690
1691 while (!NowDeadInsts.empty()) {
1692 Instruction *DeadInst = NowDeadInsts.pop_back_val();
1693 ++NumFastOther;
1694
1695 // Try to preserve debug information attached to the dead instruction.
1696 salvageDebugInfo(*DeadInst);
1697 salvageKnowledge(DeadInst);
1698
1699 // Remove the Instruction from MSSA.
1700 if (MemoryAccess *MA = MSSA.getMemoryAccess(DeadInst)) {
1701 if (MemoryDef *MD = dyn_cast<MemoryDef>(MA)) {
1702 SkipStores.insert(MD);
1703 }
1704 Updater.removeMemoryAccess(MA);
1705 }
1706
1707 auto I = IOLs.find(DeadInst->getParent());
1708 if (I != IOLs.end())
1709 I->second.erase(DeadInst);
1710 // Remove its operands
1711 for (Use &O : DeadInst->operands())
1712 if (Instruction *OpI = dyn_cast<Instruction>(O)) {
1713 O = nullptr;
1714 if (isInstructionTriviallyDead(OpI, &TLI))
1715 NowDeadInsts.push_back(OpI);
1716 }
1717
1718 DeadInst->eraseFromParent();
1719 }
1720 }
1721
1722 // Check for any extra throws between SI and NI that block DSE. This only
1723 // checks extra maythrows (those that aren't MemoryDef's). MemoryDef that may
1724 // throw are handled during the walk from one def to the next.
1725 bool mayThrowBetween(Instruction *SI, Instruction *NI,
1726 const Value *SILocUnd) {
1727 // First see if we can ignore it by using the fact that SI is an
1728 // alloca/alloca like object that is not visible to the caller during
1729 // execution of the function.
1730 if (SILocUnd && isInvisibleToCallerBeforeRet(SILocUnd))
1731 return false;
1732
1733 if (SI->getParent() == NI->getParent())
1734 return ThrowingBlocks.count(SI->getParent());
1735 return !ThrowingBlocks.empty();
1736 }
1737
1738 // Check if \p NI acts as a DSE barrier for \p SI. The following instructions
1739 // act as barriers:
1740 // * A memory instruction that may throw and \p SI accesses a non-stack
1741 // object.
1742 // * Atomic stores stronger that monotonic.
1743 bool isDSEBarrier(const Value *SILocUnd, Instruction *NI) {
1744 // If NI may throw it acts as a barrier, unless we are to an alloca/alloca
1745 // like object that does not escape.
1746 if (NI->mayThrow() && !isInvisibleToCallerBeforeRet(SILocUnd))
1747 return true;
1748
1749 // If NI is an atomic load/store stronger than monotonic, do not try to
1750 // eliminate/reorder it.
1751 if (NI->isAtomic()) {
1752 if (auto *LI = dyn_cast<LoadInst>(NI))
1753 return isStrongerThanMonotonic(LI->getOrdering());
1754 if (auto *SI = dyn_cast<StoreInst>(NI))
1755 return isStrongerThanMonotonic(SI->getOrdering());
1756 if (auto *ARMW = dyn_cast<AtomicRMWInst>(NI))
1757 return isStrongerThanMonotonic(ARMW->getOrdering());
1758 if (auto *CmpXchg = dyn_cast<AtomicCmpXchgInst>(NI))
1759 return isStrongerThanMonotonic(CmpXchg->getSuccessOrdering()) ||
1760 isStrongerThanMonotonic(CmpXchg->getFailureOrdering());
1761 llvm_unreachable("other instructions should be skipped in MemorySSA")__builtin_unreachable();
1762 }
1763 return false;
1764 }
1765
1766 /// Eliminate writes to objects that are not visible in the caller and are not
1767 /// accessed before returning from the function.
1768 bool eliminateDeadWritesAtEndOfFunction() {
1769 bool MadeChange = false;
1770 LLVM_DEBUG(do { } while (false)
1771 dbgs()do { } while (false)
1772 << "Trying to eliminate MemoryDefs at the end of the function\n")do { } while (false);
1773 for (int I = MemDefs.size() - 1; I >= 0; I--) {
1774 MemoryDef *Def = MemDefs[I];
1775 if (SkipStores.contains(Def) || !isRemovable(Def->getMemoryInst()))
1776 continue;
1777
1778 Instruction *DefI = Def->getMemoryInst();
1779 SmallVector<const Value *, 4> Pointers;
1780 auto DefLoc = getLocForWriteEx(DefI);
1781 if (!DefLoc)
1782 continue;
1783
1784 // NOTE: Currently eliminating writes at the end of a function is limited
1785 // to MemoryDefs with a single underlying object, to save compile-time. In
1786 // practice it appears the case with multiple underlying objects is very
1787 // uncommon. If it turns out to be important, we can use
1788 // getUnderlyingObjects here instead.
1789 const Value *UO = getUnderlyingObject(DefLoc->Ptr);
1790 if (!UO || !isInvisibleToCallerAfterRet(UO))
1791 continue;
1792
1793 if (isWriteAtEndOfFunction(Def)) {
1794 // See through pointer-to-pointer bitcasts
1795 LLVM_DEBUG(dbgs() << " ... MemoryDef is not accessed until the end "do { } while (false)
1796 "of the function\n")do { } while (false);
1797 deleteDeadInstruction(DefI);
1798 ++NumFastStores;
1799 MadeChange = true;
1800 }
1801 }
1802 return MadeChange;
1803 }
1804
1805 /// \returns true if \p Def is a no-op store, either because it
1806 /// directly stores back a loaded value or stores zero to a calloced object.
1807 bool storeIsNoop(MemoryDef *Def, const MemoryLocation &DefLoc,
1808 const Value *DefUO) {
1809 StoreInst *Store = dyn_cast<StoreInst>(Def->getMemoryInst());
1810 MemSetInst *MemSet = dyn_cast<MemSetInst>(Def->getMemoryInst());
1811 Constant *StoredConstant = nullptr;
1812 if (Store)
1813 StoredConstant = dyn_cast<Constant>(Store->getOperand(0));
1814 if (MemSet)
1815 StoredConstant = dyn_cast<Constant>(MemSet->getValue());
1816
1817 if (StoredConstant && StoredConstant->isNullValue()) {
1818 auto *DefUOInst = dyn_cast<Instruction>(DefUO);
1819 if (DefUOInst && isCallocLikeFn(DefUOInst, &TLI)) {
1820 auto *UnderlyingDef = cast<MemoryDef>(MSSA.getMemoryAccess(DefUOInst));
1821 // If UnderlyingDef is the clobbering access of Def, no instructions
1822 // between them can modify the memory location.
1823 auto *ClobberDef =
1824 MSSA.getSkipSelfWalker()->getClobberingMemoryAccess(Def);
1825 return UnderlyingDef == ClobberDef;
1826 }
1827 }
1828
1829 if (!Store)
1830 return false;
1831
1832 if (auto *LoadI = dyn_cast<LoadInst>(Store->getOperand(0))) {
1833 if (LoadI->getPointerOperand() == Store->getOperand(1)) {
1834 // Get the defining access for the load.
1835 auto *LoadAccess = MSSA.getMemoryAccess(LoadI)->getDefiningAccess();
1836 // Fast path: the defining accesses are the same.
1837 if (LoadAccess == Def->getDefiningAccess())
1838 return true;
1839
1840 // Look through phi accesses. Recursively scan all phi accesses by
1841 // adding them to a worklist. Bail when we run into a memory def that
1842 // does not match LoadAccess.
1843 SetVector<MemoryAccess *> ToCheck;
1844 MemoryAccess *Current =
1845 MSSA.getWalker()->getClobberingMemoryAccess(Def);
1846 // We don't want to bail when we run into the store memory def. But,
1847 // the phi access may point to it. So, pretend like we've already
1848 // checked it.
1849 ToCheck.insert(Def);
1850 ToCheck.insert(Current);
1851 // Start at current (1) to simulate already having checked Def.
1852 for (unsigned I = 1; I < ToCheck.size(); ++I) {
1853 Current = ToCheck[I];
1854 if (auto PhiAccess = dyn_cast<MemoryPhi>(Current)) {
1855 // Check all the operands.
1856 for (auto &Use : PhiAccess->incoming_values())
1857 ToCheck.insert(cast<MemoryAccess>(&Use));
1858 continue;
1859 }
1860
1861 // If we found a memory def, bail. This happens when we have an
1862 // unrelated write in between an otherwise noop store.
1863 assert(isa<MemoryDef>(Current) &&((void)0)
1864 "Only MemoryDefs should reach here.")((void)0);
1865 // TODO: Skip no alias MemoryDefs that have no aliasing reads.
1866 // We are searching for the definition of the store's destination.
1867 // So, if that is the same definition as the load, then this is a
1868 // noop. Otherwise, fail.
1869 if (LoadAccess != Current)
1870 return false;
1871 }
1872 return true;
1873 }
1874 }
1875
1876 return false;
1877 }
1878};
1879
1880static bool eliminateDeadStores(Function &F, AliasAnalysis &AA, MemorySSA &MSSA,
1881 DominatorTree &DT, PostDominatorTree &PDT,
1882 const TargetLibraryInfo &TLI,
1883 const LoopInfo &LI) {
1884 bool MadeChange = false;
1885
1886 DSEState State = DSEState::get(F, AA, MSSA, DT, PDT, TLI, LI);
1887 // For each store:
1888 for (unsigned I = 0; I < State.MemDefs.size(); I++) {
2
Assuming the condition is false
3
Loop condition is false. Execution continues on line 2041
1889 MemoryDef *KillingDef = State.MemDefs[I];
1890 if (State.SkipStores.count(KillingDef))
1891 continue;
1892 Instruction *SI = KillingDef->getMemoryInst();
1893
1894 Optional<MemoryLocation> MaybeSILoc;
1895 if (State.isMemTerminatorInst(SI))
1896 MaybeSILoc = State.getLocForTerminator(SI).map(
1897 [](const std::pair<MemoryLocation, bool> &P) { return P.first; });
1898 else
1899 MaybeSILoc = State.getLocForWriteEx(SI);
1900
1901 if (!MaybeSILoc) {
1902 LLVM_DEBUG(dbgs() << "Failed to find analyzable write location for "do { } while (false)
1903 << *SI << "\n")do { } while (false);
1904 continue;
1905 }
1906 MemoryLocation SILoc = *MaybeSILoc;
1907 assert(SILoc.Ptr && "SILoc should not be null")((void)0);
1908 const Value *SILocUnd = getUnderlyingObject(SILoc.Ptr);
1909
1910 MemoryAccess *Current = KillingDef;
1911 LLVM_DEBUG(dbgs() << "Trying to eliminate MemoryDefs killed by "do { } while (false)
1912 << *Current << " (" << *SI << ")\n")do { } while (false);
1913
1914 unsigned ScanLimit = MemorySSAScanLimit;
1915 unsigned WalkerStepLimit = MemorySSAUpwardsStepLimit;
1916 unsigned PartialLimit = MemorySSAPartialStoreLimit;
1917 // Worklist of MemoryAccesses that may be killed by KillingDef.
1918 SetVector<MemoryAccess *> ToCheck;
1919
1920 if (SILocUnd)
1921 ToCheck.insert(KillingDef->getDefiningAccess());
1922
1923 bool Shortend = false;
1924 bool IsMemTerm = State.isMemTerminatorInst(SI);
1925 // Check if MemoryAccesses in the worklist are killed by KillingDef.
1926 for (unsigned I = 0; I < ToCheck.size(); I++) {
1927 Current = ToCheck[I];
1928 if (State.SkipStores.count(Current))
1929 continue;
1930
1931 Optional<MemoryAccess *> Next = State.getDomMemoryDef(
1932 KillingDef, Current, SILoc, SILocUnd, ScanLimit, WalkerStepLimit,
1933 IsMemTerm, PartialLimit);
1934
1935 if (!Next) {
1936 LLVM_DEBUG(dbgs() << " finished walk\n")do { } while (false);
1937 continue;
1938 }
1939
1940 MemoryAccess *EarlierAccess = *Next;
1941 LLVM_DEBUG(dbgs() << " Checking if we can kill " << *EarlierAccess)do { } while (false);
1942 if (isa<MemoryPhi>(EarlierAccess)) {
1943 LLVM_DEBUG(dbgs() << "\n ... adding incoming values to worklist\n")do { } while (false);
1944 for (Value *V : cast<MemoryPhi>(EarlierAccess)->incoming_values()) {
1945 MemoryAccess *IncomingAccess = cast<MemoryAccess>(V);
1946 BasicBlock *IncomingBlock = IncomingAccess->getBlock();
1947 BasicBlock *PhiBlock = EarlierAccess->getBlock();
1948
1949 // We only consider incoming MemoryAccesses that come before the
1950 // MemoryPhi. Otherwise we could discover candidates that do not
1951 // strictly dominate our starting def.
1952 if (State.PostOrderNumbers[IncomingBlock] >
1953 State.PostOrderNumbers[PhiBlock])
1954 ToCheck.insert(IncomingAccess);
1955 }
1956 continue;
1957 }
1958 auto *NextDef = cast<MemoryDef>(EarlierAccess);
1959 Instruction *NI = NextDef->getMemoryInst();
1960 LLVM_DEBUG(dbgs() << " (" << *NI << ")\n")do { } while (false);
1961 ToCheck.insert(NextDef->getDefiningAccess());
1962 NumGetDomMemoryDefPassed++;
1963
1964 if (!DebugCounter::shouldExecute(MemorySSACounter))
1965 continue;
1966
1967 MemoryLocation NILoc = *State.getLocForWriteEx(NI);
1968
1969 if (IsMemTerm) {
1970 const Value *NIUnd = getUnderlyingObject(NILoc.Ptr);
1971 if (SILocUnd != NIUnd)
1972 continue;
1973 LLVM_DEBUG(dbgs() << "DSE: Remove Dead Store:\n DEAD: " << *NIdo { } while (false)
1974 << "\n KILLER: " << *SI << '\n')do { } while (false);
1975 State.deleteDeadInstruction(NI);
1976 ++NumFastStores;
1977 MadeChange = true;
1978 } else {
1979 // Check if NI overwrites SI.
1980 int64_t InstWriteOffset, DepWriteOffset;
1981 OverwriteResult OR = State.isOverwrite(SI, NI, SILoc, NILoc,
1982 DepWriteOffset, InstWriteOffset);
1983 if (OR == OW_MaybePartial) {
1984 auto Iter = State.IOLs.insert(
1985 std::make_pair<BasicBlock *, InstOverlapIntervalsTy>(
1986 NI->getParent(), InstOverlapIntervalsTy()));
1987 auto &IOL = Iter.first->second;
1988 OR = isPartialOverwrite(SILoc, NILoc, DepWriteOffset, InstWriteOffset,
1989 NI, IOL);
1990 }
1991
1992 if (EnablePartialStoreMerging && OR == OW_PartialEarlierWithFullLater) {
1993 auto *Earlier = dyn_cast<StoreInst>(NI);
1994 auto *Later = dyn_cast<StoreInst>(SI);
1995 // We are re-using tryToMergePartialOverlappingStores, which requires
1996 // Earlier to domiante Later.
1997 // TODO: implement tryToMergeParialOverlappingStores using MemorySSA.
1998 if (Earlier && Later && DT.dominates(Earlier, Later)) {
1999 if (Constant *Merged = tryToMergePartialOverlappingStores(
2000 Earlier, Later, InstWriteOffset, DepWriteOffset, State.DL,
2001 State.BatchAA, &DT)) {
2002
2003 // Update stored value of earlier store to merged constant.
2004 Earlier->setOperand(0, Merged);
2005 ++NumModifiedStores;
2006 MadeChange = true;
2007
2008 Shortend = true;
2009 // Remove later store and remove any outstanding overlap intervals
2010 // for the updated store.
2011 State.deleteDeadInstruction(Later);
2012 auto I = State.IOLs.find(Earlier->getParent());
2013 if (I != State.IOLs.end())
2014 I->second.erase(Earlier);
2015 break;
2016 }
2017 }
2018 }
2019
2020 if (OR == OW_Complete) {
2021 LLVM_DEBUG(dbgs() << "DSE: Remove Dead Store:\n DEAD: " << *NIdo { } while (false)
2022 << "\n KILLER: " << *SI << '\n')do { } while (false);
2023 State.deleteDeadInstruction(NI);
2024 ++NumFastStores;
2025 MadeChange = true;
2026 }
2027 }
2028 }
2029
2030 // Check if the store is a no-op.
2031 if (!Shortend && isRemovable(SI) &&
2032 State.storeIsNoop(KillingDef, SILoc, SILocUnd)) {
2033 LLVM_DEBUG(dbgs() << "DSE: Remove No-Op Store:\n DEAD: " << *SI << '\n')do { } while (false);
2034 State.deleteDeadInstruction(SI);
2035 NumRedundantStores++;
2036 MadeChange = true;
2037 continue;
2038 }
2039 }
2040
2041 if (EnablePartialOverwriteTracking)
4
Assuming the condition is true
5
Taking true branch
2042 for (auto &KV : State.IOLs)
2043 MadeChange |= removePartiallyOverlappedStores(State.DL, KV.second, TLI);
6
Calling 'removePartiallyOverlappedStores'
2044
2045 MadeChange |= State.eliminateDeadWritesAtEndOfFunction();
2046 return MadeChange;
2047}
2048} // end anonymous namespace
2049
2050//===----------------------------------------------------------------------===//
2051// DSE Pass
2052//===----------------------------------------------------------------------===//
2053PreservedAnalyses DSEPass::run(Function &F, FunctionAnalysisManager &AM) {
2054 AliasAnalysis &AA = AM.getResult<AAManager>(F);
2055 const TargetLibraryInfo &TLI = AM.getResult<TargetLibraryAnalysis>(F);
2056 DominatorTree &DT = AM.getResult<DominatorTreeAnalysis>(F);
2057 MemorySSA &MSSA = AM.getResult<MemorySSAAnalysis>(F).getMSSA();
2058 PostDominatorTree &PDT = AM.getResult<PostDominatorTreeAnalysis>(F);
2059 LoopInfo &LI = AM.getResult<LoopAnalysis>(F);
2060
2061 bool Changed = eliminateDeadStores(F, AA, MSSA, DT, PDT, TLI, LI);
1
Calling 'eliminateDeadStores'
2062
2063#ifdef LLVM_ENABLE_STATS0
2064 if (AreStatisticsEnabled())
2065 for (auto &I : instructions(F))
2066 NumRemainingStores += isa<StoreInst>(&I);
2067#endif
2068
2069 if (!Changed)
2070 return PreservedAnalyses::all();
2071
2072 PreservedAnalyses PA;
2073 PA.preserveSet<CFGAnalyses>();
2074 PA.preserve<MemorySSAAnalysis>();
2075 PA.preserve<LoopAnalysis>();
2076 return PA;
2077}
2078
2079namespace {
2080
2081/// A legacy pass for the legacy pass manager that wraps \c DSEPass.
2082class DSELegacyPass : public FunctionPass {
2083public:
2084 static char ID; // Pass identification, replacement for typeid
2085
2086 DSELegacyPass() : FunctionPass(ID) {
2087 initializeDSELegacyPassPass(*PassRegistry::getPassRegistry());
2088 }
2089
2090 bool runOnFunction(Function &F) override {
2091 if (skipFunction(F))
2092 return false;
2093
2094 AliasAnalysis &AA = getAnalysis<AAResultsWrapperPass>().getAAResults();
2095 DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
2096 const TargetLibraryInfo &TLI =
2097 getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F);
2098 MemorySSA &MSSA = getAnalysis<MemorySSAWrapperPass>().getMSSA();
2099 PostDominatorTree &PDT =
2100 getAnalysis<PostDominatorTreeWrapperPass>().getPostDomTree();
2101 LoopInfo &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
2102
2103 bool Changed = eliminateDeadStores(F, AA, MSSA, DT, PDT, TLI, LI);
2104
2105#ifdef LLVM_ENABLE_STATS0
2106 if (AreStatisticsEnabled())
2107 for (auto &I : instructions(F))
2108 NumRemainingStores += isa<StoreInst>(&I);
2109#endif
2110
2111 return Changed;
2112 }
2113
2114 void getAnalysisUsage(AnalysisUsage &AU) const override {
2115 AU.setPreservesCFG();
2116 AU.addRequired<AAResultsWrapperPass>();
2117 AU.addRequired<TargetLibraryInfoWrapperPass>();
2118 AU.addPreserved<GlobalsAAWrapperPass>();
2119 AU.addRequired<DominatorTreeWrapperPass>();
2120 AU.addPreserved<DominatorTreeWrapperPass>();
2121 AU.addRequired<PostDominatorTreeWrapperPass>();
2122 AU.addRequired<MemorySSAWrapperPass>();
2123 AU.addPreserved<PostDominatorTreeWrapperPass>();
2124 AU.addPreserved<MemorySSAWrapperPass>();
2125 AU.addRequired<LoopInfoWrapperPass>();
2126 AU.addPreserved<LoopInfoWrapperPass>();
2127 }
2128};
2129
2130} // end anonymous namespace
2131
2132char DSELegacyPass::ID = 0;
2133
2134INITIALIZE_PASS_BEGIN(DSELegacyPass, "dse", "Dead Store Elimination", false,static void *initializeDSELegacyPassPassOnce(PassRegistry &
Registry) {
2135 false)static void *initializeDSELegacyPassPassOnce(PassRegistry &
Registry) {
2136INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)initializeDominatorTreeWrapperPassPass(Registry);
2137INITIALIZE_PASS_DEPENDENCY(PostDominatorTreeWrapperPass)initializePostDominatorTreeWrapperPassPass(Registry);
2138INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)initializeAAResultsWrapperPassPass(Registry);
2139INITIALIZE_PASS_DEPENDENCY(GlobalsAAWrapperPass)initializeGlobalsAAWrapperPassPass(Registry);
2140INITIALIZE_PASS_DEPENDENCY(MemorySSAWrapperPass)initializeMemorySSAWrapperPassPass(Registry);
2141INITIALIZE_PASS_DEPENDENCY(MemoryDependenceWrapperPass)initializeMemoryDependenceWrapperPassPass(Registry);
2142INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)initializeTargetLibraryInfoWrapperPassPass(Registry);
2143INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)initializeLoopInfoWrapperPassPass(Registry);
2144INITIALIZE_PASS_END(DSELegacyPass, "dse", "Dead Store Elimination", false,PassInfo *PI = new PassInfo( "Dead Store Elimination", "dse",
&DSELegacyPass::ID, PassInfo::NormalCtor_t(callDefaultCtor
<DSELegacyPass>), false, false); Registry.registerPass(
*PI, true); return PI; } static llvm::once_flag InitializeDSELegacyPassPassFlag
; void llvm::initializeDSELegacyPassPass(PassRegistry &Registry
) { llvm::call_once(InitializeDSELegacyPassPassFlag, initializeDSELegacyPassPassOnce
, std::ref(Registry)); }
2145 false)PassInfo *PI = new PassInfo( "Dead Store Elimination", "dse",
&DSELegacyPass::ID, PassInfo::NormalCtor_t(callDefaultCtor
<DSELegacyPass>), false, false); Registry.registerPass(
*PI, true); return PI; } static llvm::once_flag InitializeDSELegacyPassPassFlag
; void llvm::initializeDSELegacyPassPass(PassRegistry &Registry
) { llvm::call_once(InitializeDSELegacyPassPassFlag, initializeDSELegacyPassPassOnce
, std::ref(Registry)); }
2146
2147FunctionPass *llvm::createDeadStoreEliminationPass() {
2148 return new DSELegacyPass();
2149}

/usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Analysis/MemoryLocation.h

1//===- MemoryLocation.h - Memory location descriptions ----------*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8/// \file
9/// This file provides utility analysis objects describing memory locations.
10/// These are used both by the Alias Analysis infrastructure and more
11/// specialized memory analysis layers.
12///
13//===----------------------------------------------------------------------===//
14
15#ifndef LLVM_ANALYSIS_MEMORYLOCATION_H
16#define LLVM_ANALYSIS_MEMORYLOCATION_H
17
18#include "llvm/ADT/DenseMapInfo.h"
19#include "llvm/ADT/Optional.h"
20#include "llvm/IR/Metadata.h"
21#include "llvm/Support/TypeSize.h"
22
23namespace llvm {
24
25class CallBase;
26class Instruction;
27class LoadInst;
28class StoreInst;
29class MemTransferInst;
30class MemIntrinsic;
31class AtomicCmpXchgInst;
32class AtomicMemTransferInst;
33class AtomicMemIntrinsic;
34class AtomicRMWInst;
35class AnyMemTransferInst;
36class AnyMemIntrinsic;
37class TargetLibraryInfo;
38class VAArgInst;
39
40// Represents the size of a MemoryLocation. Logically, it's an
41// Optional<uint63_t> that also carries a bit to represent whether the integer
42// it contains, N, is 'precise'. Precise, in this context, means that we know
43// that the area of storage referenced by the given MemoryLocation must be
44// precisely N bytes. An imprecise value is formed as the union of two or more
45// precise values, and can conservatively represent all of the values unioned
46// into it. Importantly, imprecise values are an *upper-bound* on the size of a
47// MemoryLocation.
48//
49// Concretely, a precise MemoryLocation is (%p, 4) in
50// store i32 0, i32* %p
51//
52// Since we know that %p must be at least 4 bytes large at this point.
53// Otherwise, we have UB. An example of an imprecise MemoryLocation is (%p, 4)
54// at the memcpy in
55//
56// %n = select i1 %foo, i64 1, i64 4
57// call void @llvm.memcpy.p0i8.p0i8.i64(i8* %p, i8* %baz, i64 %n, i32 1,
58// i1 false)
59//
60// ...Since we'll copy *up to* 4 bytes into %p, but we can't guarantee that
61// we'll ever actually do so.
62//
63// If asked to represent a pathologically large value, this will degrade to
64// None.
65class LocationSize {
66 enum : uint64_t {
67 BeforeOrAfterPointer = ~uint64_t(0),
68 AfterPointer = BeforeOrAfterPointer - 1,
69 MapEmpty = BeforeOrAfterPointer - 2,
70 MapTombstone = BeforeOrAfterPointer - 3,
71 ImpreciseBit = uint64_t(1) << 63,
72
73 // The maximum value we can represent without falling back to 'unknown'.
74 MaxValue = (MapTombstone - 1) & ~ImpreciseBit,
75 };
76
77 uint64_t Value;
78
79 // Hack to support implicit construction. This should disappear when the
80 // public LocationSize ctor goes away.
81 enum DirectConstruction { Direct };
82
83 constexpr LocationSize(uint64_t Raw, DirectConstruction): Value(Raw) {}
84
85 static_assert(AfterPointer & ImpreciseBit,
86 "AfterPointer is imprecise by definition.");
87 static_assert(BeforeOrAfterPointer & ImpreciseBit,
88 "BeforeOrAfterPointer is imprecise by definition.");
89
90public:
91 // FIXME: Migrate all users to construct via either `precise` or `upperBound`,
92 // to make it more obvious at the callsite the kind of size that they're
93 // providing.
94 //
95 // Since the overwhelming majority of users of this provide precise values,
96 // this assumes the provided value is precise.
97 constexpr LocationSize(uint64_t Raw)
98 : Value(Raw > MaxValue ? AfterPointer : Raw) {}
99
100 static LocationSize precise(uint64_t Value) { return LocationSize(Value); }
101 static LocationSize precise(TypeSize Value) {
102 if (Value.isScalable())
103 return afterPointer();
104 return precise(Value.getFixedSize());
105 }
106
107 static LocationSize upperBound(uint64_t Value) {
108 // You can't go lower than 0, so give a precise result.
109 if (LLVM_UNLIKELY(Value == 0)__builtin_expect((bool)(Value == 0), false))
110 return precise(0);
111 if (LLVM_UNLIKELY(Value > MaxValue)__builtin_expect((bool)(Value > MaxValue), false))
112 return afterPointer();
113 return LocationSize(Value | ImpreciseBit, Direct);
114 }
115 static LocationSize upperBound(TypeSize Value) {
116 if (Value.isScalable())
117 return afterPointer();
118 return upperBound(Value.getFixedSize());
119 }
120
121 /// Any location after the base pointer (but still within the underlying
122 /// object).
123 constexpr static LocationSize afterPointer() {
124 return LocationSize(AfterPointer, Direct);
125 }
126
127 /// Any location before or after the base pointer (but still within the
128 /// underlying object).
129 constexpr static LocationSize beforeOrAfterPointer() {
130 return LocationSize(BeforeOrAfterPointer, Direct);
131 }
132
133 // Sentinel values, generally used for maps.
134 constexpr static LocationSize mapTombstone() {
135 return LocationSize(MapTombstone, Direct);
136 }
137 constexpr static LocationSize mapEmpty() {
138 return LocationSize(MapEmpty, Direct);
139 }
140
141 // Returns a LocationSize that can correctly represent either `*this` or
142 // `Other`.
143 LocationSize unionWith(LocationSize Other) const {
144 if (Other == *this)
145 return *this;
146
147 if (Value == BeforeOrAfterPointer || Other.Value == BeforeOrAfterPointer)
148 return beforeOrAfterPointer();
149 if (Value == AfterPointer || Other.Value == AfterPointer)
150 return afterPointer();
151
152 return upperBound(std::max(getValue(), Other.getValue()));
153 }
154
155 bool hasValue() const {
156 return Value != AfterPointer && Value != BeforeOrAfterPointer;
157 }
158 uint64_t getValue() const {
159 assert(hasValue() && "Getting value from an unknown LocationSize!")((void)0);
160 return Value & ~ImpreciseBit;
161 }
162
163 // Returns whether or not this value is precise. Note that if a value is
164 // precise, it's guaranteed to not be unknown.
165 bool isPrecise() const {
166 return (Value & ImpreciseBit) == 0;
167 }
168
169 // Convenience method to check if this LocationSize's value is 0.
170 bool isZero() const { return hasValue() && getValue() == 0; }
171
172 /// Whether accesses before the base pointer are possible.
173 bool mayBeBeforePointer() const { return Value == BeforeOrAfterPointer; }
174
175 bool operator==(const LocationSize &Other) const {
176 return Value == Other.Value;
177 }
178
179 bool operator!=(const LocationSize &Other) const {
180 return !(*this == Other);
181 }
182
183 // Ordering operators are not provided, since it's unclear if there's only one
184 // reasonable way to compare:
185 // - values that don't exist against values that do, and
186 // - precise values to imprecise values
187
188 void print(raw_ostream &OS) const;
189
190 // Returns an opaque value that represents this LocationSize. Cannot be
191 // reliably converted back into a LocationSize.
192 uint64_t toRaw() const { return Value; }
193};
194
195inline raw_ostream &operator<<(raw_ostream &OS, LocationSize Size) {
196 Size.print(OS);
197 return OS;
198}
199
200/// Representation for a specific memory location.
201///
202/// This abstraction can be used to represent a specific location in memory.
203/// The goal of the location is to represent enough information to describe
204/// abstract aliasing, modification, and reference behaviors of whatever
205/// value(s) are stored in memory at the particular location.
206///
207/// The primary user of this interface is LLVM's Alias Analysis, but other
208/// memory analyses such as MemoryDependence can use it as well.
209class MemoryLocation {
210public:
211 /// UnknownSize - This is a special value which can be used with the
212 /// size arguments in alias queries to indicate that the caller does not
213 /// know the sizes of the potential memory references.
214 enum : uint64_t { UnknownSize = ~UINT64_C(0)0ULL };
215
216 /// The address of the start of the location.
217 const Value *Ptr;
218
219 /// The maximum size of the location, in address-units, or
220 /// UnknownSize if the size is not known.
221 ///
222 /// Note that an unknown size does not mean the pointer aliases the entire
223 /// virtual address space, because there are restrictions on stepping out of
224 /// one object and into another. See
225 /// http://llvm.org/docs/LangRef.html#pointeraliasing
226 LocationSize Size;
227
228 /// The metadata nodes which describes the aliasing of the location (each
229 /// member is null if that kind of information is unavailable).
230 AAMDNodes AATags;
231
232 void print(raw_ostream &OS) const { OS << *Ptr << " " << Size << "\n"; }
233
234 /// Return a location with information about the memory reference by the given
235 /// instruction.
236 static MemoryLocation get(const LoadInst *LI);
237 static MemoryLocation get(const StoreInst *SI);
238 static MemoryLocation get(const VAArgInst *VI);
239 static MemoryLocation get(const AtomicCmpXchgInst *CXI);
240 static MemoryLocation get(const AtomicRMWInst *RMWI);
241 static MemoryLocation get(const Instruction *Inst) {
242 return *MemoryLocation::getOrNone(Inst);
243 }
244 static Optional<MemoryLocation> getOrNone(const Instruction *Inst);
245
246 /// Return a location representing the source of a memory transfer.
247 static MemoryLocation getForSource(const MemTransferInst *MTI);
248 static MemoryLocation getForSource(const AtomicMemTransferInst *MTI);
249 static MemoryLocation getForSource(const AnyMemTransferInst *MTI);
250
251 /// Return a location representing the destination of a memory set or
252 /// transfer.
253 static MemoryLocation getForDest(const MemIntrinsic *MI);
254 static MemoryLocation getForDest(const AtomicMemIntrinsic *MI);
255 static MemoryLocation getForDest(const AnyMemIntrinsic *MI);
256
257 /// Return a location representing a particular argument of a call.
258 static MemoryLocation getForArgument(const CallBase *Call, unsigned ArgIdx,
259 const TargetLibraryInfo *TLI);
260 static MemoryLocation getForArgument(const CallBase *Call, unsigned ArgIdx,
261 const TargetLibraryInfo &TLI) {
262 return getForArgument(Call, ArgIdx, &TLI);
263 }
264
265 /// Return a location that may access any location after Ptr, while remaining
266 /// within the underlying object.
267 static MemoryLocation getAfter(const Value *Ptr,
268 const AAMDNodes &AATags = AAMDNodes()) {
269 return MemoryLocation(Ptr, LocationSize::afterPointer(), AATags);
270 }
271
272 /// Return a location that may access any location before or after Ptr, while
273 /// remaining within the underlying object.
274 static MemoryLocation
275 getBeforeOrAfter(const Value *Ptr, const AAMDNodes &AATags = AAMDNodes()) {
276 return MemoryLocation(Ptr, LocationSize::beforeOrAfterPointer(), AATags);
277 }
278
279 // Return the exact size if the exact size is known at compiletime,
280 // otherwise return MemoryLocation::UnknownSize.
281 static uint64_t getSizeOrUnknown(const TypeSize &T) {
282 return T.isScalable() ? UnknownSize : T.getFixedSize();
283 }
284
285 MemoryLocation()
286 : Ptr(nullptr), Size(LocationSize::beforeOrAfterPointer()), AATags() {}
17
Null pointer value stored to 'Loc.Ptr'
287
288 explicit MemoryLocation(const Value *Ptr, LocationSize Size,
289 const AAMDNodes &AATags = AAMDNodes())
290 : Ptr(Ptr), Size(Size), AATags(AATags) {}
291
292 MemoryLocation getWithNewPtr(const Value *NewPtr) const {
293 MemoryLocation Copy(*this);
294 Copy.Ptr = NewPtr;
295 return Copy;
296 }
297
298 MemoryLocation getWithNewSize(LocationSize NewSize) const {
299 MemoryLocation Copy(*this);
300 Copy.Size = NewSize;
301 return Copy;
302 }
303
304 MemoryLocation getWithoutAATags() const {
305 MemoryLocation Copy(*this);
306 Copy.AATags = AAMDNodes();
307 return Copy;
308 }
309
310 bool operator==(const MemoryLocation &Other) const {
311 return Ptr == Other.Ptr && Size == Other.Size && AATags == Other.AATags;
312 }
313};
314
315// Specialize DenseMapInfo.
316template <> struct DenseMapInfo<LocationSize> {
317 static inline LocationSize getEmptyKey() {
318 return LocationSize::mapEmpty();
319 }
320 static inline LocationSize getTombstoneKey() {
321 return LocationSize::mapTombstone();
322 }
323 static unsigned getHashValue(const LocationSize &Val) {
324 return DenseMapInfo<uint64_t>::getHashValue(Val.toRaw());
325 }
326 static bool isEqual(const LocationSize &LHS, const LocationSize &RHS) {
327 return LHS == RHS;
328 }
329};
330
331template <> struct DenseMapInfo<MemoryLocation> {
332 static inline MemoryLocation getEmptyKey() {
333 return MemoryLocation(DenseMapInfo<const Value *>::getEmptyKey(),
334 DenseMapInfo<LocationSize>::getEmptyKey());
335 }
336 static inline MemoryLocation getTombstoneKey() {
337 return MemoryLocation(DenseMapInfo<const Value *>::getTombstoneKey(),
338 DenseMapInfo<LocationSize>::getTombstoneKey());
339 }
340 static unsigned getHashValue(const MemoryLocation &Val) {
341 return DenseMapInfo<const Value *>::getHashValue(Val.Ptr) ^
342 DenseMapInfo<LocationSize>::getHashValue(Val.Size) ^
343 DenseMapInfo<AAMDNodes>::getHashValue(Val.AATags);
344 }
345 static bool isEqual(const MemoryLocation &LHS, const MemoryLocation &RHS) {
346 return LHS == RHS;
347 }
348};
349}
350
351#endif