Bug Summary

File:llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
Warning:line 1543, column 34
Called C++ object pointer is null

Annotated Source Code

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clang -cc1 -cc1 -triple x86_64-pc-linux-gnu -analyze -disable-free -disable-llvm-verifier -discard-value-names -main-file-name MemCpyOptimizer.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 -analyzer-config-compatibility-mode=true -mrelocation-model pic -pic-level 2 -fhalf-no-semantic-interposition -mframe-pointer=none -fmath-errno -fno-rounding-math -mconstructor-aliases -munwind-tables -target-cpu x86-64 -tune-cpu generic -fno-split-dwarf-inlining -debugger-tuning=gdb -ffunction-sections -fdata-sections -resource-dir /usr/lib/llvm-12/lib/clang/12.0.0 -D _DEBUG -D _GNU_SOURCE -D __STDC_CONSTANT_MACROS -D __STDC_FORMAT_MACROS -D __STDC_LIMIT_MACROS -I /build/llvm-toolchain-snapshot-12~++20210124100612+2afaf072f5c1/build-llvm/lib/Transforms/Scalar -I /build/llvm-toolchain-snapshot-12~++20210124100612+2afaf072f5c1/llvm/lib/Transforms/Scalar -I /build/llvm-toolchain-snapshot-12~++20210124100612+2afaf072f5c1/build-llvm/include -I /build/llvm-toolchain-snapshot-12~++20210124100612+2afaf072f5c1/llvm/include -U NDEBUG -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/c++/6.3.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/x86_64-linux-gnu/c++/6.3.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/x86_64-linux-gnu/c++/6.3.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/c++/6.3.0/backward -internal-isystem /usr/local/include -internal-isystem /usr/lib/llvm-12/lib/clang/12.0.0/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -O2 -Wno-unused-parameter -Wwrite-strings -Wno-missing-field-initializers -Wno-long-long -Wno-maybe-uninitialized -Wno-comment -std=c++14 -fdeprecated-macro -fdebug-compilation-dir /build/llvm-toolchain-snapshot-12~++20210124100612+2afaf072f5c1/build-llvm/lib/Transforms/Scalar -fdebug-prefix-map=/build/llvm-toolchain-snapshot-12~++20210124100612+2afaf072f5c1=. -ferror-limit 19 -fvisibility-inlines-hidden -stack-protector 2 -fgnuc-version=4.2.1 -vectorize-loops -vectorize-slp -analyzer-output=html -analyzer-config stable-report-filename=true -faddrsig -o /tmp/scan-build-2021-01-24-223304-31662-1 -x c++ /build/llvm-toolchain-snapshot-12~++20210124100612+2afaf072f5c1/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
1//===- MemCpyOptimizer.cpp - Optimize use of memcpy and friends -----------===//
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// This pass performs various transformations related to eliminating memcpy
10// calls, or transforming sets of stores into memset's.
11//
12//===----------------------------------------------------------------------===//
13
14#include "llvm/Transforms/Scalar/MemCpyOptimizer.h"
15#include "llvm/ADT/DenseSet.h"
16#include "llvm/ADT/None.h"
17#include "llvm/ADT/STLExtras.h"
18#include "llvm/ADT/SmallVector.h"
19#include "llvm/ADT/Statistic.h"
20#include "llvm/ADT/iterator_range.h"
21#include "llvm/Analysis/AliasAnalysis.h"
22#include "llvm/Analysis/AssumptionCache.h"
23#include "llvm/Analysis/GlobalsModRef.h"
24#include "llvm/Analysis/Loads.h"
25#include "llvm/Analysis/MemoryDependenceAnalysis.h"
26#include "llvm/Analysis/MemoryLocation.h"
27#include "llvm/Analysis/MemorySSA.h"
28#include "llvm/Analysis/MemorySSAUpdater.h"
29#include "llvm/Analysis/TargetLibraryInfo.h"
30#include "llvm/Analysis/ValueTracking.h"
31#include "llvm/IR/Argument.h"
32#include "llvm/IR/BasicBlock.h"
33#include "llvm/IR/Constants.h"
34#include "llvm/IR/DataLayout.h"
35#include "llvm/IR/DerivedTypes.h"
36#include "llvm/IR/Dominators.h"
37#include "llvm/IR/Function.h"
38#include "llvm/IR/GetElementPtrTypeIterator.h"
39#include "llvm/IR/GlobalVariable.h"
40#include "llvm/IR/IRBuilder.h"
41#include "llvm/IR/InstrTypes.h"
42#include "llvm/IR/Instruction.h"
43#include "llvm/IR/Instructions.h"
44#include "llvm/IR/IntrinsicInst.h"
45#include "llvm/IR/Intrinsics.h"
46#include "llvm/IR/LLVMContext.h"
47#include "llvm/IR/Module.h"
48#include "llvm/IR/Operator.h"
49#include "llvm/IR/PassManager.h"
50#include "llvm/IR/Type.h"
51#include "llvm/IR/User.h"
52#include "llvm/IR/Value.h"
53#include "llvm/InitializePasses.h"
54#include "llvm/Pass.h"
55#include "llvm/Support/Casting.h"
56#include "llvm/Support/Debug.h"
57#include "llvm/Support/MathExtras.h"
58#include "llvm/Support/raw_ostream.h"
59#include "llvm/Transforms/Scalar.h"
60#include "llvm/Transforms/Utils/Local.h"
61#include <algorithm>
62#include <cassert>
63#include <cstdint>
64#include <utility>
65
66using namespace llvm;
67
68#define DEBUG_TYPE"memcpyopt" "memcpyopt"
69
70static cl::opt<bool>
71 EnableMemorySSA("enable-memcpyopt-memoryssa", cl::init(false), cl::Hidden,
72 cl::desc("Use MemorySSA-backed MemCpyOpt."));
73
74STATISTIC(NumMemCpyInstr, "Number of memcpy instructions deleted")static llvm::Statistic NumMemCpyInstr = {"memcpyopt", "NumMemCpyInstr"
, "Number of memcpy instructions deleted"}
;
75STATISTIC(NumMemSetInfer, "Number of memsets inferred")static llvm::Statistic NumMemSetInfer = {"memcpyopt", "NumMemSetInfer"
, "Number of memsets inferred"}
;
76STATISTIC(NumMoveToCpy, "Number of memmoves converted to memcpy")static llvm::Statistic NumMoveToCpy = {"memcpyopt", "NumMoveToCpy"
, "Number of memmoves converted to memcpy"}
;
77STATISTIC(NumCpyToSet, "Number of memcpys converted to memset")static llvm::Statistic NumCpyToSet = {"memcpyopt", "NumCpyToSet"
, "Number of memcpys converted to memset"}
;
78STATISTIC(NumCallSlot, "Number of call slot optimizations performed")static llvm::Statistic NumCallSlot = {"memcpyopt", "NumCallSlot"
, "Number of call slot optimizations performed"}
;
79
80namespace {
81
82/// Represents a range of memset'd bytes with the ByteVal value.
83/// This allows us to analyze stores like:
84/// store 0 -> P+1
85/// store 0 -> P+0
86/// store 0 -> P+3
87/// store 0 -> P+2
88/// which sometimes happens with stores to arrays of structs etc. When we see
89/// the first store, we make a range [1, 2). The second store extends the range
90/// to [0, 2). The third makes a new range [2, 3). The fourth store joins the
91/// two ranges into [0, 3) which is memset'able.
92struct MemsetRange {
93 // Start/End - A semi range that describes the span that this range covers.
94 // The range is closed at the start and open at the end: [Start, End).
95 int64_t Start, End;
96
97 /// StartPtr - The getelementptr instruction that points to the start of the
98 /// range.
99 Value *StartPtr;
100
101 /// Alignment - The known alignment of the first store.
102 unsigned Alignment;
103
104 /// TheStores - The actual stores that make up this range.
105 SmallVector<Instruction*, 16> TheStores;
106
107 bool isProfitableToUseMemset(const DataLayout &DL) const;
108};
109
110} // end anonymous namespace
111
112bool MemsetRange::isProfitableToUseMemset(const DataLayout &DL) const {
113 // If we found more than 4 stores to merge or 16 bytes, use memset.
114 if (TheStores.size() >= 4 || End-Start >= 16) return true;
115
116 // If there is nothing to merge, don't do anything.
117 if (TheStores.size() < 2) return false;
118
119 // If any of the stores are a memset, then it is always good to extend the
120 // memset.
121 for (Instruction *SI : TheStores)
122 if (!isa<StoreInst>(SI))
123 return true;
124
125 // Assume that the code generator is capable of merging pairs of stores
126 // together if it wants to.
127 if (TheStores.size() == 2) return false;
128
129 // If we have fewer than 8 stores, it can still be worthwhile to do this.
130 // For example, merging 4 i8 stores into an i32 store is useful almost always.
131 // However, merging 2 32-bit stores isn't useful on a 32-bit architecture (the
132 // memset will be split into 2 32-bit stores anyway) and doing so can
133 // pessimize the llvm optimizer.
134 //
135 // Since we don't have perfect knowledge here, make some assumptions: assume
136 // the maximum GPR width is the same size as the largest legal integer
137 // size. If so, check to see whether we will end up actually reducing the
138 // number of stores used.
139 unsigned Bytes = unsigned(End-Start);
140 unsigned MaxIntSize = DL.getLargestLegalIntTypeSizeInBits() / 8;
141 if (MaxIntSize == 0)
142 MaxIntSize = 1;
143 unsigned NumPointerStores = Bytes / MaxIntSize;
144
145 // Assume the remaining bytes if any are done a byte at a time.
146 unsigned NumByteStores = Bytes % MaxIntSize;
147
148 // If we will reduce the # stores (according to this heuristic), do the
149 // transformation. This encourages merging 4 x i8 -> i32 and 2 x i16 -> i32
150 // etc.
151 return TheStores.size() > NumPointerStores+NumByteStores;
152}
153
154namespace {
155
156class MemsetRanges {
157 using range_iterator = SmallVectorImpl<MemsetRange>::iterator;
158
159 /// A sorted list of the memset ranges.
160 SmallVector<MemsetRange, 8> Ranges;
161
162 const DataLayout &DL;
163
164public:
165 MemsetRanges(const DataLayout &DL) : DL(DL) {}
166
167 using const_iterator = SmallVectorImpl<MemsetRange>::const_iterator;
168
169 const_iterator begin() const { return Ranges.begin(); }
170 const_iterator end() const { return Ranges.end(); }
171 bool empty() const { return Ranges.empty(); }
172
173 void addInst(int64_t OffsetFromFirst, Instruction *Inst) {
174 if (StoreInst *SI = dyn_cast<StoreInst>(Inst))
175 addStore(OffsetFromFirst, SI);
176 else
177 addMemSet(OffsetFromFirst, cast<MemSetInst>(Inst));
178 }
179
180 void addStore(int64_t OffsetFromFirst, StoreInst *SI) {
181 int64_t StoreSize = DL.getTypeStoreSize(SI->getOperand(0)->getType());
182
183 addRange(OffsetFromFirst, StoreSize, SI->getPointerOperand(),
184 SI->getAlign().value(), SI);
185 }
186
187 void addMemSet(int64_t OffsetFromFirst, MemSetInst *MSI) {
188 int64_t Size = cast<ConstantInt>(MSI->getLength())->getZExtValue();
189 addRange(OffsetFromFirst, Size, MSI->getDest(), MSI->getDestAlignment(), MSI);
190 }
191
192 void addRange(int64_t Start, int64_t Size, Value *Ptr,
193 unsigned Alignment, Instruction *Inst);
194};
195
196} // end anonymous namespace
197
198/// Add a new store to the MemsetRanges data structure. This adds a
199/// new range for the specified store at the specified offset, merging into
200/// existing ranges as appropriate.
201void MemsetRanges::addRange(int64_t Start, int64_t Size, Value *Ptr,
202 unsigned Alignment, Instruction *Inst) {
203 int64_t End = Start+Size;
204
205 range_iterator I = partition_point(
206 Ranges, [=](const MemsetRange &O) { return O.End < Start; });
207
208 // We now know that I == E, in which case we didn't find anything to merge
209 // with, or that Start <= I->End. If End < I->Start or I == E, then we need
210 // to insert a new range. Handle this now.
211 if (I == Ranges.end() || End < I->Start) {
212 MemsetRange &R = *Ranges.insert(I, MemsetRange());
213 R.Start = Start;
214 R.End = End;
215 R.StartPtr = Ptr;
216 R.Alignment = Alignment;
217 R.TheStores.push_back(Inst);
218 return;
219 }
220
221 // This store overlaps with I, add it.
222 I->TheStores.push_back(Inst);
223
224 // At this point, we may have an interval that completely contains our store.
225 // If so, just add it to the interval and return.
226 if (I->Start <= Start && I->End >= End)
227 return;
228
229 // Now we know that Start <= I->End and End >= I->Start so the range overlaps
230 // but is not entirely contained within the range.
231
232 // See if the range extends the start of the range. In this case, it couldn't
233 // possibly cause it to join the prior range, because otherwise we would have
234 // stopped on *it*.
235 if (Start < I->Start) {
236 I->Start = Start;
237 I->StartPtr = Ptr;
238 I->Alignment = Alignment;
239 }
240
241 // Now we know that Start <= I->End and Start >= I->Start (so the startpoint
242 // is in or right at the end of I), and that End >= I->Start. Extend I out to
243 // End.
244 if (End > I->End) {
245 I->End = End;
246 range_iterator NextI = I;
247 while (++NextI != Ranges.end() && End >= NextI->Start) {
248 // Merge the range in.
249 I->TheStores.append(NextI->TheStores.begin(), NextI->TheStores.end());
250 if (NextI->End > I->End)
251 I->End = NextI->End;
252 Ranges.erase(NextI);
253 NextI = I;
254 }
255 }
256}
257
258//===----------------------------------------------------------------------===//
259// MemCpyOptLegacyPass Pass
260//===----------------------------------------------------------------------===//
261
262namespace {
263
264class MemCpyOptLegacyPass : public FunctionPass {
265 MemCpyOptPass Impl;
266
267public:
268 static char ID; // Pass identification, replacement for typeid
269
270 MemCpyOptLegacyPass() : FunctionPass(ID) {
271 initializeMemCpyOptLegacyPassPass(*PassRegistry::getPassRegistry());
272 }
273
274 bool runOnFunction(Function &F) override;
275
276private:
277 // This transformation requires dominator postdominator info
278 void getAnalysisUsage(AnalysisUsage &AU) const override {
279 AU.setPreservesCFG();
280 AU.addRequired<AssumptionCacheTracker>();
281 AU.addRequired<DominatorTreeWrapperPass>();
282 AU.addPreserved<DominatorTreeWrapperPass>();
283 AU.addPreserved<GlobalsAAWrapperPass>();
284 AU.addRequired<TargetLibraryInfoWrapperPass>();
285 if (!EnableMemorySSA)
286 AU.addRequired<MemoryDependenceWrapperPass>();
287 AU.addPreserved<MemoryDependenceWrapperPass>();
288 AU.addRequired<AAResultsWrapperPass>();
289 AU.addPreserved<AAResultsWrapperPass>();
290 if (EnableMemorySSA)
291 AU.addRequired<MemorySSAWrapperPass>();
292 AU.addPreserved<MemorySSAWrapperPass>();
293 }
294};
295
296} // end anonymous namespace
297
298char MemCpyOptLegacyPass::ID = 0;
299
300/// The public interface to this file...
301FunctionPass *llvm::createMemCpyOptPass() { return new MemCpyOptLegacyPass(); }
302
303INITIALIZE_PASS_BEGIN(MemCpyOptLegacyPass, "memcpyopt", "MemCpy Optimization",static void *initializeMemCpyOptLegacyPassPassOnce(PassRegistry
&Registry) {
304 false, false)static void *initializeMemCpyOptLegacyPassPassOnce(PassRegistry
&Registry) {
305INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)initializeAssumptionCacheTrackerPass(Registry);
306INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)initializeDominatorTreeWrapperPassPass(Registry);
307INITIALIZE_PASS_DEPENDENCY(MemoryDependenceWrapperPass)initializeMemoryDependenceWrapperPassPass(Registry);
308INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)initializeTargetLibraryInfoWrapperPassPass(Registry);
309INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)initializeAAResultsWrapperPassPass(Registry);
310INITIALIZE_PASS_DEPENDENCY(GlobalsAAWrapperPass)initializeGlobalsAAWrapperPassPass(Registry);
311INITIALIZE_PASS_END(MemCpyOptLegacyPass, "memcpyopt", "MemCpy Optimization",PassInfo *PI = new PassInfo( "MemCpy Optimization", "memcpyopt"
, &MemCpyOptLegacyPass::ID, PassInfo::NormalCtor_t(callDefaultCtor
<MemCpyOptLegacyPass>), false, false); Registry.registerPass
(*PI, true); return PI; } static llvm::once_flag InitializeMemCpyOptLegacyPassPassFlag
; void llvm::initializeMemCpyOptLegacyPassPass(PassRegistry &
Registry) { llvm::call_once(InitializeMemCpyOptLegacyPassPassFlag
, initializeMemCpyOptLegacyPassPassOnce, std::ref(Registry));
}
312 false, false)PassInfo *PI = new PassInfo( "MemCpy Optimization", "memcpyopt"
, &MemCpyOptLegacyPass::ID, PassInfo::NormalCtor_t(callDefaultCtor
<MemCpyOptLegacyPass>), false, false); Registry.registerPass
(*PI, true); return PI; } static llvm::once_flag InitializeMemCpyOptLegacyPassPassFlag
; void llvm::initializeMemCpyOptLegacyPassPass(PassRegistry &
Registry) { llvm::call_once(InitializeMemCpyOptLegacyPassPassFlag
, initializeMemCpyOptLegacyPassPassOnce, std::ref(Registry));
}
313
314// Check that V is either not accessible by the caller, or unwinding cannot
315// occur between Start and End.
316static bool mayBeVisibleThroughUnwinding(Value *V, Instruction *Start,
317 Instruction *End) {
318 assert(Start->getParent() == End->getParent() && "Must be in same block")((Start->getParent() == End->getParent() && "Must be in same block"
) ? static_cast<void> (0) : __assert_fail ("Start->getParent() == End->getParent() && \"Must be in same block\""
, "/build/llvm-toolchain-snapshot-12~++20210124100612+2afaf072f5c1/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp"
, 318, __PRETTY_FUNCTION__))
;
319 if (!Start->getFunction()->doesNotThrow() &&
320 !isa<AllocaInst>(getUnderlyingObject(V))) {
321 for (const Instruction &I :
322 make_range(Start->getIterator(), End->getIterator())) {
323 if (I.mayThrow())
324 return true;
325 }
326 }
327 return false;
328}
329
330void MemCpyOptPass::eraseInstruction(Instruction *I) {
331 if (MSSAU)
332 MSSAU->removeMemoryAccess(I);
333 if (MD)
334 MD->removeInstruction(I);
335 I->eraseFromParent();
336}
337
338// Check for mod or ref of Loc between Start and End, excluding both boundaries.
339// Start and End must be in the same block
340static bool accessedBetween(AliasAnalysis &AA, MemoryLocation Loc,
341 const MemoryUseOrDef *Start,
342 const MemoryUseOrDef *End) {
343 assert(Start->getBlock() == End->getBlock() && "Only local supported")((Start->getBlock() == End->getBlock() && "Only local supported"
) ? static_cast<void> (0) : __assert_fail ("Start->getBlock() == End->getBlock() && \"Only local supported\""
, "/build/llvm-toolchain-snapshot-12~++20210124100612+2afaf072f5c1/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp"
, 343, __PRETTY_FUNCTION__))
;
344 for (const MemoryAccess &MA :
345 make_range(++Start->getIterator(), End->getIterator())) {
346 if (isModOrRefSet(AA.getModRefInfo(cast<MemoryUseOrDef>(MA).getMemoryInst(),
347 Loc)))
348 return true;
349 }
350 return false;
351}
352
353// Check for mod of Loc between Start and End, excluding both boundaries.
354// Start and End can be in different blocks.
355static bool writtenBetween(MemorySSA *MSSA, MemoryLocation Loc,
356 const MemoryUseOrDef *Start,
357 const MemoryUseOrDef *End) {
358 // TODO: Only walk until we hit Start.
359 MemoryAccess *Clobber = MSSA->getWalker()->getClobberingMemoryAccess(
360 End->getDefiningAccess(), Loc);
361 return !MSSA->dominates(Clobber, Start);
362}
363
364/// When scanning forward over instructions, we look for some other patterns to
365/// fold away. In particular, this looks for stores to neighboring locations of
366/// memory. If it sees enough consecutive ones, it attempts to merge them
367/// together into a memcpy/memset.
368Instruction *MemCpyOptPass::tryMergingIntoMemset(Instruction *StartInst,
369 Value *StartPtr,
370 Value *ByteVal) {
371 const DataLayout &DL = StartInst->getModule()->getDataLayout();
372
373 // Okay, so we now have a single store that can be splatable. Scan to find
374 // all subsequent stores of the same value to offset from the same pointer.
375 // Join these together into ranges, so we can decide whether contiguous blocks
376 // are stored.
377 MemsetRanges Ranges(DL);
378
379 BasicBlock::iterator BI(StartInst);
380
381 // Keeps track of the last memory use or def before the insertion point for
382 // the new memset. The new MemoryDef for the inserted memsets will be inserted
383 // after MemInsertPoint. It points to either LastMemDef or to the last user
384 // before the insertion point of the memset, if there are any such users.
385 MemoryUseOrDef *MemInsertPoint = nullptr;
386 // Keeps track of the last MemoryDef between StartInst and the insertion point
387 // for the new memset. This will become the defining access of the inserted
388 // memsets.
389 MemoryDef *LastMemDef = nullptr;
390 for (++BI; !BI->isTerminator(); ++BI) {
391 if (MSSAU) {
392 auto *CurrentAcc = cast_or_null<MemoryUseOrDef>(
393 MSSAU->getMemorySSA()->getMemoryAccess(&*BI));
394 if (CurrentAcc) {
395 MemInsertPoint = CurrentAcc;
396 if (auto *CurrentDef = dyn_cast<MemoryDef>(CurrentAcc))
397 LastMemDef = CurrentDef;
398 }
399 }
400
401 if (!isa<StoreInst>(BI) && !isa<MemSetInst>(BI)) {
402 // If the instruction is readnone, ignore it, otherwise bail out. We
403 // don't even allow readonly here because we don't want something like:
404 // A[1] = 2; strlen(A); A[2] = 2; -> memcpy(A, ...); strlen(A).
405 if (BI->mayWriteToMemory() || BI->mayReadFromMemory())
406 break;
407 continue;
408 }
409
410 if (StoreInst *NextStore = dyn_cast<StoreInst>(BI)) {
411 // If this is a store, see if we can merge it in.
412 if (!NextStore->isSimple()) break;
413
414 Value *StoredVal = NextStore->getValueOperand();
415
416 // Don't convert stores of non-integral pointer types to memsets (which
417 // stores integers).
418 if (DL.isNonIntegralPointerType(StoredVal->getType()->getScalarType()))
419 break;
420
421 // Check to see if this stored value is of the same byte-splattable value.
422 Value *StoredByte = isBytewiseValue(StoredVal, DL);
423 if (isa<UndefValue>(ByteVal) && StoredByte)
424 ByteVal = StoredByte;
425 if (ByteVal != StoredByte)
426 break;
427
428 // Check to see if this store is to a constant offset from the start ptr.
429 Optional<int64_t> Offset =
430 isPointerOffset(StartPtr, NextStore->getPointerOperand(), DL);
431 if (!Offset)
432 break;
433
434 Ranges.addStore(*Offset, NextStore);
435 } else {
436 MemSetInst *MSI = cast<MemSetInst>(BI);
437
438 if (MSI->isVolatile() || ByteVal != MSI->getValue() ||
439 !isa<ConstantInt>(MSI->getLength()))
440 break;
441
442 // Check to see if this store is to a constant offset from the start ptr.
443 Optional<int64_t> Offset = isPointerOffset(StartPtr, MSI->getDest(), DL);
444 if (!Offset)
445 break;
446
447 Ranges.addMemSet(*Offset, MSI);
448 }
449 }
450
451 // If we have no ranges, then we just had a single store with nothing that
452 // could be merged in. This is a very common case of course.
453 if (Ranges.empty())
454 return nullptr;
455
456 // If we had at least one store that could be merged in, add the starting
457 // store as well. We try to avoid this unless there is at least something
458 // interesting as a small compile-time optimization.
459 Ranges.addInst(0, StartInst);
460
461 // If we create any memsets, we put it right before the first instruction that
462 // isn't part of the memset block. This ensure that the memset is dominated
463 // by any addressing instruction needed by the start of the block.
464 IRBuilder<> Builder(&*BI);
465
466 // Now that we have full information about ranges, loop over the ranges and
467 // emit memset's for anything big enough to be worthwhile.
468 Instruction *AMemSet = nullptr;
469 for (const MemsetRange &Range : Ranges) {
470 if (Range.TheStores.size() == 1) continue;
471
472 // If it is profitable to lower this range to memset, do so now.
473 if (!Range.isProfitableToUseMemset(DL))
474 continue;
475
476 // Otherwise, we do want to transform this! Create a new memset.
477 // Get the starting pointer of the block.
478 StartPtr = Range.StartPtr;
479
480 AMemSet = Builder.CreateMemSet(StartPtr, ByteVal, Range.End - Range.Start,
481 MaybeAlign(Range.Alignment));
482 LLVM_DEBUG(dbgs() << "Replace stores:\n"; for (Instruction *SIdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("memcpyopt")) { dbgs() << "Replace stores:\n"; for (Instruction
*SI : Range.TheStores) dbgs() << *SI << '\n'; dbgs
() << "With: " << *AMemSet << '\n'; } } while
(false)
483 : Range.TheStores) dbgs()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("memcpyopt")) { dbgs() << "Replace stores:\n"; for (Instruction
*SI : Range.TheStores) dbgs() << *SI << '\n'; dbgs
() << "With: " << *AMemSet << '\n'; } } while
(false)
484 << *SI << '\n';do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("memcpyopt")) { dbgs() << "Replace stores:\n"; for (Instruction
*SI : Range.TheStores) dbgs() << *SI << '\n'; dbgs
() << "With: " << *AMemSet << '\n'; } } while
(false)
485 dbgs() << "With: " << *AMemSet << '\n')do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("memcpyopt")) { dbgs() << "Replace stores:\n"; for (Instruction
*SI : Range.TheStores) dbgs() << *SI << '\n'; dbgs
() << "With: " << *AMemSet << '\n'; } } while
(false)
;
486 if (!Range.TheStores.empty())
487 AMemSet->setDebugLoc(Range.TheStores[0]->getDebugLoc());
488
489 if (MSSAU) {
490 assert(LastMemDef && MemInsertPoint &&((LastMemDef && MemInsertPoint && "Both LastMemDef and MemInsertPoint need to be set"
) ? static_cast<void> (0) : __assert_fail ("LastMemDef && MemInsertPoint && \"Both LastMemDef and MemInsertPoint need to be set\""
, "/build/llvm-toolchain-snapshot-12~++20210124100612+2afaf072f5c1/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp"
, 491, __PRETTY_FUNCTION__))
491 "Both LastMemDef and MemInsertPoint need to be set")((LastMemDef && MemInsertPoint && "Both LastMemDef and MemInsertPoint need to be set"
) ? static_cast<void> (0) : __assert_fail ("LastMemDef && MemInsertPoint && \"Both LastMemDef and MemInsertPoint need to be set\""
, "/build/llvm-toolchain-snapshot-12~++20210124100612+2afaf072f5c1/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp"
, 491, __PRETTY_FUNCTION__))
;
492 auto *NewDef =
493 cast<MemoryDef>(MemInsertPoint->getMemoryInst() == &*BI
494 ? MSSAU->createMemoryAccessBefore(
495 AMemSet, LastMemDef, MemInsertPoint)
496 : MSSAU->createMemoryAccessAfter(
497 AMemSet, LastMemDef, MemInsertPoint));
498 MSSAU->insertDef(NewDef, /*RenameUses=*/true);
499 LastMemDef = NewDef;
500 MemInsertPoint = NewDef;
501 }
502
503 // Zap all the stores.
504 for (Instruction *SI : Range.TheStores)
505 eraseInstruction(SI);
506
507 ++NumMemSetInfer;
508 }
509
510 return AMemSet;
511}
512
513// This method try to lift a store instruction before position P.
514// It will lift the store and its argument + that anything that
515// may alias with these.
516// The method returns true if it was successful.
517bool MemCpyOptPass::moveUp(StoreInst *SI, Instruction *P, const LoadInst *LI) {
518 // If the store alias this position, early bail out.
519 MemoryLocation StoreLoc = MemoryLocation::get(SI);
520 if (isModOrRefSet(AA->getModRefInfo(P, StoreLoc)))
521 return false;
522
523 // Keep track of the arguments of all instruction we plan to lift
524 // so we can make sure to lift them as well if appropriate.
525 DenseSet<Instruction*> Args;
526 if (auto *Ptr = dyn_cast<Instruction>(SI->getPointerOperand()))
527 if (Ptr->getParent() == SI->getParent())
528 Args.insert(Ptr);
529
530 // Instruction to lift before P.
531 SmallVector<Instruction *, 8> ToLift{SI};
532
533 // Memory locations of lifted instructions.
534 SmallVector<MemoryLocation, 8> MemLocs{StoreLoc};
535
536 // Lifted calls.
537 SmallVector<const CallBase *, 8> Calls;
538
539 const MemoryLocation LoadLoc = MemoryLocation::get(LI);
540
541 for (auto I = --SI->getIterator(), E = P->getIterator(); I != E; --I) {
542 auto *C = &*I;
543
544 // Make sure hoisting does not perform a store that was not guaranteed to
545 // happen.
546 if (!isGuaranteedToTransferExecutionToSuccessor(C))
547 return false;
548
549 bool MayAlias = isModOrRefSet(AA->getModRefInfo(C, None));
550
551 bool NeedLift = false;
552 if (Args.erase(C))
553 NeedLift = true;
554 else if (MayAlias) {
555 NeedLift = llvm::any_of(MemLocs, [C, this](const MemoryLocation &ML) {
556 return isModOrRefSet(AA->getModRefInfo(C, ML));
557 });
558
559 if (!NeedLift)
560 NeedLift = llvm::any_of(Calls, [C, this](const CallBase *Call) {
561 return isModOrRefSet(AA->getModRefInfo(C, Call));
562 });
563 }
564
565 if (!NeedLift)
566 continue;
567
568 if (MayAlias) {
569 // Since LI is implicitly moved downwards past the lifted instructions,
570 // none of them may modify its source.
571 if (isModSet(AA->getModRefInfo(C, LoadLoc)))
572 return false;
573 else if (const auto *Call = dyn_cast<CallBase>(C)) {
574 // If we can't lift this before P, it's game over.
575 if (isModOrRefSet(AA->getModRefInfo(P, Call)))
576 return false;
577
578 Calls.push_back(Call);
579 } else if (isa<LoadInst>(C) || isa<StoreInst>(C) || isa<VAArgInst>(C)) {
580 // If we can't lift this before P, it's game over.
581 auto ML = MemoryLocation::get(C);
582 if (isModOrRefSet(AA->getModRefInfo(P, ML)))
583 return false;
584
585 MemLocs.push_back(ML);
586 } else
587 // We don't know how to lift this instruction.
588 return false;
589 }
590
591 ToLift.push_back(C);
592 for (unsigned k = 0, e = C->getNumOperands(); k != e; ++k)
593 if (auto *A = dyn_cast<Instruction>(C->getOperand(k))) {
594 if (A->getParent() == SI->getParent()) {
595 // Cannot hoist user of P above P
596 if(A == P) return false;
597 Args.insert(A);
598 }
599 }
600 }
601
602 // Find MSSA insertion point. Normally P will always have a corresponding
603 // memory access before which we can insert. However, with non-standard AA
604 // pipelines, there may be a mismatch between AA and MSSA, in which case we
605 // will scan for a memory access before P. In either case, we know for sure
606 // that at least the load will have a memory access.
607 // TODO: Simplify this once P will be determined by MSSA, in which case the
608 // discrepancy can no longer occur.
609 MemoryUseOrDef *MemInsertPoint = nullptr;
610 if (MSSAU) {
611 if (MemoryUseOrDef *MA = MSSAU->getMemorySSA()->getMemoryAccess(P)) {
612 MemInsertPoint = cast<MemoryUseOrDef>(--MA->getIterator());
613 } else {
614 const Instruction *ConstP = P;
615 for (const Instruction &I : make_range(++ConstP->getReverseIterator(),
616 ++LI->getReverseIterator())) {
617 if (MemoryUseOrDef *MA = MSSAU->getMemorySSA()->getMemoryAccess(&I)) {
618 MemInsertPoint = MA;
619 break;
620 }
621 }
622 }
623 }
624
625 // We made it, we need to lift.
626 for (auto *I : llvm::reverse(ToLift)) {
627 LLVM_DEBUG(dbgs() << "Lifting " << *I << " before " << *P << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("memcpyopt")) { dbgs() << "Lifting " << *I <<
" before " << *P << "\n"; } } while (false)
;
628 I->moveBefore(P);
629 if (MSSAU) {
630 assert(MemInsertPoint && "Must have found insert point")((MemInsertPoint && "Must have found insert point") ?
static_cast<void> (0) : __assert_fail ("MemInsertPoint && \"Must have found insert point\""
, "/build/llvm-toolchain-snapshot-12~++20210124100612+2afaf072f5c1/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp"
, 630, __PRETTY_FUNCTION__))
;
631 if (MemoryUseOrDef *MA = MSSAU->getMemorySSA()->getMemoryAccess(I)) {
632 MSSAU->moveAfter(MA, MemInsertPoint);
633 MemInsertPoint = MA;
634 }
635 }
636 }
637
638 return true;
639}
640
641bool MemCpyOptPass::processStore(StoreInst *SI, BasicBlock::iterator &BBI) {
642 if (!SI->isSimple()) return false;
643
644 // Avoid merging nontemporal stores since the resulting
645 // memcpy/memset would not be able to preserve the nontemporal hint.
646 // In theory we could teach how to propagate the !nontemporal metadata to
647 // memset calls. However, that change would force the backend to
648 // conservatively expand !nontemporal memset calls back to sequences of
649 // store instructions (effectively undoing the merging).
650 if (SI->getMetadata(LLVMContext::MD_nontemporal))
651 return false;
652
653 const DataLayout &DL = SI->getModule()->getDataLayout();
654
655 Value *StoredVal = SI->getValueOperand();
656
657 // Not all the transforms below are correct for non-integral pointers, bail
658 // until we've audited the individual pieces.
659 if (DL.isNonIntegralPointerType(StoredVal->getType()->getScalarType()))
660 return false;
661
662 // Load to store forwarding can be interpreted as memcpy.
663 if (LoadInst *LI = dyn_cast<LoadInst>(StoredVal)) {
664 if (LI->isSimple() && LI->hasOneUse() &&
665 LI->getParent() == SI->getParent()) {
666
667 auto *T = LI->getType();
668 if (T->isAggregateType()) {
669 MemoryLocation LoadLoc = MemoryLocation::get(LI);
670
671 // We use alias analysis to check if an instruction may store to
672 // the memory we load from in between the load and the store. If
673 // such an instruction is found, we try to promote there instead
674 // of at the store position.
675 // TODO: Can use MSSA for this.
676 Instruction *P = SI;
677 for (auto &I : make_range(++LI->getIterator(), SI->getIterator())) {
678 if (isModSet(AA->getModRefInfo(&I, LoadLoc))) {
679 P = &I;
680 break;
681 }
682 }
683
684 // We found an instruction that may write to the loaded memory.
685 // We can try to promote at this position instead of the store
686 // position if nothing alias the store memory after this and the store
687 // destination is not in the range.
688 if (P && P != SI) {
689 if (!moveUp(SI, P, LI))
690 P = nullptr;
691 }
692
693 // If a valid insertion position is found, then we can promote
694 // the load/store pair to a memcpy.
695 if (P) {
696 // If we load from memory that may alias the memory we store to,
697 // memmove must be used to preserve semantic. If not, memcpy can
698 // be used.
699 bool UseMemMove = false;
700 if (!AA->isNoAlias(MemoryLocation::get(SI), LoadLoc))
701 UseMemMove = true;
702
703 uint64_t Size = DL.getTypeStoreSize(T);
704
705 IRBuilder<> Builder(P);
706 Instruction *M;
707 if (UseMemMove)
708 M = Builder.CreateMemMove(
709 SI->getPointerOperand(), SI->getAlign(),
710 LI->getPointerOperand(), LI->getAlign(), Size);
711 else
712 M = Builder.CreateMemCpy(
713 SI->getPointerOperand(), SI->getAlign(),
714 LI->getPointerOperand(), LI->getAlign(), Size);
715
716 LLVM_DEBUG(dbgs() << "Promoting " << *LI << " to " << *SI << " => "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("memcpyopt")) { dbgs() << "Promoting " << *LI <<
" to " << *SI << " => " << *M << "\n"
; } } while (false)
717 << *M << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("memcpyopt")) { dbgs() << "Promoting " << *LI <<
" to " << *SI << " => " << *M << "\n"
; } } while (false)
;
718
719 if (MSSAU) {
720 auto *LastDef =
721 cast<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess(SI));
722 auto *NewAccess =
723 MSSAU->createMemoryAccessAfter(M, LastDef, LastDef);
724 MSSAU->insertDef(cast<MemoryDef>(NewAccess), /*RenameUses=*/true);
725 }
726
727 eraseInstruction(SI);
728 eraseInstruction(LI);
729 ++NumMemCpyInstr;
730
731 // Make sure we do not invalidate the iterator.
732 BBI = M->getIterator();
733 return true;
734 }
735 }
736
737 // Detect cases where we're performing call slot forwarding, but
738 // happen to be using a load-store pair to implement it, rather than
739 // a memcpy.
740 CallInst *C = nullptr;
741 if (EnableMemorySSA) {
742 if (auto *LoadClobber = dyn_cast<MemoryUseOrDef>(
743 MSSA->getWalker()->getClobberingMemoryAccess(LI))) {
744 // The load most post-dom the call. Limit to the same block for now.
745 // TODO: Support non-local call-slot optimization?
746 if (LoadClobber->getBlock() == SI->getParent())
747 C = dyn_cast_or_null<CallInst>(LoadClobber->getMemoryInst());
748 }
749 } else {
750 MemDepResult ldep = MD->getDependency(LI);
751 if (ldep.isClobber() && !isa<MemCpyInst>(ldep.getInst()))
752 C = dyn_cast<CallInst>(ldep.getInst());
753 }
754
755 if (C) {
756 // Check that nothing touches the dest of the "copy" between
757 // the call and the store.
758 MemoryLocation StoreLoc = MemoryLocation::get(SI);
759 if (EnableMemorySSA) {
760 if (accessedBetween(*AA, StoreLoc, MSSA->getMemoryAccess(C),
761 MSSA->getMemoryAccess(SI)))
762 C = nullptr;
763 } else {
764 for (BasicBlock::iterator I = --SI->getIterator(),
765 E = C->getIterator();
766 I != E; --I) {
767 if (isModOrRefSet(AA->getModRefInfo(&*I, StoreLoc))) {
768 C = nullptr;
769 break;
770 }
771 }
772 }
773 }
774
775 if (C) {
776 bool changed = performCallSlotOptzn(
777 LI, SI, SI->getPointerOperand()->stripPointerCasts(),
778 LI->getPointerOperand()->stripPointerCasts(),
779 DL.getTypeStoreSize(SI->getOperand(0)->getType()),
780 commonAlignment(SI->getAlign(), LI->getAlign()), C);
781 if (changed) {
782 eraseInstruction(SI);
783 eraseInstruction(LI);
784 ++NumMemCpyInstr;
785 return true;
786 }
787 }
788 }
789 }
790
791 // There are two cases that are interesting for this code to handle: memcpy
792 // and memset. Right now we only handle memset.
793
794 // Ensure that the value being stored is something that can be memset'able a
795 // byte at a time like "0" or "-1" or any width, as well as things like
796 // 0xA0A0A0A0 and 0.0.
797 auto *V = SI->getOperand(0);
798 if (Value *ByteVal = isBytewiseValue(V, DL)) {
799 if (Instruction *I = tryMergingIntoMemset(SI, SI->getPointerOperand(),
800 ByteVal)) {
801 BBI = I->getIterator(); // Don't invalidate iterator.
802 return true;
803 }
804
805 // If we have an aggregate, we try to promote it to memset regardless
806 // of opportunity for merging as it can expose optimization opportunities
807 // in subsequent passes.
808 auto *T = V->getType();
809 if (T->isAggregateType()) {
810 uint64_t Size = DL.getTypeStoreSize(T);
811 IRBuilder<> Builder(SI);
812 auto *M = Builder.CreateMemSet(SI->getPointerOperand(), ByteVal, Size,
813 SI->getAlign());
814
815 LLVM_DEBUG(dbgs() << "Promoting " << *SI << " to " << *M << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("memcpyopt")) { dbgs() << "Promoting " << *SI <<
" to " << *M << "\n"; } } while (false)
;
816
817 if (MSSAU) {
818 assert(isa<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess(SI)))((isa<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess
(SI))) ? static_cast<void> (0) : __assert_fail ("isa<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess(SI))"
, "/build/llvm-toolchain-snapshot-12~++20210124100612+2afaf072f5c1/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp"
, 818, __PRETTY_FUNCTION__))
;
819 auto *LastDef =
820 cast<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess(SI));
821 auto *NewAccess = MSSAU->createMemoryAccessAfter(M, LastDef, LastDef);
822 MSSAU->insertDef(cast<MemoryDef>(NewAccess), /*RenameUses=*/true);
823 }
824
825 eraseInstruction(SI);
826 NumMemSetInfer++;
827
828 // Make sure we do not invalidate the iterator.
829 BBI = M->getIterator();
830 return true;
831 }
832 }
833
834 return false;
835}
836
837bool MemCpyOptPass::processMemSet(MemSetInst *MSI, BasicBlock::iterator &BBI) {
838 // See if there is another memset or store neighboring this memset which
839 // allows us to widen out the memset to do a single larger store.
840 if (isa<ConstantInt>(MSI->getLength()) && !MSI->isVolatile())
841 if (Instruction *I = tryMergingIntoMemset(MSI, MSI->getDest(),
842 MSI->getValue())) {
843 BBI = I->getIterator(); // Don't invalidate iterator.
844 return true;
845 }
846 return false;
847}
848
849/// Takes a memcpy and a call that it depends on,
850/// and checks for the possibility of a call slot optimization by having
851/// the call write its result directly into the destination of the memcpy.
852bool MemCpyOptPass::performCallSlotOptzn(Instruction *cpyLoad,
853 Instruction *cpyStore, Value *cpyDest,
854 Value *cpySrc, uint64_t cpyLen,
855 Align cpyAlign, CallInst *C) {
856 // The general transformation to keep in mind is
857 //
858 // call @func(..., src, ...)
859 // memcpy(dest, src, ...)
860 //
861 // ->
862 //
863 // memcpy(dest, src, ...)
864 // call @func(..., dest, ...)
865 //
866 // Since moving the memcpy is technically awkward, we additionally check that
867 // src only holds uninitialized values at the moment of the call, meaning that
868 // the memcpy can be discarded rather than moved.
869
870 // Lifetime marks shouldn't be operated on.
871 if (Function *F = C->getCalledFunction())
872 if (F->isIntrinsic() && F->getIntrinsicID() == Intrinsic::lifetime_start)
873 return false;
874
875 // Require that src be an alloca. This simplifies the reasoning considerably.
876 AllocaInst *srcAlloca = dyn_cast<AllocaInst>(cpySrc);
877 if (!srcAlloca)
878 return false;
879
880 ConstantInt *srcArraySize = dyn_cast<ConstantInt>(srcAlloca->getArraySize());
881 if (!srcArraySize)
882 return false;
883
884 const DataLayout &DL = cpyLoad->getModule()->getDataLayout();
885 uint64_t srcSize = DL.getTypeAllocSize(srcAlloca->getAllocatedType()) *
886 srcArraySize->getZExtValue();
887
888 if (cpyLen < srcSize)
889 return false;
890
891 // Check that accessing the first srcSize bytes of dest will not cause a
892 // trap. Otherwise the transform is invalid since it might cause a trap
893 // to occur earlier than it otherwise would.
894 if (!isDereferenceableAndAlignedPointer(cpyDest, Align(1), APInt(64, cpyLen),
895 DL, C, DT))
896 return false;
897
898 // Make sure that nothing can observe cpyDest being written early. There are
899 // a number of cases to consider:
900 // 1. cpyDest cannot be accessed between C and cpyStore as a precondition of
901 // the transform.
902 // 2. C itself may not access cpyDest (prior to the transform). This is
903 // checked further below.
904 // 3. If cpyDest is accessible to the caller of this function (potentially
905 // captured and not based on an alloca), we need to ensure that we cannot
906 // unwind between C and cpyStore. This is checked here.
907 // 4. If cpyDest is potentially captured, there may be accesses to it from
908 // another thread. In this case, we need to check that cpyStore is
909 // guaranteed to be executed if C is. As it is a non-atomic access, it
910 // renders accesses from other threads undefined.
911 // TODO: This is currently not checked.
912 if (mayBeVisibleThroughUnwinding(cpyDest, C, cpyStore))
913 return false;
914
915 // Check that dest points to memory that is at least as aligned as src.
916 Align srcAlign = srcAlloca->getAlign();
917 bool isDestSufficientlyAligned = srcAlign <= cpyAlign;
918 // If dest is not aligned enough and we can't increase its alignment then
919 // bail out.
920 if (!isDestSufficientlyAligned && !isa<AllocaInst>(cpyDest))
921 return false;
922
923 // Check that src is not accessed except via the call and the memcpy. This
924 // guarantees that it holds only undefined values when passed in (so the final
925 // memcpy can be dropped), that it is not read or written between the call and
926 // the memcpy, and that writing beyond the end of it is undefined.
927 SmallVector<User *, 8> srcUseList(srcAlloca->users());
928 while (!srcUseList.empty()) {
929 User *U = srcUseList.pop_back_val();
930
931 if (isa<BitCastInst>(U) || isa<AddrSpaceCastInst>(U)) {
932 append_range(srcUseList, U->users());
933 continue;
934 }
935 if (GetElementPtrInst *G = dyn_cast<GetElementPtrInst>(U)) {
936 if (!G->hasAllZeroIndices())
937 return false;
938
939 append_range(srcUseList, U->users());
940 continue;
941 }
942 if (const IntrinsicInst *IT = dyn_cast<IntrinsicInst>(U))
943 if (IT->isLifetimeStartOrEnd())
944 continue;
945
946 if (U != C && U != cpyLoad)
947 return false;
948 }
949
950 // Check that src isn't captured by the called function since the
951 // transformation can cause aliasing issues in that case.
952 for (unsigned ArgI = 0, E = C->arg_size(); ArgI != E; ++ArgI)
953 if (C->getArgOperand(ArgI) == cpySrc && !C->doesNotCapture(ArgI))
954 return false;
955
956 // Since we're changing the parameter to the callsite, we need to make sure
957 // that what would be the new parameter dominates the callsite.
958 if (!DT->dominates(cpyDest, C)) {
959 // Support moving a constant index GEP before the call.
960 auto *GEP = dyn_cast<GetElementPtrInst>(cpyDest);
961 if (GEP && GEP->hasAllConstantIndices() &&
962 DT->dominates(GEP->getPointerOperand(), C))
963 GEP->moveBefore(C);
964 else
965 return false;
966 }
967
968 // In addition to knowing that the call does not access src in some
969 // unexpected manner, for example via a global, which we deduce from
970 // the use analysis, we also need to know that it does not sneakily
971 // access dest. We rely on AA to figure this out for us.
972 ModRefInfo MR = AA->getModRefInfo(C, cpyDest, LocationSize::precise(srcSize));
973 // If necessary, perform additional analysis.
974 if (isModOrRefSet(MR))
975 MR = AA->callCapturesBefore(C, cpyDest, LocationSize::precise(srcSize), DT);
976 if (isModOrRefSet(MR))
977 return false;
978
979 // We can't create address space casts here because we don't know if they're
980 // safe for the target.
981 if (cpySrc->getType()->getPointerAddressSpace() !=
982 cpyDest->getType()->getPointerAddressSpace())
983 return false;
984 for (unsigned ArgI = 0; ArgI < C->arg_size(); ++ArgI)
985 if (C->getArgOperand(ArgI)->stripPointerCasts() == cpySrc &&
986 cpySrc->getType()->getPointerAddressSpace() !=
987 C->getArgOperand(ArgI)->getType()->getPointerAddressSpace())
988 return false;
989
990 // All the checks have passed, so do the transformation.
991 bool changedArgument = false;
992 for (unsigned ArgI = 0; ArgI < C->arg_size(); ++ArgI)
993 if (C->getArgOperand(ArgI)->stripPointerCasts() == cpySrc) {
994 Value *Dest = cpySrc->getType() == cpyDest->getType() ? cpyDest
995 : CastInst::CreatePointerCast(cpyDest, cpySrc->getType(),
996 cpyDest->getName(), C);
997 changedArgument = true;
998 if (C->getArgOperand(ArgI)->getType() == Dest->getType())
999 C->setArgOperand(ArgI, Dest);
1000 else
1001 C->setArgOperand(ArgI, CastInst::CreatePointerCast(
1002 Dest, C->getArgOperand(ArgI)->getType(),
1003 Dest->getName(), C));
1004 }
1005
1006 if (!changedArgument)
1007 return false;
1008
1009 // If the destination wasn't sufficiently aligned then increase its alignment.
1010 if (!isDestSufficientlyAligned) {
1011 assert(isa<AllocaInst>(cpyDest) && "Can only increase alloca alignment!")((isa<AllocaInst>(cpyDest) && "Can only increase alloca alignment!"
) ? static_cast<void> (0) : __assert_fail ("isa<AllocaInst>(cpyDest) && \"Can only increase alloca alignment!\""
, "/build/llvm-toolchain-snapshot-12~++20210124100612+2afaf072f5c1/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp"
, 1011, __PRETTY_FUNCTION__))
;
1012 cast<AllocaInst>(cpyDest)->setAlignment(srcAlign);
1013 }
1014
1015 // Drop any cached information about the call, because we may have changed
1016 // its dependence information by changing its parameter.
1017 if (MD)
1018 MD->removeInstruction(C);
1019
1020 // Update AA metadata
1021 // FIXME: MD_tbaa_struct and MD_mem_parallel_loop_access should also be
1022 // handled here, but combineMetadata doesn't support them yet
1023 unsigned KnownIDs[] = {LLVMContext::MD_tbaa, LLVMContext::MD_alias_scope,
1024 LLVMContext::MD_noalias,
1025 LLVMContext::MD_invariant_group,
1026 LLVMContext::MD_access_group};
1027 combineMetadata(C, cpyLoad, KnownIDs, true);
1028
1029 ++NumCallSlot;
1030 return true;
1031}
1032
1033/// We've found that the (upward scanning) memory dependence of memcpy 'M' is
1034/// the memcpy 'MDep'. Try to simplify M to copy from MDep's input if we can.
1035bool MemCpyOptPass::processMemCpyMemCpyDependence(MemCpyInst *M,
1036 MemCpyInst *MDep) {
1037 // We can only transforms memcpy's where the dest of one is the source of the
1038 // other.
1039 if (M->getSource() != MDep->getDest() || MDep->isVolatile())
1040 return false;
1041
1042 // If dep instruction is reading from our current input, then it is a noop
1043 // transfer and substituting the input won't change this instruction. Just
1044 // ignore the input and let someone else zap MDep. This handles cases like:
1045 // memcpy(a <- a)
1046 // memcpy(b <- a)
1047 if (M->getSource() == MDep->getSource())
1048 return false;
1049
1050 // Second, the length of the memcpy's must be the same, or the preceding one
1051 // must be larger than the following one.
1052 ConstantInt *MDepLen = dyn_cast<ConstantInt>(MDep->getLength());
1053 ConstantInt *MLen = dyn_cast<ConstantInt>(M->getLength());
1054 if (!MDepLen || !MLen || MDepLen->getZExtValue() < MLen->getZExtValue())
1055 return false;
1056
1057 // Verify that the copied-from memory doesn't change in between the two
1058 // transfers. For example, in:
1059 // memcpy(a <- b)
1060 // *b = 42;
1061 // memcpy(c <- a)
1062 // It would be invalid to transform the second memcpy into memcpy(c <- b).
1063 //
1064 // TODO: If the code between M and MDep is transparent to the destination "c",
1065 // then we could still perform the xform by moving M up to the first memcpy.
1066 if (EnableMemorySSA) {
1067 // TODO: It would be sufficient to check the MDep source up to the memcpy
1068 // size of M, rather than MDep.
1069 if (writtenBetween(MSSA, MemoryLocation::getForSource(MDep),
1070 MSSA->getMemoryAccess(MDep), MSSA->getMemoryAccess(M)))
1071 return false;
1072 } else {
1073 // NOTE: This is conservative, it will stop on any read from the source loc,
1074 // not just the defining memcpy.
1075 MemDepResult SourceDep =
1076 MD->getPointerDependencyFrom(MemoryLocation::getForSource(MDep), false,
1077 M->getIterator(), M->getParent());
1078 if (!SourceDep.isClobber() || SourceDep.getInst() != MDep)
1079 return false;
1080 }
1081
1082 // If the dest of the second might alias the source of the first, then the
1083 // source and dest might overlap. We still want to eliminate the intermediate
1084 // value, but we have to generate a memmove instead of memcpy.
1085 bool UseMemMove = false;
1086 if (!AA->isNoAlias(MemoryLocation::getForDest(M),
1087 MemoryLocation::getForSource(MDep)))
1088 UseMemMove = true;
1089
1090 // If all checks passed, then we can transform M.
1091 LLVM_DEBUG(dbgs() << "MemCpyOptPass: Forwarding memcpy->memcpy src:\n"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("memcpyopt")) { dbgs() << "MemCpyOptPass: Forwarding memcpy->memcpy src:\n"
<< *MDep << '\n' << *M << '\n'; } } while
(false)
1092 << *MDep << '\n' << *M << '\n')do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("memcpyopt")) { dbgs() << "MemCpyOptPass: Forwarding memcpy->memcpy src:\n"
<< *MDep << '\n' << *M << '\n'; } } while
(false)
;
1093
1094 // TODO: Is this worth it if we're creating a less aligned memcpy? For
1095 // example we could be moving from movaps -> movq on x86.
1096 IRBuilder<> Builder(M);
1097 Instruction *NewM;
1098 if (UseMemMove)
1099 NewM = Builder.CreateMemMove(M->getRawDest(), M->getDestAlign(),
1100 MDep->getRawSource(), MDep->getSourceAlign(),
1101 M->getLength(), M->isVolatile());
1102 else
1103 NewM = Builder.CreateMemCpy(M->getRawDest(), M->getDestAlign(),
1104 MDep->getRawSource(), MDep->getSourceAlign(),
1105 M->getLength(), M->isVolatile());
1106
1107 if (MSSAU) {
1108 assert(isa<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess(M)))((isa<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess
(M))) ? static_cast<void> (0) : __assert_fail ("isa<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess(M))"
, "/build/llvm-toolchain-snapshot-12~++20210124100612+2afaf072f5c1/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp"
, 1108, __PRETTY_FUNCTION__))
;
1109 auto *LastDef = cast<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess(M));
1110 auto *NewAccess = MSSAU->createMemoryAccessAfter(NewM, LastDef, LastDef);
1111 MSSAU->insertDef(cast<MemoryDef>(NewAccess), /*RenameUses=*/true);
1112 }
1113
1114 // Remove the instruction we're replacing.
1115 eraseInstruction(M);
1116 ++NumMemCpyInstr;
1117 return true;
1118}
1119
1120/// We've found that the (upward scanning) memory dependence of \p MemCpy is
1121/// \p MemSet. Try to simplify \p MemSet to only set the trailing bytes that
1122/// weren't copied over by \p MemCpy.
1123///
1124/// In other words, transform:
1125/// \code
1126/// memset(dst, c, dst_size);
1127/// memcpy(dst, src, src_size);
1128/// \endcode
1129/// into:
1130/// \code
1131/// memcpy(dst, src, src_size);
1132/// memset(dst + src_size, c, dst_size <= src_size ? 0 : dst_size - src_size);
1133/// \endcode
1134bool MemCpyOptPass::processMemSetMemCpyDependence(MemCpyInst *MemCpy,
1135 MemSetInst *MemSet) {
1136 // We can only transform memset/memcpy with the same destination.
1137 if (MemSet->getDest() != MemCpy->getDest())
1138 return false;
1139
1140 // Check that src and dst of the memcpy aren't the same. While memcpy
1141 // operands cannot partially overlap, exact equality is allowed.
1142 if (!AA->isNoAlias(MemoryLocation(MemCpy->getSource(),
1143 LocationSize::precise(1)),
1144 MemoryLocation(MemCpy->getDest(),
1145 LocationSize::precise(1))))
1146 return false;
1147
1148 if (EnableMemorySSA) {
1149 // We know that dst up to src_size is not written. We now need to make sure
1150 // that dst up to dst_size is not accessed. (If we did not move the memset,
1151 // checking for reads would be sufficient.)
1152 if (accessedBetween(*AA, MemoryLocation::getForDest(MemSet),
1153 MSSA->getMemoryAccess(MemSet),
1154 MSSA->getMemoryAccess(MemCpy))) {
1155 return false;
1156 }
1157 } else {
1158 // We have already checked that dst up to src_size is not accessed. We
1159 // need to make sure that there are no accesses up to dst_size either.
1160 MemDepResult DstDepInfo = MD->getPointerDependencyFrom(
1161 MemoryLocation::getForDest(MemSet), false, MemCpy->getIterator(),
1162 MemCpy->getParent());
1163 if (DstDepInfo.getInst() != MemSet)
1164 return false;
1165 }
1166
1167 // Use the same i8* dest as the memcpy, killing the memset dest if different.
1168 Value *Dest = MemCpy->getRawDest();
1169 Value *DestSize = MemSet->getLength();
1170 Value *SrcSize = MemCpy->getLength();
1171
1172 if (mayBeVisibleThroughUnwinding(Dest, MemSet, MemCpy))
1173 return false;
1174
1175 // By default, create an unaligned memset.
1176 unsigned Align = 1;
1177 // If Dest is aligned, and SrcSize is constant, use the minimum alignment
1178 // of the sum.
1179 const unsigned DestAlign =
1180 std::max(MemSet->getDestAlignment(), MemCpy->getDestAlignment());
1181 if (DestAlign > 1)
1182 if (ConstantInt *SrcSizeC = dyn_cast<ConstantInt>(SrcSize))
1183 Align = MinAlign(SrcSizeC->getZExtValue(), DestAlign);
1184
1185 IRBuilder<> Builder(MemCpy);
1186
1187 // If the sizes have different types, zext the smaller one.
1188 if (DestSize->getType() != SrcSize->getType()) {
1189 if (DestSize->getType()->getIntegerBitWidth() >
1190 SrcSize->getType()->getIntegerBitWidth())
1191 SrcSize = Builder.CreateZExt(SrcSize, DestSize->getType());
1192 else
1193 DestSize = Builder.CreateZExt(DestSize, SrcSize->getType());
1194 }
1195
1196 Value *Ule = Builder.CreateICmpULE(DestSize, SrcSize);
1197 Value *SizeDiff = Builder.CreateSub(DestSize, SrcSize);
1198 Value *MemsetLen = Builder.CreateSelect(
1199 Ule, ConstantInt::getNullValue(DestSize->getType()), SizeDiff);
1200 Instruction *NewMemSet = Builder.CreateMemSet(
1201 Builder.CreateGEP(Dest->getType()->getPointerElementType(), Dest,
1202 SrcSize),
1203 MemSet->getOperand(1), MemsetLen, MaybeAlign(Align));
1204
1205 if (MSSAU) {
1206 assert(isa<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess(MemCpy)) &&((isa<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess
(MemCpy)) && "MemCpy must be a MemoryDef") ? static_cast
<void> (0) : __assert_fail ("isa<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess(MemCpy)) && \"MemCpy must be a MemoryDef\""
, "/build/llvm-toolchain-snapshot-12~++20210124100612+2afaf072f5c1/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp"
, 1207, __PRETTY_FUNCTION__))
1207 "MemCpy must be a MemoryDef")((isa<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess
(MemCpy)) && "MemCpy must be a MemoryDef") ? static_cast
<void> (0) : __assert_fail ("isa<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess(MemCpy)) && \"MemCpy must be a MemoryDef\""
, "/build/llvm-toolchain-snapshot-12~++20210124100612+2afaf072f5c1/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp"
, 1207, __PRETTY_FUNCTION__))
;
1208 // The new memset is inserted after the memcpy, but it is known that its
1209 // defining access is the memset about to be removed which immediately
1210 // precedes the memcpy.
1211 auto *LastDef =
1212 cast<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess(MemCpy));
1213 auto *NewAccess = MSSAU->createMemoryAccessBefore(
1214 NewMemSet, LastDef->getDefiningAccess(), LastDef);
1215 MSSAU->insertDef(cast<MemoryDef>(NewAccess), /*RenameUses=*/true);
1216 }
1217
1218 eraseInstruction(MemSet);
1219 return true;
1220}
1221
1222/// Determine whether the instruction has undefined content for the given Size,
1223/// either because it was freshly alloca'd or started its lifetime.
1224static bool hasUndefContents(Instruction *I, ConstantInt *Size) {
1225 if (isa<AllocaInst>(I))
1226 return true;
1227
1228 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
1229 if (II->getIntrinsicID() == Intrinsic::lifetime_start)
1230 if (ConstantInt *LTSize = dyn_cast<ConstantInt>(II->getArgOperand(0)))
1231 if (LTSize->getZExtValue() >= Size->getZExtValue())
1232 return true;
1233
1234 return false;
1235}
1236
1237static bool hasUndefContentsMSSA(MemorySSA *MSSA, AliasAnalysis *AA, Value *V,
1238 MemoryDef *Def, ConstantInt *Size) {
1239 if (MSSA->isLiveOnEntryDef(Def))
1240 return isa<AllocaInst>(getUnderlyingObject(V));
1241
1242 if (IntrinsicInst *II =
1243 dyn_cast_or_null<IntrinsicInst>(Def->getMemoryInst())) {
1244 if (II->getIntrinsicID() == Intrinsic::lifetime_start) {
1245 ConstantInt *LTSize = cast<ConstantInt>(II->getArgOperand(0));
1246 if (AA->isMustAlias(V, II->getArgOperand(1)) &&
1247 LTSize->getZExtValue() >= Size->getZExtValue())
1248 return true;
1249 }
1250 }
1251
1252 return false;
1253}
1254
1255/// Transform memcpy to memset when its source was just memset.
1256/// In other words, turn:
1257/// \code
1258/// memset(dst1, c, dst1_size);
1259/// memcpy(dst2, dst1, dst2_size);
1260/// \endcode
1261/// into:
1262/// \code
1263/// memset(dst1, c, dst1_size);
1264/// memset(dst2, c, dst2_size);
1265/// \endcode
1266/// When dst2_size <= dst1_size.
1267///
1268/// The \p MemCpy must have a Constant length.
1269bool MemCpyOptPass::performMemCpyToMemSetOptzn(MemCpyInst *MemCpy,
1270 MemSetInst *MemSet) {
1271 // Make sure that memcpy(..., memset(...), ...), that is we are memsetting and
1272 // memcpying from the same address. Otherwise it is hard to reason about.
1273 if (!AA->isMustAlias(MemSet->getRawDest(), MemCpy->getRawSource()))
1274 return false;
1275
1276 // A known memset size is required.
1277 ConstantInt *MemSetSize = dyn_cast<ConstantInt>(MemSet->getLength());
1278 if (!MemSetSize)
1279 return false;
1280
1281 // Make sure the memcpy doesn't read any more than what the memset wrote.
1282 // Don't worry about sizes larger than i64.
1283 ConstantInt *CopySize = cast<ConstantInt>(MemCpy->getLength());
1284 if (CopySize->getZExtValue() > MemSetSize->getZExtValue()) {
1285 // If the memcpy is larger than the memset, but the memory was undef prior
1286 // to the memset, we can just ignore the tail. Technically we're only
1287 // interested in the bytes from MemSetSize..CopySize here, but as we can't
1288 // easily represent this location, we use the full 0..CopySize range.
1289 MemoryLocation MemCpyLoc = MemoryLocation::getForSource(MemCpy);
1290 bool CanReduceSize = false;
1291 if (EnableMemorySSA) {
1292 MemoryUseOrDef *MemSetAccess = MSSA->getMemoryAccess(MemSet);
1293 MemoryAccess *Clobber = MSSA->getWalker()->getClobberingMemoryAccess(
1294 MemSetAccess->getDefiningAccess(), MemCpyLoc);
1295 if (auto *MD = dyn_cast<MemoryDef>(Clobber))
1296 if (hasUndefContentsMSSA(MSSA, AA, MemCpy->getSource(), MD, CopySize))
1297 CanReduceSize = true;
1298 } else {
1299 MemDepResult DepInfo = MD->getPointerDependencyFrom(
1300 MemCpyLoc, true, MemSet->getIterator(), MemSet->getParent());
1301 if (DepInfo.isDef() && hasUndefContents(DepInfo.getInst(), CopySize))
1302 CanReduceSize = true;
1303 }
1304
1305 if (!CanReduceSize)
1306 return false;
1307 CopySize = MemSetSize;
1308 }
1309
1310 IRBuilder<> Builder(MemCpy);
1311 Instruction *NewM =
1312 Builder.CreateMemSet(MemCpy->getRawDest(), MemSet->getOperand(1),
1313 CopySize, MaybeAlign(MemCpy->getDestAlignment()));
1314 if (MSSAU) {
1315 auto *LastDef =
1316 cast<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess(MemCpy));
1317 auto *NewAccess = MSSAU->createMemoryAccessAfter(NewM, LastDef, LastDef);
1318 MSSAU->insertDef(cast<MemoryDef>(NewAccess), /*RenameUses=*/true);
1319 }
1320
1321 return true;
1322}
1323
1324/// Perform simplification of memcpy's. If we have memcpy A
1325/// which copies X to Y, and memcpy B which copies Y to Z, then we can rewrite
1326/// B to be a memcpy from X to Z (or potentially a memmove, depending on
1327/// circumstances). This allows later passes to remove the first memcpy
1328/// altogether.
1329bool MemCpyOptPass::processMemCpy(MemCpyInst *M, BasicBlock::iterator &BBI) {
1330 // We can only optimize non-volatile memcpy's.
1331 if (M->isVolatile()) return false;
1332
1333 // If the source and destination of the memcpy are the same, then zap it.
1334 if (M->getSource() == M->getDest()) {
1335 ++BBI;
1336 eraseInstruction(M);
1337 return true;
1338 }
1339
1340 // If copying from a constant, try to turn the memcpy into a memset.
1341 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(M->getSource()))
1342 if (GV->isConstant() && GV->hasDefinitiveInitializer())
1343 if (Value *ByteVal = isBytewiseValue(GV->getInitializer(),
1344 M->getModule()->getDataLayout())) {
1345 IRBuilder<> Builder(M);
1346 Instruction *NewM =
1347 Builder.CreateMemSet(M->getRawDest(), ByteVal, M->getLength(),
1348 MaybeAlign(M->getDestAlignment()), false);
1349 if (MSSAU) {
1350 auto *LastDef =
1351 cast<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess(M));
1352 auto *NewAccess =
1353 MSSAU->createMemoryAccessAfter(NewM, LastDef, LastDef);
1354 MSSAU->insertDef(cast<MemoryDef>(NewAccess), /*RenameUses=*/true);
1355 }
1356
1357 eraseInstruction(M);
1358 ++NumCpyToSet;
1359 return true;
1360 }
1361
1362 if (EnableMemorySSA) {
1363 MemoryUseOrDef *MA = MSSA->getMemoryAccess(M);
1364 MemoryAccess *AnyClobber = MSSA->getWalker()->getClobberingMemoryAccess(MA);
1365 MemoryLocation DestLoc = MemoryLocation::getForDest(M);
1366 const MemoryAccess *DestClobber =
1367 MSSA->getWalker()->getClobberingMemoryAccess(AnyClobber, DestLoc);
1368
1369 // Try to turn a partially redundant memset + memcpy into
1370 // memcpy + smaller memset. We don't need the memcpy size for this.
1371 // The memcpy most post-dom the memset, so limit this to the same basic
1372 // block. A non-local generalization is likely not worthwhile.
1373 if (auto *MD = dyn_cast<MemoryDef>(DestClobber))
1374 if (auto *MDep = dyn_cast_or_null<MemSetInst>(MD->getMemoryInst()))
1375 if (DestClobber->getBlock() == M->getParent())
1376 if (processMemSetMemCpyDependence(M, MDep))
1377 return true;
1378
1379 // The optimizations after this point require the memcpy size.
1380 ConstantInt *CopySize = dyn_cast<ConstantInt>(M->getLength());
1381 if (!CopySize) return false;
1382
1383 MemoryAccess *SrcClobber = MSSA->getWalker()->getClobberingMemoryAccess(
1384 AnyClobber, MemoryLocation::getForSource(M));
1385
1386 // There are four possible optimizations we can do for memcpy:
1387 // a) memcpy-memcpy xform which exposes redundance for DSE.
1388 // b) call-memcpy xform for return slot optimization.
1389 // c) memcpy from freshly alloca'd space or space that has just started
1390 // its lifetime copies undefined data, and we can therefore eliminate
1391 // the memcpy in favor of the data that was already at the destination.
1392 // d) memcpy from a just-memset'd source can be turned into memset.
1393 if (auto *MD = dyn_cast<MemoryDef>(SrcClobber)) {
1394 if (Instruction *MI = MD->getMemoryInst()) {
1395 if (auto *C = dyn_cast<CallInst>(MI)) {
1396 // The memcpy must post-dom the call. Limit to the same block for now.
1397 // Additionally, we need to ensure that there are no accesses to dest
1398 // between the call and the memcpy. Accesses to src will be checked
1399 // by performCallSlotOptzn().
1400 // TODO: Support non-local call-slot optimization?
1401 if (C->getParent() == M->getParent() &&
1402 !accessedBetween(*AA, DestLoc, MD, MA)) {
1403 // FIXME: Can we pass in either of dest/src alignment here instead
1404 // of conservatively taking the minimum?
1405 Align Alignment = std::min(M->getDestAlign().valueOrOne(),
1406 M->getSourceAlign().valueOrOne());
1407 if (performCallSlotOptzn(M, M, M->getDest(), M->getSource(),
1408 CopySize->getZExtValue(), Alignment, C)) {
1409 LLVM_DEBUG(dbgs() << "Performed call slot optimization:\n"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("memcpyopt")) { dbgs() << "Performed call slot optimization:\n"
<< " call: " << *C << "\n" << " memcpy: "
<< *M << "\n"; } } while (false)
1410 << " call: " << *C << "\n"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("memcpyopt")) { dbgs() << "Performed call slot optimization:\n"
<< " call: " << *C << "\n" << " memcpy: "
<< *M << "\n"; } } while (false)
1411 << " memcpy: " << *M << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("memcpyopt")) { dbgs() << "Performed call slot optimization:\n"
<< " call: " << *C << "\n" << " memcpy: "
<< *M << "\n"; } } while (false)
;
1412 eraseInstruction(M);
1413 ++NumMemCpyInstr;
1414 return true;
1415 }
1416 }
1417 }
1418 if (auto *MDep = dyn_cast<MemCpyInst>(MI))
1419 return processMemCpyMemCpyDependence(M, MDep);
1420 if (auto *MDep = dyn_cast<MemSetInst>(MI)) {
1421 if (performMemCpyToMemSetOptzn(M, MDep)) {
1422 LLVM_DEBUG(dbgs() << "Converted memcpy to memset\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("memcpyopt")) { dbgs() << "Converted memcpy to memset\n"
; } } while (false)
;
1423 eraseInstruction(M);
1424 ++NumCpyToSet;
1425 return true;
1426 }
1427 }
1428 }
1429
1430 if (hasUndefContentsMSSA(MSSA, AA, M->getSource(), MD, CopySize)) {
1431 LLVM_DEBUG(dbgs() << "Removed memcpy from undef\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("memcpyopt")) { dbgs() << "Removed memcpy from undef\n"
; } } while (false)
;
1432 eraseInstruction(M);
1433 ++NumMemCpyInstr;
1434 return true;
1435 }
1436 }
1437 } else {
1438 MemDepResult DepInfo = MD->getDependency(M);
1439
1440 // Try to turn a partially redundant memset + memcpy into
1441 // memcpy + smaller memset. We don't need the memcpy size for this.
1442 if (DepInfo.isClobber())
1443 if (MemSetInst *MDep = dyn_cast<MemSetInst>(DepInfo.getInst()))
1444 if (processMemSetMemCpyDependence(M, MDep))
1445 return true;
1446
1447 // The optimizations after this point require the memcpy size.
1448 ConstantInt *CopySize = dyn_cast<ConstantInt>(M->getLength());
1449 if (!CopySize) return false;
1450
1451 // There are four possible optimizations we can do for memcpy:
1452 // a) memcpy-memcpy xform which exposes redundance for DSE.
1453 // b) call-memcpy xform for return slot optimization.
1454 // c) memcpy from freshly alloca'd space or space that has just started
1455 // its lifetime copies undefined data, and we can therefore eliminate
1456 // the memcpy in favor of the data that was already at the destination.
1457 // d) memcpy from a just-memset'd source can be turned into memset.
1458 if (DepInfo.isClobber()) {
1459 if (CallInst *C = dyn_cast<CallInst>(DepInfo.getInst())) {
1460 // FIXME: Can we pass in either of dest/src alignment here instead
1461 // of conservatively taking the minimum?
1462 Align Alignment = std::min(M->getDestAlign().valueOrOne(),
1463 M->getSourceAlign().valueOrOne());
1464 if (performCallSlotOptzn(M, M, M->getDest(), M->getSource(),
1465 CopySize->getZExtValue(), Alignment, C)) {
1466 eraseInstruction(M);
1467 ++NumMemCpyInstr;
1468 return true;
1469 }
1470 }
1471 }
1472
1473 MemoryLocation SrcLoc = MemoryLocation::getForSource(M);
1474 MemDepResult SrcDepInfo = MD->getPointerDependencyFrom(
1475 SrcLoc, true, M->getIterator(), M->getParent());
1476
1477 if (SrcDepInfo.isClobber()) {
1478 if (MemCpyInst *MDep = dyn_cast<MemCpyInst>(SrcDepInfo.getInst()))
1479 return processMemCpyMemCpyDependence(M, MDep);
1480 } else if (SrcDepInfo.isDef()) {
1481 if (hasUndefContents(SrcDepInfo.getInst(), CopySize)) {
1482 eraseInstruction(M);
1483 ++NumMemCpyInstr;
1484 return true;
1485 }
1486 }
1487
1488 if (SrcDepInfo.isClobber())
1489 if (MemSetInst *MDep = dyn_cast<MemSetInst>(SrcDepInfo.getInst()))
1490 if (performMemCpyToMemSetOptzn(M, MDep)) {
1491 eraseInstruction(M);
1492 ++NumCpyToSet;
1493 return true;
1494 }
1495 }
1496
1497 return false;
1498}
1499
1500/// Transforms memmove calls to memcpy calls when the src/dst are guaranteed
1501/// not to alias.
1502bool MemCpyOptPass::processMemMove(MemMoveInst *M) {
1503 if (!TLI->has(LibFunc_memmove))
1504 return false;
1505
1506 // See if the pointers alias.
1507 if (!AA->isNoAlias(MemoryLocation::getForDest(M),
1508 MemoryLocation::getForSource(M)))
1509 return false;
1510
1511 LLVM_DEBUG(dbgs() << "MemCpyOptPass: Optimizing memmove -> memcpy: " << *Mdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("memcpyopt")) { dbgs() << "MemCpyOptPass: Optimizing memmove -> memcpy: "
<< *M << "\n"; } } while (false)
1512 << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("memcpyopt")) { dbgs() << "MemCpyOptPass: Optimizing memmove -> memcpy: "
<< *M << "\n"; } } while (false)
;
1513
1514 // If not, then we know we can transform this.
1515 Type *ArgTys[3] = { M->getRawDest()->getType(),
1516 M->getRawSource()->getType(),
1517 M->getLength()->getType() };
1518 M->setCalledFunction(Intrinsic::getDeclaration(M->getModule(),
1519 Intrinsic::memcpy, ArgTys));
1520
1521 // For MemorySSA nothing really changes (except that memcpy may imply stricter
1522 // aliasing guarantees).
1523
1524 // MemDep may have over conservative information about this instruction, just
1525 // conservatively flush it from the cache.
1526 if (MD)
1527 MD->removeInstruction(M);
1528
1529 ++NumMoveToCpy;
1530 return true;
1531}
1532
1533/// This is called on every byval argument in call sites.
1534bool MemCpyOptPass::processByValArgument(CallBase &CB, unsigned ArgNo) {
1535 const DataLayout &DL = CB.getCaller()->getParent()->getDataLayout();
1536 // Find out what feeds this byval argument.
1537 Value *ByValArg = CB.getArgOperand(ArgNo);
1538 Type *ByValTy = cast<PointerType>(ByValArg->getType())->getElementType();
35
The object is a 'PointerType'
1539 uint64_t ByValSize = DL.getTypeAllocSize(ByValTy);
1540 MemoryLocation Loc(ByValArg, LocationSize::precise(ByValSize));
1541 MemCpyInst *MDep = nullptr;
1542 if (EnableMemorySSA) {
36
Assuming the condition is true
37
Taking true branch
1543 MemoryUseOrDef *CallAccess = MSSA->getMemoryAccess(&CB);
38
Called C++ object pointer is null
1544 MemoryAccess *Clobber = MSSA->getWalker()->getClobberingMemoryAccess(
1545 CallAccess->getDefiningAccess(), Loc);
1546 if (auto *MD = dyn_cast<MemoryDef>(Clobber))
1547 MDep = dyn_cast_or_null<MemCpyInst>(MD->getMemoryInst());
1548 } else {
1549 MemDepResult DepInfo = MD->getPointerDependencyFrom(
1550 Loc, true, CB.getIterator(), CB.getParent());
1551 if (!DepInfo.isClobber())
1552 return false;
1553 MDep = dyn_cast<MemCpyInst>(DepInfo.getInst());
1554 }
1555
1556 // If the byval argument isn't fed by a memcpy, ignore it. If it is fed by
1557 // a memcpy, see if we can byval from the source of the memcpy instead of the
1558 // result.
1559 if (!MDep || MDep->isVolatile() ||
1560 ByValArg->stripPointerCasts() != MDep->getDest())
1561 return false;
1562
1563 // The length of the memcpy must be larger or equal to the size of the byval.
1564 ConstantInt *C1 = dyn_cast<ConstantInt>(MDep->getLength());
1565 if (!C1 || C1->getValue().getZExtValue() < ByValSize)
1566 return false;
1567
1568 // Get the alignment of the byval. If the call doesn't specify the alignment,
1569 // then it is some target specific value that we can't know.
1570 MaybeAlign ByValAlign = CB.getParamAlign(ArgNo);
1571 if (!ByValAlign) return false;
1572
1573 // If it is greater than the memcpy, then we check to see if we can force the
1574 // source of the memcpy to the alignment we need. If we fail, we bail out.
1575 MaybeAlign MemDepAlign = MDep->getSourceAlign();
1576 if ((!MemDepAlign || *MemDepAlign < *ByValAlign) &&
1577 getOrEnforceKnownAlignment(MDep->getSource(), ByValAlign, DL, &CB, AC,
1578 DT) < *ByValAlign)
1579 return false;
1580
1581 // The address space of the memcpy source must match the byval argument
1582 if (MDep->getSource()->getType()->getPointerAddressSpace() !=
1583 ByValArg->getType()->getPointerAddressSpace())
1584 return false;
1585
1586 // Verify that the copied-from memory doesn't change in between the memcpy and
1587 // the byval call.
1588 // memcpy(a <- b)
1589 // *b = 42;
1590 // foo(*a)
1591 // It would be invalid to transform the second memcpy into foo(*b).
1592 if (EnableMemorySSA) {
1593 if (writtenBetween(MSSA, MemoryLocation::getForSource(MDep),
1594 MSSA->getMemoryAccess(MDep), MSSA->getMemoryAccess(&CB)))
1595 return false;
1596 } else {
1597 // NOTE: This is conservative, it will stop on any read from the source loc,
1598 // not just the defining memcpy.
1599 MemDepResult SourceDep = MD->getPointerDependencyFrom(
1600 MemoryLocation::getForSource(MDep), false,
1601 CB.getIterator(), MDep->getParent());
1602 if (!SourceDep.isClobber() || SourceDep.getInst() != MDep)
1603 return false;
1604 }
1605
1606 Value *TmpCast = MDep->getSource();
1607 if (MDep->getSource()->getType() != ByValArg->getType()) {
1608 BitCastInst *TmpBitCast = new BitCastInst(MDep->getSource(), ByValArg->getType(),
1609 "tmpcast", &CB);
1610 // Set the tmpcast's DebugLoc to MDep's
1611 TmpBitCast->setDebugLoc(MDep->getDebugLoc());
1612 TmpCast = TmpBitCast;
1613 }
1614
1615 LLVM_DEBUG(dbgs() << "MemCpyOptPass: Forwarding memcpy to byval:\n"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("memcpyopt")) { dbgs() << "MemCpyOptPass: Forwarding memcpy to byval:\n"
<< " " << *MDep << "\n" << " " <<
CB << "\n"; } } while (false)
1616 << " " << *MDep << "\n"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("memcpyopt")) { dbgs() << "MemCpyOptPass: Forwarding memcpy to byval:\n"
<< " " << *MDep << "\n" << " " <<
CB << "\n"; } } while (false)
1617 << " " << CB << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("memcpyopt")) { dbgs() << "MemCpyOptPass: Forwarding memcpy to byval:\n"
<< " " << *MDep << "\n" << " " <<
CB << "\n"; } } while (false)
;
1618
1619 // Otherwise we're good! Update the byval argument.
1620 CB.setArgOperand(ArgNo, TmpCast);
1621 ++NumMemCpyInstr;
1622 return true;
1623}
1624
1625/// Executes one iteration of MemCpyOptPass.
1626bool MemCpyOptPass::iterateOnFunction(Function &F) {
1627 bool MadeChange = false;
1628
1629 // Walk all instruction in the function.
1630 for (BasicBlock &BB : F) {
1631 // Skip unreachable blocks. For example processStore assumes that an
1632 // instruction in a BB can't be dominated by a later instruction in the
1633 // same BB (which is a scenario that can happen for an unreachable BB that
1634 // has itself as a predecessor).
1635 if (!DT->isReachableFromEntry(&BB))
17
Assuming the condition is false
18
Taking false branch
1636 continue;
1637
1638 for (BasicBlock::iterator BI = BB.begin(), BE = BB.end(); BI != BE;) {
19
Loop condition is true. Entering loop body
1639 // Avoid invalidating the iterator.
1640 Instruction *I = &*BI++;
1641
1642 bool RepeatInstruction = false;
1643
1644 if (StoreInst *SI
20.1
'SI' is null
= dyn_cast<StoreInst>(I))
20
Assuming 'I' is not a 'StoreInst'
21
Taking false branch
1645 MadeChange |= processStore(SI, BI);
1646 else if (MemSetInst *M
22.1
'M' is null
= dyn_cast<MemSetInst>(I))
22
Assuming 'I' is not a 'MemSetInst'
23
Taking false branch
1647 RepeatInstruction = processMemSet(M, BI);
1648 else if (MemCpyInst *M
24.1
'M' is null
= dyn_cast<MemCpyInst>(I))
24
Assuming 'I' is not a 'MemCpyInst'
25
Taking false branch
1649 RepeatInstruction = processMemCpy(M, BI);
1650 else if (MemMoveInst *M
26.1
'M' is null
= dyn_cast<MemMoveInst>(I))
26
Assuming 'I' is not a 'MemMoveInst'
27
Taking false branch
1651 RepeatInstruction = processMemMove(M);
1652 else if (auto *CB
28.1
'CB' is non-null
= dyn_cast<CallBase>(I)) {
28
Assuming 'I' is a 'CallBase'
29
Taking true branch
1653 for (unsigned i = 0, e = CB->arg_size(); i != e; ++i)
30
Assuming 'i' is not equal to 'e'
31
Loop condition is true. Entering loop body
1654 if (CB->isByValArgument(i))
32
Assuming the condition is true
33
Taking true branch
1655 MadeChange |= processByValArgument(*CB, i);
34
Calling 'MemCpyOptPass::processByValArgument'
1656 }
1657
1658 // Reprocess the instruction if desired.
1659 if (RepeatInstruction) {
1660 if (BI != BB.begin())
1661 --BI;
1662 MadeChange = true;
1663 }
1664 }
1665 }
1666
1667 return MadeChange;
1668}
1669
1670PreservedAnalyses MemCpyOptPass::run(Function &F, FunctionAnalysisManager &AM) {
1671 auto *MD = !EnableMemorySSA ? &AM.getResult<MemoryDependenceAnalysis>(F)
1672 : AM.getCachedResult<MemoryDependenceAnalysis>(F);
1673 auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
1674 auto *AA = &AM.getResult<AAManager>(F);
1675 auto *AC = &AM.getResult<AssumptionAnalysis>(F);
1676 auto *DT = &AM.getResult<DominatorTreeAnalysis>(F);
1677 auto *MSSA = EnableMemorySSA ? &AM.getResult<MemorySSAAnalysis>(F)
1678 : AM.getCachedResult<MemorySSAAnalysis>(F);
1679
1680 bool MadeChange =
1681 runImpl(F, MD, &TLI, AA, AC, DT, MSSA ? &MSSA->getMSSA() : nullptr);
1682 if (!MadeChange)
1683 return PreservedAnalyses::all();
1684
1685 PreservedAnalyses PA;
1686 PA.preserveSet<CFGAnalyses>();
1687 PA.preserve<GlobalsAA>();
1688 if (MD)
1689 PA.preserve<MemoryDependenceAnalysis>();
1690 if (MSSA)
1691 PA.preserve<MemorySSAAnalysis>();
1692 return PA;
1693}
1694
1695bool MemCpyOptPass::runImpl(Function &F, MemoryDependenceResults *MD_,
1696 TargetLibraryInfo *TLI_, AliasAnalysis *AA_,
1697 AssumptionCache *AC_, DominatorTree *DT_,
1698 MemorySSA *MSSA_) {
1699 bool MadeChange = false;
1700 MD = MD_;
1701 TLI = TLI_;
1702 AA = AA_;
1703 AC = AC_;
1704 DT = DT_;
1705 MSSA = MSSA_;
12
Null pointer value stored to field 'MSSA'
1706 MemorySSAUpdater MSSAU_(MSSA_);
1707 MSSAU = MSSA_
12.1
'MSSA_' is null
? &MSSAU_ : nullptr;
13
'?' condition is false
1708 // If we don't have at least memset and memcpy, there is little point of doing
1709 // anything here. These are required by a freestanding implementation, so if
1710 // even they are disabled, there is no point in trying hard.
1711 if (!TLI->has(LibFunc_memset) || !TLI->has(LibFunc_memcpy))
14
Taking false branch
1712 return false;
1713
1714 while (true) {
15
Loop condition is true. Entering loop body
1715 if (!iterateOnFunction(F))
16
Calling 'MemCpyOptPass::iterateOnFunction'
1716 break;
1717 MadeChange = true;
1718 }
1719
1720 if (MSSA_ && VerifyMemorySSA)
1721 MSSA_->verifyMemorySSA();
1722
1723 MD = nullptr;
1724 return MadeChange;
1725}
1726
1727/// This is the main transformation entry point for a function.
1728bool MemCpyOptLegacyPass::runOnFunction(Function &F) {
1729 if (skipFunction(F))
1
Assuming the condition is false
2
Taking false branch
1730 return false;
1731
1732 auto *MDWP = !EnableMemorySSA
3
Assuming the condition is false
4
'?' condition is false
1733 ? &getAnalysis<MemoryDependenceWrapperPass>()
1734 : getAnalysisIfAvailable<MemoryDependenceWrapperPass>();
1735 auto *TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F);
1736 auto *AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
1737 auto *AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
1738 auto *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
1739 auto *MSSAWP = EnableMemorySSA
5
Assuming the condition is false
6
'?' condition is false
1740 ? &getAnalysis<MemorySSAWrapperPass>()
1741 : getAnalysisIfAvailable<MemorySSAWrapperPass>();
1742
1743 return Impl.runImpl(F, MDWP ? & MDWP->getMemDep() : nullptr, TLI, AA, AC, DT,
7
Assuming 'MDWP' is null
8
'?' condition is false
11
Calling 'MemCpyOptPass::runImpl'
1744 MSSAWP
8.1
'MSSAWP' is null
? &MSSAWP->getMSSA() : nullptr)
;
9
'?' condition is false
10
Passing null pointer value via 7th parameter 'MSSA_'
1745}