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Diffstat (limited to 'contrib/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp')
| -rw-r--r-- | contrib/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp | 1533 |
1 files changed, 0 insertions, 1533 deletions
diff --git a/contrib/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp b/contrib/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp deleted file mode 100644 index 5a055139be4f..000000000000 --- a/contrib/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp +++ /dev/null @@ -1,1533 +0,0 @@ -//===- MemCpyOptimizer.cpp - Optimize use of memcpy and friends -----------===// -// -// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. -// See https://llvm.org/LICENSE.txt for license information. -// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception -// -//===----------------------------------------------------------------------===// -// -// This pass performs various transformations related to eliminating memcpy -// calls, or transforming sets of stores into memset's. -// -//===----------------------------------------------------------------------===// - -#include "llvm/Transforms/Scalar/MemCpyOptimizer.h" -#include "llvm/ADT/DenseSet.h" -#include "llvm/ADT/None.h" -#include "llvm/ADT/STLExtras.h" -#include "llvm/ADT/SmallVector.h" -#include "llvm/ADT/Statistic.h" -#include "llvm/ADT/iterator_range.h" -#include "llvm/Analysis/AliasAnalysis.h" -#include "llvm/Analysis/AssumptionCache.h" -#include "llvm/Analysis/GlobalsModRef.h" -#include "llvm/Analysis/MemoryDependenceAnalysis.h" -#include "llvm/Analysis/MemoryLocation.h" -#include "llvm/Analysis/TargetLibraryInfo.h" -#include "llvm/Transforms/Utils/Local.h" -#include "llvm/Analysis/ValueTracking.h" -#include "llvm/IR/Argument.h" -#include "llvm/IR/BasicBlock.h" -#include "llvm/IR/CallSite.h" -#include "llvm/IR/Constants.h" -#include "llvm/IR/DataLayout.h" -#include "llvm/IR/DerivedTypes.h" -#include "llvm/IR/Dominators.h" -#include "llvm/IR/Function.h" -#include "llvm/IR/GetElementPtrTypeIterator.h" -#include "llvm/IR/GlobalVariable.h" -#include "llvm/IR/IRBuilder.h" -#include "llvm/IR/InstrTypes.h" -#include "llvm/IR/Instruction.h" -#include "llvm/IR/Instructions.h" -#include "llvm/IR/IntrinsicInst.h" -#include "llvm/IR/Intrinsics.h" -#include "llvm/IR/LLVMContext.h" -#include "llvm/IR/Module.h" -#include "llvm/IR/Operator.h" -#include "llvm/IR/PassManager.h" -#include "llvm/IR/Type.h" -#include "llvm/IR/User.h" -#include "llvm/IR/Value.h" -#include "llvm/Pass.h" -#include "llvm/Support/Casting.h" -#include "llvm/Support/Debug.h" -#include "llvm/Support/MathExtras.h" -#include "llvm/Support/raw_ostream.h" -#include "llvm/Transforms/Scalar.h" -#include <algorithm> -#include <cassert> -#include <cstdint> -#include <utility> - -using namespace llvm; - -#define DEBUG_TYPE "memcpyopt" - -STATISTIC(NumMemCpyInstr, "Number of memcpy instructions deleted"); -STATISTIC(NumMemSetInfer, "Number of memsets inferred"); -STATISTIC(NumMoveToCpy, "Number of memmoves converted to memcpy"); -STATISTIC(NumCpyToSet, "Number of memcpys converted to memset"); - -static int64_t GetOffsetFromIndex(const GEPOperator *GEP, unsigned Idx, - bool &VariableIdxFound, - const DataLayout &DL) { - // Skip over the first indices. - gep_type_iterator GTI = gep_type_begin(GEP); - for (unsigned i = 1; i != Idx; ++i, ++GTI) - /*skip along*/; - - // Compute the offset implied by the rest of the indices. - int64_t Offset = 0; - for (unsigned i = Idx, e = GEP->getNumOperands(); i != e; ++i, ++GTI) { - ConstantInt *OpC = dyn_cast<ConstantInt>(GEP->getOperand(i)); - if (!OpC) - return VariableIdxFound = true; - if (OpC->isZero()) continue; // No offset. - - // Handle struct indices, which add their field offset to the pointer. - if (StructType *STy = GTI.getStructTypeOrNull()) { - Offset += DL.getStructLayout(STy)->getElementOffset(OpC->getZExtValue()); - continue; - } - - // Otherwise, we have a sequential type like an array or vector. Multiply - // the index by the ElementSize. - uint64_t Size = DL.getTypeAllocSize(GTI.getIndexedType()); - Offset += Size*OpC->getSExtValue(); - } - - return Offset; -} - -/// Return true if Ptr1 is provably equal to Ptr2 plus a constant offset, and -/// return that constant offset. For example, Ptr1 might be &A[42], and Ptr2 -/// might be &A[40]. In this case offset would be -8. -static bool IsPointerOffset(Value *Ptr1, Value *Ptr2, int64_t &Offset, - const DataLayout &DL) { - Ptr1 = Ptr1->stripPointerCasts(); - Ptr2 = Ptr2->stripPointerCasts(); - - // Handle the trivial case first. - if (Ptr1 == Ptr2) { - Offset = 0; - return true; - } - - GEPOperator *GEP1 = dyn_cast<GEPOperator>(Ptr1); - GEPOperator *GEP2 = dyn_cast<GEPOperator>(Ptr2); - - bool VariableIdxFound = false; - - // If one pointer is a GEP and the other isn't, then see if the GEP is a - // constant offset from the base, as in "P" and "gep P, 1". - if (GEP1 && !GEP2 && GEP1->getOperand(0)->stripPointerCasts() == Ptr2) { - Offset = -GetOffsetFromIndex(GEP1, 1, VariableIdxFound, DL); - return !VariableIdxFound; - } - - if (GEP2 && !GEP1 && GEP2->getOperand(0)->stripPointerCasts() == Ptr1) { - Offset = GetOffsetFromIndex(GEP2, 1, VariableIdxFound, DL); - return !VariableIdxFound; - } - - // Right now we handle the case when Ptr1/Ptr2 are both GEPs with an identical - // base. After that base, they may have some number of common (and - // potentially variable) indices. After that they handle some constant - // offset, which determines their offset from each other. At this point, we - // handle no other case. - if (!GEP1 || !GEP2 || GEP1->getOperand(0) != GEP2->getOperand(0)) - return false; - - // Skip any common indices and track the GEP types. - unsigned Idx = 1; - for (; Idx != GEP1->getNumOperands() && Idx != GEP2->getNumOperands(); ++Idx) - if (GEP1->getOperand(Idx) != GEP2->getOperand(Idx)) - break; - - int64_t Offset1 = GetOffsetFromIndex(GEP1, Idx, VariableIdxFound, DL); - int64_t Offset2 = GetOffsetFromIndex(GEP2, Idx, VariableIdxFound, DL); - if (VariableIdxFound) return false; - - Offset = Offset2-Offset1; - return true; -} - -namespace { - -/// Represents a range of memset'd bytes with the ByteVal value. -/// This allows us to analyze stores like: -/// store 0 -> P+1 -/// store 0 -> P+0 -/// store 0 -> P+3 -/// store 0 -> P+2 -/// which sometimes happens with stores to arrays of structs etc. When we see -/// the first store, we make a range [1, 2). The second store extends the range -/// to [0, 2). The third makes a new range [2, 3). The fourth store joins the -/// two ranges into [0, 3) which is memset'able. -struct MemsetRange { - // Start/End - A semi range that describes the span that this range covers. - // The range is closed at the start and open at the end: [Start, End). - int64_t Start, End; - - /// StartPtr - The getelementptr instruction that points to the start of the - /// range. - Value *StartPtr; - - /// Alignment - The known alignment of the first store. - unsigned Alignment; - - /// TheStores - The actual stores that make up this range. - SmallVector<Instruction*, 16> TheStores; - - bool isProfitableToUseMemset(const DataLayout &DL) const; -}; - -} // end anonymous namespace - -bool MemsetRange::isProfitableToUseMemset(const DataLayout &DL) const { - // If we found more than 4 stores to merge or 16 bytes, use memset. - if (TheStores.size() >= 4 || End-Start >= 16) return true; - - // If there is nothing to merge, don't do anything. - if (TheStores.size() < 2) return false; - - // If any of the stores are a memset, then it is always good to extend the - // memset. - for (Instruction *SI : TheStores) - if (!isa<StoreInst>(SI)) - return true; - - // Assume that the code generator is capable of merging pairs of stores - // together if it wants to. - if (TheStores.size() == 2) return false; - - // If we have fewer than 8 stores, it can still be worthwhile to do this. - // For example, merging 4 i8 stores into an i32 store is useful almost always. - // However, merging 2 32-bit stores isn't useful on a 32-bit architecture (the - // memset will be split into 2 32-bit stores anyway) and doing so can - // pessimize the llvm optimizer. - // - // Since we don't have perfect knowledge here, make some assumptions: assume - // the maximum GPR width is the same size as the largest legal integer - // size. If so, check to see whether we will end up actually reducing the - // number of stores used. - unsigned Bytes = unsigned(End-Start); - unsigned MaxIntSize = DL.getLargestLegalIntTypeSizeInBits() / 8; - if (MaxIntSize == 0) - MaxIntSize = 1; - unsigned NumPointerStores = Bytes / MaxIntSize; - - // Assume the remaining bytes if any are done a byte at a time. - unsigned NumByteStores = Bytes % MaxIntSize; - - // If we will reduce the # stores (according to this heuristic), do the - // transformation. This encourages merging 4 x i8 -> i32 and 2 x i16 -> i32 - // etc. - return TheStores.size() > NumPointerStores+NumByteStores; -} - -namespace { - -class MemsetRanges { - using range_iterator = SmallVectorImpl<MemsetRange>::iterator; - - /// A sorted list of the memset ranges. - SmallVector<MemsetRange, 8> Ranges; - - const DataLayout &DL; - -public: - MemsetRanges(const DataLayout &DL) : DL(DL) {} - - using const_iterator = SmallVectorImpl<MemsetRange>::const_iterator; - - const_iterator begin() const { return Ranges.begin(); } - const_iterator end() const { return Ranges.end(); } - bool empty() const { return Ranges.empty(); } - - void addInst(int64_t OffsetFromFirst, Instruction *Inst) { - if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) - addStore(OffsetFromFirst, SI); - else - addMemSet(OffsetFromFirst, cast<MemSetInst>(Inst)); - } - - void addStore(int64_t OffsetFromFirst, StoreInst *SI) { - int64_t StoreSize = DL.getTypeStoreSize(SI->getOperand(0)->getType()); - - addRange(OffsetFromFirst, StoreSize, - SI->getPointerOperand(), SI->getAlignment(), SI); - } - - void addMemSet(int64_t OffsetFromFirst, MemSetInst *MSI) { - int64_t Size = cast<ConstantInt>(MSI->getLength())->getZExtValue(); - addRange(OffsetFromFirst, Size, MSI->getDest(), MSI->getDestAlignment(), MSI); - } - - void addRange(int64_t Start, int64_t Size, Value *Ptr, - unsigned Alignment, Instruction *Inst); -}; - -} // end anonymous namespace - -/// Add a new store to the MemsetRanges data structure. This adds a -/// new range for the specified store at the specified offset, merging into -/// existing ranges as appropriate. -void MemsetRanges::addRange(int64_t Start, int64_t Size, Value *Ptr, - unsigned Alignment, Instruction *Inst) { - int64_t End = Start+Size; - - range_iterator I = partition_point( - Ranges, [=](const MemsetRange &O) { return O.End < Start; }); - - // We now know that I == E, in which case we didn't find anything to merge - // with, or that Start <= I->End. If End < I->Start or I == E, then we need - // to insert a new range. Handle this now. - if (I == Ranges.end() || End < I->Start) { - MemsetRange &R = *Ranges.insert(I, MemsetRange()); - R.Start = Start; - R.End = End; - R.StartPtr = Ptr; - R.Alignment = Alignment; - R.TheStores.push_back(Inst); - return; - } - - // This store overlaps with I, add it. - I->TheStores.push_back(Inst); - - // At this point, we may have an interval that completely contains our store. - // If so, just add it to the interval and return. - if (I->Start <= Start && I->End >= End) - return; - - // Now we know that Start <= I->End and End >= I->Start so the range overlaps - // but is not entirely contained within the range. - - // See if the range extends the start of the range. In this case, it couldn't - // possibly cause it to join the prior range, because otherwise we would have - // stopped on *it*. - if (Start < I->Start) { - I->Start = Start; - I->StartPtr = Ptr; - I->Alignment = Alignment; - } - - // Now we know that Start <= I->End and Start >= I->Start (so the startpoint - // is in or right at the end of I), and that End >= I->Start. Extend I out to - // End. - if (End > I->End) { - I->End = End; - range_iterator NextI = I; - while (++NextI != Ranges.end() && End >= NextI->Start) { - // Merge the range in. - I->TheStores.append(NextI->TheStores.begin(), NextI->TheStores.end()); - if (NextI->End > I->End) - I->End = NextI->End; - Ranges.erase(NextI); - NextI = I; - } - } -} - -//===----------------------------------------------------------------------===// -// MemCpyOptLegacyPass Pass -//===----------------------------------------------------------------------===// - -namespace { - -class MemCpyOptLegacyPass : public FunctionPass { - MemCpyOptPass Impl; - -public: - static char ID; // Pass identification, replacement for typeid - - MemCpyOptLegacyPass() : FunctionPass(ID) { - initializeMemCpyOptLegacyPassPass(*PassRegistry::getPassRegistry()); - } - - bool runOnFunction(Function &F) override; - -private: - // This transformation requires dominator postdominator info - void getAnalysisUsage(AnalysisUsage &AU) const override { - AU.setPreservesCFG(); - AU.addRequired<AssumptionCacheTracker>(); - AU.addRequired<DominatorTreeWrapperPass>(); - AU.addRequired<MemoryDependenceWrapperPass>(); - AU.addRequired<AAResultsWrapperPass>(); - AU.addRequired<TargetLibraryInfoWrapperPass>(); - AU.addPreserved<GlobalsAAWrapperPass>(); - AU.addPreserved<MemoryDependenceWrapperPass>(); - } -}; - -} // end anonymous namespace - -char MemCpyOptLegacyPass::ID = 0; - -/// The public interface to this file... -FunctionPass *llvm::createMemCpyOptPass() { return new MemCpyOptLegacyPass(); } - -INITIALIZE_PASS_BEGIN(MemCpyOptLegacyPass, "memcpyopt", "MemCpy Optimization", - false, false) -INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker) -INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) -INITIALIZE_PASS_DEPENDENCY(MemoryDependenceWrapperPass) -INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass) -INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass) -INITIALIZE_PASS_DEPENDENCY(GlobalsAAWrapperPass) -INITIALIZE_PASS_END(MemCpyOptLegacyPass, "memcpyopt", "MemCpy Optimization", - false, false) - -/// When scanning forward over instructions, we look for some other patterns to -/// fold away. In particular, this looks for stores to neighboring locations of -/// memory. If it sees enough consecutive ones, it attempts to merge them -/// together into a memcpy/memset. -Instruction *MemCpyOptPass::tryMergingIntoMemset(Instruction *StartInst, - Value *StartPtr, - Value *ByteVal) { - const DataLayout &DL = StartInst->getModule()->getDataLayout(); - - // Okay, so we now have a single store that can be splatable. Scan to find - // all subsequent stores of the same value to offset from the same pointer. - // Join these together into ranges, so we can decide whether contiguous blocks - // are stored. - MemsetRanges Ranges(DL); - - BasicBlock::iterator BI(StartInst); - for (++BI; !BI->isTerminator(); ++BI) { - if (!isa<StoreInst>(BI) && !isa<MemSetInst>(BI)) { - // If the instruction is readnone, ignore it, otherwise bail out. We - // don't even allow readonly here because we don't want something like: - // A[1] = 2; strlen(A); A[2] = 2; -> memcpy(A, ...); strlen(A). - if (BI->mayWriteToMemory() || BI->mayReadFromMemory()) - break; - continue; - } - - if (StoreInst *NextStore = dyn_cast<StoreInst>(BI)) { - // If this is a store, see if we can merge it in. - if (!NextStore->isSimple()) break; - - // Check to see if this stored value is of the same byte-splattable value. - Value *StoredByte = isBytewiseValue(NextStore->getOperand(0), DL); - if (isa<UndefValue>(ByteVal) && StoredByte) - ByteVal = StoredByte; - if (ByteVal != StoredByte) - break; - - // Check to see if this store is to a constant offset from the start ptr. - int64_t Offset; - if (!IsPointerOffset(StartPtr, NextStore->getPointerOperand(), Offset, - DL)) - break; - - Ranges.addStore(Offset, NextStore); - } else { - MemSetInst *MSI = cast<MemSetInst>(BI); - - if (MSI->isVolatile() || ByteVal != MSI->getValue() || - !isa<ConstantInt>(MSI->getLength())) - break; - - // Check to see if this store is to a constant offset from the start ptr. - int64_t Offset; - if (!IsPointerOffset(StartPtr, MSI->getDest(), Offset, DL)) - break; - - Ranges.addMemSet(Offset, MSI); - } - } - - // If we have no ranges, then we just had a single store with nothing that - // could be merged in. This is a very common case of course. - if (Ranges.empty()) - return nullptr; - - // If we had at least one store that could be merged in, add the starting - // store as well. We try to avoid this unless there is at least something - // interesting as a small compile-time optimization. - Ranges.addInst(0, StartInst); - - // If we create any memsets, we put it right before the first instruction that - // isn't part of the memset block. This ensure that the memset is dominated - // by any addressing instruction needed by the start of the block. - IRBuilder<> Builder(&*BI); - - // Now that we have full information about ranges, loop over the ranges and - // emit memset's for anything big enough to be worthwhile. - Instruction *AMemSet = nullptr; - for (const MemsetRange &Range : Ranges) { - if (Range.TheStores.size() == 1) continue; - - // If it is profitable to lower this range to memset, do so now. - if (!Range.isProfitableToUseMemset(DL)) - continue; - - // Otherwise, we do want to transform this! Create a new memset. - // Get the starting pointer of the block. - StartPtr = Range.StartPtr; - - // Determine alignment - unsigned Alignment = Range.Alignment; - if (Alignment == 0) { - Type *EltType = - cast<PointerType>(StartPtr->getType())->getElementType(); - Alignment = DL.getABITypeAlignment(EltType); - } - - AMemSet = - Builder.CreateMemSet(StartPtr, ByteVal, Range.End-Range.Start, Alignment); - - LLVM_DEBUG(dbgs() << "Replace stores:\n"; for (Instruction *SI - : Range.TheStores) dbgs() - << *SI << '\n'; - dbgs() << "With: " << *AMemSet << '\n'); - - if (!Range.TheStores.empty()) - AMemSet->setDebugLoc(Range.TheStores[0]->getDebugLoc()); - - // Zap all the stores. - for (Instruction *SI : Range.TheStores) { - MD->removeInstruction(SI); - SI->eraseFromParent(); - } - ++NumMemSetInfer; - } - - return AMemSet; -} - -static unsigned findStoreAlignment(const DataLayout &DL, const StoreInst *SI) { - unsigned StoreAlign = SI->getAlignment(); - if (!StoreAlign) - StoreAlign = DL.getABITypeAlignment(SI->getOperand(0)->getType()); - return StoreAlign; -} - -static unsigned findLoadAlignment(const DataLayout &DL, const LoadInst *LI) { - unsigned LoadAlign = LI->getAlignment(); - if (!LoadAlign) - LoadAlign = DL.getABITypeAlignment(LI->getType()); - return LoadAlign; -} - -static unsigned findCommonAlignment(const DataLayout &DL, const StoreInst *SI, - const LoadInst *LI) { - unsigned StoreAlign = findStoreAlignment(DL, SI); - unsigned LoadAlign = findLoadAlignment(DL, LI); - return MinAlign(StoreAlign, LoadAlign); -} - -// This method try to lift a store instruction before position P. -// It will lift the store and its argument + that anything that -// may alias with these. -// The method returns true if it was successful. -static bool moveUp(AliasAnalysis &AA, StoreInst *SI, Instruction *P, - const LoadInst *LI) { - // If the store alias this position, early bail out. - MemoryLocation StoreLoc = MemoryLocation::get(SI); - if (isModOrRefSet(AA.getModRefInfo(P, StoreLoc))) - return false; - - // Keep track of the arguments of all instruction we plan to lift - // so we can make sure to lift them as well if appropriate. - DenseSet<Instruction*> Args; - if (auto *Ptr = dyn_cast<Instruction>(SI->getPointerOperand())) - if (Ptr->getParent() == SI->getParent()) - Args.insert(Ptr); - - // Instruction to lift before P. - SmallVector<Instruction*, 8> ToLift; - - // Memory locations of lifted instructions. - SmallVector<MemoryLocation, 8> MemLocs{StoreLoc}; - - // Lifted calls. - SmallVector<const CallBase *, 8> Calls; - - const MemoryLocation LoadLoc = MemoryLocation::get(LI); - - for (auto I = --SI->getIterator(), E = P->getIterator(); I != E; --I) { - auto *C = &*I; - - bool MayAlias = isModOrRefSet(AA.getModRefInfo(C, None)); - - bool NeedLift = false; - if (Args.erase(C)) - NeedLift = true; - else if (MayAlias) { - NeedLift = llvm::any_of(MemLocs, [C, &AA](const MemoryLocation &ML) { - return isModOrRefSet(AA.getModRefInfo(C, ML)); - }); - - if (!NeedLift) - NeedLift = llvm::any_of(Calls, [C, &AA](const CallBase *Call) { - return isModOrRefSet(AA.getModRefInfo(C, Call)); - }); - } - - if (!NeedLift) - continue; - - if (MayAlias) { - // Since LI is implicitly moved downwards past the lifted instructions, - // none of them may modify its source. - if (isModSet(AA.getModRefInfo(C, LoadLoc))) - return false; - else if (const auto *Call = dyn_cast<CallBase>(C)) { - // If we can't lift this before P, it's game over. - if (isModOrRefSet(AA.getModRefInfo(P, Call))) - return false; - - Calls.push_back(Call); - } else if (isa<LoadInst>(C) || isa<StoreInst>(C) || isa<VAArgInst>(C)) { - // If we can't lift this before P, it's game over. - auto ML = MemoryLocation::get(C); - if (isModOrRefSet(AA.getModRefInfo(P, ML))) - return false; - - MemLocs.push_back(ML); - } else - // We don't know how to lift this instruction. - return false; - } - - ToLift.push_back(C); - for (unsigned k = 0, e = C->getNumOperands(); k != e; ++k) - if (auto *A = dyn_cast<Instruction>(C->getOperand(k))) - if (A->getParent() == SI->getParent()) - Args.insert(A); - } - - // We made it, we need to lift - for (auto *I : llvm::reverse(ToLift)) { - LLVM_DEBUG(dbgs() << "Lifting " << *I << " before " << *P << "\n"); - I->moveBefore(P); - } - - return true; -} - -bool MemCpyOptPass::processStore(StoreInst *SI, BasicBlock::iterator &BBI) { - if (!SI->isSimple()) return false; - - // Avoid merging nontemporal stores since the resulting - // memcpy/memset would not be able to preserve the nontemporal hint. - // In theory we could teach how to propagate the !nontemporal metadata to - // memset calls. However, that change would force the backend to - // conservatively expand !nontemporal memset calls back to sequences of - // store instructions (effectively undoing the merging). - if (SI->getMetadata(LLVMContext::MD_nontemporal)) - return false; - - const DataLayout &DL = SI->getModule()->getDataLayout(); - - // Load to store forwarding can be interpreted as memcpy. - if (LoadInst *LI = dyn_cast<LoadInst>(SI->getOperand(0))) { - if (LI->isSimple() && LI->hasOneUse() && - LI->getParent() == SI->getParent()) { - - auto *T = LI->getType(); - if (T->isAggregateType()) { - AliasAnalysis &AA = LookupAliasAnalysis(); - MemoryLocation LoadLoc = MemoryLocation::get(LI); - - // We use alias analysis to check if an instruction may store to - // the memory we load from in between the load and the store. If - // such an instruction is found, we try to promote there instead - // of at the store position. - Instruction *P = SI; - for (auto &I : make_range(++LI->getIterator(), SI->getIterator())) { - if (isModSet(AA.getModRefInfo(&I, LoadLoc))) { - P = &I; - break; - } - } - - // We found an instruction that may write to the loaded memory. - // We can try to promote at this position instead of the store - // position if nothing alias the store memory after this and the store - // destination is not in the range. - if (P && P != SI) { - if (!moveUp(AA, SI, P, LI)) - P = nullptr; - } - - // If a valid insertion position is found, then we can promote - // the load/store pair to a memcpy. - if (P) { - // If we load from memory that may alias the memory we store to, - // memmove must be used to preserve semantic. If not, memcpy can - // be used. - bool UseMemMove = false; - if (!AA.isNoAlias(MemoryLocation::get(SI), LoadLoc)) - UseMemMove = true; - - uint64_t Size = DL.getTypeStoreSize(T); - - IRBuilder<> Builder(P); - Instruction *M; - if (UseMemMove) - M = Builder.CreateMemMove( - SI->getPointerOperand(), findStoreAlignment(DL, SI), - LI->getPointerOperand(), findLoadAlignment(DL, LI), Size); - else - M = Builder.CreateMemCpy( - SI->getPointerOperand(), findStoreAlignment(DL, SI), - LI->getPointerOperand(), findLoadAlignment(DL, LI), Size); - - LLVM_DEBUG(dbgs() << "Promoting " << *LI << " to " << *SI << " => " - << *M << "\n"); - - MD->removeInstruction(SI); - SI->eraseFromParent(); - MD->removeInstruction(LI); - LI->eraseFromParent(); - ++NumMemCpyInstr; - - // Make sure we do not invalidate the iterator. - BBI = M->getIterator(); - return true; - } - } - - // Detect cases where we're performing call slot forwarding, but - // happen to be using a load-store pair to implement it, rather than - // a memcpy. - MemDepResult ldep = MD->getDependency(LI); - CallInst *C = nullptr; - if (ldep.isClobber() && !isa<MemCpyInst>(ldep.getInst())) - C = dyn_cast<CallInst>(ldep.getInst()); - - if (C) { - // Check that nothing touches the dest of the "copy" between - // the call and the store. - Value *CpyDest = SI->getPointerOperand()->stripPointerCasts(); - bool CpyDestIsLocal = isa<AllocaInst>(CpyDest); - AliasAnalysis &AA = LookupAliasAnalysis(); - MemoryLocation StoreLoc = MemoryLocation::get(SI); - for (BasicBlock::iterator I = --SI->getIterator(), E = C->getIterator(); - I != E; --I) { - if (isModOrRefSet(AA.getModRefInfo(&*I, StoreLoc))) { - C = nullptr; - break; - } - // The store to dest may never happen if an exception can be thrown - // between the load and the store. - if (I->mayThrow() && !CpyDestIsLocal) { - C = nullptr; - break; - } - } - } - - if (C) { - bool changed = performCallSlotOptzn( - LI, SI->getPointerOperand()->stripPointerCasts(), - LI->getPointerOperand()->stripPointerCasts(), - DL.getTypeStoreSize(SI->getOperand(0)->getType()), - findCommonAlignment(DL, SI, LI), C); - if (changed) { - MD->removeInstruction(SI); - SI->eraseFromParent(); - MD->removeInstruction(LI); - LI->eraseFromParent(); - ++NumMemCpyInstr; - return true; - } - } - } - } - - // There are two cases that are interesting for this code to handle: memcpy - // and memset. Right now we only handle memset. - - // Ensure that the value being stored is something that can be memset'able a - // byte at a time like "0" or "-1" or any width, as well as things like - // 0xA0A0A0A0 and 0.0. - auto *V = SI->getOperand(0); - if (Value *ByteVal = isBytewiseValue(V, DL)) { - if (Instruction *I = tryMergingIntoMemset(SI, SI->getPointerOperand(), - ByteVal)) { - BBI = I->getIterator(); // Don't invalidate iterator. - return true; - } - - // If we have an aggregate, we try to promote it to memset regardless - // of opportunity for merging as it can expose optimization opportunities - // in subsequent passes. - auto *T = V->getType(); - if (T->isAggregateType()) { - uint64_t Size = DL.getTypeStoreSize(T); - unsigned Align = SI->getAlignment(); - if (!Align) - Align = DL.getABITypeAlignment(T); - IRBuilder<> Builder(SI); - auto *M = - Builder.CreateMemSet(SI->getPointerOperand(), ByteVal, Size, Align); - - LLVM_DEBUG(dbgs() << "Promoting " << *SI << " to " << *M << "\n"); - - MD->removeInstruction(SI); - SI->eraseFromParent(); - NumMemSetInfer++; - - // Make sure we do not invalidate the iterator. - BBI = M->getIterator(); - return true; - } - } - - return false; -} - -bool MemCpyOptPass::processMemSet(MemSetInst *MSI, BasicBlock::iterator &BBI) { - // See if there is another memset or store neighboring this memset which - // allows us to widen out the memset to do a single larger store. - if (isa<ConstantInt>(MSI->getLength()) && !MSI->isVolatile()) - if (Instruction *I = tryMergingIntoMemset(MSI, MSI->getDest(), - MSI->getValue())) { - BBI = I->getIterator(); // Don't invalidate iterator. - return true; - } - return false; -} - -/// Takes a memcpy and a call that it depends on, -/// and checks for the possibility of a call slot optimization by having -/// the call write its result directly into the destination of the memcpy. -bool MemCpyOptPass::performCallSlotOptzn(Instruction *cpy, Value *cpyDest, - Value *cpySrc, uint64_t cpyLen, - unsigned cpyAlign, CallInst *C) { - // The general transformation to keep in mind is - // - // call @func(..., src, ...) - // memcpy(dest, src, ...) - // - // -> - // - // memcpy(dest, src, ...) - // call @func(..., dest, ...) - // - // Since moving the memcpy is technically awkward, we additionally check that - // src only holds uninitialized values at the moment of the call, meaning that - // the memcpy can be discarded rather than moved. - - // Lifetime marks shouldn't be operated on. - if (Function *F = C->getCalledFunction()) - if (F->isIntrinsic() && F->getIntrinsicID() == Intrinsic::lifetime_start) - return false; - - // Deliberately get the source and destination with bitcasts stripped away, - // because we'll need to do type comparisons based on the underlying type. - CallSite CS(C); - - // Require that src be an alloca. This simplifies the reasoning considerably. - AllocaInst *srcAlloca = dyn_cast<AllocaInst>(cpySrc); - if (!srcAlloca) - return false; - - ConstantInt *srcArraySize = dyn_cast<ConstantInt>(srcAlloca->getArraySize()); - if (!srcArraySize) - return false; - - const DataLayout &DL = cpy->getModule()->getDataLayout(); - uint64_t srcSize = DL.getTypeAllocSize(srcAlloca->getAllocatedType()) * - srcArraySize->getZExtValue(); - - if (cpyLen < srcSize) - return false; - - // Check that accessing the first srcSize bytes of dest will not cause a - // trap. Otherwise the transform is invalid since it might cause a trap - // to occur earlier than it otherwise would. - if (AllocaInst *A = dyn_cast<AllocaInst>(cpyDest)) { - // The destination is an alloca. Check it is larger than srcSize. - ConstantInt *destArraySize = dyn_cast<ConstantInt>(A->getArraySize()); - if (!destArraySize) - return false; - - uint64_t destSize = DL.getTypeAllocSize(A->getAllocatedType()) * - destArraySize->getZExtValue(); - - if (destSize < srcSize) - return false; - } else if (Argument *A = dyn_cast<Argument>(cpyDest)) { - // The store to dest may never happen if the call can throw. - if (C->mayThrow()) - return false; - - if (A->getDereferenceableBytes() < srcSize) { - // If the destination is an sret parameter then only accesses that are - // outside of the returned struct type can trap. - if (!A->hasStructRetAttr()) - return false; - - Type *StructTy = cast<PointerType>(A->getType())->getElementType(); - if (!StructTy->isSized()) { - // The call may never return and hence the copy-instruction may never - // be executed, and therefore it's not safe to say "the destination - // has at least <cpyLen> bytes, as implied by the copy-instruction", - return false; - } - - uint64_t destSize = DL.getTypeAllocSize(StructTy); - if (destSize < srcSize) - return false; - } - } else { - return false; - } - - // Check that dest points to memory that is at least as aligned as src. - unsigned srcAlign = srcAlloca->getAlignment(); - if (!srcAlign) - srcAlign = DL.getABITypeAlignment(srcAlloca->getAllocatedType()); - bool isDestSufficientlyAligned = srcAlign <= cpyAlign; - // If dest is not aligned enough and we can't increase its alignment then - // bail out. - if (!isDestSufficientlyAligned && !isa<AllocaInst>(cpyDest)) - return false; - - // Check that src is not accessed except via the call and the memcpy. This - // guarantees that it holds only undefined values when passed in (so the final - // memcpy can be dropped), that it is not read or written between the call and - // the memcpy, and that writing beyond the end of it is undefined. - SmallVector<User*, 8> srcUseList(srcAlloca->user_begin(), - srcAlloca->user_end()); - while (!srcUseList.empty()) { - User *U = srcUseList.pop_back_val(); - - if (isa<BitCastInst>(U) || isa<AddrSpaceCastInst>(U)) { - for (User *UU : U->users()) - srcUseList.push_back(UU); - continue; - } - if (GetElementPtrInst *G = dyn_cast<GetElementPtrInst>(U)) { - if (!G->hasAllZeroIndices()) - return false; - - for (User *UU : U->users()) - srcUseList.push_back(UU); - continue; - } - if (const IntrinsicInst *IT = dyn_cast<IntrinsicInst>(U)) - if (IT->isLifetimeStartOrEnd()) - continue; - - if (U != C && U != cpy) - return false; - } - - // Check that src isn't captured by the called function since the - // transformation can cause aliasing issues in that case. - for (unsigned i = 0, e = CS.arg_size(); i != e; ++i) - if (CS.getArgument(i) == cpySrc && !CS.doesNotCapture(i)) - return false; - - // Since we're changing the parameter to the callsite, we need to make sure - // that what would be the new parameter dominates the callsite. - DominatorTree &DT = LookupDomTree(); - if (Instruction *cpyDestInst = dyn_cast<Instruction>(cpyDest)) - if (!DT.dominates(cpyDestInst, C)) - return false; - - // In addition to knowing that the call does not access src in some - // unexpected manner, for example via a global, which we deduce from - // the use analysis, we also need to know that it does not sneakily - // access dest. We rely on AA to figure this out for us. - AliasAnalysis &AA = LookupAliasAnalysis(); - ModRefInfo MR = AA.getModRefInfo(C, cpyDest, LocationSize::precise(srcSize)); - // If necessary, perform additional analysis. - if (isModOrRefSet(MR)) - MR = AA.callCapturesBefore(C, cpyDest, LocationSize::precise(srcSize), &DT); - if (isModOrRefSet(MR)) - return false; - - // We can't create address space casts here because we don't know if they're - // safe for the target. - if (cpySrc->getType()->getPointerAddressSpace() != - cpyDest->getType()->getPointerAddressSpace()) - return false; - for (unsigned i = 0; i < CS.arg_size(); ++i) - if (CS.getArgument(i)->stripPointerCasts() == cpySrc && - cpySrc->getType()->getPointerAddressSpace() != - CS.getArgument(i)->getType()->getPointerAddressSpace()) - return false; - - // All the checks have passed, so do the transformation. - bool changedArgument = false; - for (unsigned i = 0; i < CS.arg_size(); ++i) - if (CS.getArgument(i)->stripPointerCasts() == cpySrc) { - Value *Dest = cpySrc->getType() == cpyDest->getType() ? cpyDest - : CastInst::CreatePointerCast(cpyDest, cpySrc->getType(), - cpyDest->getName(), C); - changedArgument = true; - if (CS.getArgument(i)->getType() == Dest->getType()) - CS.setArgument(i, Dest); - else - CS.setArgument(i, CastInst::CreatePointerCast(Dest, - CS.getArgument(i)->getType(), Dest->getName(), C)); - } - - if (!changedArgument) - return false; - - // If the destination wasn't sufficiently aligned then increase its alignment. - if (!isDestSufficientlyAligned) { - assert(isa<AllocaInst>(cpyDest) && "Can only increase alloca alignment!"); - cast<AllocaInst>(cpyDest)->setAlignment(srcAlign); - } - - // Drop any cached information about the call, because we may have changed - // its dependence information by changing its parameter. - MD->removeInstruction(C); - - // Update AA metadata - // FIXME: MD_tbaa_struct and MD_mem_parallel_loop_access should also be - // handled here, but combineMetadata doesn't support them yet - unsigned KnownIDs[] = {LLVMContext::MD_tbaa, LLVMContext::MD_alias_scope, - LLVMContext::MD_noalias, - LLVMContext::MD_invariant_group, - LLVMContext::MD_access_group}; - combineMetadata(C, cpy, KnownIDs, true); - - // Remove the memcpy. - MD->removeInstruction(cpy); - ++NumMemCpyInstr; - - return true; -} - -/// We've found that the (upward scanning) memory dependence of memcpy 'M' is -/// the memcpy 'MDep'. Try to simplify M to copy from MDep's input if we can. -bool MemCpyOptPass::processMemCpyMemCpyDependence(MemCpyInst *M, - MemCpyInst *MDep) { - // We can only transforms memcpy's where the dest of one is the source of the - // other. - if (M->getSource() != MDep->getDest() || MDep->isVolatile()) - return false; - - // If dep instruction is reading from our current input, then it is a noop - // transfer and substituting the input won't change this instruction. Just - // ignore the input and let someone else zap MDep. This handles cases like: - // memcpy(a <- a) - // memcpy(b <- a) - if (M->getSource() == MDep->getSource()) - return false; - - // Second, the length of the memcpy's must be the same, or the preceding one - // must be larger than the following one. - ConstantInt *MDepLen = dyn_cast<ConstantInt>(MDep->getLength()); - ConstantInt *MLen = dyn_cast<ConstantInt>(M->getLength()); - if (!MDepLen || !MLen || MDepLen->getZExtValue() < MLen->getZExtValue()) - return false; - - AliasAnalysis &AA = LookupAliasAnalysis(); - - // Verify that the copied-from memory doesn't change in between the two - // transfers. For example, in: - // memcpy(a <- b) - // *b = 42; - // memcpy(c <- a) - // It would be invalid to transform the second memcpy into memcpy(c <- b). - // - // TODO: If the code between M and MDep is transparent to the destination "c", - // then we could still perform the xform by moving M up to the first memcpy. - // - // NOTE: This is conservative, it will stop on any read from the source loc, - // not just the defining memcpy. - MemDepResult SourceDep = - MD->getPointerDependencyFrom(MemoryLocation::getForSource(MDep), false, - M->getIterator(), M->getParent()); - if (!SourceDep.isClobber() || SourceDep.getInst() != MDep) - return false; - - // If the dest of the second might alias the source of the first, then the - // source and dest might overlap. We still want to eliminate the intermediate - // value, but we have to generate a memmove instead of memcpy. - bool UseMemMove = false; - if (!AA.isNoAlias(MemoryLocation::getForDest(M), - MemoryLocation::getForSource(MDep))) - UseMemMove = true; - - // If all checks passed, then we can transform M. - LLVM_DEBUG(dbgs() << "MemCpyOptPass: Forwarding memcpy->memcpy src:\n" - << *MDep << '\n' << *M << '\n'); - - // TODO: Is this worth it if we're creating a less aligned memcpy? For - // example we could be moving from movaps -> movq on x86. - IRBuilder<> Builder(M); - if (UseMemMove) - Builder.CreateMemMove(M->getRawDest(), M->getDestAlignment(), - MDep->getRawSource(), MDep->getSourceAlignment(), - M->getLength(), M->isVolatile()); - else - Builder.CreateMemCpy(M->getRawDest(), M->getDestAlignment(), - MDep->getRawSource(), MDep->getSourceAlignment(), - M->getLength(), M->isVolatile()); - - // Remove the instruction we're replacing. - MD->removeInstruction(M); - M->eraseFromParent(); - ++NumMemCpyInstr; - return true; -} - -/// We've found that the (upward scanning) memory dependence of \p MemCpy is -/// \p MemSet. Try to simplify \p MemSet to only set the trailing bytes that -/// weren't copied over by \p MemCpy. -/// -/// In other words, transform: -/// \code -/// memset(dst, c, dst_size); -/// memcpy(dst, src, src_size); -/// \endcode -/// into: -/// \code -/// memcpy(dst, src, src_size); -/// memset(dst + src_size, c, dst_size <= src_size ? 0 : dst_size - src_size); -/// \endcode -bool MemCpyOptPass::processMemSetMemCpyDependence(MemCpyInst *MemCpy, - MemSetInst *MemSet) { - // We can only transform memset/memcpy with the same destination. - if (MemSet->getDest() != MemCpy->getDest()) - return false; - - // Check that there are no other dependencies on the memset destination. - MemDepResult DstDepInfo = - MD->getPointerDependencyFrom(MemoryLocation::getForDest(MemSet), false, - MemCpy->getIterator(), MemCpy->getParent()); - if (DstDepInfo.getInst() != MemSet) - return false; - - // Use the same i8* dest as the memcpy, killing the memset dest if different. - Value *Dest = MemCpy->getRawDest(); - Value *DestSize = MemSet->getLength(); - Value *SrcSize = MemCpy->getLength(); - - // By default, create an unaligned memset. - unsigned Align = 1; - // If Dest is aligned, and SrcSize is constant, use the minimum alignment - // of the sum. - const unsigned DestAlign = - std::max(MemSet->getDestAlignment(), MemCpy->getDestAlignment()); - if (DestAlign > 1) - if (ConstantInt *SrcSizeC = dyn_cast<ConstantInt>(SrcSize)) - Align = MinAlign(SrcSizeC->getZExtValue(), DestAlign); - - IRBuilder<> Builder(MemCpy); - - // If the sizes have different types, zext the smaller one. - if (DestSize->getType() != SrcSize->getType()) { - if (DestSize->getType()->getIntegerBitWidth() > - SrcSize->getType()->getIntegerBitWidth()) - SrcSize = Builder.CreateZExt(SrcSize, DestSize->getType()); - else - DestSize = Builder.CreateZExt(DestSize, SrcSize->getType()); - } - - Value *Ule = Builder.CreateICmpULE(DestSize, SrcSize); - Value *SizeDiff = Builder.CreateSub(DestSize, SrcSize); - Value *MemsetLen = Builder.CreateSelect( - Ule, ConstantInt::getNullValue(DestSize->getType()), SizeDiff); - Builder.CreateMemSet( - Builder.CreateGEP(Dest->getType()->getPointerElementType(), Dest, - SrcSize), - MemSet->getOperand(1), MemsetLen, Align); - - MD->removeInstruction(MemSet); - MemSet->eraseFromParent(); - return true; -} - -/// Determine whether the instruction has undefined content for the given Size, -/// either because it was freshly alloca'd or started its lifetime. -static bool hasUndefContents(Instruction *I, ConstantInt *Size) { - if (isa<AllocaInst>(I)) - return true; - - if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) - if (II->getIntrinsicID() == Intrinsic::lifetime_start) - if (ConstantInt *LTSize = dyn_cast<ConstantInt>(II->getArgOperand(0))) - if (LTSize->getZExtValue() >= Size->getZExtValue()) - return true; - - return false; -} - -/// Transform memcpy to memset when its source was just memset. -/// In other words, turn: -/// \code -/// memset(dst1, c, dst1_size); -/// memcpy(dst2, dst1, dst2_size); -/// \endcode -/// into: -/// \code -/// memset(dst1, c, dst1_size); -/// memset(dst2, c, dst2_size); -/// \endcode -/// When dst2_size <= dst1_size. -/// -/// The \p MemCpy must have a Constant length. -bool MemCpyOptPass::performMemCpyToMemSetOptzn(MemCpyInst *MemCpy, - MemSetInst *MemSet) { - AliasAnalysis &AA = LookupAliasAnalysis(); - - // Make sure that memcpy(..., memset(...), ...), that is we are memsetting and - // memcpying from the same address. Otherwise it is hard to reason about. - if (!AA.isMustAlias(MemSet->getRawDest(), MemCpy->getRawSource())) - return false; - - // A known memset size is required. - ConstantInt *MemSetSize = dyn_cast<ConstantInt>(MemSet->getLength()); - if (!MemSetSize) - return false; - - // Make sure the memcpy doesn't read any more than what the memset wrote. - // Don't worry about sizes larger than i64. - ConstantInt *CopySize = cast<ConstantInt>(MemCpy->getLength()); - if (CopySize->getZExtValue() > MemSetSize->getZExtValue()) { - // If the memcpy is larger than the memset, but the memory was undef prior - // to the memset, we can just ignore the tail. Technically we're only - // interested in the bytes from MemSetSize..CopySize here, but as we can't - // easily represent this location, we use the full 0..CopySize range. - MemoryLocation MemCpyLoc = MemoryLocation::getForSource(MemCpy); - MemDepResult DepInfo = MD->getPointerDependencyFrom( - MemCpyLoc, true, MemSet->getIterator(), MemSet->getParent()); - if (DepInfo.isDef() && hasUndefContents(DepInfo.getInst(), CopySize)) - CopySize = MemSetSize; - else - return false; - } - - IRBuilder<> Builder(MemCpy); - Builder.CreateMemSet(MemCpy->getRawDest(), MemSet->getOperand(1), - CopySize, MemCpy->getDestAlignment()); - return true; -} - -/// Perform simplification of memcpy's. If we have memcpy A -/// which copies X to Y, and memcpy B which copies Y to Z, then we can rewrite -/// B to be a memcpy from X to Z (or potentially a memmove, depending on -/// circumstances). This allows later passes to remove the first memcpy -/// altogether. -bool MemCpyOptPass::processMemCpy(MemCpyInst *M) { - // We can only optimize non-volatile memcpy's. - if (M->isVolatile()) return false; - - // If the source and destination of the memcpy are the same, then zap it. - if (M->getSource() == M->getDest()) { - MD->removeInstruction(M); - M->eraseFromParent(); - return false; - } - - // If copying from a constant, try to turn the memcpy into a memset. - if (GlobalVariable *GV = dyn_cast<GlobalVariable>(M->getSource())) - if (GV->isConstant() && GV->hasDefinitiveInitializer()) - if (Value *ByteVal = isBytewiseValue(GV->getInitializer(), - M->getModule()->getDataLayout())) { - IRBuilder<> Builder(M); - Builder.CreateMemSet(M->getRawDest(), ByteVal, M->getLength(), - M->getDestAlignment(), false); - MD->removeInstruction(M); - M->eraseFromParent(); - ++NumCpyToSet; - return true; - } - - MemDepResult DepInfo = MD->getDependency(M); - - // Try to turn a partially redundant memset + memcpy into - // memcpy + smaller memset. We don't need the memcpy size for this. - if (DepInfo.isClobber()) - if (MemSetInst *MDep = dyn_cast<MemSetInst>(DepInfo.getInst())) - if (processMemSetMemCpyDependence(M, MDep)) - return true; - - // The optimizations after this point require the memcpy size. - ConstantInt *CopySize = dyn_cast<ConstantInt>(M->getLength()); - if (!CopySize) return false; - - // There are four possible optimizations we can do for memcpy: - // a) memcpy-memcpy xform which exposes redundance for DSE. - // b) call-memcpy xform for return slot optimization. - // c) memcpy from freshly alloca'd space or space that has just started its - // lifetime copies undefined data, and we can therefore eliminate the - // memcpy in favor of the data that was already at the destination. - // d) memcpy from a just-memset'd source can be turned into memset. - if (DepInfo.isClobber()) { - if (CallInst *C = dyn_cast<CallInst>(DepInfo.getInst())) { - // FIXME: Can we pass in either of dest/src alignment here instead - // of conservatively taking the minimum? - unsigned Align = MinAlign(M->getDestAlignment(), M->getSourceAlignment()); - if (performCallSlotOptzn(M, M->getDest(), M->getSource(), - CopySize->getZExtValue(), Align, - C)) { - MD->removeInstruction(M); - M->eraseFromParent(); - return true; - } - } - } - - MemoryLocation SrcLoc = MemoryLocation::getForSource(M); - MemDepResult SrcDepInfo = MD->getPointerDependencyFrom( - SrcLoc, true, M->getIterator(), M->getParent()); - - if (SrcDepInfo.isClobber()) { - if (MemCpyInst *MDep = dyn_cast<MemCpyInst>(SrcDepInfo.getInst())) - return processMemCpyMemCpyDependence(M, MDep); - } else if (SrcDepInfo.isDef()) { - if (hasUndefContents(SrcDepInfo.getInst(), CopySize)) { - MD->removeInstruction(M); - M->eraseFromParent(); - ++NumMemCpyInstr; - return true; - } - } - - if (SrcDepInfo.isClobber()) - if (MemSetInst *MDep = dyn_cast<MemSetInst>(SrcDepInfo.getInst())) - if (performMemCpyToMemSetOptzn(M, MDep)) { - MD->removeInstruction(M); - M->eraseFromParent(); - ++NumCpyToSet; - return true; - } - - return false; -} - -/// Transforms memmove calls to memcpy calls when the src/dst are guaranteed -/// not to alias. -bool MemCpyOptPass::processMemMove(MemMoveInst *M) { - AliasAnalysis &AA = LookupAliasAnalysis(); - - if (!TLI->has(LibFunc_memmove)) - return false; - - // See if the pointers alias. - if (!AA.isNoAlias(MemoryLocation::getForDest(M), - MemoryLocation::getForSource(M))) - return false; - - LLVM_DEBUG(dbgs() << "MemCpyOptPass: Optimizing memmove -> memcpy: " << *M - << "\n"); - - // If not, then we know we can transform this. - Type *ArgTys[3] = { M->getRawDest()->getType(), - M->getRawSource()->getType(), - M->getLength()->getType() }; - M->setCalledFunction(Intrinsic::getDeclaration(M->getModule(), - Intrinsic::memcpy, ArgTys)); - - // MemDep may have over conservative information about this instruction, just - // conservatively flush it from the cache. - MD->removeInstruction(M); - - ++NumMoveToCpy; - return true; -} - -/// This is called on every byval argument in call sites. -bool MemCpyOptPass::processByValArgument(CallSite CS, unsigned ArgNo) { - const DataLayout &DL = CS.getCaller()->getParent()->getDataLayout(); - // Find out what feeds this byval argument. - Value *ByValArg = CS.getArgument(ArgNo); - Type *ByValTy = cast<PointerType>(ByValArg->getType())->getElementType(); - uint64_t ByValSize = DL.getTypeAllocSize(ByValTy); - MemDepResult DepInfo = MD->getPointerDependencyFrom( - MemoryLocation(ByValArg, LocationSize::precise(ByValSize)), true, - CS.getInstruction()->getIterator(), CS.getInstruction()->getParent()); - if (!DepInfo.isClobber()) - return false; - - // If the byval argument isn't fed by a memcpy, ignore it. If it is fed by - // a memcpy, see if we can byval from the source of the memcpy instead of the - // result. - MemCpyInst *MDep = dyn_cast<MemCpyInst>(DepInfo.getInst()); - if (!MDep || MDep->isVolatile() || - ByValArg->stripPointerCasts() != MDep->getDest()) - return false; - - // The length of the memcpy must be larger or equal to the size of the byval. - ConstantInt *C1 = dyn_cast<ConstantInt>(MDep->getLength()); - if (!C1 || C1->getValue().getZExtValue() < ByValSize) - return false; - - // Get the alignment of the byval. If the call doesn't specify the alignment, - // then it is some target specific value that we can't know. - unsigned ByValAlign = CS.getParamAlignment(ArgNo); - if (ByValAlign == 0) return false; - - // If it is greater than the memcpy, then we check to see if we can force the - // source of the memcpy to the alignment we need. If we fail, we bail out. - AssumptionCache &AC = LookupAssumptionCache(); - DominatorTree &DT = LookupDomTree(); - if (MDep->getSourceAlignment() < ByValAlign && - getOrEnforceKnownAlignment(MDep->getSource(), ByValAlign, DL, - CS.getInstruction(), &AC, &DT) < ByValAlign) - return false; - - // The address space of the memcpy source must match the byval argument - if (MDep->getSource()->getType()->getPointerAddressSpace() != - ByValArg->getType()->getPointerAddressSpace()) - return false; - - // Verify that the copied-from memory doesn't change in between the memcpy and - // the byval call. - // memcpy(a <- b) - // *b = 42; - // foo(*a) - // It would be invalid to transform the second memcpy into foo(*b). - // - // NOTE: This is conservative, it will stop on any read from the source loc, - // not just the defining memcpy. - MemDepResult SourceDep = MD->getPointerDependencyFrom( - MemoryLocation::getForSource(MDep), false, - CS.getInstruction()->getIterator(), MDep->getParent()); - if (!SourceDep.isClobber() || SourceDep.getInst() != MDep) - return false; - - Value *TmpCast = MDep->getSource(); - if (MDep->getSource()->getType() != ByValArg->getType()) - TmpCast = new BitCastInst(MDep->getSource(), ByValArg->getType(), - "tmpcast", CS.getInstruction()); - - LLVM_DEBUG(dbgs() << "MemCpyOptPass: Forwarding memcpy to byval:\n" - << " " << *MDep << "\n" - << " " << *CS.getInstruction() << "\n"); - - // Otherwise we're good! Update the byval argument. - CS.setArgument(ArgNo, TmpCast); - ++NumMemCpyInstr; - return true; -} - -/// Executes one iteration of MemCpyOptPass. -bool MemCpyOptPass::iterateOnFunction(Function &F) { - bool MadeChange = false; - - DominatorTree &DT = LookupDomTree(); - - // Walk all instruction in the function. - for (BasicBlock &BB : F) { - // Skip unreachable blocks. For example processStore assumes that an - // instruction in a BB can't be dominated by a later instruction in the - // same BB (which is a scenario that can happen for an unreachable BB that - // has itself as a predecessor). - if (!DT.isReachableFromEntry(&BB)) - continue; - - for (BasicBlock::iterator BI = BB.begin(), BE = BB.end(); BI != BE;) { - // Avoid invalidating the iterator. - Instruction *I = &*BI++; - - bool RepeatInstruction = false; - - if (StoreInst *SI = dyn_cast<StoreInst>(I)) - MadeChange |= processStore(SI, BI); - else if (MemSetInst *M = dyn_cast<MemSetInst>(I)) - RepeatInstruction = processMemSet(M, BI); - else if (MemCpyInst *M = dyn_cast<MemCpyInst>(I)) - RepeatInstruction = processMemCpy(M); - else if (MemMoveInst *M = dyn_cast<MemMoveInst>(I)) - RepeatInstruction = processMemMove(M); - else if (auto CS = CallSite(I)) { - for (unsigned i = 0, e = CS.arg_size(); i != e; ++i) - if (CS.isByValArgument(i)) - MadeChange |= processByValArgument(CS, i); - } - - // Reprocess the instruction if desired. - if (RepeatInstruction) { - if (BI != BB.begin()) - --BI; - MadeChange = true; - } - } - } - - return MadeChange; -} - -PreservedAnalyses MemCpyOptPass::run(Function &F, FunctionAnalysisManager &AM) { - auto &MD = AM.getResult<MemoryDependenceAnalysis>(F); - auto &TLI = AM.getResult<TargetLibraryAnalysis>(F); - - auto LookupAliasAnalysis = [&]() -> AliasAnalysis & { - return AM.getResult<AAManager>(F); - }; - auto LookupAssumptionCache = [&]() -> AssumptionCache & { - return AM.getResult<AssumptionAnalysis>(F); - }; - auto LookupDomTree = [&]() -> DominatorTree & { - return AM.getResult<DominatorTreeAnalysis>(F); - }; - - bool MadeChange = runImpl(F, &MD, &TLI, LookupAliasAnalysis, - LookupAssumptionCache, LookupDomTree); - if (!MadeChange) - return PreservedAnalyses::all(); - - PreservedAnalyses PA; - PA.preserveSet<CFGAnalyses>(); - PA.preserve<GlobalsAA>(); - PA.preserve<MemoryDependenceAnalysis>(); - return PA; -} - -bool MemCpyOptPass::runImpl( - Function &F, MemoryDependenceResults *MD_, TargetLibraryInfo *TLI_, - std::function<AliasAnalysis &()> LookupAliasAnalysis_, - std::function<AssumptionCache &()> LookupAssumptionCache_, - std::function<DominatorTree &()> LookupDomTree_) { - bool MadeChange = false; - MD = MD_; - TLI = TLI_; - LookupAliasAnalysis = std::move(LookupAliasAnalysis_); - LookupAssumptionCache = std::move(LookupAssumptionCache_); - LookupDomTree = std::move(LookupDomTree_); - - // If we don't have at least memset and memcpy, there is little point of doing - // anything here. These are required by a freestanding implementation, so if - // even they are disabled, there is no point in trying hard. - if (!TLI->has(LibFunc_memset) || !TLI->has(LibFunc_memcpy)) - return false; - - while (true) { - if (!iterateOnFunction(F)) - break; - MadeChange = true; - } - - MD = nullptr; - return MadeChange; -} - -/// This is the main transformation entry point for a function. -bool MemCpyOptLegacyPass::runOnFunction(Function &F) { - if (skipFunction(F)) - return false; - - auto *MD = &getAnalysis<MemoryDependenceWrapperPass>().getMemDep(); - auto *TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(); - - auto LookupAliasAnalysis = [this]() -> AliasAnalysis & { - return getAnalysis<AAResultsWrapperPass>().getAAResults(); - }; - auto LookupAssumptionCache = [this, &F]() -> AssumptionCache & { - return getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F); - }; - auto LookupDomTree = [this]() -> DominatorTree & { - return getAnalysis<DominatorTreeWrapperPass>().getDomTree(); - }; - - return Impl.runImpl(F, MD, TLI, LookupAliasAnalysis, LookupAssumptionCache, - LookupDomTree); -} |