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llvm-mirror/lib/Transforms/Scalar/MemCpyOptimizer.cpp
Hans Wennborg 8f776fd787 Revert r319482 and r319483 "[memcpyopt] Teach memcpyopt to optimize across basic blocks" 
This caused PR35519.

> [memcpyopt] Teach memcpyopt to optimize across basic blocks
>
> This teaches memcpyopt to make a non-local memdep query when a local query
> indicates that the dependency is non-local. This notably allows it to
> eliminate many more llvm.memcpy calls in common Rust code, often by 20-30%.
>
> Fixes PR28958.
>
> Differential Revision: https://reviews.llvm.org/D38374
>

> [memcpyopt] Commit file missed in r319482.
>
> This change was meant to be included with r319482 but was accidentally
> omitted.

llvm-svn: 319873
2017-12-06 01:47:55 +00:00

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//===- MemCpyOptimizer.cpp - Optimize use of memcpy and friends -----------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// 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/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 "llvm/Transforms/Utils/Local.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->getAlignment(), 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 = std::lower_bound(Ranges.begin(), Ranges.end(), Start,
[](const MemsetRange &LHS, int64_t RHS) { return LHS.End < RHS; });
// 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; !isa<TerminatorInst>(BI); ++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.
if (ByteVal != isBytewiseValue(NextStore->getOperand(0)))
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);
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 findCommonAlignment(const DataLayout &DL, const StoreInst *SI,
const LoadInst *LI) {
unsigned StoreAlign = SI->getAlignment();
if (!StoreAlign)
StoreAlign = DL.getABITypeAlignment(SI->getOperand(0)->getType());
unsigned LoadAlign = LI->getAlignment();
if (!LoadAlign)
LoadAlign = DL.getABITypeAlignment(LI->getType());
return std::min(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 apropriate.
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 callsites.
SmallVector<ImmutableCallSite, 8> CallSites;
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(CallSites, [C, &AA](const ImmutableCallSite &CS) {
return isModOrRefSet(AA.getModRefInfo(C, CS));
});
}
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 (auto CS = ImmutableCallSite(C)) {
// If we can't lift this before P, it's game over.
if (isModOrRefSet(AA.getModRefInfo(P, CS)))
return false;
CallSites.push_back(CS);
} 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)) {
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;
unsigned Align = findCommonAlignment(DL, SI, LI);
uint64_t Size = DL.getTypeStoreSize(T);
IRBuilder<> Builder(P);
Instruction *M;
if (UseMemMove)
M = Builder.CreateMemMove(SI->getPointerOperand(),
LI->getPointerOperand(), Size,
Align, SI->isVolatile());
else
M = Builder.CreateMemCpy(SI->getPointerOperand(),
LI->getPointerOperand(), Size,
Align, SI->isVolatile());
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)) {
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, SI->isVolatile());
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->getIntrinsicID() == Intrinsic::lifetime_start ||
IT->getIntrinsicID() == Intrinsic::lifetime_end)
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, srcSize);
// If necessary, perform additional analysis.
if (isModOrRefSet(MR))
MR = AA.callCapturesBefore(C, cpyDest, 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};
combineMetadata(C, cpy, KnownIDs);
// 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.
// Make sure to use the lesser of the alignment of the source and the dest
// since we're changing where we're reading from, but don't want to increase
// the alignment past what can be read from or written to.
// TODO: Is this worth it if we're creating a less aligned memcpy? For
// example we could be moving from movaps -> movq on x86.
unsigned Align = std::min(MDep->getAlignment(), M->getAlignment());
IRBuilder<> Builder(M);
if (UseMemMove)
Builder.CreateMemMove(M->getRawDest(), MDep->getRawSource(), M->getLength(),
Align, M->isVolatile());
else
Builder.CreateMemCpy(M->getRawDest(), MDep->getRawSource(), M->getLength(),
Align, 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->getAlignment(), MemCpy->getAlignment());
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, SrcSize), MemSet->getOperand(1),
MemsetLen, Align);
MD->removeInstruction(MemSet);
MemSet->eraseFromParent();
return true;
}
/// 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;
ConstantInt *CopySize = cast<ConstantInt>(MemCpy->getLength());
ConstantInt *MemSetSize = dyn_cast<ConstantInt>(MemSet->getLength());
// Make sure the memcpy doesn't read any more than what the memset wrote.
// Don't worry about sizes larger than i64.
if (!MemSetSize || CopySize->getZExtValue() > MemSetSize->getZExtValue())
return false;
IRBuilder<> Builder(MemCpy);
Builder.CreateMemSet(MemCpy->getRawDest(), MemSet->getOperand(1),
CopySize, MemCpy->getAlignment());
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())) {
IRBuilder<> Builder(M);
Builder.CreateMemSet(M->getRawDest(), ByteVal, M->getLength(),
M->getAlignment(), 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())) {
if (performCallSlotOptzn(M, M->getDest(), M->getSource(),
CopySize->getZExtValue(), M->getAlignment(),
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()) {
Instruction *I = SrcDepInfo.getInst();
bool hasUndefContents = false;
if (isa<AllocaInst>(I)) {
hasUndefContents = true;
} else 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() >= CopySize->getZExtValue())
hasUndefContents = true;
}
if (hasUndefContents) {
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;
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, 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->getAlignment() < 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());
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;
// Walk all instruction in the function.
for (BasicBlock &BB : F) {
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);
}
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