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Implement PR8644: forwarding a memcpy value to a byval,

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allowing the memcpy to be eliminated.

Unfortunately, the requirements on byval's without explicit 
alignment are really weak and impossible to predict in the 
mid-level optimizer, so this doesn't kick in much with current
frontends.  The fix is to change clang to set alignment on all
byval arguments.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@119916 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2010-11-21 00:28:59 +00:00
parent a6fd81dd7f
commit 2f5f90ad3e
4 changed files with 144 additions and 51 deletions
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5
include/llvm/Support/CallSite.h
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@ -52,11 +52,6 @@ public:
CallSiteBase(CallTy *CI) : I(CI, true) { assert(CI); }
CallSiteBase(InvokeTy *II) : I(II, false) { assert(II); }
CallSiteBase(ValTy *II) { *this = get(II); }
CallSiteBase(InstrTy *II) {
assert(II && "Null instruction given?");
*this = get(II);
assert(I.getPointer() && "Not a call?");
}
protected:
/// CallSiteBase::get - This static method is sort of like a constructor. It
/// will create an appropriate call site for a Call or Invoke instruction, but

171
lib/Transforms/Scalar/MemCpyOptimizer.cpp
View File

@ -301,11 +301,13 @@ void MemsetRanges::addStore(int64_t Start, StoreInst *SI) {
namespace {
class MemCpyOpt : public FunctionPass {
MemoryDependenceAnalysis *MD;
bool runOnFunction(Function &F);
public:
static char ID; // Pass identification, replacement for typeid
MemCpyOpt() : FunctionPass(ID) {
initializeMemCpyOptPass(*PassRegistry::getPassRegistry());
MD = 0;
}
private:
@ -327,6 +329,7 @@ namespace {
uint64_t cpyLen, CallInst *C);
bool processMemCpyMemCpyDependence(MemCpyInst *M, MemCpyInst *MDep,
uint64_t MSize);
bool processByValArgument(CallSite CS, unsigned ArgNo);
bool iterateOnFunction(Function &F);
};
@ -359,9 +362,7 @@ bool MemCpyOpt::processStore(StoreInst *SI, BasicBlock::iterator &BBI) {
// a memcpy.
if (LoadInst *LI = dyn_cast<LoadInst>(SI->getOperand(0))) {
if (!LI->isVolatile() && LI->hasOneUse()) {
MemoryDependenceAnalysis &MD = getAnalysis<MemoryDependenceAnalysis>();
MemDepResult dep = MD.getDependency(LI);
MemDepResult dep = MD->getDependency(LI);
CallInst *C = 0;
if (dep.isClobber() && !isa<MemCpyInst>(dep.getInst()))
C = dyn_cast<CallInst>(dep.getInst());
@ -372,7 +373,7 @@ bool MemCpyOpt::processStore(StoreInst *SI, BasicBlock::iterator &BBI) {
LI->getPointerOperand()->stripPointerCasts(),
TD->getTypeStoreSize(SI->getOperand(0)->getType()), C);
if (changed) {
MD.removeInstruction(SI);
MD->removeInstruction(SI);
SI->eraseFromParent();
LI->eraseFromParent();
++NumMemCpyInstr;
@ -505,8 +506,8 @@ bool MemCpyOpt::processStore(StoreInst *SI, BasicBlock::iterator &BBI) {
Value *C = CallInst::Create(MemSetF, Ops, Ops+5, "", InsertPt);
DEBUG(dbgs() << "Replace stores:\n";
for (unsigned i = 0, e = Range.TheStores.size(); i != e; ++i)
dbgs() << *Range.TheStores[i];
dbgs() << "With: " << *C); C=C;
dbgs() << *Range.TheStores[i] << '\n';
dbgs() << "With: " << *C << '\n'); C=C;
// Don't invalidate the iterator
BBI = BI;
@ -657,11 +658,10 @@ bool MemCpyOpt::performCallSlotOptzn(Instruction *cpy,
// Drop any cached information about the call, because we may have changed
// its dependence information by changing its parameter.
MemoryDependenceAnalysis &MD = getAnalysis<MemoryDependenceAnalysis>();
MD.removeInstruction(C);
MD->removeInstruction(C);
// Remove the memcpy
MD.removeInstruction(cpy);
// Remove the memcpy.
MD->removeInstruction(cpy);
++NumMemCpyInstr;
return true;
@ -675,7 +675,7 @@ bool MemCpyOpt::processMemCpyMemCpyDependence(MemCpyInst *M, MemCpyInst *MDep,
uint64_t MSize) {
// We can only transforms memcpy's where the dest of one is the source of the
// other.
if (M->getSource() != MDep->getDest())
if (M->getSource() != MDep->getDest() || MDep->isVolatile())
return false;
// Second, the length of the memcpy's must be the same, or the preceeding one
@ -684,27 +684,26 @@ bool MemCpyOpt::processMemCpyMemCpyDependence(MemCpyInst *M, MemCpyInst *MDep,
if (!C1) return false;
uint64_t DepSize = C1->getValue().getZExtValue();
if (DepSize < MSize)
return false;
Intrinsic::ID ResultFn = Intrinsic::memcpy;
AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
// 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.
AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
Intrinsic::ID ResultFn = Intrinsic::memcpy;
if (!AA.isNoAlias(M->getRawDest(), MSize, MDep->getRawSource(), DepSize))
ResultFn = Intrinsic::memmove;
// If all checks passed, then we can transform these memcpy's
// If all checks passed, then we can transform M.
const Type *ArgTys[3] = {
M->getRawDest()->getType(),
MDep->getRawSource()->getType(),
M->getLength()->getType()
};
Function *MemCpyFun =
Intrinsic::getDeclaration(M->getParent()->getParent()->getParent(),
Intrinsic::getDeclaration(MDep->getParent()->getParent()->getParent(),
ResultFn, ArgTys, 3);
// Make sure to use the lesser of the alignment of the source and the dest
@ -717,29 +716,30 @@ bool MemCpyOpt::processMemCpyMemCpyDependence(MemCpyInst *M, MemCpyInst *MDep,
M->getRawDest(),
MDep->getRawSource(),
M->getLength(),
ConstantInt::get(Type::getInt32Ty(M->getContext()), Align),
ConstantInt::get(Type::getInt32Ty(MemCpyFun->getContext()), Align),
M->getVolatileCst()
};
CallInst *C = CallInst::Create(MemCpyFun, Args, Args+5, "", M);
MemoryDependenceAnalysis &MD = getAnalysis<MemoryDependenceAnalysis>();
// 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).
MemDepResult NewDep = MD.getDependency(C);
//
// 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.
MemDepResult NewDep = MD->getDependency(C);
if (!NewDep.isClobber() || NewDep.getInst() != MDep) {
MD.removeInstruction(C);
MD->removeInstruction(C);
C->eraseFromParent();
return false;
}
// Otherwise we're good! Nuke the instruction we're replacing.
MD.removeInstruction(M);
MD->removeInstruction(M);
M->eraseFromParent();
++NumMemCpyInstr;
return true;
@ -752,25 +752,23 @@ bool MemCpyOpt::processMemCpyMemCpyDependence(MemCpyInst *M, MemCpyInst *MDep,
/// circumstances). This allows later passes to remove the first memcpy
/// altogether.
bool MemCpyOpt::processMemCpy(MemCpyInst *M) {
MemoryDependenceAnalysis &MD = getAnalysis<MemoryDependenceAnalysis>();
// We can only optimize statically-sized memcpy's.
ConstantInt *cpyLen = dyn_cast<ConstantInt>(M->getLength());
if (!cpyLen) return false;
// We can only optimize statically-sized memcpy's that are non-volatile.
ConstantInt *CopySize = dyn_cast<ConstantInt>(M->getLength());
if (CopySize == 0 || M->isVolatile()) return false;
// The are two possible optimizations we can do for memcpy:
// a) memcpy-memcpy xform which exposes redundance for DSE.
// b) call-memcpy xform for return slot optimization.
MemDepResult dep = MD.getDependency(M);
if (!dep.isClobber())
MemDepResult DepInfo = MD->getDependency(M);
if (!DepInfo.isClobber())
return false;
if (MemCpyInst *MDep = dyn_cast<MemCpyInst>(dep.getInst()))
return processMemCpyMemCpyDependence(M, MDep, cpyLen->getZExtValue());
if (MemCpyInst *MDep = dyn_cast<MemCpyInst>(DepInfo.getInst()))
return processMemCpyMemCpyDependence(M, MDep, CopySize->getZExtValue());
if (CallInst *C = dyn_cast<CallInst>(dep.getInst())) {
if (CallInst *C = dyn_cast<CallInst>(DepInfo.getInst())) {
bool changed = performCallSlotOptzn(M, M->getDest(), M->getSource(),
cpyLen->getZExtValue(), C);
CopySize->getZExtValue(), C);
if (changed) M->eraseFromParent();
return changed;
}
@ -805,33 +803,116 @@ bool MemCpyOpt::processMemMove(MemMoveInst *M) {
// MemDep may have over conservative information about this instruction, just
// conservatively flush it from the cache.
getAnalysis<MemoryDependenceAnalysis>().removeInstruction(M);
MD->removeInstruction(M);
++NumMoveToCpy;
return true;
}
/// processByValArgument - This is called on every byval argument in call sites.
bool MemCpyOpt::processByValArgument(CallSite CS, unsigned ArgNo) {
TargetData *TD = getAnalysisIfAvailable<TargetData>();
if (!TD) return false;
// MemCpyOpt::iterateOnFunction - Executes one iteration of GVN.
Value *ByValArg = CS.getArgument(ArgNo);
// MemDep doesn't have a way to do a local query with a memory location.
// Instead, just insert a load and ask for its dependences.
LoadInst *TmpLoad = new LoadInst(ByValArg, "", CS.getInstruction());
MemDepResult DepInfo = MD->getDependency(TmpLoad);
MD->removeInstruction(TmpLoad);
TmpLoad->eraseFromParent();
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 == 0 || MDep->isVolatile() ||
ByValArg->stripPointerCasts() != MDep->getDest())
return false;
// The length of the memcpy must be larger or equal to the size of the byval.
// must be larger than the following one.
ConstantInt *C1 = dyn_cast<ConstantInt>(MDep->getLength());
if (C1 == 0 ||
C1->getValue().getZExtValue() < TD->getTypeAllocSize(ByValArg->getType()))
return false;
// Get the alignment of the byval. If it is greater than the memcpy, then we
// can't do the substitution. 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+1);
if (ByValAlign == 0 || MDep->getAlignment() < ByValAlign)
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).
Value *TmpCast = MDep->getSource();
if (MDep->getSource()->getType() != ByValArg->getType())
TmpCast = new BitCastInst(MDep->getSource(), ByValArg->getType(),
"tmpcast", CS.getInstruction());
Value *TmpVal =
UndefValue::get(cast<PointerType>(TmpCast->getType())->getElementType());
Instruction *TmpStore = new StoreInst(TmpVal, TmpCast, false,
CS.getInstruction());
DepInfo = MD->getDependency(TmpStore);
bool isUnsafe = !DepInfo.isClobber() || DepInfo.getInst() != MDep;
MD->removeInstruction(TmpStore);
TmpStore->eraseFromParent();
if (isUnsafe) {
// Clean up the inserted cast instruction.
if (TmpCast != MDep->getSource())
cast<Instruction>(TmpCast)->eraseFromParent();
return false;
}
DEBUG(dbgs() << "MemCpyOpt: 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;
}
/// iterateOnFunction - Executes one iteration of MemCpyOpt.
bool MemCpyOpt::iterateOnFunction(Function &F) {
bool MadeChange = false;
// Walk all instruction in the function.
for (Function::iterator BB = F.begin(), BBE = F.end(); BB != BBE; ++BB) {
for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
BI != BE;) {
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 (MemCpyInst *M = dyn_cast<MemCpyInst>(I))
MadeChange |= processMemCpy(M);
else if (MemMoveInst *M = dyn_cast<MemMoveInst>(I)) {
if (processMemMove(M)) {
--BI; // Reprocess the new memcpy.
MadeChange = true;
}
else if (MemCpyInst *M = dyn_cast<MemCpyInst>(I)) {
RepeatInstruction = processMemCpy(M);
} else if (MemMoveInst *M = dyn_cast<MemMoveInst>(I)) {
RepeatInstruction = processMemMove(M);
} else if (CallSite CS = (Value*)I) {
for (unsigned i = 0, e = CS.arg_size(); i != e; ++i)
if (CS.paramHasAttr(i+1, Attribute::ByVal))
MadeChange |= processByValArgument(CS, i);
}
// Reprocess the instruction if desired.
if (RepeatInstruction) {
--BI;
MadeChange = true;
}
}
}
@ -844,12 +925,14 @@ bool MemCpyOpt::iterateOnFunction(Function &F) {
//
bool MemCpyOpt::runOnFunction(Function &F) {
bool MadeChange = false;
MD = &getAnalysis<MemoryDependenceAnalysis>();
while (1) {
if (!iterateOnFunction(F))
break;
MadeChange = true;
}
MD = 0;
return MadeChange;
}

15
test/Transforms/MemCpyOpt/memcpy.ll
View File

@ -62,3 +62,18 @@ define void @test3({ x86_fp80, x86_fp80 }* noalias sret %agg.result) nounwind {
; CHECK-NEXT: call void @llvm.memcpy
; CHECK-NEXT: ret void
}
; PR8644
define void @test4(i8 *%P) {
%A = alloca {i32, i32}
%a = bitcast {i32, i32}* %A to i8*
call void @llvm.memcpy.p0i8.p0i8.i64(i8* %a, i8* %P, i64 8, i32 4, i1 false)
call void @test4a(i8* byval align 1 %a)
ret void
; CHECK: @test4
; CHECK-NEXT: call void @test4a(
}
declare void @test4a(i8* byval align 1)
declare void @llvm.memcpy.p0i8.p0i8.i64(i8* nocapture, i8* nocapture, i64, i32, i1) nounwind

4
test/Transforms/MemCpyOpt/sret.ll
View File

@ -3,7 +3,7 @@
target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
target triple = "i686-apple-darwin9"
define void @ccosl({ x86_fp80, x86_fp80 }* noalias sret %agg.result, { x86_fp80, x86_fp80 }* byval %z) nounwind {
define void @ccosl({ x86_fp80, x86_fp80 }* noalias sret %agg.result, { x86_fp80, x86_fp80 }* byval align 8 %z) nounwind {
entry:
%iz = alloca { x86_fp80, x86_fp80 } ; <{ x86_fp80, x86_fp80 }*> [#uses=3]
%memtmp = alloca { x86_fp80, x86_fp80 }, align 16 ; <{ x86_fp80, x86_fp80 }*> [#uses=2]
@ -16,7 +16,7 @@ entry:
%tmp8 = load x86_fp80* %tmp7, align 16 ; <x86_fp80> [#uses=1]
store x86_fp80 %tmp3, x86_fp80* %real, align 16
store x86_fp80 %tmp8, x86_fp80* %tmp4, align 16
call void @ccoshl( { x86_fp80, x86_fp80 }* noalias sret %memtmp, { x86_fp80, x86_fp80 }* byval %iz ) nounwind
call void @ccoshl( { x86_fp80, x86_fp80 }* noalias sret %memtmp, { x86_fp80, x86_fp80 }* byval align 8 %iz ) nounwind
%memtmp14 = bitcast { x86_fp80, x86_fp80 }* %memtmp to i8* ; <i8*> [#uses=1]
%agg.result15 = bitcast { x86_fp80, x86_fp80 }* %agg.result to i8* ; <i8*> [#uses=1]
call void @llvm.memcpy.i32( i8* %agg.result15, i8* %memtmp14, i32 32, i32 16 )