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constant fold loads from memcpy's from global constants. This is important

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because clang lowers nontrivial automatic struct/array inits to memcpy from
a global array.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@90698 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner
2009-12-06 05:29:56 +00:00
parent cb9cbc4949
commit bc9a28dd54
2 changed files with 62 additions and 6 deletions
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52
lib/Transforms/Scalar/GVN.cpp
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@@ -31,8 +31,9 @@
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/MemoryBuiltins.h"
#include "llvm/Analysis/MemoryDependenceAnalysis.h"
#include "llvm/Support/CFG.h"
@@ -1094,11 +1095,39 @@ static int AnalyzeLoadFromClobberingMemInst(LoadInst *L, MemIntrinsic *MI,
ConstantInt *SizeCst = dyn_cast<ConstantInt>(MI->getLength());
if (SizeCst == 0) return -1;
uint64_t MemSizeInBits = SizeCst->getZExtValue()*8;
// If this is memset, we just need to see if the offset is valid in the size
// of the memset..
if (MI->getIntrinsicID() == Intrinsic::memset)
return AnalyzeLoadFromClobberingWrite(L, MI->getDest(), MemSizeInBits, TD);
// Unhandled memcpy/memmove.
// If we have a memcpy/memmove, the only case we can handle is if this is a
// copy from constant memory. In that case, we can read directly from the
// constant memory.
MemTransferInst *MTI = cast<MemTransferInst>(MI);
Constant *Src = dyn_cast<Constant>(MTI->getSource());
if (Src == 0) return -1;
GlobalVariable *GV = dyn_cast<GlobalVariable>(Src->getUnderlyingObject());
if (GV == 0 || !GV->isConstant()) return -1;
// See if the access is within the bounds of the transfer.
int Offset =
AnalyzeLoadFromClobberingWrite(L, MI->getDest(), MemSizeInBits, TD);
if (Offset == -1)
return Offset;
// Otherwise, see if we can constant fold a load from the constant with the
// offset applied as appropriate.
Src = ConstantExpr::getBitCast(Src,
llvm::Type::getInt8PtrTy(Src->getContext()));
Constant *OffsetCst =
ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset);
Src = ConstantExpr::getGetElementPtr(Src, &OffsetCst, 1);
Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(L->getType()));
if (ConstantFoldLoadFromConstPtr(Src, &TD))
return Offset;
return -1;
}
@@ -1182,9 +1211,20 @@ static Value *GetMemInstValueForLoad(MemIntrinsic *SrcInst, unsigned Offset,
return CoerceAvailableValueToLoadType(Val, LoadTy, InsertPt, TD);
}
// ABORT;
return 0;
// Otherwise, this is a memcpy/memmove from a constant global.
MemTransferInst *MTI = cast<MemTransferInst>(SrcInst);
Constant *Src = cast<Constant>(MTI->getSource());
// Otherwise, see if we can constant fold a load from the constant with the
// offset applied as appropriate.
Src = ConstantExpr::getBitCast(Src,
llvm::Type::getInt8PtrTy(Src->getContext()));
Constant *OffsetCst =
ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset);
Src = ConstantExpr::getGetElementPtr(Src, &OffsetCst, 1);
Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy));
return ConstantFoldLoadFromConstPtr(Src, &TD);
}