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Teach instcombine to increase the alignment of memset/memcpy/memmove when

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the pointer is known to come from either a global variable, alloca or
malloc.  This allows us to compile this:

  P = malloc(28);
  memset(P, 0, 28);

into explicit stores on PPC instead of a memset call.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@26577 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2006-03-06 20:18:44 +00:00
parent 6af7ef8da8
commit 95a959dc1a
1 changed files with 74 additions and 3 deletions
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77
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -5264,6 +5264,60 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
return 0;
}
/// GetKnownAlignment - If the specified pointer has an alignment that we can
/// determine, return it, otherwise return 0.
static unsigned GetKnownAlignment(Value *V, TargetData *TD) {
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) {
unsigned Align = GV->getAlignment();
if (Align == 0 && TD)
Align = TD->getTypeAlignment(GV->getType()->getElementType());
return Align;
} else if (AllocationInst *AI = dyn_cast<AllocationInst>(V)) {
unsigned Align = AI->getAlignment();
if (Align == 0 && TD) {
if (isa<AllocaInst>(AI))
Align = TD->getTypeAlignment(AI->getType()->getElementType());
else if (isa<MallocInst>(AI)) {
// Malloc returns maximally aligned memory.
Align = TD->getTypeAlignment(AI->getType()->getElementType());
Align = std::max(Align, (unsigned)TD->getTypeAlignment(Type::DoubleTy));
Align = std::max(Align, (unsigned)TD->getTypeAlignment(Type::LongTy));
}
}
return Align;
} else if (CastInst *CI = dyn_cast<CastInst>(V)) {
if (isa<PointerType>(CI->getOperand(0)->getType()))
return GetKnownAlignment(CI->getOperand(0), TD);
return 0;
} else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(V)) {
unsigned BaseAlignment = GetKnownAlignment(GEPI->getOperand(0), TD);
if (BaseAlignment == 0) return 0;
// If all indexes are zero, it is just the alignment of the base pointer.
bool AllZeroOperands = true;
for (unsigned i = 1, e = GEPI->getNumOperands(); i != e; ++i)
if (!isa<Constant>(GEPI->getOperand(i)) ||
!cast<Constant>(GEPI->getOperand(i))->isNullValue()) {
AllZeroOperands = false;
break;
}
if (AllZeroOperands)
return BaseAlignment;
// Otherwise, if the base alignment is >= the alignment we expect for the
// base pointer type, then we know that the resultant pointer is aligned at
// least as much as its type requires.
if (!TD) return 0;
const Type *BasePtrTy = GEPI->getOperand(0)->getType();
if (TD->getTypeAlignment(cast<PointerType>(BasePtrTy)->getElementType())
<= BaseAlignment)
return TD->getTypeAlignment(GEPI->getType()->getElementType());
return 0;
}
return 0;
}
/// visitCallInst - CallInst simplification. This mostly only handles folding
/// of intrinsic instructions. For normal calls, it allows visitCallSite to do
@ -5282,8 +5336,6 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
if (Constant *NumBytes = dyn_cast<Constant>(MI->getLength())) {
if (NumBytes->isNullValue()) return EraseInstFromFunction(CI);
// FIXME: Increase alignment here.
if (ConstantInt *CI = dyn_cast<ConstantInt>(NumBytes))
if (CI->getRawValue() == 1) {
// Replace the instruction with just byte operations. We would
@ -5295,7 +5347,7 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
// If we have a memmove and the source operation is a constant global,
// then the source and dest pointers can't alias, so we can change this
// into a call to memcpy.
if (MemMoveInst *MMI = dyn_cast<MemMoveInst>(II))
if (MemMoveInst *MMI = dyn_cast<MemMoveInst>(II)) {
if (GlobalVariable *GVSrc = dyn_cast<GlobalVariable>(MMI->getSource()))
if (GVSrc->isConstant()) {
Module *M = CI.getParent()->getParent()->getParent();
@ -5310,7 +5362,26 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
CI.setOperand(0, MemCpy);
Changed = true;
}
}
// If we can determine a pointer alignment that is bigger than currently
// set, update the alignment.
if (isa<MemCpyInst>(MI) || isa<MemMoveInst>(MI)) {
unsigned Alignment1 = GetKnownAlignment(MI->getOperand(1), TD);
unsigned Alignment2 = GetKnownAlignment(MI->getOperand(2), TD);
unsigned Align = std::min(Alignment1, Alignment2);
if (MI->getAlignment()->getRawValue() < Align) {
MI->setAlignment(ConstantUInt::get(Type::UIntTy, Align));
Changed = true;
}
} else if (isa<MemSetInst>(MI)) {
unsigned Alignment = GetKnownAlignment(MI->getDest(), TD);
if (MI->getAlignment()->getRawValue() < Alignment) {
MI->setAlignment(ConstantUInt::get(Type::UIntTy, Alignment));
Changed = true;
}
}
if (Changed) return II;
} else if (DbgStopPointInst *SPI = dyn_cast<DbgStopPointInst>(II)) {
// If this stoppoint is at the same source location as the previous