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apply Dan's fix for PR8268 which allows constant folding to handle indexes over

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zero sized elements.  This allows us to compile:

  #include <string>
  void foo() { std::string s; }

into an empty function.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@119933 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2010-11-21 08:39:01 +00:00
parent cbd323ad52
commit c1da204c43
1 changed files with 15 additions and 7 deletions
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22
lib/Analysis/ConstantFolding.cpp
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@ -538,7 +538,7 @@ static Constant *CastGEPIndices(Constant *const *Ops, unsigned NumOps,
for (unsigned i = 1; i != NumOps; ++i) {
if ((i == 1 ||
!isa<StructType>(GetElementPtrInst::getIndexedType(Ops[0]->getType(),
reinterpret_cast<Value *const *>(Ops+1),
reinterpret_cast<Value *const *>(Ops+1),
i-1))) &&
Ops[i]->getType() != IntPtrTy) {
Any = true;
@ -639,12 +639,19 @@ static Constant *SymbolicallyEvaluateGEP(Constant *const *Ops, unsigned NumOps,
// Determine which element of the array the offset points into.
APInt ElemSize(BitWidth, TD->getTypeAllocSize(ATy->getElementType()));
const IntegerType *IntPtrTy = TD->getIntPtrType(Ty->getContext());
if (ElemSize == 0)
return 0;
APInt NewIdx = Offset.udiv(ElemSize);
Offset -= NewIdx * ElemSize;
NewIdxs.push_back(ConstantInt::get(TD->getIntPtrType(Ty->getContext()),
NewIdx));
// The element size is 0. This may be [0 x Ty]*, so just use a zero
// index for this level and procede to the next level to see if it can
// accomodate the offset.
NewIdxs.push_back(ConstantInt::get(IntPtrTy, 0));
else {
// The element size is non-zero divide the offset by the element
// size (rounding down), to compute the index at this level.
APInt NewIdx = Offset.udiv(ElemSize);
Offset -= NewIdx * ElemSize;
NewIdxs.push_back(ConstantInt::get(IntPtrTy, NewIdx));
}
Ty = ATy->getElementType();
} else if (const StructType *STy = dyn_cast<StructType>(Ty)) {
// Determine which field of the struct the offset points into. The
@ -743,7 +750,8 @@ Constant *llvm::ConstantFoldInstruction(Instruction *I, const TargetData *TD) {
Constant *llvm::ConstantFoldConstantExpression(const ConstantExpr *CE,
const TargetData *TD) {
SmallVector<Constant*, 8> Ops;
for (User::const_op_iterator i = CE->op_begin(), e = CE->op_end(); i != e; ++i) {
for (User::const_op_iterator i = CE->op_begin(), e = CE->op_end();
i != e; ++i) {
Constant *NewC = cast<Constant>(*i);
// Recursively fold the ConstantExpr's operands.
if (ConstantExpr *NewCE = dyn_cast<ConstantExpr>(NewC))