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Implement InstCombine/getelementptr.ll:test9, which is the source of many

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ugly and giant constnat exprs in some programs.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@17066 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner
2004-10-16 19:44:59 +00:00
parent 51a2c5aebf
commit 061718cba8
1 changed files with 18 additions and 0 deletions
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18
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -4018,6 +4018,24 @@ bool InstCombiner::runOnFunction(Function &F) {
// Instruction isn't dead, see if we can constant propagate it... // Instruction isn't dead, see if we can constant propagate it...
if (Constant *C = ConstantFoldInstruction(I)) { if (Constant *C = ConstantFoldInstruction(I)) {
if (isa<GetElementPtrInst>(I) &&
cast<Constant>(I->getOperand(0))->isNullValue() &&
!isa<ConstantPointerNull>(C)) {
// If this is a constant expr gep that is effectively computing an
// "offsetof", fold it into 'cast int X to T*' instead of 'gep 0, 0, 12'
bool isFoldableGEP = true;
for (unsigned i = 1, e = I->getNumOperands(); i != e; ++i)
if (!isa<ConstantInt>(I->getOperand(i)))
isFoldableGEP = false;
if (isFoldableGEP) {
uint64_t Offset = TD->getIndexedOffset(I->getOperand(0)->getType(),
std::vector<Value*>(I->op_begin()+1, I->op_end()));
C = ConstantUInt::get(Type::ULongTy, Offset);
C = ConstantUInt::getCast(C, TD->getIntPtrType());
C = ConstantExpr::getCast(C, I->getType());
}
}
// Add operands to the worklist... // Add operands to the worklist...
AddUsesToWorkList(*I); AddUsesToWorkList(*I);
ReplaceInstUsesWith(*I, C); ReplaceInstUsesWith(*I, C);