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InstCombine: Canonicalize (gep i8* X, -(ptrtoint Y)) to (sub (ptrtoint X), (ptrtoint Y))

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The GEP pattern is what SCEV expander emits for "ugly geps". The latter is what
you get for pointer subtraction in C code. The rest of instcombine already
knows how to deal with that so just canonicalize on that.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191090 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Benjamin Kramer
2013-09-20 14:38:44 +00:00
parent 8607525110
commit 4c332fa5a5
2 changed files with 28 additions and 0 deletions
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14
lib/Transforms/InstCombine/InstructionCombining.cpp
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@ -1182,6 +1182,20 @@ Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst &GEP) {
GetElementPtrInst::Create(Src->getOperand(0), Indices, GEP.getName());
}
// Canonicalize (gep i8* X, -(ptrtoint Y)) to (sub (ptrtoint X), (ptrtoint Y))
// The GEP pattern is emitted by the SCEV expander for certain kinds of
// pointer arithmetic.
if (TD && GEP.getNumIndices() == 1 &&
match(GEP.getOperand(1), m_Neg(m_PtrToInt(m_Value()))) &&
GEP.getType() == Builder->getInt8PtrTy() &&
GEP.getOperand(1)->getType()->getScalarSizeInBits() ==
TD->getPointerSizeInBits(GEP.getPointerAddressSpace())) {
Operator *Index = cast<Operator>(GEP.getOperand(1));
Value *PtrToInt = Builder->CreatePtrToInt(PtrOp, Index->getType());
Value *NewSub = Builder->CreateSub(PtrToInt, Index->getOperand(1));
return CastInst::Create(Instruction::IntToPtr, NewSub, GEP.getType());
}
// Handle gep(bitcast x) and gep(gep x, 0, 0, 0).
Value *StrippedPtr = PtrOp->stripPointerCasts();
PointerType *StrippedPtrTy = dyn_cast<PointerType>(StrippedPtr->getType());