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InstCombine: Combine gep X, (Y-X) to Y

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We try to perform this transform in InstSimplify but we aren't always
able to.  Sometimes, we need to insert a bitcast if X and Y don't have
the same time.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216598 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer 2014-08-27 20:08:37 +00:00
parent 48164ed24d
commit 8ee308f499
2 changed files with 38 additions and 14 deletions
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39
lib/Transforms/InstCombine/InstructionCombining.cpp
View File

@ -1516,28 +1516,39 @@ Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst &GEP) {
Type *Ty = PtrTy->getPointerElementType();
uint64_t TyAllocSize = DL->getTypeAllocSize(Ty);
// 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.
uint64_t C;
Value *NegPtrToInt = nullptr;
Value *V = nullptr;
if (TyAllocSize == 1) {
NegPtrToInt = GEP.getOperand(1);
V = GEP.getOperand(1);
} else if (match(GEP.getOperand(1),
m_AShr(m_Value(NegPtrToInt), m_ConstantInt(C)))) {
m_AShr(m_Value(V), m_ConstantInt(C)))) {
if (TyAllocSize != 1ULL << C)
NegPtrToInt = nullptr;
V = nullptr;
} else if (match(GEP.getOperand(1),
m_SDiv(m_Value(NegPtrToInt), m_ConstantInt(C)))) {
m_SDiv(m_Value(V), m_ConstantInt(C)))) {
if (TyAllocSize != C)
NegPtrToInt = nullptr;
V = nullptr;
}
if (NegPtrToInt && match(NegPtrToInt, m_Neg(m_PtrToInt(m_Value())))) {
Operator *Index = cast<Operator>(NegPtrToInt);
Value *PtrToInt = Builder->CreatePtrToInt(PtrOp, Index->getType());
Value *NewSub = Builder->CreateSub(PtrToInt, Index->getOperand(1));
return CastInst::Create(Instruction::IntToPtr, NewSub, GEP.getType());
if (V) {
// Canonicalize (gep i8* X, -(ptrtoint Y))
// to (inttoptr (sub (ptrtoint X), (ptrtoint Y)))
// The GEP pattern is emitted by the SCEV expander for certain kinds of
// pointer arithmetic.
if (match(V, m_Neg(m_PtrToInt(m_Value())))) {
Operator *Index = cast<Operator>(V);
Value *PtrToInt = Builder->CreatePtrToInt(PtrOp, Index->getType());
Value *NewSub = Builder->CreateSub(PtrToInt, Index->getOperand(1));
return CastInst::Create(Instruction::IntToPtr, NewSub, GEP.getType());
}
// Canonicalize (gep i8* X, (ptrtoint Y)-(ptrtoint X))
// to (bitcast Y)
Value *Y;
if (match(V, m_Sub(m_PtrToInt(m_Value(Y)),
m_PtrToInt(m_Specific(GEP.getOperand(0)))))) {
return CastInst::CreatePointerBitCastOrAddrSpaceCast(Y,
GEP.getType());
}
}
}
}

13
test/Transforms/InstCombine/getelementptr.ll
View File

@ -858,6 +858,19 @@ define %struct.C* @test44(%struct.C* %c1, %struct.C* %c2) {
; CHECK-NEXT: ret %struct.C* [[INTTOPTR]]
}
define %struct.C* @test45(%struct.C* %c1, %struct.C** %c2) {
%ptrtoint1 = ptrtoint %struct.C* %c1 to i64
%ptrtoint2 = ptrtoint %struct.C** %c2 to i64
%sub = sub i64 %ptrtoint2, %ptrtoint1 ; C2 - C1
%shr = sdiv i64 %sub, 7
%gep = getelementptr inbounds %struct.C* %c1, i64 %shr ; C1 + (C2 - C1)
ret %struct.C* %gep
; CHECK-LABEL: @test45(
; CHECK-NEXT: [[BITCAST:%.*]] = bitcast %struct.C** %c2 to %struct.C*
; CHECK-NEXT: ret %struct.C* [[BITCAST]]
}
define i32 addrspace(1)* @ascast_0_gep(i32* %p) nounwind {
; CHECK-LABEL: @ascast_0_gep(
; CHECK-NOT: getelementptr