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[InstSimplify] Fold gep (gep V, C), (sub 0, V) to C 

llvm-svn: 277952
This commit is contained in:
David Majnemer 2016-08-07 07:58:12 +00:00
parent dc8767a49a
commit d150137f64
2 changed files with 33 additions and 0 deletions
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20
llvm/lib/Analysis/InstructionSimplify.cpp
View File

@ -3645,6 +3645,26 @@ static Value *SimplifyGEPInst(Type *SrcTy, ArrayRef<Value *> Ops,
}
}
// gep (gep V, C), (sub 0, V) -> C
if (Q.DL.getTypeAllocSize(LastType) == 1 &&
all_of(Ops.slice(1).drop_back(1),
[](Value *Idx) { return match(Idx, m_Zero()); })) {
unsigned PtrWidth =
Q.DL.getPointerSizeInBits(Ops[0]->getType()->getPointerAddressSpace());
if (Q.DL.getTypeSizeInBits(Ops.back()->getType()) == PtrWidth) {
APInt BasePtrOffset(PtrWidth, 0);
Value *StrippedBasePtr =
Ops[0]->stripAndAccumulateInBoundsConstantOffsets(Q.DL,
BasePtrOffset);
if (match(Ops.back(),
m_Sub(m_Zero(), m_PtrToInt(m_Specific(StrippedBasePtr))))) {
auto *CI = ConstantInt::get(GEPTy->getContext(), BasePtrOffset);
return ConstantExpr::getIntToPtr(CI, GEPTy);
}
}
}
// Check to see if this is constant foldable.
for (unsigned i = 0, e = Ops.size(); i != e; ++i)
if (!isa<Constant>(Ops[i]))

13
llvm/test/Transforms/InstSimplify/compare.ll
View File

@ -219,6 +219,19 @@ define i1 @gep17() {
; CHECK-NEXT: ret i1 true
}
define i32 @gep18() {
; CHECK-LABEL: @gep18(
%alloca = alloca i32, align 4 ; alloca + 0
%gep = getelementptr inbounds i32, i32* %alloca, i32 1 ; alloca + 4
%bc = bitcast i32* %gep to [4 x i8]* ; alloca + 4
%pti = ptrtoint i32* %alloca to i32 ; alloca
%sub = sub i32 0, %pti ; -alloca
%add = getelementptr [4 x i8], [4 x i8]* %bc, i32 0, i32 %sub ; alloca + 4 - alloca == 4
%add_to_int = ptrtoint i8* %add to i32 ; 4
ret i32 %add_to_int ; 4
; CHECK-NEXT: ret i32 4
}
define i1 @zext(i32 %x) {
; CHECK-LABEL: @zext(
%e1 = zext i32 %x to i64