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[InstCombine] Check inbounds in load/store of gep null transform (PR48577)

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If the GEP isn't inbounds, then accessing a GEP of null location
is generally not UB.

While this is a minimal fix, the GEP of null handling should
probably be its own fold.
This commit is contained in:
Nikita Popov 2020-12-23 21:01:00 +01:00
parent 3617de4f6b
commit c4040d942a
3 changed files with 7 additions and 5 deletions
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5
lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
View File

@ -908,7 +908,8 @@ static bool canSimplifyNullStoreOrGEP(StoreInst &SI) {
auto *Ptr = SI.getPointerOperand();
if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(Ptr))
Ptr = GEPI->getOperand(0);
if (GEPI->isInBounds())
Ptr = GEPI->getOperand(0);
return (isa<ConstantPointerNull>(Ptr) &&
!NullPointerIsDefined(SI.getFunction(), SI.getPointerAddressSpace()));
}
@ -916,7 +917,7 @@ static bool canSimplifyNullStoreOrGEP(StoreInst &SI) {
static bool canSimplifyNullLoadOrGEP(LoadInst &LI, Value *Op) {
if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(Op)) {
const Value *GEPI0 = GEPI->getOperand(0);
if (isa<ConstantPointerNull>(GEPI0) &&
if (isa<ConstantPointerNull>(GEPI0) && GEPI->isInBounds() &&
!NullPointerIsDefined(LI.getFunction(), GEPI->getPointerAddressSpace()))
return true;
}

5
test/Transforms/InstCombine/load.ll
View File

@ -69,8 +69,9 @@ define i32 @load_gep_null_inbounds(i64 %X) {
define i32 @load_gep_null_not_inbounds(i64 %X) {
; CHECK-LABEL: @load_gep_null_not_inbounds(
; CHECK-NEXT: store i32 undef, i32* null, align 536870912
; CHECK-NEXT: ret i32 undef
; CHECK-NEXT: [[V:%.*]] = getelementptr i32, i32* null, i64 [[X:%.*]]
; CHECK-NEXT: [[R:%.*]] = load i32, i32* [[V]], align 4
; CHECK-NEXT: ret i32 [[R]]
;
%V = getelementptr i32, i32* null, i64 %X
%R = load i32, i32* %V

2
test/Transforms/InstCombine/store.ll
View File

@ -37,7 +37,7 @@ define void @store_at_gep_off_null_inbounds(i64 %offset) {
define void @store_at_gep_off_null_not_inbounds(i64 %offset) {
; CHECK-LABEL: @store_at_gep_off_null_not_inbounds(
; CHECK-NEXT: [[PTR:%.*]] = getelementptr i32, i32* null, i64 [[OFFSET:%.*]]
; CHECK-NEXT: store i32 undef, i32* [[PTR]], align 4
; CHECK-NEXT: store i32 24, i32* [[PTR]], align 4
; CHECK-NEXT: ret void
;
%ptr = getelementptr i32, i32 *null, i64 %offset