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[ConstantFold] Don't incorrectly infer inbounds on array GEP

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The many levels of nesting inside the responsible code made it easy for
bugs to sneak in.  Flattening the logic makes it easier to see what's
going on.

llvm-svn: 275244
This commit is contained in:
David Majnemer 2016-07-13 03:24:41 +00:00
parent 255f536228
commit 1f224c132e
2 changed files with 69 additions and 42 deletions
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101
lib/IR/ConstantFold.cpp
View File

@ -2192,51 +2192,68 @@ static Constant *ConstantFoldGetElementPtrImpl(Type *PointeeTy, Constant *C,
bool Unknown = !isa<ConstantInt>(Idxs[0]);
for (unsigned i = 1, e = Idxs.size(); i != e;
Prev = Ty, Ty = cast<CompositeType>(Ty)->getTypeAtIndex(Idxs[i]), ++i) {
if (ConstantInt *CI = dyn_cast<ConstantInt>(Idxs[i])) {
if (isa<ArrayType>(Ty) && CI->getSExtValue() > 0 &&
!isIndexInRangeOfSequentialType(cast<ArrayType>(Ty), CI)) {
if (isa<SequentialType>(Prev)) {
// It's out of range, but we can factor it into the prior
// dimension.
NewIdxs.resize(Idxs.size());
uint64_t NumElements = 0;
if (auto *ATy = dyn_cast<ArrayType>(Ty))
NumElements = ATy->getNumElements();
else
NumElements = cast<VectorType>(Ty)->getNumElements();
ConstantInt *Factor = ConstantInt::get(CI->getType(), NumElements);
NewIdxs[i] = ConstantExpr::getSRem(CI, Factor);
Constant *PrevIdx = cast<Constant>(Idxs[i - 1]);
Constant *Div = ConstantExpr::getSDiv(CI, Factor);
unsigned CommonExtendedWidth =
std::max(PrevIdx->getType()->getIntegerBitWidth(),
Div->getType()->getIntegerBitWidth());
CommonExtendedWidth = std::max(CommonExtendedWidth, 64U);
// Before adding, extend both operands to i64 to avoid
// overflow trouble.
if (!PrevIdx->getType()->isIntegerTy(CommonExtendedWidth))
PrevIdx = ConstantExpr::getSExt(
PrevIdx,
Type::getIntNTy(Div->getContext(), CommonExtendedWidth));
if (!Div->getType()->isIntegerTy(CommonExtendedWidth))
Div = ConstantExpr::getSExt(
Div, Type::getIntNTy(Div->getContext(), CommonExtendedWidth));
NewIdxs[i - 1] = ConstantExpr::getAdd(PrevIdx, Div);
} else {
// It's out of range, but the prior dimension is a struct
// so we can't do anything about it.
Unknown = true;
}
}
} else {
auto *CI = dyn_cast<ConstantInt>(Idxs[i]);
if (!CI) {
// We don't know if it's in range or not.
Unknown = true;
continue;
}
if (isa<StructType>(Ty)) {
// The verify makes sure that GEPs into a struct are in range.
continue;
}
auto *STy = cast<SequentialType>(Ty);
if (isa<PointerType>(STy)) {
// We don't know if it's in range or not.
Unknown = true;
continue;
}
if (isa<VectorType>(STy)) {
// There can be awkward padding in after a non-power of two vector.
Unknown = true;
continue;
}
if (isIndexInRangeOfSequentialType(STy, CI))
// It's in range, skip to the next index.
continue;
if (!isa<SequentialType>(Prev)) {
// It's out of range, but the prior dimension is a struct
// so we can't do anything about it.
Unknown = true;
continue;
}
if (CI->getSExtValue() < 0) {
// It's out of range and negative, don't try to factor it.
Unknown = true;
continue;
}
// It's out of range, but we can factor it into the prior
// dimension.
NewIdxs.resize(Idxs.size());
// Determine the number of elements in our sequential type.
uint64_t NumElements = STy->getArrayNumElements();
ConstantInt *Factor = ConstantInt::get(CI->getType(), NumElements);
NewIdxs[i] = ConstantExpr::getSRem(CI, Factor);
Constant *PrevIdx = cast<Constant>(Idxs[i - 1]);
Constant *Div = ConstantExpr::getSDiv(CI, Factor);
unsigned CommonExtendedWidth =
std::max(PrevIdx->getType()->getIntegerBitWidth(),
Div->getType()->getIntegerBitWidth());
CommonExtendedWidth = std::max(CommonExtendedWidth, 64U);
// Before adding, extend both operands to i64 to avoid
// overflow trouble.
if (!PrevIdx->getType()->isIntegerTy(CommonExtendedWidth))
PrevIdx = ConstantExpr::getSExt(
PrevIdx, Type::getIntNTy(Div->getContext(), CommonExtendedWidth));
if (!Div->getType()->isIntegerTy(CommonExtendedWidth))
Div = ConstantExpr::getSExt(
Div, Type::getIntNTy(Div->getContext(), CommonExtendedWidth));
NewIdxs[i - 1] = ConstantExpr::getAdd(PrevIdx, Div);
}
// If we did any factoring, start over with the adjusted indices.

10
test/Assembler/getelementptr.ll
View File

@ -46,3 +46,13 @@ define <2 x i8*> @test8(<2 x [2 x i8]*> %a) {
%w = getelementptr [2 x i8], <2 x [2 x i8]*> %a, <2 x i32> <i32 0, i32 0>, <2 x i8> <i8 0, i8 1>
ret <2 x i8*> %w
}
@array = internal global [16 x i32] [i32 -200, i32 -199, i32 -198, i32 -197, i32 -196, i32 -195, i32 -194, i32 -193, i32 -192, i32 -191, i32 -190, i32 -189, i32 -188, i32 -187, i32 -186, i32 -185], align 16
; Verify that array GEP doesn't incorrectly infer inbounds.
define i32* @test9() {
entry:
ret i32* getelementptr ([16 x i32], [16 x i32]* @array, i64 0, i64 -13)
; CHECK-LABEL: define i32* @test9(
; CHECK: ret i32* getelementptr ([16 x i32], [16 x i32]* @array, i64 0, i64 -13)
}