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When determining the new index for an insertelement, we may not assume that an

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index greater than the size of the vector is invalid. The shuffle may be
shrinking the size of the vector. Fixes a crash!

Also drop the maximum recursion depth of the safety check for this
optimization to five.

llvm-svn: 183080
This commit is contained in:
Nick Lewycky 2013-06-01 20:51:31 +00:00
parent 2425aef2ad
commit 8e323b56b7
2 changed files with 20 additions and 7 deletions
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16
lib/Transforms/InstCombine/InstCombineVectorOps.cpp
View File

@ -497,7 +497,7 @@ Instruction *InstCombiner::visitInsertElementInst(InsertElementInst &IE) {
/// Return true if we can evaluate the specified expression tree if the vector
/// elements were shuffled in a different order.
static bool CanEvaluateShuffled(Value *V, ArrayRef<int> Mask,
unsigned Depth = 100) {
unsigned Depth = 5) {
// We can always reorder the elements of a constant.
if (isa<Constant>(V))
return true;
@ -718,19 +718,21 @@ InstCombiner::EvaluateInDifferentElementOrder(Value *V, ArrayRef<int> Mask) {
}
case Instruction::InsertElement: {
int Element = cast<ConstantInt>(I->getOperand(2))->getLimitedValue();
if (Element < 0 || Element >= (int)Mask.size()) {
// Such instructions are valid and exhibit undefined behaviour.
return UndefValue::get(I->getType());
}
// The insertelement was inserting at Element. Figure out which element
// that becomes after shuffling. The answer is guaranteed to be unique
// by CanEvaluateShuffled.
bool Found = false;
int Index = 0;
for (int e = Mask.size(); Index != e; ++Index)
if (Mask[Index] == Element)
for (int e = Mask.size(); Index != e; ++Index) {
if (Mask[Index] == Element) {
Found = true;
break;
}
}
if (!Found)
return UndefValue::get(I->getType());
Value *V = EvaluateInDifferentElementOrder(I->getOperand(0), Mask);
return InsertElementInst::Create(V, I->getOperand(1),
Builder->getInt32(Index), "", I);

11
test/Transforms/InstCombine/vec_shuffle.ll
View File

@ -174,3 +174,14 @@ define <2 x i8> @test13b(i8 %x) {
%B = shufflevector <2 x i8> %A, <2 x i8> undef, <2 x i32> <i32 undef, i32 0>
ret <2 x i8> %B
}
define <2 x i8> @test13c(i8 %x1, i8 %x2) {
; CHECK: @test13c
; CHECK-NEXT: insertelement <2 x i8> {{.*}}, i32 0
; CHECK-NEXT: insertelement <2 x i8> {{.*}}, i32 1
; CHECK-NEXT: ret
%A = insertelement <4 x i8> undef, i8 %x1, i32 0
%B = insertelement <4 x i8> %A, i8 %x2, i32 2
%C = shufflevector <4 x i8> %B, <4 x i8> undef, <2 x i32> <i32 0, i32 2>
ret <2 x i8> %C
}