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[InstCombine] Fix miscompile bug in canEvaluateShuffled 

Summary:
Add restrictions in canEvaluateShuffled to prevent that we for example
transform

  %0 = insertelement <2 x i16> undef, i16 %a, i32 0
  %1 = srem <2 x i16> %0, <i16 2, i16 1>
  %2 = shufflevector <2 x i16> %1, <2 x i16> undef, <2 x i32> <i32 undef, i32 0>

into

   %1 = insertelement <2 x i16> undef, i16 %a, i32 1
   %2 = srem <2 x i16> %1, <i16 undef, i16 2>

as having an undef denominator makes the srem undefined (for all
vector elements).

Fixes: https://bugs.llvm.org/show_bug.cgi?id=43689

Reviewers: spatel, lebedev.ri

Reviewed By: spatel, lebedev.ri

Subscribers: lebedev.ri, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D69038

llvm-svn: 375208
This commit is contained in:
Bjorn Pettersson 2019-10-18 07:42:02 +00:00
parent 459134064d
commit 6456252dbf
2 changed files with 37 additions and 12 deletions
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18
llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
View File

@ -1061,17 +1061,23 @@ static bool canEvaluateShuffled(Value *V, ArrayRef<int> Mask,
if (Depth == 0) return false;
switch (I->getOpcode()) {
case Instruction::UDiv:
case Instruction::SDiv:
case Instruction::URem:
case Instruction::SRem:
// Propagating an undefined shuffle mask element to integer div/rem is not
// allowed because those opcodes can create immediate undefined behavior
// from an undefined element in an operand.
if (llvm::any_of(Mask, [](int M){ return M == -1; }))
return false;
LLVM_FALLTHROUGH;
case Instruction::Add:
case Instruction::FAdd:
case Instruction::Sub:
case Instruction::FSub:
case Instruction::Mul:
case Instruction::FMul:
case Instruction::UDiv:
case Instruction::SDiv:
case Instruction::FDiv:
case Instruction::URem:
case Instruction::SRem:
case Instruction::FRem:
case Instruction::Shl:
case Instruction::LShr:
@ -1092,9 +1098,7 @@ static bool canEvaluateShuffled(Value *V, ArrayRef<int> Mask,
case Instruction::FPExt:
case Instruction::GetElementPtr: {
// Bail out if we would create longer vector ops. We could allow creating
// longer vector ops, but that may result in more expensive codegen. We
// would also need to limit the transform to avoid undefined behavior for
// integer div/rem.
// longer vector ops, but that may result in more expensive codegen.
Type *ITy = I->getType();
if (ITy->isVectorTy() && Mask.size() > ITy->getVectorNumElements())
return false;

31
llvm/test/Transforms/InstCombine/shufflevector-div-rem.ll
View File

@ -8,7 +8,12 @@
; extracting the second element in the vector).
define i16 @test_srem_orig(i16 %a, i1 %cmp) {
; CHECK-LABEL: @test_srem_orig(
; CHECK-NEXT: ret i16 1
; CHECK-NEXT: [[SPLATINSERT:%.*]] = insertelement <2 x i16> undef, i16 [[A:%.*]], i32 0
; CHECK-NEXT: [[TMP1:%.*]] = srem <2 x i16> [[SPLATINSERT]], <i16 2, i16 1>
; CHECK-NEXT: [[SPLAT_OP:%.*]] = shufflevector <2 x i16> [[TMP1]], <2 x i16> undef, <2 x i32> <i32 undef, i32 0>
; CHECK-NEXT: [[T2:%.*]] = select i1 [[CMP:%.*]], <2 x i16> <i16 undef, i16 1>, <2 x i16> [[SPLAT_OP]]
; CHECK-NEXT: [[T3:%.*]] = extractelement <2 x i16> [[T2]], i32 1
; CHECK-NEXT: ret i16 [[T3]]
;
%splatinsert = insertelement <2 x i16> undef, i16 %a, i32 0
%splat = shufflevector <2 x i16> %splatinsert, <2 x i16> undef, <2 x i32> zeroinitializer
@ -24,7 +29,11 @@ define i16 @test_srem_orig(i16 %a, i1 %cmp) {
; "evaluateInDifferentElementOrder".
define <2 x i16> @test_srem(i16 %a, i1 %cmp) {
; CHECK-LABEL: @test_srem(
; CHECK-NEXT: ret <2 x i16> <i16 77, i16 99>
; CHECK-NEXT: [[SPLATINSERT:%.*]] = insertelement <2 x i16> undef, i16 [[A:%.*]], i32 0
; CHECK-NEXT: [[T1:%.*]] = srem <2 x i16> [[SPLATINSERT]], <i16 2, i16 1>
; CHECK-NEXT: [[SPLAT_OP:%.*]] = shufflevector <2 x i16> [[T1]], <2 x i16> undef, <2 x i32> <i32 undef, i32 0>
; CHECK-NEXT: [[T2:%.*]] = select i1 [[CMP:%.*]], <2 x i16> <i16 77, i16 99>, <2 x i16> [[SPLAT_OP]]
; CHECK-NEXT: ret <2 x i16> [[T2]]
;
%splatinsert = insertelement <2 x i16> undef, i16 %a, i32 0
%t1 = srem <2 x i16> %splatinsert, <i16 2, i16 1>
@ -35,7 +44,11 @@ define <2 x i16> @test_srem(i16 %a, i1 %cmp) {
define <2 x i16> @test_urem(i16 %a, i1 %cmp) {
; CHECK-LABEL: @test_urem(
; CHECK-NEXT: ret <2 x i16> <i16 77, i16 99>
; CHECK-NEXT: [[SPLATINSERT:%.*]] = insertelement <2 x i16> undef, i16 [[A:%.*]], i32 0
; CHECK-NEXT: [[T1:%.*]] = urem <2 x i16> [[SPLATINSERT]], <i16 3, i16 1>
; CHECK-NEXT: [[SPLAT_OP:%.*]] = shufflevector <2 x i16> [[T1]], <2 x i16> undef, <2 x i32> <i32 undef, i32 0>
; CHECK-NEXT: [[T2:%.*]] = select i1 [[CMP:%.*]], <2 x i16> <i16 77, i16 99>, <2 x i16> [[SPLAT_OP]]
; CHECK-NEXT: ret <2 x i16> [[T2]]
;
%splatinsert = insertelement <2 x i16> undef, i16 %a, i32 0
%t1 = urem <2 x i16> %splatinsert, <i16 3, i16 1>
@ -46,7 +59,11 @@ define <2 x i16> @test_urem(i16 %a, i1 %cmp) {
define <2 x i16> @test_sdiv(i16 %a, i1 %cmp) {
; CHECK-LABEL: @test_sdiv(
; CHECK-NEXT: ret <2 x i16> <i16 77, i16 99>
; CHECK-NEXT: [[SPLATINSERT:%.*]] = insertelement <2 x i16> undef, i16 [[A:%.*]], i32 0
; CHECK-NEXT: [[T1:%.*]] = sdiv <2 x i16> [[SPLATINSERT]], <i16 2, i16 1>
; CHECK-NEXT: [[SPLAT_OP:%.*]] = shufflevector <2 x i16> [[T1]], <2 x i16> undef, <2 x i32> <i32 undef, i32 0>
; CHECK-NEXT: [[T2:%.*]] = select i1 [[CMP:%.*]], <2 x i16> <i16 77, i16 99>, <2 x i16> [[SPLAT_OP]]
; CHECK-NEXT: ret <2 x i16> [[T2]]
;
%splatinsert = insertelement <2 x i16> undef, i16 %a, i32 0
%t1 = sdiv <2 x i16> %splatinsert, <i16 2, i16 1>
@ -57,7 +74,11 @@ define <2 x i16> @test_sdiv(i16 %a, i1 %cmp) {
define <2 x i16> @test_udiv(i16 %a, i1 %cmp) {
; CHECK-LABEL: @test_udiv(
; CHECK-NEXT: ret <2 x i16> <i16 77, i16 99>
; CHECK-NEXT: [[SPLATINSERT:%.*]] = insertelement <2 x i16> undef, i16 [[A:%.*]], i32 0
; CHECK-NEXT: [[T1:%.*]] = udiv <2 x i16> [[SPLATINSERT]], <i16 3, i16 1>
; CHECK-NEXT: [[SPLAT_OP:%.*]] = shufflevector <2 x i16> [[T1]], <2 x i16> undef, <2 x i32> <i32 undef, i32 0>
; CHECK-NEXT: [[T2:%.*]] = select i1 [[CMP:%.*]], <2 x i16> <i16 77, i16 99>, <2 x i16> [[SPLAT_OP]]
; CHECK-NEXT: ret <2 x i16> [[T2]]
;
%splatinsert = insertelement <2 x i16> undef, i16 %a, i32 0
%t1 = udiv <2 x i16> %splatinsert, <i16 3, i16 1>