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[InstCombine] Don't cover up poison elements for shifts when folding shuffles thru binops #141303

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Merged
lukel97 merged 2 commits into from
May 24, 2025
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[InstCombine] Don't cover up poison elements for shifts when folding shuffles thru binops #141303

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[InstCombine] Don't cover up poison elements for shifts when folding …
lukel97 May 23, 2025
eb8c2e1
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lukel97 May 24, 2025
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8 changes: 3 additions & 5 deletions llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
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Expand Up @@ -2257,11 +2257,9 @@ Instruction *InstCombinerImpl::foldVectorBinop(BinaryOperator &Inst) {
}
if (MayChange) {
Constant *NewC = ConstantVector::get(NewVecC);
// It may not be safe to execute a binop on a vector with poison elements
// because the entire instruction can be folded to undef or create poison
// that did not exist in the original code.
// TODO: The shift case should not be necessary.
if (Inst.isIntDivRem() || (Inst.isShift() && ConstOp1))
// Lanes of NewC not used by the shuffle will be poison which will cause
// UB for div/rem. Mask them with a safe constant.
if (Inst.isIntDivRem())
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@dtcxzyw dtcxzyw May 24, 2025

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The comment above is outdated.
See also 7cd3241

NewC = getSafeVectorConstantForBinop(Opcode, NewC, ConstOp1);

// Op(shuffle(V1, Mask), C) -> shuffle(Op(V1, NewC), Mask)
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8 changes: 4 additions & 4 deletions llvm/test/Transforms/InstCombine/vec_shuffle-inseltpoison.ll
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Expand Up @@ -880,7 +880,7 @@ define <2 x i32> @shl_splat_constant0(<2 x i32> %x) {

define <2 x i32> @shl_splat_constant1(<2 x i32> %x) {
; CHECK-LABEL: @shl_splat_constant1(
; CHECK-NEXT: [[TMP1:%.*]] = shl <2 x i32> [[X:%.*]], <i32 5, i32 0>
; CHECK-NEXT: [[TMP1:%.*]] = shl <2 x i32> [[X:%.*]], <i32 5, i32 poison>
; CHECK-NEXT: [[R:%.*]] = shufflevector <2 x i32> [[TMP1]], <2 x i32> poison, <2 x i32> zeroinitializer
; CHECK-NEXT: ret <2 x i32> [[R]]
;
Expand All @@ -902,7 +902,7 @@ define <2 x i32> @ashr_splat_constant0(<2 x i32> %x) {

define <2 x i32> @ashr_splat_constant1(<2 x i32> %x) {
; CHECK-LABEL: @ashr_splat_constant1(
; CHECK-NEXT: [[TMP1:%.*]] = ashr <2 x i32> [[X:%.*]], <i32 5, i32 0>
; CHECK-NEXT: [[TMP1:%.*]] = ashr <2 x i32> [[X:%.*]], <i32 5, i32 poison>
; CHECK-NEXT: [[R:%.*]] = shufflevector <2 x i32> [[TMP1]], <2 x i32> poison, <2 x i32> zeroinitializer
; CHECK-NEXT: ret <2 x i32> [[R]]
;
Expand All @@ -924,7 +924,7 @@ define <2 x i32> @lshr_splat_constant0(<2 x i32> %x) {

define <2 x i32> @lshr_splat_constant1(<2 x i32> %x) {
; CHECK-LABEL: @lshr_splat_constant1(
; CHECK-NEXT: [[TMP1:%.*]] = lshr <2 x i32> [[X:%.*]], <i32 5, i32 0>
; CHECK-NEXT: [[TMP1:%.*]] = lshr <2 x i32> [[X:%.*]], <i32 5, i32 poison>
; CHECK-NEXT: [[R:%.*]] = shufflevector <2 x i32> [[TMP1]], <2 x i32> poison, <2 x i32> zeroinitializer
; CHECK-NEXT: ret <2 x i32> [[R]]
;
Expand Down Expand Up @@ -1161,7 +1161,7 @@ entry:
define <4 x i16> @shl_constant_mask_undef(<4 x i16> %in) {
; CHECK-LABEL: @shl_constant_mask_undef(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[TMP0:%.*]] = shl <4 x i16> [[IN:%.*]], <i16 10, i16 0, i16 0, i16 0>
; CHECK-NEXT: [[TMP0:%.*]] = shl <4 x i16> [[IN:%.*]], <i16 10, i16 0, i16 poison, i16 poison>
; CHECK-NEXT: [[SHL:%.*]] = shufflevector <4 x i16> [[TMP0]], <4 x i16> poison, <4 x i32> <i32 0, i32 poison, i32 1, i32 1>
; CHECK-NEXT: ret <4 x i16> [[SHL]]
;
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8 changes: 4 additions & 4 deletions llvm/test/Transforms/InstCombine/vec_shuffle.ll
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Expand Up @@ -929,7 +929,7 @@ define <2 x i32> @shl_splat_constant0(<2 x i32> %x) {

define <2 x i32> @shl_splat_constant1(<2 x i32> %x) {
; CHECK-LABEL: @shl_splat_constant1(
; CHECK-NEXT: [[TMP1:%.*]] = shl <2 x i32> [[X:%.*]], <i32 5, i32 0>
; CHECK-NEXT: [[TMP1:%.*]] = shl <2 x i32> [[X:%.*]], <i32 5, i32 poison>
; CHECK-NEXT: [[R:%.*]] = shufflevector <2 x i32> [[TMP1]], <2 x i32> poison, <2 x i32> zeroinitializer
; CHECK-NEXT: ret <2 x i32> [[R]]
;
Expand All @@ -951,7 +951,7 @@ define <2 x i32> @ashr_splat_constant0(<2 x i32> %x) {

define <2 x i32> @ashr_splat_constant1(<2 x i32> %x) {
; CHECK-LABEL: @ashr_splat_constant1(
; CHECK-NEXT: [[TMP1:%.*]] = ashr <2 x i32> [[X:%.*]], <i32 5, i32 0>
; CHECK-NEXT: [[TMP1:%.*]] = ashr <2 x i32> [[X:%.*]], <i32 5, i32 poison>
; CHECK-NEXT: [[R:%.*]] = shufflevector <2 x i32> [[TMP1]], <2 x i32> poison, <2 x i32> zeroinitializer
; CHECK-NEXT: ret <2 x i32> [[R]]
;
Expand All @@ -973,7 +973,7 @@ define <2 x i32> @lshr_splat_constant0(<2 x i32> %x) {

define <2 x i32> @lshr_splat_constant1(<2 x i32> %x) {
; CHECK-LABEL: @lshr_splat_constant1(
; CHECK-NEXT: [[TMP1:%.*]] = lshr <2 x i32> [[X:%.*]], <i32 5, i32 0>
; CHECK-NEXT: [[TMP1:%.*]] = lshr <2 x i32> [[X:%.*]], <i32 5, i32 poison>
; CHECK-NEXT: [[R:%.*]] = shufflevector <2 x i32> [[TMP1]], <2 x i32> poison, <2 x i32> zeroinitializer
; CHECK-NEXT: ret <2 x i32> [[R]]
;
Expand Down Expand Up @@ -1210,7 +1210,7 @@ entry:
define <4 x i16> @shl_constant_mask_undef(<4 x i16> %in) {
; CHECK-LABEL: @shl_constant_mask_undef(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[TMP0:%.*]] = shl <4 x i16> [[IN:%.*]], <i16 10, i16 0, i16 0, i16 0>
; CHECK-NEXT: [[TMP0:%.*]] = shl <4 x i16> [[IN:%.*]], <i16 10, i16 0, i16 poison, i16 poison>
; CHECK-NEXT: [[SHL:%.*]] = shufflevector <4 x i16> [[TMP0]], <4 x i16> poison, <4 x i32> <i32 0, i32 poison, i32 1, i32 1>
; CHECK-NEXT: ret <4 x i16> [[SHL]]
;
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8 changes: 4 additions & 4 deletions llvm/test/Transforms/LoopVectorize/AArch64/deterministic-type-shrinkage.ll
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Expand Up @@ -164,8 +164,8 @@ define void @test_shrink_zext_in_preheader(ptr noalias %src, ptr noalias %dst, i
; CHECK-NEXT: [[TMP1:%.*]] = insertelement <16 x i16> poison, i16 [[TMP0]], i64 0
; CHECK-NEXT: [[TMP2:%.*]] = insertelement <16 x i16> poison, i16 [[B]], i64 0
; CHECK-NEXT: [[TMP3:%.*]] = mul <16 x i16> [[TMP1]], [[TMP2]]
; CHECK-NEXT: [[TMP4:%.*]] = lshr <16 x i16> [[TMP3]], <i16 8, i16 0, i16 0, i16 0, i16 0, i16 0, i16 0, i16 0, i16 0, i16 0, i16 0, i16 0, i16 0, i16 0, i16 0, i16 0>
; CHECK-NEXT: [[TMP5:%.*]] = trunc <16 x i16> [[TMP4]] to <16 x i8>
; CHECK-NEXT: [[TMP4:%.*]] = lshr <16 x i16> [[TMP3]], <i16 8, i16 poison, i16 poison, i16 poison, i16 poison, i16 poison, i16 poison, i16 poison, i16 poison, i16 poison, i16 poison, i16 poison, i16 poison, i16 poison, i16 poison, i16 poison>
; CHECK-NEXT: [[TMP5:%.*]] = trunc nuw <16 x i16> [[TMP4]] to <16 x i8>
; CHECK-NEXT: [[TMP6:%.*]] = shufflevector <16 x i8> [[TMP5]], <16 x i8> poison, <16 x i32> zeroinitializer
; CHECK-NEXT: br label [[VECTOR_BODY:%.*]]
; CHECK: vector.body:
Expand All @@ -187,8 +187,8 @@ define void @test_shrink_zext_in_preheader(ptr noalias %src, ptr noalias %dst, i
; CHECK-NEXT: [[TMP12:%.*]] = insertelement <8 x i16> poison, i16 [[TMP11]], i64 0
; CHECK-NEXT: [[TMP13:%.*]] = insertelement <8 x i16> poison, i16 [[B]], i64 0
; CHECK-NEXT: [[TMP14:%.*]] = mul <8 x i16> [[TMP12]], [[TMP13]]
; CHECK-NEXT: [[TMP15:%.*]] = lshr <8 x i16> [[TMP14]], <i16 8, i16 0, i16 0, i16 0, i16 0, i16 0, i16 0, i16 0>
; CHECK-NEXT: [[TMP16:%.*]] = trunc <8 x i16> [[TMP15]] to <8 x i8>
; CHECK-NEXT: [[TMP15:%.*]] = lshr <8 x i16> [[TMP14]], <i16 8, i16 poison, i16 poison, i16 poison, i16 poison, i16 poison, i16 poison, i16 poison>
; CHECK-NEXT: [[TMP16:%.*]] = trunc nuw <8 x i16> [[TMP15]] to <8 x i8>
; CHECK-NEXT: [[TMP17:%.*]] = shufflevector <8 x i8> [[TMP16]], <8 x i8> poison, <8 x i32> zeroinitializer
; CHECK-NEXT: br label [[VEC_EPILOG_VECTOR_BODY:%.*]]
; CHECK: vec.epilog.vector.body:
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