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[InstCombine] Let shrinkSplatShuffle act on vectors of different lengths (#148593)

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shrinkSplatShuffle in InstCombine would only move truncs up through
shuffles if those shuffles inputs had the exact same type as their
output, this PR weakens this constraint to only requiring that the
scalar type of the input and output match.
This commit is contained in:
Adar Dagan
2025-07-28 14:00:37 +03:00
committed by GitHub
parent 5ad7ef6fec
commit 1afb42bc10
3 changed files with 23 additions and 6 deletions
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8
llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
View File

@@ -708,10 +708,14 @@ static Instruction *shrinkSplatShuffle(TruncInst &Trunc,
auto *Shuf = dyn_cast<ShuffleVectorInst>(Trunc.getOperand(0));
if (Shuf && Shuf->hasOneUse() && match(Shuf->getOperand(1), m_Undef()) &&
all_equal(Shuf->getShuffleMask()) &&
Shuf->getType() == Shuf->getOperand(0)->getType()) {
ElementCount::isKnownGE(Shuf->getType()->getElementCount(),
cast<VectorType>(Shuf->getOperand(0)->getType())
->getElementCount())) {
// trunc (shuf X, Undef, SplatMask) --> shuf (trunc X), Poison, SplatMask
// trunc (shuf X, Poison, SplatMask) --> shuf (trunc X), Poison, SplatMask
Value *NarrowOp = Builder.CreateTrunc(Shuf->getOperand(0), Trunc.getType());
Type *NewTruncTy = Shuf->getOperand(0)->getType()->getWithNewType(
Trunc.getType()->getScalarType());
Value *NarrowOp = Builder.CreateTrunc(Shuf->getOperand(0), NewTruncTy);
return new ShuffleVectorInst(NarrowOp, Shuf->getShuffleMask());
}

4
llvm/test/Transforms/InstCombine/trunc-inseltpoison.ll
View File

@@ -959,8 +959,8 @@ define <3 x i31> @wide_splat3(<3 x i33> %x) {
define <8 x i8> @wide_lengthening_splat(<4 x i16> %v) {
; CHECK-LABEL: @wide_lengthening_splat(
; CHECK-NEXT: [[SHUF:%.*]] = shufflevector <4 x i16> [[V:%.*]], <4 x i16> poison, <8 x i32> zeroinitializer
; CHECK-NEXT: [[TR:%.*]] = trunc <8 x i16> [[SHUF]] to <8 x i8>
; CHECK-NEXT: [[TMP1:%.*]] = trunc <4 x i16> [[V:%.*]] to <4 x i8>
; CHECK-NEXT: [[TR:%.*]] = shufflevector <4 x i8> [[TMP1]], <4 x i8> poison, <8 x i32> zeroinitializer
; CHECK-NEXT: ret <8 x i8> [[TR]]
;
%shuf = shufflevector <4 x i16> %v, <4 x i16> %v, <8 x i32> zeroinitializer

17
llvm/test/Transforms/InstCombine/trunc.ll
View File

@@ -960,8 +960,8 @@ define <3 x i31> @wide_splat3(<3 x i33> %x) {
define <8 x i8> @wide_lengthening_splat(<4 x i16> %v) {
; CHECK-LABEL: @wide_lengthening_splat(
; CHECK-NEXT: [[SHUF:%.*]] = shufflevector <4 x i16> [[V:%.*]], <4 x i16> poison, <8 x i32> zeroinitializer
; CHECK-NEXT: [[TR:%.*]] = trunc <8 x i16> [[SHUF]] to <8 x i8>
; CHECK-NEXT: [[TMP1:%.*]] = trunc <4 x i16> [[V:%.*]] to <4 x i8>
; CHECK-NEXT: [[TR:%.*]] = shufflevector <4 x i8> [[TMP1]], <4 x i8> poison, <8 x i32> zeroinitializer
; CHECK-NEXT: ret <8 x i8> [[TR]]
;
%shuf = shufflevector <4 x i16> %v, <4 x i16> %v, <8 x i32> zeroinitializer
@@ -969,6 +969,19 @@ define <8 x i8> @wide_lengthening_splat(<4 x i16> %v) {
ret <8 x i8> %tr
}
; This is a negative test, we expect the trunc to remain after the shuffle as it
; might not be beneficial to preform trunc on a wider type
define <4 x i8> @wide_shortening_splat(<8 x i16> %v) {
; CHECK-LABEL: @wide_shortening_splat(
; CHECK-NEXT: [[SHUF:%.*]] = shufflevector <8 x i16> [[V:%.*]], <8 x i16> poison, <4 x i32> zeroinitializer
; CHECK-NEXT: [[TR:%.*]] = trunc <4 x i16> [[SHUF]] to <4 x i8>
; CHECK-NEXT: ret <4 x i8> [[TR]]
;
%shuf = shufflevector <8 x i16> %v, <8 x i16> %v, <4 x i32> zeroinitializer
%tr = trunc <4 x i16> %shuf to <4 x i8>
ret <4 x i8> %tr
}
define <2 x i8> @narrow_add_vec_constant(<2 x i32> %x) {
; CHECK-LABEL: @narrow_add_vec_constant(
; CHECK-NEXT: [[TMP1:%.*]] = trunc <2 x i32> [[X:%.*]] to <2 x i8>