[llvm] 9d25b28 - [InstCombine] Explicitly canonicalize splat shuffles to use poison RHS

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2023-12-18T16:30:40+01:00
New Revision: 9d25b28b9e412b66bb58993dff6646a8f08b8c8c

URL: https://github.com/llvm/llvm-project/commit/9d25b28b9e412b66bb58993dff6646a8f08b8c8c
DIFF: https://github.com/llvm/llvm-project/commit/9d25b28b9e412b66bb58993dff6646a8f08b8c8c.diff

LOG: [InstCombine] Explicitly canonicalize splat shuffles to use poison RHS

This is usually handled by demanded elements simplification. However,
as that is not supported for scalable vectors, also handle it
explicitly here.

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
    llvm/test/Transforms/InstCombine/vec_shuffle.ll
    llvm/test/Transforms/InstCombine/vscale_extractelement.ll
    llvm/test/Transforms/InstCombine/vscale_insertelement.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp b/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
index c18fd5d99d0974..7a9a0950c2b6b8 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
@@ -2774,6 +2774,11 @@ Instruction *InstCombinerImpl::visitShuffleVectorInst(ShuffleVectorInst &SVI) {
   if (Instruction *I = simplifyBinOpSplats(SVI))
     return I;
 
+  // Canonicalize splat shuffle to use poison RHS. Handle this explicitly in
+  // order to support scalable vectors.
+  if (match(SVI.getShuffleMask(), m_ZeroMask()) && !isa<PoisonValue>(RHS))
+    return replaceOperand(SVI, 1, PoisonValue::get(RHS->getType()));
+
   if (isa<ScalableVectorType>(LHS->getType()))
     return nullptr;
 

diff  --git a/llvm/test/Transforms/InstCombine/vec_shuffle.ll b/llvm/test/Transforms/InstCombine/vec_shuffle.ll
index bef201196e6158..0c21dc88f8569e 100644
--- a/llvm/test/Transforms/InstCombine/vec_shuffle.ll
+++ b/llvm/test/Transforms/InstCombine/vec_shuffle.ll
@@ -67,7 +67,7 @@ define float @test6(<4 x float> %X) {
 
 define float @testvscale6(<vscale x 4 x float> %X) {
 ; CHECK-LABEL: @testvscale6(
-; CHECK-NEXT:    [[T2:%.*]] = shufflevector <vscale x 4 x float> [[X:%.*]], <vscale x 4 x float> undef, <vscale x 4 x i32> zeroinitializer
+; CHECK-NEXT:    [[T2:%.*]] = shufflevector <vscale x 4 x float> [[X:%.*]], <vscale x 4 x float> poison, <vscale x 4 x i32> zeroinitializer
 ; CHECK-NEXT:    [[R:%.*]] = extractelement <vscale x 4 x float> [[T2]], i64 0
 ; CHECK-NEXT:    ret float [[R]]
 ;

diff  --git a/llvm/test/Transforms/InstCombine/vscale_extractelement.ll b/llvm/test/Transforms/InstCombine/vscale_extractelement.ll
index 784229c948a6d3..f696ff469e205a 100644
--- a/llvm/test/Transforms/InstCombine/vscale_extractelement.ll
+++ b/llvm/test/Transforms/InstCombine/vscale_extractelement.ll
@@ -56,7 +56,7 @@ define i8 @extractelement_bitcast_useless_insert(<vscale x 2 x i32> %a, i32 %x)
 define i32 @extractelement_shuffle_maybe_out_of_range(i32 %v) {
 ; CHECK-LABEL: @extractelement_shuffle_maybe_out_of_range(
 ; CHECK-NEXT:    [[IN:%.*]] = insertelement <vscale x 4 x i32> undef, i32 [[V:%.*]], i64 0
-; CHECK-NEXT:    [[SPLAT:%.*]] = shufflevector <vscale x 4 x i32> [[IN]], <vscale x 4 x i32> undef, <vscale x 4 x i32> zeroinitializer
+; CHECK-NEXT:    [[SPLAT:%.*]] = shufflevector <vscale x 4 x i32> [[IN]], <vscale x 4 x i32> poison, <vscale x 4 x i32> zeroinitializer
 ; CHECK-NEXT:    [[R:%.*]] = extractelement <vscale x 4 x i32> [[SPLAT]], i64 4
 ; CHECK-NEXT:    ret i32 [[R]]
 ;
@@ -69,7 +69,7 @@ define i32 @extractelement_shuffle_maybe_out_of_range(i32 %v) {
 define i32 @extractelement_shuffle_invalid_index(i32 %v) {
 ; CHECK-LABEL: @extractelement_shuffle_invalid_index(
 ; CHECK-NEXT:    [[IN:%.*]] = insertelement <vscale x 4 x i32> undef, i32 [[V:%.*]], i64 0
-; CHECK-NEXT:    [[SPLAT:%.*]] = shufflevector <vscale x 4 x i32> [[IN]], <vscale x 4 x i32> undef, <vscale x 4 x i32> zeroinitializer
+; CHECK-NEXT:    [[SPLAT:%.*]] = shufflevector <vscale x 4 x i32> [[IN]], <vscale x 4 x i32> poison, <vscale x 4 x i32> zeroinitializer
 ; CHECK-NEXT:    [[R:%.*]] = extractelement <vscale x 4 x i32> [[SPLAT]], i64 4294967295
 ; CHECK-NEXT:    ret i32 [[R]]
 ;

diff  --git a/llvm/test/Transforms/InstCombine/vscale_insertelement.ll b/llvm/test/Transforms/InstCombine/vscale_insertelement.ll
index e9dc7f75eb5432..db22b3b657fb3f 100644
--- a/llvm/test/Transforms/InstCombine/vscale_insertelement.ll
+++ b/llvm/test/Transforms/InstCombine/vscale_insertelement.ll
@@ -89,7 +89,7 @@ define <vscale x 4 x float> @insertelement_sequene_may_not_be_splat(float %x) {
 define void @ossfuzz_27416(i32 %v, ptr %p) {
 ; CHECK-LABEL: @ossfuzz_27416(
 ; CHECK-NEXT:    [[IN:%.*]] = insertelement <vscale x 4 x i32> undef, i32 [[V:%.*]], i64 0
-; CHECK-NEXT:    [[SPLAT:%.*]] = shufflevector <vscale x 4 x i32> [[IN]], <vscale x 4 x i32> undef, <vscale x 4 x i32> zeroinitializer
+; CHECK-NEXT:    [[SPLAT:%.*]] = shufflevector <vscale x 4 x i32> [[IN]], <vscale x 4 x i32> poison, <vscale x 4 x i32> zeroinitializer
 ; CHECK-NEXT:    [[I1:%.*]] = insertelement <vscale x 4 x i32> [[SPLAT]], i32 undef, i64 128
 ; CHECK-NEXT:    store <vscale x 4 x i32> [[I1]], ptr [[P:%.*]], align 16
 ; CHECK-NEXT:    ret void