[llvm] [X86] combineConcatVectorOps - convert PSHUFB/PSADBW/VPMADDUBSW/VPMADDUBSW concatenation to use combineConcatVectorOps recursion (PR #130592)

[Simon Pilgrim via llvm-commits]

https://github.com/RKSimon created https://github.com/llvm/llvm-project/pull/130592

Only concatenate nodes if at least one operand is beneficial to concatenate

>From 527ab9ff6bf46c709c5ffc9666384e012f9d6cd7 Mon Sep 17 00:00:00 2001
From: Simon Pilgrim <llvm-dev at redking.me.uk>
Date: Mon, 10 Mar 2025 12:35:45 +0000
Subject: [PATCH] [X86] combineConcatVectorOps - convert
 PSHUFB/PSADBW/VPMADDUBSW/VPMADDUBSW concatenation to use
 combineConcatVectorOps recursion

Only concatenate nodes if at least one operand is beneficial to concatenate
---
 llvm/lib/Target/X86/X86ISelLowering.cpp        | 10 +++++++---
 llvm/test/CodeGen/X86/combine-pmadd.ll         | 18 +++++++-----------
 .../X86/vector-shuffle-combining-avx2.ll       | 10 ++++------
 3 files changed, 18 insertions(+), 20 deletions(-)

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index ccd7f2418fcd1..3bfd902b7a83b 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -58095,9 +58095,13 @@ static SDValue combineConcatVectorOps(const SDLoc &DL, MVT VT,
         MVT SrcVT = Op0.getOperand(0).getSimpleValueType();
         SrcVT = MVT::getVectorVT(SrcVT.getScalarType(),
                                  NumOps * SrcVT.getVectorNumElements());
-        return DAG.getNode(Op0.getOpcode(), DL, VT,
-                           ConcatSubOperand(SrcVT, Ops, 0),
-                           ConcatSubOperand(SrcVT, Ops, 1));
+        SDValue Concat0 = CombineSubOperand(SrcVT, Ops, 0);
+        SDValue Concat1 = CombineSubOperand(SrcVT, Ops, 1);
+        if (Concat0 || Concat1)
+          return DAG.getNode(
+              Op0.getOpcode(), DL, VT,
+              Concat0 ? Concat0 : ConcatSubOperand(SrcVT, Ops, 0),
+              Concat1 ? Concat1 : ConcatSubOperand(SrcVT, Ops, 1));
       }
       break;
     case X86ISD::VPERMV:
diff --git a/llvm/test/CodeGen/X86/combine-pmadd.ll b/llvm/test/CodeGen/X86/combine-pmadd.ll
index 242dfb030d2f8..d9283aa8591fc 100644
--- a/llvm/test/CodeGen/X86/combine-pmadd.ll
+++ b/llvm/test/CodeGen/X86/combine-pmadd.ll
@@ -51,11 +51,9 @@ define <8 x i32> @combine_pmaddwd_concat(<8 x i16> %a0, <8 x i16> %a1, <8 x i16>
 ;
 ; AVX2-LABEL: combine_pmaddwd_concat:
 ; AVX2:       # %bb.0:
-; AVX2-NEXT:    # kill: def $xmm1 killed $xmm1 def $ymm1
-; AVX2-NEXT:    # kill: def $xmm0 killed $xmm0 def $ymm0
-; AVX2-NEXT:    vinserti128 $1, %xmm3, %ymm1, %ymm1
-; AVX2-NEXT:    vinserti128 $1, %xmm2, %ymm0, %ymm0
-; AVX2-NEXT:    vpmaddwd %ymm1, %ymm0, %ymm0
+; AVX2-NEXT:    vpmaddwd %xmm1, %xmm0, %xmm0
+; AVX2-NEXT:    vpmaddwd %xmm3, %xmm2, %xmm1
+; AVX2-NEXT:    vinserti128 $1, %xmm1, %ymm0, %ymm0
 ; AVX2-NEXT:    retq
   %1 = call <4 x i32> @llvm.x86.sse2.pmadd.wd(<8 x i16> %a0, <8 x i16> %a1)
   %2 = call <4 x i32> @llvm.x86.sse2.pmadd.wd(<8 x i16> %a2, <8 x i16> %a3)
@@ -209,7 +207,7 @@ define <16 x i16> @combine_pmaddubsw_concat(<32 x i8> %a0, <32 x i8> %a1) {
   ret <16 x i16> %res
 }
 
-; TODO: Not beneficial to concatenate both inputs just to create a 256-bit pmaddubsw
+; Not beneficial to concatenate both inputs just to create a 256-bit pmaddubsw
 define <16 x i16> @combine_pmaddubsw_concat_unecessary(<16 x i8> %a0, <16 x i8> %a1, <16 x i8> %a2, <16 x i8> %a3) {
 ; SSE-LABEL: combine_pmaddubsw_concat_unecessary:
 ; SSE:       # %bb.0:
@@ -227,11 +225,9 @@ define <16 x i16> @combine_pmaddubsw_concat_unecessary(<16 x i8> %a0, <16 x i8>
 ;
 ; AVX2-LABEL: combine_pmaddubsw_concat_unecessary:
 ; AVX2:       # %bb.0:
-; AVX2-NEXT:    # kill: def $xmm1 killed $xmm1 def $ymm1
-; AVX2-NEXT:    # kill: def $xmm0 killed $xmm0 def $ymm0
-; AVX2-NEXT:    vinserti128 $1, %xmm3, %ymm1, %ymm1
-; AVX2-NEXT:    vinserti128 $1, %xmm2, %ymm0, %ymm0
-; AVX2-NEXT:    vpmaddubsw %ymm1, %ymm0, %ymm0
+; AVX2-NEXT:    vpmaddubsw %xmm1, %xmm0, %xmm0
+; AVX2-NEXT:    vpmaddubsw %xmm3, %xmm2, %xmm1
+; AVX2-NEXT:    vinserti128 $1, %xmm1, %ymm0, %ymm0
 ; AVX2-NEXT:    retq
   %1 = call <8 x i16> @llvm.x86.ssse3.pmadd.ub.sw.128(<16 x i8> %a0, <16 x i8> %a1)
   %2 = call <8 x i16> @llvm.x86.ssse3.pmadd.ub.sw.128(<16 x i8> %a2, <16 x i8> %a3)
diff --git a/llvm/test/CodeGen/X86/vector-shuffle-combining-avx2.ll b/llvm/test/CodeGen/X86/vector-shuffle-combining-avx2.ll
index 65358c3ac7a3c..b18a32d7d0459 100644
--- a/llvm/test/CodeGen/X86/vector-shuffle-combining-avx2.ll
+++ b/llvm/test/CodeGen/X86/vector-shuffle-combining-avx2.ll
@@ -806,15 +806,13 @@ define <32 x i8> @concat_packsr_unnecessary(<8 x i16> %a0, <8 x i16> %a1, <8 x i
 }
 declare <16 x i8> @llvm.x86.sse2.packsswb.128(<8 x i16>, <8 x i16>)
 
-; TODO: Not beneficial to concatenate both inputs just to create a 256-bit pshufb
+; Not beneficial to concatenate both inputs just to create a 256-bit pshufb
 define <32 x i8> @concat_pshufb_unnecessary(<16 x i8> %a0, <16 x i8> %a1, <16 x i8> %a2) nounwind {
 ; CHECK-LABEL: concat_pshufb_unnecessary:
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    # kill: def $xmm1 killed $xmm1 def $ymm1
-; CHECK-NEXT:    # kill: def $xmm0 killed $xmm0 def $ymm0
-; CHECK-NEXT:    vinserti128 $1, %xmm2, %ymm1, %ymm1
-; CHECK-NEXT:    vinserti128 $1, %xmm0, %ymm0, %ymm0
-; CHECK-NEXT:    vpshufb %ymm1, %ymm0, %ymm0
+; CHECK-NEXT:    vpshufb %xmm1, %xmm0, %xmm1
+; CHECK-NEXT:    vpshufb %xmm2, %xmm0, %xmm0
+; CHECK-NEXT:    vinserti128 $1, %xmm0, %ymm1, %ymm0
 ; CHECK-NEXT:    ret{{[l|q]}}
   %lo = tail call <16 x i8> @llvm.x86.ssse3.pshuf.b.128(<16 x i8> %a0, <16 x i8> %a1)
   %hi = tail call <16 x i8> @llvm.x86.ssse3.pshuf.b.128(<16 x i8> %a0, <16 x i8> %a2)