[llvm] [X86] combineConcatVectorOps - convert X86ISD::PCMPEQ/PCMPGT concatenation to use combineConcatVectorOps recursion instead of IsConcatFree (PR #130814)

[Simon Pilgrim via llvm-commits]

https://github.com/RKSimon created https://github.com/llvm/llvm-project/pull/130814

Only concatenate X86ISD::PCMPEQ/PCMPGT nodes (or convert to CMPPS on AVX1) if at least one operand is beneficial to concatenate

>From 85b1e34a9ace2db1b3f68e2622809dffb8289625 Mon Sep 17 00:00:00 2001
From: Simon Pilgrim <llvm-dev at redking.me.uk>
Date: Tue, 11 Mar 2025 18:29:12 +0000
Subject: [PATCH] [X86] combineConcatVectorOps - convert X86ISD::PCMPEQ/PCMPGT
 concatenation to use combineConcatVectorOps recursion instead of IsConcatFree

Only concatenate X86ISD::PCMPEQ/PCMPGT nodes (or convert to CMPPS on AVX1) if at least one operand is beneficial to concatenate
---
 llvm/lib/Target/X86/X86ISelLowering.cpp | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 030d3acefcf3b..24e5d8bfc404c 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -58352,14 +58352,17 @@ static SDValue combineConcatVectorOps(const SDLoc &DL, MVT VT,
       break;
     case X86ISD::PCMPEQ:
     case X86ISD::PCMPGT:
-      if (!IsSplat && VT.is256BitVector() &&
-          (Subtarget.hasInt256() || VT == MVT::v8i32) &&
-          (IsConcatFree(VT, Ops, 0) || IsConcatFree(VT, Ops, 1))) {
-        if (Subtarget.hasInt256())
+      if (!IsSplat && VT.is256BitVector() && Subtarget.hasInt256()) {
+        SDValue Concat0 = CombineSubOperand(VT, Ops, 0);
+        SDValue Concat1 = CombineSubOperand(VT, Ops, 1);
+        if (Concat0 || Concat1)
           return DAG.getNode(Op0.getOpcode(), DL, VT,
-                             ConcatSubOperand(VT, Ops, 0),
-                             ConcatSubOperand(VT, Ops, 1));
+                             Concat0 ? Concat0 : ConcatSubOperand(VT, Ops, 0),
+                             Concat1 ? Concat1 : ConcatSubOperand(VT, Ops, 1));
+        break;
+      }
 
+      if (!IsSplat && VT == MVT::v8i32) {
         // Without AVX2, see if we can cast the values to v8f32 and use fcmp.
         // TODO: Handle v4f64 as well?
         unsigned MaxSigBitsLHS = 0, MaxSigBitsRHS = 0;
@@ -58384,8 +58387,10 @@ static SDValue combineConcatVectorOps(const SDLoc &DL, MVT VT,
 
         if (std::optional<unsigned> CastOpc =
                 CastIntSETCCtoFP(FpVT, ICC, MaxSigBitsLHS, MaxSigBitsRHS)) {
-          SDValue LHS = ConcatSubOperand(VT, Ops, 0);
-          SDValue RHS = ConcatSubOperand(VT, Ops, 1);
+          SDValue LHS = CombineSubOperand(VT, Ops, 0);
+          SDValue RHS = CombineSubOperand(VT, Ops, 1);
+          LHS = LHS ? LHS : ConcatSubOperand(VT, Ops, 0);
+          RHS = RHS ? RHS : ConcatSubOperand(VT, Ops, 1);
           LHS = DAG.getNode(*CastOpc, DL, FpVT, LHS);
           RHS = DAG.getNode(*CastOpc, DL, FpVT, RHS);