[llvm] [X86] IsElementEquivalent - pull out exact matching for same index/op. (PR #143367)

[Simon Pilgrim via llvm-commits]

https://github.com/RKSimon updated https://github.com/llvm/llvm-project/pull/143367

>From 686b20a216a80a0a7f0e4f1415b7315388f268ea Mon Sep 17 00:00:00 2001
From: Simon Pilgrim <llvm-dev at redking.me.uk>
Date: Mon, 9 Jun 2025 11:58:48 +0100
Subject: [PATCH] [X86] IsElementEquivalent - pull out exact matching for same
 index/op. NFC.

The types must still be vectors matching MaskSize
---
 llvm/lib/Target/X86/X86ISelLowering.cpp | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 2badf2f6942d5..2994036b5f908 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -9790,6 +9790,10 @@ static bool IsElementEquivalent(int MaskSize, SDValue Op, SDValue ExpectedOp,
       (int)ExpectedVT.getVectorNumElements() != MaskSize)
     return false;
 
+  // Exact match.
+  if (Idx == ExpectedIdx && Op == ExpectedOp)
+    return true;
+
   switch (Op.getOpcode()) {
   case ISD::BUILD_VECTOR:
     // If the values are build vectors, we can look through them to find
@@ -9837,8 +9841,7 @@ static bool IsElementEquivalent(int MaskSize, SDValue Op, SDValue ExpectedOp,
       SmallVector<int, 8> Mask;
       DecodeVPERMMask(MaskSize, Op.getConstantOperandVal(1), Mask);
       SDValue Src = Op.getOperand(0);
-      return (Mask[Idx] == Mask[ExpectedIdx]) ||
-             IsElementEquivalent(MaskSize, Src, Src, Mask[Idx],
+      return IsElementEquivalent(MaskSize, Src, Src, Mask[Idx],
                                  Mask[ExpectedIdx]);
     }
     break;