[llvm] [X86] PromoteMaskArithmetic - use similar code for LHS/RHS trunc pattern. NFC. (PR #157426)

[Simon Pilgrim via llvm-commits]

https://github.com/RKSimon created https://github.com/llvm/llvm-project/pull/157426

Make it more obvious that LHS/RHS truncation patterns are the same.

Noticed while working on #157425

>From 0654e5e287882359c2992f4c16023144fec87346 Mon Sep 17 00:00:00 2001
From: Simon Pilgrim <llvm-dev at redking.me.uk>
Date: Mon, 8 Sep 2025 12:11:53 +0100
Subject: [PATCH] [X86] PromoteMaskArithmetic - use similar code for LHS/RHS
 trunc pattern. NFC.

Make it more obvious that LHS/RHS truncation patterns are the same.

Noticed while working on #157425
---
 llvm/lib/Target/X86/X86ISelLowering.cpp | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index cdc97faf394ca..15b59afabc61f 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -50957,15 +50957,13 @@ static SDValue PromoteMaskArithmetic(SDValue N, const SDLoc &DL, EVT VT,
   if (SDValue NN0 = PromoteMaskArithmetic(N0, DL, VT, DAG, Depth + 1))
     N0 = NN0;
   else {
-    // The left side has to be a trunc.
-    if (N0.getOpcode() != ISD::TRUNCATE)
-      return SDValue();
-
-    // The type of the truncated inputs.
-    if (N0.getOperand(0).getValueType() != VT)
+    // The left side has to be a 'trunc'.
+    bool LHSTrunc = N0.getOpcode() == ISD::TRUNCATE &&
+                    N0.getOperand(0).getValueType() == VT;
+    if (LHSTrunc)
+      N0 = N0.getOperand(0);
+    else
       return SDValue();
-
-    N0 = N0.getOperand(0);
   }
 
   if (SDValue NN1 = PromoteMaskArithmetic(N1, DL, VT, DAG, Depth + 1))