[llvm] [X86] combineVectorSizedSetCCEquality - convert to mayFoldIntoVector helper (PR #172215)

[Simon Pilgrim via llvm-commits]

https://github.com/RKSimon created https://github.com/llvm/llvm-project/pull/172215

Add AssumeSingleUse (default = false) argument to mayFoldIntoVector to allow us to match combineVectorSizedSetCCEquality behaviour with AssumeSingleUse=true

Hopefully we can drop the AssumeSingleUse entirely soon, but there are a number of messy test regressions that need handling first

>From 6a2cc671245add5aee2511c759ee3de87d2fae9e Mon Sep 17 00:00:00 2001
From: Simon Pilgrim <llvm-dev at redking.me.uk>
Date: Sun, 14 Dec 2025 15:31:36 +0000
Subject: [PATCH] [X86] combineVectorSizedSetCCEquality - convert to
 mayFoldIntoVector helper

Add AssumeSingleUse (default = false) argument to mayFoldIntoVector to allow us to match combineVectorSizedSetCCEquality AssumeSingleUse=true behaviour

Hopefully we can drop the AssumeSingleUse entirely soon, but there are a number of messy test regressions that need handling first
---
 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 c28584cc14991..a85ed96e11158 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -2860,12 +2860,13 @@ bool X86::mayFoldIntoZeroExtend(SDValue Op) {
 }
 
 // Return true if its cheap to bitcast this to a vector type.
-static bool mayFoldIntoVector(SDValue Op, const X86Subtarget &Subtarget) {
+static bool mayFoldIntoVector(SDValue Op, const X86Subtarget &Subtarget,
+                              bool AssumeSingleUse = false) {
   if (peekThroughBitcasts(Op).getValueType().isVector())
     return true;
   if (isa<ConstantSDNode>(Op) || isa<ConstantFPSDNode>(Op))
     return true;
-  return X86::mayFoldLoad(Op, Subtarget, /*AssumeSingleUse=*/false,
+  return X86::mayFoldLoad(Op, Subtarget, AssumeSingleUse,
                           /*IgnoreAlignment=*/true);
 }
 
@@ -23122,12 +23123,9 @@ static SDValue combineVectorSizedSetCCEquality(EVT VT, SDValue X, SDValue Y,
     return SDValue();
 
   // Don't perform this combine if constructing the vector will be expensive.
-  auto IsVectorBitCastCheap = [](SDValue X) {
-    X = peekThroughBitcasts(X);
-    return isa<ConstantSDNode>(X) || X.getValueType().isVector() ||
-           ISD::isNormalLoad(X.getNode());
-  };
-  if ((!IsVectorBitCastCheap(X) || !IsVectorBitCastCheap(Y)) &&
+  // TODO: Drop AssumeSingleUse = true override.
+  if ((!mayFoldIntoVector(X, Subtarget, /*AssumeSingleUse=*/true) ||
+       !mayFoldIntoVector(Y, Subtarget, /*AssumeSingleUse=*/true)) &&
       !IsOrXorXorTreeCCZero)
     return SDValue();