[llvm] ba769e1 - [X86] combinePTESTCC - canonicalize constants to the RHS if the PTEST/TESTP node just uses the ZF flag (#165601)

[via llvm-commits]

Author: Simon Pilgrim
Date: 2025-10-29T18:16:36Z
New Revision: ba769e125b106c059321de16a760658449b02c8a

URL: https://github.com/llvm/llvm-project/commit/ba769e125b106c059321de16a760658449b02c8a
DIFF: https://github.com/llvm/llvm-project/commit/ba769e125b106c059321de16a760658449b02c8a.diff

LOG: [X86] combinePTESTCC - canonicalize constants to the RHS if the PTEST/TESTP node just uses the ZF flag (#165601)

If we're just comparing against zero then move the constant to the RHS to reduce duplicated folds.

Noticed while triaging #156233

Added: 
    

Modified: 
    llvm/lib/Target/X86/X86ISelLowering.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 89b42da9a40f0..624cff24ddf03 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -48787,6 +48787,11 @@ static SDValue combinePTESTCC(SDValue EFLAGS, X86::CondCode &CC,
   }
 
   if (CC == X86::COND_E || CC == X86::COND_NE) {
+    // Canonicalize constant to RHS if we're just using ZF.
+    if (Op0 != Op1 && DAG.isConstantIntBuildVectorOrConstantInt(Op0) &&
+        !DAG.isConstantIntBuildVectorOrConstantInt(Op1))
+      return DAG.getNode(EFLAGS.getOpcode(), SDLoc(EFLAGS), VT, Op1, Op0);
+
     // TESTZ(X,~Y) == TESTC(Y,X)
     if (SDValue NotOp1 = IsNOT(Op1, DAG)) {
       CC = (CC == X86::COND_E ? X86::COND_B : X86::COND_AE);
@@ -48850,10 +48855,6 @@ static SDValue combinePTESTCC(SDValue EFLAGS, X86::CondCode &CC,
       }
     }
 
-    // TESTZ(-1,X) == TESTZ(X,X)
-    if (ISD::isBuildVectorAllOnes(Op0.getNode()))
-      return DAG.getNode(EFLAGS.getOpcode(), SDLoc(EFLAGS), VT, Op1, Op1);
-
     // TESTZ(X,-1) == TESTZ(X,X)
     if (ISD::isBuildVectorAllOnes(Op1.getNode()))
       return DAG.getNode(EFLAGS.getOpcode(), SDLoc(EFLAGS), VT, Op0, Op0);