[llvm] 3902f9b - [X86] PromoteMaskArithmetic - explicitly attempt to constant fold zext(c) instead of relying on getNode()

[Simon Pilgrim via llvm-commits]

Author: Simon Pilgrim
Date: 2024-02-09T10:34:25Z
New Revision: 3902f9b6e2d925d50f9a4861d78e5aba07b6ef11

URL: https://github.com/llvm/llvm-project/commit/3902f9b6e2d925d50f9a4861d78e5aba07b6ef11
DIFF: https://github.com/llvm/llvm-project/commit/3902f9b6e2d925d50f9a4861d78e5aba07b6ef11.diff

LOG: [X86] PromoteMaskArithmetic - explicitly attempt to constant fold zext(c) instead of relying on getNode()

Don't rely on isBuildVectorOfConstantSDNodes/getNode to constant fold, this could also help in cases where the constant is behind a bitcast.

Noticed while investigating #80668

Added: 
    

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

Removed: 
    


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diff  --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 7db1b8d4ab74f..5d8a3a9bd5826 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -48026,7 +48026,7 @@ static SDValue PromoteMaskArithmetic(SDValue N, EVT VT, SelectionDAG &DAG,
   if (SDValue NN0 = PromoteMaskArithmetic(N0, VT, DAG, Depth + 1))
     N0 = NN0;
   else {
-    // The Left side has to be a trunc.
+    // The left side has to be a trunc.
     if (N0.getOpcode() != ISD::TRUNCATE)
       return SDValue();
 
@@ -48040,16 +48040,16 @@ static SDValue PromoteMaskArithmetic(SDValue N, EVT VT, SelectionDAG &DAG,
   if (SDValue NN1 = PromoteMaskArithmetic(N1, VT, DAG, Depth + 1))
     N1 = NN1;
   else {
-    // The right side has to be a 'trunc' or a constant vector.
+    // The right side has to be a 'trunc' or a (foldable) constant.
     bool RHSTrunc = N1.getOpcode() == ISD::TRUNCATE &&
                     N1.getOperand(0).getValueType() == VT;
-    if (!RHSTrunc && !ISD::isBuildVectorOfConstantSDNodes(N1.getNode()))
-      return SDValue();
-
     if (RHSTrunc)
       N1 = N1.getOperand(0);
+    else if (SDValue Cst =
+                 DAG.FoldConstantArithmetic(ISD::ZERO_EXTEND, DL, VT, {N1}))
+      N1 = Cst;
     else
-      N1 = DAG.getNode(ISD::ZERO_EXTEND, DL, VT, N1);
+      return SDValue();
   }
 
   return DAG.getNode(N.getOpcode(), DL, VT, N0, N1);