[llvm] e7a0fa4 - [DAG] foldAddSubOfSignBit - don't bother creating the new shift node unless constant folding succeeds

[Simon Pilgrim via llvm-commits]

Author: Simon Pilgrim
Date: 2022-07-05T16:44:31+01:00
New Revision: e7a0fa4df00c6386632d1395799c6150f39a3e33

URL: https://github.com/llvm/llvm-project/commit/e7a0fa4df00c6386632d1395799c6150f39a3e33
DIFF: https://github.com/llvm/llvm-project/commit/e7a0fa4df00c6386632d1395799c6150f39a3e33.diff

LOG: [DAG] foldAddSubOfSignBit - don't bother creating the new shift node unless constant folding succeeds

Noticed by inspection - the new shift is only ever used if the constant fold occurs

Added: 
    

Modified: 
    llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

Removed: 
    


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diff  --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index ce570abef92e6..dbb81ab65ebbe 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -2392,12 +2392,14 @@ static SDValue foldAddSubOfSignBit(SDNode *N, SelectionDAG &DAG) {
   // add (srl (not X), 31), C --> add (sra X, 31), (C + 1)
   // sub C, (srl (not X), 31) --> add (srl X, 31), (C - 1)
   SDLoc DL(N);
-  auto ShOpcode = IsAdd ? ISD::SRA : ISD::SRL;
-  SDValue NewShift = DAG.getNode(ShOpcode, DL, VT, Not.getOperand(0), ShAmt);
-  if (SDValue NewC =
-          DAG.FoldConstantArithmetic(IsAdd ? ISD::ADD : ISD::SUB, DL, VT,
-                                     {ConstantOp, DAG.getConstant(1, DL, VT)}))
+  if (SDValue NewC = DAG.FoldConstantArithmetic(
+          IsAdd ? ISD::ADD : ISD::SUB, DL, VT,
+          {ConstantOp, DAG.getConstant(1, DL, VT)})) {
+    SDValue NewShift = DAG.getNode(IsAdd ? ISD::SRA : ISD::SRL, DL, VT,
+                                   Not.getOperand(0), ShAmt);
     return DAG.getNode(ISD::ADD, DL, VT, NewShift, NewC);
+  }
+
   return SDValue();
 }