[llvm] 6547a5c - [DAG] Add TODO comment regarding ADD(X,X) -> SHL(X,1) canonicalization

[Simon Pilgrim via llvm-commits]

Author: Simon Pilgrim
Date: 2020-04-30T12:57:16+01:00
New Revision: 6547a5ceb2213dc49ba2b8a7d98913b39cb331d9

URL: https://github.com/llvm/llvm-project/commit/6547a5ceb2213dc49ba2b8a7d98913b39cb331d9
DIFF: https://github.com/llvm/llvm-project/commit/6547a5ceb2213dc49ba2b8a7d98913b39cb331d9.diff

LOG: [DAG] Add TODO comment regarding ADD(X,X) -> SHL(X,1) canonicalization

As discussed on D78935

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 9042f519d8de..9b00ff84300b 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -6098,6 +6098,7 @@ static SDValue extractShiftForRotate(SelectionDAG &DAG, SDValue OppShift,
   ConstantSDNode *OppShiftCst = isConstOrConstSplat(OppShift.getOperand(1));
 
   // (add v v) -> (shl v 1)
+  // TODO: Should this be a general DAG canonicalization?
   if (OppShift.getOpcode() == ISD::SRL && OppShiftCst &&
       ExtractFrom.getOpcode() == ISD::ADD &&
       ExtractFrom.getOperand(0) == ExtractFrom.getOperand(1) &&