[llvm] 6a06c7a - [X86] isHorizontalBinOp - only update LHS/RHS references on success

[Simon Pilgrim via llvm-commits]

Author: Simon Pilgrim
Date: 2020-08-05T15:09:52+01:00
New Revision: 6a06c7a0a7688ce142865e92d879b8bece79de7a

URL: https://github.com/llvm/llvm-project/commit/6a06c7a0a7688ce142865e92d879b8bece79de7a
DIFF: https://github.com/llvm/llvm-project/commit/6a06c7a0a7688ce142865e92d879b8bece79de7a.diff

LOG: [X86] isHorizontalBinOp - only update LHS/RHS references on success

We've had issues in the past where isHorizontalBinOp calls would affect later combines as the LHS/RHS references had been commuted but still failed to match.

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 82459f509668..04dde4b15514 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -44580,8 +44580,8 @@ static bool isHorizontalBinOp(SDValue &LHS, SDValue &RHS, SelectionDAG &DAG,
     }
   }
 
-  LHS = A.getNode() ? A : B; // If A is 'UNDEF', use B for it.
-  RHS = B.getNode() ? B : A; // If B is 'UNDEF', use A for it.
+  SDValue NewLHS = A.getNode() ? A : B; // If A is 'UNDEF', use B for it.
+  SDValue NewRHS = B.getNode() ? B : A; // If B is 'UNDEF', use A for it.
 
   bool IsIdentityPostShuffle =
       isSequentialOrUndefInRange(PostShuffleMask, 0, NumElts, 0);
@@ -44595,13 +44595,13 @@ static bool isHorizontalBinOp(SDValue &LHS, SDValue &RHS, SelectionDAG &DAG,
 
   // Assume a SingleSource HOP if we only shuffle one input and don't need to
   // shuffle the result.
-  if (!shouldUseHorizontalOp(LHS == RHS &&
+  if (!shouldUseHorizontalOp(NewLHS == NewRHS &&
                                  (NumShuffles < 2 || !IsIdentityPostShuffle),
                              DAG, Subtarget))
     return false;
 
-  LHS = DAG.getBitcast(VT, LHS);
-  RHS = DAG.getBitcast(VT, RHS);
+  LHS = DAG.getBitcast(VT, NewLHS);
+  RHS = DAG.getBitcast(VT, NewRHS);
   return true;
 }
 
@@ -44627,8 +44627,6 @@ static SDValue combineFaddFsub(SDNode *N, SelectionDAG &DAG,
     return HorizBinOp;
   }
 
-  // NOTE: isHorizontalBinOp may have changed LHS/RHS variables.
-
   return SDValue();
 }