[SLPVectorizer] reorderInputsAccordingToOpcode - remove non-Instruction canonicalization

Remove attempts to commute non-Instructions to the LHS - the codegen changes appear to rely on chance more than anything else and also have a tendency to fight existing instcombine canonicalization which moves constants to the RHS of commutable binary ops.

This is prep work towards:
(a) reusing reorderInputsAccordingToOpcode for alt-shuffles and removing the similar reorderAltShuffleOperands
(b) improving reordering to optimized cases with commutable and non-commutable instructions to still find splat/consecutive ops.

Differential Revision: https://reviews.llvm.org/D59738

llvm-svn: 356913

1 files changed, 2 insertions, 7 deletions

diff --git a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
index 7ed1183c05f..983b8fa4af1 100644
--- a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -2922,13 +2922,8 @@ void BoUpSLP::reorderInputsAccordingToOpcode(const InstructionsState &S,
     // Peel the first iteration out of the loop since there's nothing
     // interesting to do anyway and it simplifies the checks in the loop.
     auto *I = cast<Instruction>(VL[0]);
-    Value *VLeft = I->getOperand(0);
-    Value *VRight = I->getOperand(1);
-    if (!isa<Instruction>(VRight) && isa<Instruction>(VLeft))
-      // Favor having instruction to the right. FIXME: why?
-      std::swap(VLeft, VRight);
-    Left.push_back(VLeft);
-    Right.push_back(VRight);
+    Left.push_back(I->getOperand(0));
+    Right.push_back(I->getOperand(1));
   }
 
   // Keep track if we have instructions with all the same opcode on one side.