[PATCH] DAGCombiner: don't duplicate (fmul x, c) when folding fneg if fneg is free

[escha]

Hi resistor, t.p.northover,

The fold (fneg (fmul x, c)) -> (fmul x, -c) duplicates the fmul if the fmul has multiple uses. If fneg is free, this is even worse, since we didn't actually gain anything by doing so. Check hasOneUse or fneg not being free before doing this fold.

REPOSITORY
  rL LLVM

http://reviews.llvm.org/D10277

Files:
  lib/CodeGen/SelectionDAG/DAGCombiner.cpp

Index: lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -8781,7 +8781,8 @@
   }
 
   // (fneg (fmul c, x)) -> (fmul -c, x)
-  if (N0.getOpcode() == ISD::FMUL) {
+  if (N0.getOpcode() == ISD::FMUL &&
+      (N0.getNode()->hasOneUse() || !TLI.isFNegFree(VT))) {
     ConstantFPSDNode *CFP1 = dyn_cast<ConstantFPSDNode>(N0.getOperand(1));
     if (CFP1) {
       APFloat CVal = CFP1->getValueAPF();

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