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

[escha]

I've updated one of the R600 tests to check that it doesn't duplicate the fmul-by-constant when it has one negated use and one regular use.


REPOSITORY
  rL LLVM

http://reviews.llvm.org/D10277

Files:
  lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  test/CodeGen/R600/fmul.ll

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();
Index: test/CodeGen/R600/fmul.ll
===================================================================
--- test/CodeGen/R600/fmul.ll
+++ test/CodeGen/R600/fmul.ll
@@ -73,4 +73,20 @@
   ret void
 }
 
+; There should be three multiplies here; %a should be used twice (once
+; negated), not duplicated into mul x, 5.0 and mul x, -5.0.
+; FUNC-LABEL: {{^}}test_mul_twouse:
+; SI: v_mul_f32
+; SI: v_mul_f32
+; SI: v_mul_f32
+; SI-NOT: v_mul_f32
+define void @test_mul_twouse(float addrspace(1)* %out, float %x, float %y) #0 {
+  %a = fmul float %x, 5.0
+  %b = fsub float -0.0, %a
+  %c = fmul float %b, %y
+  %d = fmul float %c, %a
+  store float %d, float addrspace(1)* %out
+  ret void
+}
+
 attributes #0 = { "less-precise-fpmad"="true" "no-infs-fp-math"="true" "no-nans-fp-math"="true" "unsafe-fp-math"="true" }

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