DAGCombiner: don't duplicate (fmul x, c) in visitFNEG if fneg is free

For targets with a free fneg, this fold is always a net loss if it
ends up duplicating the multiply, so definitely avoid it.

This might be true for some targets without a free fneg too, but
I'll leave that for future investigation.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239167 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 0619c945fd26484500010578ccf8aecd2556d4cc..d5b2f3658bc48dc4ca0ad4d9e4718c9e746e49f4 100644 (file)
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -8781,7 +8781,8 @@ SDValue DAGCombiner::visitFNEG(SDNode *N) {
   }
 
   // (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();

diff --git a/test/CodeGen/R600/fmul.ll b/test/CodeGen/R600/fmul.ll
index 68ebc4dedfe05b871970b047ce00f86aef75cf86..addc409c9eb15b23d4ef2a8f9cf32765c8c57d18 100644 (file)
--- a/test/CodeGen/R600/fmul.ll
+++ b/test/CodeGen/R600/fmul.ll
@@ -73,4 +73,20 @@ define void @test_mul_2_k_inv(float addrspace(1)* %out, float %x) #0 {
   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" }