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

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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
This commit is contained in:
Fiona Glaser 2015-06-05 17:52:34 +00:00
parent 485adcac20
commit 5a0d6b758c
2 changed files with 18 additions and 1 deletions
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3
lib/CodeGen/SelectionDAG/DAGCombiner.cpp
View File

@ -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();

16
test/CodeGen/R600/fmul.ll
View File

@ -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" }