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Add a few more simple fast-math constant propagations and cancellations.

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llvm-svn: 167200
This commit is contained in:
Owen Anderson 2012-11-01 02:00:53 +00:00
parent 88f83a03e9
commit 8f66d7107c
2 changed files with 38 additions and 0 deletions
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18
lib/CodeGen/SelectionDAG/DAGCombiner.cpp
View File

@ -5729,6 +5729,18 @@ SDValue DAGCombiner::visitFADD(SDNode *N) {
DAG.getNode(ISD::FADD, N->getDebugLoc(), VT,
N0.getOperand(1), N1));
// If allow, fold (fadd (fneg x), x) -> 0.0
if (DAG.getTarget().Options.UnsafeFPMath &&
N0.getOpcode() == ISD::FNEG && N0.getOperand(0) == N1) {
return DAG.getConstantFP(0.0, VT);
}
// If allow, fold (fadd x, (fneg x)) -> 0.0
if (DAG.getTarget().Options.UnsafeFPMath &&
N1.getOpcode() == ISD::FNEG && N1.getOperand(0) == N0) {
return DAG.getConstantFP(0.0, VT);
}
// In unsafe math mode, we can fold chains of FADD's of the same value
// into multiplications. This transform is not safe in general because
// we are reducing the number of rounding steps.
@ -6038,6 +6050,12 @@ SDValue DAGCombiner::visitFMA(SDNode *N) {
EVT VT = N->getValueType(0);
DebugLoc dl = N->getDebugLoc();
if (DAG.getTarget().Options.UnsafeFPMath) {
if (N0CFP && N0CFP->isZero())
return N2;
if (N1CFP && N1CFP->isZero())
return N2;
}
if (N0CFP && N0CFP->isExactlyValue(1.0))
return DAG.getNode(ISD::FADD, N->getDebugLoc(), VT, N1, N2);
if (N1CFP && N1CFP->isExactlyValue(1.0))

20
test/CodeGen/X86/fp-fast.ll
View File

@ -35,3 +35,23 @@ define float @test3(float %a) {
ret float %r
}
; CHECK: test4
define float @test4(float %a) {
; CHECK-NOT: fma
; CHECK-NOT mul
; CHECK-NOT: add
; CHECK: ret
%t1 = fmul float %a, 0.0
%t2 = fadd float %a, %t1
ret float %t2
}
; CHECK: test5
define float @test5(float %a) {
; CHECK-NOT: add
; CHECK: vxorps
; CHECK: ret
%t1 = fsub float -0.0, %a
%t2 = fadd float %a, %t1
ret float %t2
}