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Add a comment noting that the fdiv -> fmul conversion won't generate

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multiplication by a denormal, and some tests checking that.

llvm-svn: 154431
This commit is contained in:
Duncan Sands 2012-04-10 20:35:27 +00:00
parent 11a434ab2e
commit 4f53074cca
2 changed files with 19 additions and 3 deletions
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6
llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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@ -5769,9 +5769,9 @@ SDValue DAGCombiner::visitFDIV(SDNode *N) {
APFloat N1APF = N1CFP->getValueAPF();
APFloat Recip(N1APF.getSemantics(), 1); // 1.0
APFloat::opStatus st = Recip.divide(N1APF, APFloat::rmNearestTiesToEven);
// Only do the transform if the reciprocal is not too horrible (eg not NaN)
// and the reciprocal is a legal fp imm.
if ((st == APFloat::opOK || st == APFloat::opInexact) &&
// Only do the transform if the reciprocal is a legal fp immediate that
// isn't too nasty (eg NaN, denormal, ...).
if ((st == APFloat::opOK || st == APFloat::opInexact) && // Not too nasty
(!LegalOperations ||
// FIXME: custom lowering of ConstantFP might fail (see e.g. ARM
// backend)... we should handle this gracefully after Legalize.

16
llvm/test/CodeGen/X86/fdiv.ll
View File

@ -23,3 +23,19 @@ define double @funky(double %x) {
%div = fdiv double %x, 0.0
ret double %div
}
define double @denormal1(double %x) {
; Don't generate multiplication by a denormal.
; CHECK: @denormal1
; CHECK: divsd
%div = fdiv double %x, 0x7FD0000000000001
ret double %div
}
define double @denormal2(double %x) {
; Don't generate multiplication by a denormal.
; CHECK: @denormal
; CHECK: divsd
%div = fdiv double %x, 0x7FEFFFFFFFFFFFFF
ret double %div
}