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icmpzero
2015 Jul 06
5
[LLVMdev] Why can't comparisons with negative zero be simplified?
In InstCombineCompares.cpp, routine InstCombiner::FoldFCmp_IntToFP_Cst, there are these lines:
// Comparisons with zero are a special case where we know we won't lose
// information.
bool IsCmpZero = RHS.isPosZero();
// If the conversion would lose info, don't hack on this.
if ((int)InputSize > MantissaWidth && !IsCmpZero)
return nullptr;
Why check for positive zero instead of checking for any kind of zero? My reading of IEEE 754-2008 is that floating-point compariso...