[LLVMdev] Bug 16257 - fmul of undef ConstantExpr not folded to undef

[Owen Anderson]

> On Aug 27, 2014, at 6:34 AM, Duncan Sands <duncan.sands at deepbluecap.com> wrote:
> 
> I think you should try to get LLVM floating point experts involved, to find out their opinion about whether LLVM should really assume that snans always trap.
> 
> If they think it is fine to assume trapping, then you can fold any floating point operation with an "undef" operand to "undef".
> 
> If they think it is no good, then the existing folds that use this need to be removed or weakened, though maybe another argument can be found to justify them.

LLVM is used to target many platforms for which sNaNs do not trap, and indeed many platforms that do not have floating point exceptions at all.

—Owen
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