r254574 - PR17381: Treat undefined behavior during expression evaluation as an unmodeled

[Richard Smith via cfe-commits]

On Tue, Dec 8, 2015 at 10:59 AM, Robinson, Paul <
Paul_Robinson at playstation.sony.com> wrote:

> Okay, I'll bite:  so what *does* UINT128_MAX actually convert to?
>

$ echo 'unsigned __int128 max = -1; float f = max;' |
~/clang-8/build/bin/clang -x c++ - -emit-llvm -S -o - -O3 | grep @f
@f = global float undef, align 4


> *From:* cfe-commits [mailto:cfe-commits-bounces at lists.llvm.org] *On
> Behalf Of *Richard Smith via cfe-commits
> *Sent:* Tuesday, December 08, 2015 10:52 AM
> *To:* Joerg Sonnenberger; cfe-commits
> *Subject:* Re: r254574 - PR17381: Treat undefined behavior during
> expression evaluation as an unmodeled
>
>
>
> On Tue, Dec 8, 2015 at 2:13 AM, Joerg Sonnenberger via cfe-commits <
> cfe-commits at lists.llvm.org> wrote:
>
> On Mon, Dec 07, 2015 at 01:32:14PM -0800, Richard Smith via cfe-commits
> wrote:
> > C11 6.3.1.5/1: "If the value being converted is outside the range of
> values
> > that can be represented, the behavior is undefined."
>
> The value of 1e100 can be represented as +inf, even if not precisely.
>
>
>
> Only if +inf is in the range of representable values, which, as already
> noted, is problematic.
>
>
>
> This is a bit different from non-IEEE math like VAX, that doesn't have
> infinities.
>
>
> Joerg
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