https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91323
Uroš Bizjak <ubizjak at gmail dot com> changed:
What |Removed |Added
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CC| |jakub at gcc dot gnu.org,
| |joseph at codesourcery dot com,
| |rguenth at gcc dot gnu.org
--- Comment #2 from Uroš Bizjak <ubizjak at gmail dot com> ---
(In reply to Ilya Leoshkevich from comment #0)
> I'm implementing signaling comparisons on S/390 and I'm trying to figure out
> whether or not LTGT is supposed to be signaling.
> I've decided to check what Intel does, and ran into what appears to be a bug.
>
> Consider the following functions:
>
> int f1(float a, float b) { return a < b || a > b; }
> int f2(float a, float b) { return __builtin_isless(a, b) ||
> __builtin_isgreater(a, b); }
> int f3(float a, float b) { return __builtin_islessgreater(a, b); }
>
> gcc creates LTGT rtx for f1 and UNEQ for f2 and f3.
> However, for all 3 variants it then emits UCOMISS instruction.
> I would expect f1 to be compiled to COMISS, since I believe that comparison
> operators in C are supposed to be signaling.
Based on the above observation, LTGT should trap, since either LT or GT traps.
It also means that __builtin_islessgreater is confusingly named.
