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From: "joseph at codesourcery dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug middle-end/103193] gcc for x86_64: wrong code generation:
 ucomiss instead of comiss
Date: Fri, 12 Nov 2021 23:35:37 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103193

--- Comment #5 from joseph at codesourcery dot com <joseph at codesourcery =
dot com> ---
On Fri, 12 Nov 2021, rguenth at gcc dot gnu.org via Gcc-bugs wrote:

> /* Simplify comparison of something with itself.  For IEEE
>    floating-point, we can only do some of these simplifications.  */
> (for cmp (eq ge le)
>  (simplify
>   (cmp @0 @0)
>   (if (! FLOAT_TYPE_P (TREE_TYPE (@0))
>        || ! HONOR_NANS (@0))
>    { constant_boolean_node (true, type); }
>    (if (cmp !=3D EQ_EXPR)
>     (eq @0 @0)))))
>=20
> does this.  The folding to =3D=3D happens unconditionally.  As I understa=
nd you
> the condition that applies to the constant folding should apply to the
> folding to EQ as well, which means we effectively need to remove the
> canonicalization to EQ (since when it would be valid we can fold to const=
ant
> true)?

It's invalid with -ftrapping-math because it loses an exception.  With=20
-fno-trapping-math, but NaNs supported, you can convert to EQ but can't=20
fold to constant true.=