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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/109359] [12/13 Regression] Compile-time rounding of double
 literal to float is incorrect with -frounding-math
Date: Fri, 14 Apr 2023 09:49:03 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109359

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #3)
> I think the fold-const.cc change is right though.
> I wonder if for constant evaluation (constexpr, constinit) we shouldn't
> arrange for those to be evaluated with temporarily -fno-rounding-math, I
> think C uses
> fold_init and its START_FOLD_INIT ... END_FOLD_INIT for this purpose..
> And otherwise perhaps we want dynamic initialization and do the conversion
> at runtime?
> Or disable the -frounding-math for all initializer folding?
> What we emit is definitely wrong,
> Variable which claims to have 8 bytes in size but actually has 16 under t=
he
> hood, with constants in different mode.

We should have ICEd emitting the constant.  And yes, I think -frounding-math
should be disabled for constinit initializer folding (and possibly whether
it is const or not should not depend on -frounding-math).=