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From: "bruno at clisp dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/111655] [11/12/13/14 Regression] wrong code
 generated for __builtin_signbit and 0./0. on x86-64 -O2
Date: Fri, 19 Apr 2024 11:38:48 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D111655

Bruno Haible <bruno at clisp dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bruno at clisp dot org

--- Comment #16 from Bruno Haible <bruno at clisp dot org> ---
(In reply to Paul Eggert from comment #5)
> Although it is indeed unspecified whether 0.0/0.0 yields -NaN or +NaN, it=
 is
> well understood that negating a floating point value flips its sign bit.

While I agree that this is generally true, it's not the case on mips with c=
lang
as compiler.

Namely, this compiler generates 'neg.d' instructions for the unary minus of=
 a
'double' value, and this instruction may be a no-op on NaN values, dependin=
g on
the CPU's control registers. For details, see the "MIPS=C2=AE Architecture =
for
Progreammers, Volume II-A: The MIPS=C2=AE Instruction Set Manual", page 307=
 (317).

Whereas gcc generates an integer XOR instruction (at least in my test cases=
),
so is fine.=