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From: "0xe2.0x9a.0x9b at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug other/95971] [10 regression] Optimizer converts a false boolean
 value into a true boolean value
Date: Mon, 29 Jun 2020 19:15:33 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D95971

--- Comment #9 from Jan Ziak (http://atom-symbol.net) <0xe2.0x9a.0x9b at gm=
ail dot com> ---
(In reply to Martin Li=C5=A1ka from comment #8)
> Or you can use -fno-finite-loops option.

I am sorry, but I cannot trust this compiler not to force me again spending
several hours of time just to learn that -O2 is semantically different from=
 -O1
and -O3.

The meaning of "semantically equivalent" in my mind is different from the
meaning of "semantically equivalent" in your mind. Infinite loopiness is in=
 my
opinion semantically significant, so the compiler should have printed a war=
ning
that would inform me about the fact that the compiler is changing the seman=
tics
of the code in question.

With -O3, the assembly code is:

Dump of assembler code for function main:
   <+0>:        sub    $0x8,%rsp
   <+4>:        xor    %edi,%edi
   <+6>:        callq  xbool(bool)
   <+11>:       jmp    main+11

"11: jmp 11" is a prime example of what -ffinite-loops is supposed to preve=
nt
from being generated.

Assuming that -O3 actually does include -ffinite-loops, which I am unable to
verify because "g++ --help=3Doptimizers -Q" doesn't accept the -std=3Dgnu++=
11
option.=