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From: "segher at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/112758] [13/14 Regression] Inconsistent Bitwise AND Operation Result between int and long long int
Date: Sat, 09 Dec 2023 19:25:24 +0000	[thread overview]
Message-ID: <bug-112758-4-G7AgCytlI8@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-112758-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112758

--- Comment #10 from Segher Boessenkool <segher at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #6)
> I must say I have no idea what WORD_REGISTER_OPERATION says about the upper
> bits of a paradoxical SUBREG if it is a MEM and load_extend_op (inner_mode)
> is ZERO_EXTEND (zeros then?  Then this optimization is ok), or something
> else?  And what it says on REGs.

It says those upper bits are well-defined, i.e. whatever MD pattern is used for
it eventually will emit machine code that has the exact same result for those
upper bits.  This is almost impossible to prove for any non-trivial target, and
certainly extremely fragile.

  parent reply	other threads:[~2023-12-09 19:25 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-11-29  6:05 [Bug c/112758] New: Inconsistent Bitwise AND Operation Result between int and long long int on Different Optimization Levels in GCC Trunk guminb at ajou dot ac.kr
2023-11-29 18:18 ` [Bug rtl-optimization/112758] [13/14 Regression] Inconsistent Bitwise AND Operation Result between int and long long int pinskia at gcc dot gnu.org
2023-12-08  2:57 ` guminb at ajou dot ac.kr
2023-12-08 17:01 ` jakub at gcc dot gnu.org
2023-12-08 17:37 ` segher at gcc dot gnu.org
2023-12-08 19:33 ` jakub at gcc dot gnu.org
2023-12-08 19:36 ` jakub at gcc dot gnu.org
2023-12-09  8:51 ` ebotcazou at gcc dot gnu.org
2023-12-09  9:11 ` jakub at gcc dot gnu.org
2023-12-09 11:00 ` ebotcazou at gcc dot gnu.org
2023-12-09 19:25 ` segher at gcc dot gnu.org [this message]
2023-12-09 22:06 ` ebotcazou at gcc dot gnu.org
2023-12-10 12:16 ` segher at gcc dot gnu.org
2023-12-13 22:06 ` pinskia at gcc dot gnu.org
2023-12-16 18:43 ` gkm at rivosinc dot com
2023-12-21 20:04 ` gkm at rivosinc dot com
2023-12-21 20:06 ` jakub at gcc dot gnu.org
2023-12-22 11:30 ` cvs-commit at gcc dot gnu.org
2024-03-02  0:37 ` cvs-commit at gcc dot gnu.org
2024-03-04  1:09 ` law at gcc dot gnu.org
2024-03-04 12:07 ` [Bug rtl-optimization/112758] [13 " jakub at gcc dot gnu.org

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