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From: "pc at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/104901] gcc/config/rs6000/mm_malloc.h:46: incorrectLogicOperator
Date: Mon, 21 Mar 2022 18:22:46 +0000 [thread overview]
Message-ID: <bug-104901-4-AiOLg5LT5Q@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-104901-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104901
pc at gcc dot gnu.org changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |pc at gcc dot gnu.org
--- Comment #5 from pc at gcc dot gnu.org ---
(In reply to Segher Boessenkool from comment #4)
> is this micro-optimisation useful at all, don't
> posix_memalign and malloc end up the same under the covers anyway?
posix_memalign returns memory aligned to a specified power-of-2 alignment.
malloc returns memory aligned to some ABI minimum. (You already know this, I'm
sure.) The code will use malloc if it can, and posix_memalign otherwise. There
may be a slight advantage to using malloc instead of posix_memalign. The paths
are indeed different. I'm not sure why the floor is raised after determining
not to call malloc:
--
if (__alignment == __malloc_align && __alignment == __vec_align)
return malloc (__size);
if (__alignment < __vec_align)
__alignment = __vec_align;
--
(I probably would've written the code slightly differently.)
It appears to me that the identified code would be always false on a 32-bit
system, where __malloc_align would be computed as 64 bits, and _vec_align as
128 bits. It would be always true on a 64-bit system (128 == 128).
All that being said, I'm not sure I see any problem with the code, and maybe
the analyzer is being a bit overzealous?
FWIW, the code was likely taken as an analog to gcc/config/i386/pmm_malloc.h:
--
if (__alignment == 1)
return malloc (__size);
if (__alignment == 2 || (sizeof (void *) == 8 && __alignment == 4))
__alignment = sizeof (void *);
if (posix_memalign (&__ptr, __alignment, __size) == 0)
return __ptr;
--
next prev parent reply other threads:[~2022-03-21 18:22 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-13 13:44 [Bug target/104901] New: " dcb314 at hotmail dot com
2022-03-13 13:47 ` [Bug target/104901] " dcb314 at hotmail dot com
2022-03-13 14:10 ` schwab@linux-m68k.org
2022-03-14 8:44 ` rguenth at gcc dot gnu.org
2022-03-18 14:28 ` segher at gcc dot gnu.org
2022-03-21 18:22 ` pc at gcc dot gnu.org [this message]
2022-03-21 18:49 ` segher at gcc dot gnu.org
2022-03-21 19:00 ` schwab@linux-m68k.org
2022-03-21 19:28 ` segher at gcc dot gnu.org
2022-03-21 19:33 ` dcb314 at hotmail dot com
2022-03-21 19:53 ` schwab@linux-m68k.org
2022-03-21 20:23 ` segher at gcc dot gnu.org
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