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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/102125] (ARM Cortex-M3 and newer) missed optimization. memcpy not needed operations
Date: Mon, 30 Aug 2021 11:40:45 +0000 [thread overview]
Message-ID: <bug-102125-4-ErNVIYGSDl@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-102125-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102125
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Component|c |target
Last reconfirmed| |2021-08-30
Target| |arm
Keywords| |missed-optimization
Ever confirmed|0 |1
Status|UNCONFIRMED |NEW
--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
One common source of missed optimizations is gimple_fold_builtin_memory_op
which has
/* If we can perform the copy efficiently with first doing all loads
and then all stores inline it that way. Currently efficiently
means that we can load all the memory into a single integer
register which is what MOVE_MAX gives us. */
src_align = get_pointer_alignment (src);
dest_align = get_pointer_alignment (dest);
if (tree_fits_uhwi_p (len)
&& compare_tree_int (len, MOVE_MAX) <= 0
...
/* If the destination pointer is not aligned we must be able
to emit an unaligned store. */
&& (dest_align >= GET_MODE_ALIGNMENT (mode)
|| !targetm.slow_unaligned_access (mode, dest_align)
|| (optab_handler (movmisalign_optab, mode)
!= CODE_FOR_nothing)))
where here likely the MOVE_MAX limit applies (it is 4). Since we actually
do need to perform two loads the code seems to do what is intended (but
that's of course "bad" for 64bit copies on 32bit archs and likewise for
128bit copies on 64bit archs).
It's usually too late for RTL memcpy expansion to fully elide stack storage.
next prev parent reply other threads:[~2021-08-30 11:40 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-30 8:27 [Bug c/102125] New: " jankowski938 at gmail dot com
2021-08-30 8:32 ` [Bug c/102125] " jankowski938 at gmail dot com
2021-08-30 11:40 ` rguenth at gcc dot gnu.org [this message]
2021-08-30 19:29 ` [Bug target/102125] " pinskia at gcc dot gnu.org
2021-08-30 20:14 ` jankowski938 at gmail dot com
2021-08-31 11:54 ` rearnsha at gcc dot gnu.org
2021-08-31 16:42 ` rearnsha at gcc dot gnu.org
2021-09-13 10:27 ` cvs-commit at gcc dot gnu.org
2021-09-13 10:27 ` cvs-commit at gcc dot gnu.org
2021-09-13 10:27 ` cvs-commit at gcc dot gnu.org
2021-09-13 10:29 ` rearnsha at gcc dot gnu.org
2022-03-23 14:57 ` cvs-commit at gcc dot gnu.org
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