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From: "ramana at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug target/67366] Poor assembly generation for unaligned memory accesses on ARM v6 & v7 cpus Date: Thu, 27 Aug 2015 10:47:00 -0000 [thread overview] Message-ID: <bug-67366-4-a8vtcM1qIH@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-67366-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67366 --- Comment #5 from Ramana Radhakrishnan <ramana at gcc dot gnu.org> --- (In reply to rguenther@suse.de from comment #3) > On Thu, 27 Aug 2015, rearnsha at gcc dot gnu.org wrote: > > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67366 > > > > --- Comment #2 from Richard Earnshaw <rearnsha at gcc dot gnu.org> --- > > (In reply to Richard Biener from comment #1) > > > I think this boils down to the fact that memcpy expansion is done too late > > > and > > > that (with more recent GCC) the "inlining" done on the GIMPLE level is > > > restricted > > > to !SLOW_UNALIGNED_ACCESS but arm defines STRICT_ALIGNMENT to 1 > > > unconditionally. > > > > > > > Yep, we have to define STRICT_ALIGNMENT to 1 because not all load instructions > > work with misaligned addresses (ldm, for example). The only way to handle > > misaligned copies is through the movmisalign API. > > Are the movmisalign handled ones reasonably efficient? That is, more > efficient than memcpy/memmove? Then we should experiment with What do you mean by more efficient here ? they'll end up calling down to the same unspec block if we implemented them - memcpy / memmove go through the backend block_move interface. Will try the patch with a hacked up movmisalign pattern in the backend. > > Index: gcc/gimple-fold.c > =================================================================== > --- gcc/gimple-fold.c (revision 227252) > +++ gcc/gimple-fold.c (working copy) > @@ -708,7 +708,9 @@ gimple_fold_builtin_memory_op (gimple_st > /* If the destination pointer is not aligned we must be > able > to emit an unaligned store. */ > && (dest_align >= GET_MODE_ALIGNMENT (TYPE_MODE (type)) > - || !SLOW_UNALIGNED_ACCESS (TYPE_MODE (type), > dest_align))) > + || !SLOW_UNALIGNED_ACCESS (TYPE_MODE (type), > dest_align) > + || (optab_handler (movmisalign_optab, TYPE_MODE > (type)) > + != CODE_FOR_nothing))) > { > tree srctype = type; > tree desttype = type; > @@ -720,7 +722,10 @@ gimple_fold_builtin_memory_op (gimple_st > srcmem = tem; > else if (src_align < GET_MODE_ALIGNMENT (TYPE_MODE > (type)) > && SLOW_UNALIGNED_ACCESS (TYPE_MODE (type), > - src_align)) > + src_align) > + && (optab_handler (movmisalign_optab, > + TYPE_MODE (type)) > + == CODE_FOR_nothing)) > srcmem = NULL_TREE; > if (srcmem) > {
next prev parent reply other threads:[~2015-08-27 10:47 UTC|newest] Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top 2015-08-26 21:42 [Bug c/67366] New: " yann.collet.73 at gmail dot com 2015-08-27 7:39 ` [Bug target/67366] " rguenth at gcc dot gnu.org 2015-08-27 9:36 ` rearnsha at gcc dot gnu.org 2015-08-27 10:21 ` rguenther at suse dot de 2015-08-27 10:42 ` ramana at gcc dot gnu.org 2015-08-27 10:47 ` ramana at gcc dot gnu.org [this message] 2015-08-27 11:08 ` ramana at gcc dot gnu.org 2015-08-27 11:13 ` rguenther at suse dot de 2015-08-27 11:17 ` ramana at gcc dot gnu.org 2015-08-27 14:31 ` rearnsha at gcc dot gnu.org 2015-08-27 14:36 ` rguenther at suse dot de 2015-08-27 14:45 ` ramana at gcc dot gnu.org 2015-09-09 15:28 ` ramana at gcc dot gnu.org 2015-10-09 11:08 ` ramana at gcc dot gnu.org 2015-10-11 10:33 ` fredrik.hederstierna@securitas-direct.com 2015-10-13 9:16 ` ramana at gcc dot gnu.org
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