Dorit Nuzman - Re: [PATCH] Fix PR 16660, attribute((aligned)) doesn't work for variable (original) (raw)

This is the mail archive of the gcc-patches@gcc.gnu.orgmailing list for the GCC project.

Re: [PATCH] Fix PR 16660, attribute((aligned)) doesn't work for variables on the stack for greater than required alignment

• From: Dorit Nuzman
• To: Andrew_Pinski at PlayStation dot Sony dot com
• Cc: gcc-patches at gcc dot gnu dot org, Russell_Olsen at PlayStation dot Sony dot com, Trevor_Smigiel at PlayStation dot Sony dot com
• Date: Tue, 6 Feb 2007 00:40:14 +0200
• Subject: Re: [PATCH] Fix PR 16660, attribute((aligned)) doesn't work for variables on the stack for greater than required alignment

Hi, This patch fixes PR 16660 where we ignore the user supplied allignment on stack variables if it is greater than the required alignment on the specific target. This fixes the issue by oversizing the stack variable and then manually aligning the variable.

does this mean that during vectorization we could avoid doing this in 'vect_can_force_dr_alignment_p': return (alignment <= PREFERRED_STACK_BOUNDARY); and just return 1 instead, relying on your patch to take care of things, since we mark the decl as having a user-supplied-alignment: DECL_USER_ALIGN (base) = 1; ? (i.e. - with your patch, would it be ok to let the vectorizer increase the alignment of arrays (on the stack) even if the required alignment is greater than PREFERRED_STACK_BOUNDARY?)

thanks, dorit

I had to remove some asserts from the x86 back-end as they are no longer valid from the point of view of the middle-end could have a case where preferred_alignment is greater than the target's preferred alignment and the stack alignment that is needed can be greater than the target's preferred alignment.

OK? Bootstrapped and tested on i686-linux-gnu and powerpc-linux-gnu with no regressions.

Thanks, Andrew Pinski

:ADDPATCH middle-end:

ChangeLog:

    * expr.h (allocate_dynamic_stack_space_1): New function

prototype. * functionc.c (assign_temp): Take into account the alignment of the temp if it is greater than the target's preferred alignment. * cfgexpand.c: Include optabs.h. (get_decl_align_unit): Update comment and don't lower the alignment if it is greater than the target's preferred alignment. (alloc_stack_frame_space): Take an unsigned HOST_WIDE_INT for align. Take into account the variable's alignment if it is greater than the target's preferred alignment. (expand_one_stack_var_at): Likewise. (defer_stack_allocation): Defer variables who's alignment is greater than the target's preferred alignment. * explow.c (allocate_dynamic_stack_space_1): Split out from allocate_dynamic_stack_space and take into acount the required alignment. (allocate_dynamic_stack_space): Call allocate_dynamic_stack_space_1. * Makefile.in (cfgexpand.o): Update dependecies. * stmt.c (expand_decl): Take into account the alignment of the variable if it is greater than the target's preferred alignment. * config/i386/i386.c (ix86_compute_frame_layout): Don't assert that preferred alignment is greater than the normal preferred alignment. Don't assert that the stack alignment needed is greater than the normal preferred alignment.

[attachment "attributealignedstack.diff.txt" deleted by Dorit Nuzman/Haifa/IBM]