PATCH: PR target/46519: Missing vzeroupper

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Thu, Nov 18, 2010 at 1:11 AM, Uros Bizjak <ubizjak@gmail.com> wrote:
> On Thu, Nov 18, 2010 at 12:36 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
>
>> Here is the patch for
>>
>> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46519
>>
>> We have 2 blocks pointing to each others. This patch first scans
>> all blocks without moving vzeroupper so that we can have accurate
>> information about upper 128bits at block entry.
>
> This introduces another insn scanning pass, almost the same as
> existing vzeroupper pass (modulo CALL_INSN/JUMP_INSN handling).
>
> So, if I understand correctly:
> - The patch removes the detection if the function ever touches AVX registers.
> - Due to this, all call_insn RTXes have to be decorated with
> CALL_NEEDS_VZEROUPPER.
> - A new pre-pass is required that scans all functions in order to
> detect functions with live AVX registers at exit, and at the same time
> marks the functions that *do not* use AVX registers.
> - Existing pass then re-scans everything to again detect functions
> with live AVX registers at exit and handles vzeroupper emission.
>
> I don't think this approach is acceptable. Maybe a LCM infrastructure
> can be used to handle this case?
>

Here is the rewrite of the vzeroupper optimization pass.
To avoid circular dependency, it has 2 passes.  It
delays the circular dependency to the second pass
and avoid rescan as much as possible.

I compared the bootstrap times with/wthout this patch
on 64bit Sandy Bridge with multilib and --with-fpmath=avx.
I enabled c,c++,fortran,java,lto,objc

Without patch:

12378.70user 573.02system 41:54.21elapsed 515%CPU

With patch

12580.56user 578.07system 42:25.41elapsed 516%CPU

The overhead is about 1.6%.


-- 
H.J.
---
gcc/

2010-11-19  H.J. Lu  <hongjiu.lu@intel.com>

	PR target/46519
	* config/i386/i386.c (upper_128bits_state): New.
	(block_info_def): Remove upper_128bits_set and done.  Add state,
	referenced, count, processed and rescanned.
	(check_avx256_stores): Updated.
	(move_or_delete_vzeroupper_2): Updated. Handle deleted BB_END.
	Call note_stores only if needed.  Set referenced and count.
	(move_or_delete_vzeroupper_1): Updated.  Set rescan_vzeroupper_p.
	(rescan_move_or_delete_vzeroupper): New.
	(move_or_delete_vzeroupper):  Process and rescan all all basic
	blocks instead of predecessor blocks of all exit points.
	(use_avx256_p): Removed.
	(init_cumulative_args): Don't set use_avx256_p.
	(ix86_function_arg): Likewise.
	(ix86_expand_move): Likewise.
	(ix86_expand_vector_move_misalign): Likewise.
	(ix86_local_alignment): Likewise.
	(ix86_minimum_alignment): Likewise.
	(ix86_expand_epilogue): Don't check use_avx256_p when generating
	vzeroupper.
	(ix86_expand_call): Likewise.

	* config/i386/i386.h (machine_function): Remove use_vzeroupper_p
	and use_avx256_p.  Add rescan_vzeroupper_p.

gcc/testsuite/

2010-11-17  H.J. Lu  <hongjiu.lu@intel.com>

	PR target/46519
	* gcc.target/i386/avx-vzeroupper-10.c: Expect no avx_vzeroupper.
	* gcc.target/i386/avx-vzeroupper-11.c: Likewise.

	* gcc.target/i386/avx-vzeroupper-20.c: New.
	* gcc.target/i386/avx-vzeroupper-21.c: Likewise.
	* gcc.target/i386/avx-vzeroupper-22.c: Likewise.
	* gcc.target/i386/avx-vzeroupper-23.c: Likewise.
	* gcc.target/i386/avx-vzeroupper-24.c: Likewise.

Attachment: gcc-pr46519-3.patch
Description: Text document