Re: [PATCH] Change default for --param allow-...-data-races to off

[Richard Biener <richard.guenther@gmail.com>]

On June 26, 2014 12:03:21 AM CEST, Martin Jambor <mjambor@suse.cz> wrote:
>Hi,
>
>On Wed, Jun 25, 2014 at 03:14:31PM -0600, Jeff Law wrote:
>> On 06/24/14 14:19, Martin Jambor wrote:
>> >On Mon, Jun 23, 2014 at 03:35:01PM +0200, Bernd Edlinger wrote:
>> >>Hi Martin,
>> >>
>> >>>>
>> >>>>Well actually, I am not sure if we ever wanted to have a race
>condition here.
>> >>>>Have you seen any impact of --param allow-store-data-races on any
>benchmark?
>> >>>
>> >>>It's trivially to write one. The only pass that checks the param
>is
>> >>>tree loop invariant motion and it does that when it applies
>store-motion.
>> >>>Register pressure increase is increased by a factor of two.
>> >>>
>> >>>So I'd agree that we might want to disable this again for -Ofast.
>> >>>
>> >>>As nothing tests for the PACKED variants nor for the LOAD variant
>> >>>I'd rather remove those. Claiming we don't create races for those
>> >>>when you disable it via the param is simply not true.
>> >>>
>> >>>Thanks,
>> >>>Richard.
>> >>>
>> >>
>> >>OK, please go ahead with your patch.
>> >
>> >Perhaps not unsurprisingly, the patch is very similar.  Bootstrapped
>> >and tested on x86_64-linux.  OK for trunk?
>> >
>> >Thanks,
>> >
>> >Martin
>> >
>> >
>> >2014-06-24  Martin Jambor  <mjambor@suse.cz>
>> >
>> >	* params.def (PARAM_ALLOW_LOAD_DATA_RACES)
>> >	(PARAM_ALLOW_PACKED_LOAD_DATA_RACES)
>> >	(PARAM_ALLOW_PACKED_STORE_DATA_RACES): Removed.
>> >	(PARAM_ALLOW_STORE_DATA_RACES): Set default to zero.
>> >	* opts.c (default_options_optimization): Set
>> >	PARAM_ALLOW_STORE_DATA_RACES to one at -Ofast.
>> >	* doc/invoke.texi (allow-load-data-races)
>> >	(allow-packed-load-data-races, allow-packed-store-data-races):
>> >	Removed.
>> >	(allow-store-data-races): Document the new default.
>> >
>> >testsuite/
>> >	* g++.dg/simulate-thread/bitfields-2.C: Remove
>allow-load-data-races
>> >	parameter.
>> >	* g++.dg/simulate-thread/bitfields.C: Likewise.
>> >	* gcc.dg/simulate-thread/strict-align-global.c: Remove
>> >	allow-packed-store-data-races parameter.
>> >	* gcc.dg/simulate-thread/subfields.c: Likewise.
>> >	* gcc.dg/tree-ssa/20050314-1.c: Set parameter
>allow-store-data-races
>> >	to one.
>> Don't we want to deprecate, not remove the dead options?
>> 
>
>Is there a mechanism for deprecating parameters (I could not quickly
>find any) or do you mean to leave them there and only document them as
>deprecated?
>
>I am not really concerned how we deal with the unused parameters,
>removing or any form of deprecating is fine with me.

--params are not a stable interface, so we can just remove those.  Of course this would be the opportunity to introduce a real option for this task and leave the param as an implementation detail.

Richard.

>Thanks,
>
>Martin