[PATCH] Introduce -fprofile-update=maybe-atomic

[Nathan Sidwell]

On 11/10/2016 07:43 AM, Nathan Sidwell wrote:
> On 11/10/2016 05:19 AM, Martin Liška wrote:
>
>>> On 10/13/2016 05:34 PM, Martin Liška wrote:
>>>> Hello.
>>>>
>>>> As it's very hard to guess from GCC driver whether a target supports
>>>> atomic updates
>>>> for GCOV counter or not, I decided to come up with a new option
>>>> value (maybe-atomic),
>>>> that would be transformed in a corresponding value (single or
>>>> atomic) in tree-profile.c.
>>>> The GCC driver selects the option when -pthread is present in the
>>>> command line.
>>>>
>>>> That should fix all tests failures seen on AIX target.
>>>>
>>>> Patch can bootstrap on ppc64le-redhat-linux and survives regression
>>>> tests.
>>>>
>>>> Ready to be installed?
>
> I dislike this.  If it's hard for gcc itself to know, how much harder
> for the user must it be?   (does gcc have another instance of an option
> that behaves 'prefer-A-or-B-if-you-can't'?

Thinking further.  why isn't the right solution for 
-fprofile-update=atomic when faced with a target that cannot support it to:
a) issue an error and bail out at the first opportunity
b) or issue a warning and fall back to single threaded update?

For #b presumably there'll be the capability of suppressing that 
particular warning?

nathan

-- 
Nathan Sidwell