new patches using -fopt-info (issue5294043)

Richard Guenther richard.guenther@gmail.com
Thu Oct 20 08:35:00 GMT 2011


On Thu, Oct 20, 2011 at 1:33 AM, Andi Kleen <andi@firstfloor.org> wrote:
> xur@google.com (Rong Xu) writes:
>
>> After some off-line discussion, we decided to use a more general approach
>> to control the printing of optimization messages/warnings. We will
>> introduce a new option -fopt-info:
>>  * fopt-info=0 or fno-opt-info: no message will be emitted.
>>  * fopt-info or fopt-info=1: emit important warnings and optimization
>>    messages with large performance impact.
>>  * fopt-info=2: warnings and optimization messages targeting power users.
>>  * fopt-info=3: informational messages for compiler developers.

This doesn't look scalable if you consider that each pass would print
as much of a mess like -fvectorizer-verbose=5.

I think =2 and =3 should be omitted - we do have dump-files for a reason.

Also the coverage/profile cases you changed do not at all match
"... with large performance impact".  In fact the impact is completely
unknown (as it would be the case usually).

I'd rather have a way to make dump-files more structured (so, following
some standard reporting scheme) than introducing yet another way
of output.  [after making dump-files more consistent it will be easy
to revisit patches like this, there would be a natural general central
way to implement it]

So, please fix dump-files instead.  And for coverage/profiling, fill
in stuff in a dump-file!

Richard.

> It would be interested to have some warnings about missing SRA
> opportunities in =1 or =2. I found that sometimes fixing those can give a
> large speedup.
>
> Right now a common case that prevents SRA on structure field
> is simply a memset or memcpy.
>
> -Andi
>
>
> --
> ak@linux.intel.com -- Speaking for myself only
>



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