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Re: RFC: Improving GCC8 default option settings


On Wed, Sep 13, 2017 at 5:08 PM, Allan Sandfeld Jensen
<linux@carewolf.com> wrote:
> On Mittwoch, 13. September 2017 15:46:09 CEST Jakub Jelinek wrote:
>> On Wed, Sep 13, 2017 at 03:41:19PM +0200, Richard Biener wrote:
>> > On its own -O3 doesn't add much (some loop opts and slightly more
>> > aggressive inlining/unrolling), so whatever it does we
>> > should consider doing at -O2 eventually.
>>
>> Well, -O3 adds vectorization, which we don't enable at -O2 by default.
>>
> Would it be possible to enable basic block vectorization on -O2? I assume that
> doesn't increase binary size since it doesn't unroll loops.

Somebody needs to provide benchmarking looking at the compile-time cost
vs. the runtime benefit and the code size effect.  There's also room to tune
aggressiveness of BB vectorization as it currently allows for cases where
the scalar computation is not fully replaced by vector code.

Richard.

> 'Allan
>


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