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Re: RFC: Improving GCC8 default option settings
- From: Richard Biener <richard dot guenther at gmail dot com>
- To: Nikos Chantziaras <realnc at gmail dot com>
- Cc: GCC Development <gcc at gcc dot gnu dot org>
- Date: Thu, 14 Sep 2017 11:57:00 +0200
- Subject: Re: RFC: Improving GCC8 default option settings
- Authentication-results: sourceware.org; auth=none
- References: <HE1PR0801MB2058CFEE6A9C43380337A83F83690@HE1PR0801MB2058.eurprd08.prod.outlook.com> <opblad$cto$1@blaine.gmane.org>
On Wed, Sep 13, 2017 at 6:11 PM, Nikos Chantziaras <realnc@gmail.com> wrote:
> On 12/09/17 16:57, Wilco Dijkstra wrote:
>>
>> [...] As a result users are
>> required to enable several additional optimizations by hand to get good
>> code.
>> Other compilers enable more optimizations at -O2 (loop unrolling in LLVM
>> was
>> mentioned repeatedly) which GCC could/should do as well.
>> [...]
>>
>> I'd welcome discussion and other proposals for similar improvements.
>
>
> What's the status of graphite? It's been around for years. Isn't it mature
> enough to enable these:
>
> -floop-interchange -ftree-loop-distribution -floop-strip-mine -floop-block
>
> by default for -O2? (And I'm not even sure those are the complete set of
> graphite optimization flags, or just the "useful" ones.)
It's not on by default at any optimization level. The main issue is the
lack of maintainance and a set of known common internal compiler errors
we hit. The other issue is that there's no benefit of turning those on for
SPEC CPU benchmarking as far as I remember but quite a bit of extra
compile-time cost.
Richard.