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Re: RFC: Improving GCC8 default option settings

On Wed, Sep 13, 2017 at 6:11 PM, Nikos Chantziaras <> 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.


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