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Re: Should bootstrap-O3 be the default for building/testing GCC?


On Thu, Dec 24, 2015 at 3:40 PM, Gary Funck <gary@intrepid.com> wrote:
>
> Currently, the default optimization level when building,
> bootstrapping GCC is -O2.
>
> We routinely build with --with-build-config='bootstrap-debug bootstrap-O3'
> because we want to verify that our UPC changes don't affect the
> compiler when built with full optimizations.  We also build
> with --enable-checking=all.
>
> Since most developers probably build/test GCC with the default -O2 options,
> we fairly often run into -O3 related issues when building GCC.
> Enough so that we're considering just using the default -O2 settings.
>
> I'm wondering if there might be benefit in changing the current defaults
> to use -O3 instead?  Or perhaps have the configure infrastructure
> determine that the build is for a development version of GCC
> and set the flags and options accordingly?
>
> Somewhat related: has anyone recently determined whether a GCC built
> with -O3 is generally faster/smaller than one built at -O2?

-O3 will just result in larger code IIRC.  You get benefits from
profiledboostrap,
both size and performance-wise (profiledbootstrap also enables most of what
-O3 enables).

So no, we don't want to change the defaults.

Richard.

> thanks,
> - Gary


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