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Re: Skipping assembler when producing slim LTO files


> On Wed, Sep 24, 2014 at 10:04 AM, Steven Bosscher <stevenb.gcc@gmail.com> wrote:
> > On Wed, Sep 24, 2014 at 6:32 PM, Jan Hubicka <hubicka@ucw.cz> wrote:
> >> Libreoffice shows that GCC needs about twice as much of system time. According
> >> to profiles, good part is the ugly way we pass stuff down to assembler and
> >> other part is memory use during the copmilation stage.
> >
> > Are you using -pipe? AFAIR this still isn't the default, even on
> > GNU/Linux, but it is typically a lot faster than without.
> 
> Is that true even when TMPDIR is on a ram disk?  There's no obvious
> reason that it should be true in a parallel build.  Using -pipe
> effectively constrains communication between the compiler and the
> assembler to work in PIPE_BUF blocks.  Using TMPDIR introduces no such
> constraints, and in a big program a parallel build should obscure the
> fact that the compiler and assembler are serialized for each
> individual compilation unit.

Actually I mount /tmp as tmpfs, so this should not be an issue.
Oviously for slim LTO we get more benefits from outputting binary data directly
rather than spending time to printf and scanf them ;)

Honza


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