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Re: Skipping assembler when producing slim LTO files
- From: Ian Lance Taylor <iant at google dot com>
- To: Steven Bosscher <stevenb dot gcc at gmail dot com>
- Cc: Jan Hubicka <hubicka at ucw dot cz>, Andi Kleen <andi at firstfloor dot org>, GCC Development <gcc at gcc dot gnu dot org>
- Date: Wed, 24 Sep 2014 14:47:43 -0700
- Subject: Re: Skipping assembler when producing slim LTO files
- Authentication-results: sourceware.org; auth=none
- References: <20140924054651 dot GB5371 at kam dot mff dot cuni dot cz> <878ul96pnx dot fsf at tassilo dot jf dot intel dot com> <CAKOQZ8zCs8ZjGP3JWw6HVNXGS0junJn1BuvnMXmK8Ou8WHEnvg at mail dot gmail dot com> <20140924161906 dot GA26922 at atrey dot karlin dot mff dot cuni dot cz> <20140924163227 dot GB26922 at atrey dot karlin dot mff dot cuni dot cz> <CABu31nO248rEg2xmj1MYvt-p3Y7+EbNu6U-UV6aTeMzxbiZ_Pw at mail dot gmail dot com>
On Wed, Sep 24, 2014 at 10:04 AM, Steven Bosscher <email@example.com> wrote:
> On Wed, Sep 24, 2014 at 6:32 PM, Jan Hubicka <firstname.lastname@example.org> 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.