From: Carlo Wood <carlo@alinoe.com>
To: Michel LESPINASSE <walken@zoy.org>
Cc: Andrew Haley <aph@redhat.com>, gcc@gcc.gnu.org
Subject: Re: issues with inlining
Date: Fri, 10 Jan 2003 00:15:00 -0000 [thread overview]
Message-ID: <20030109225546.GA27959@alinoe.com> (raw)
In-Reply-To: <20030109215002.GC31311@zoy.org>
On Thu, Jan 09, 2003 at 01:50:02PM -0800, Michel LESPINASSE wrote:
> > According to the docs
> >
> > `-O3' turns on all optimizations specified by `-O2' and also
> > turns on the `inline-functions' option.
But that says nothing about priority regulation.
> > so why are you using -O3 if you want to control inlining by means of
> > the "inline" kwyword?
To let the compiler decide is MORE can be inlined than what I already
marked as must-be-inlined (although it doesn't do that :/).
> >>> 4) The instruction limit that can be set with -finline-limit
> >>> seems to count instructions before optimization...
> >
> > True -- the inliner works at the source level before optimization is
> > performed. This is the best way to do it.
Of course it is best to FIRST inline and THEN optimize - but, the set
instruction limit should be on the optimized result, not on on the
number of instructions before optimization.
> You're most probably right on average. But you sometimes see code that
> use compile-time constants for specialization, i.e. one big inline
> routine that evaluates to something small based on the value of some
> constant parameters. In this case, the fact the inliner only sees the
> huge initial routine instead of the smaller one after specialization,
> combined with the fact the programmer can not use the inline keyword
> to force inlining, is an issue.
Exactly my point. I use HUGE template functions that go like:
if (constant == 1)
{
...
}
else if (constant == 2)
{
...
}
etc etc. We talk about a reduction of 100 in size ONLY because
of if (CONSTANT) { } constructs. The -finline-limit is really
un usable when it doesn't ignore the instructions in those
blocks that will not be used. Note that even with -O0 these
blocks are removed... so why the need to count those instruction
when deciding whether or not to inline the function?!
--
Carlo Wood <carlo@alinoe.com>
next prev parent reply other threads:[~2003-01-09 22:56 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-12-18 18:32 Carlo Wood
2003-01-09 21:40 ` Michel LESPINASSE
2003-01-09 21:50 ` Andrew Haley
2003-01-09 22:52 ` Michel LESPINASSE
2003-01-10 0:15 ` Carlo Wood [this message]
2003-01-19 19:16 ` Alexandre Oliva
2003-01-19 20:49 ` Diego Novillo
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