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Re: [PCH] driver, documentation
> Date: Mon, 19 Aug 2002 10:58:58 -0700
> From: Stan Shebs <shebs@apple.com>
> Mike Stump wrote:
>
> > I was wondering about flags like -fvolatile, -O2, -O0, -g and
> > -ffast-math? -UMACRO? Do they rule out pch? Should they?
> > I am thinking about C++ where it is possible to have significant
> > portions of code for an application in header files.
>
> Ideally, you'd keep around tree rather than RTL, so most backend flags
> shouldn't matter.
That would make PCH files slower to use, because RTL would need to be
regenerated (and re-optimised) if it is used.
> The most problematic backend flags are the ones that
> define cpp macros, so that would include -On because of __OPTIMIZE__
> (I think we get this one wrong now). It would be useful to have some
> way of knowing or indicating flags that don't affect a precomp, because
> it's too restrictive otherwise - consider a -Wxxx passed only to some
> files in a project.
I'm not so worried about cpp macros, I have a complete solution for
that. I _am_ worried about, for instance, building the header with
-gdwarf-2 and using it with -gstabs; this is a case we'll probably
have to disallow, because there's a tree field that means different
things between the two cases.
The thing is, though, that we _could_ make any flag combination work.
The problem is not the flag combinations that we're thinking about,
the problem is that there are far too many combinations to be able to
test or think about even a small proportion.
--
- Geoffrey Keating <geoffk@geoffk.org> <geoffk@redhat.com>