Re: using stdc++.h.gch

[Benjamin Kosnik <bkoz at redhat dot com>]

>Solaris is known to not-work, due to some weirdness in their mmap()
>implementation.  I think the current situation is that there are two
>possible design choices, one that is more portable but maybe slower,
>and another that relies on fragile OS behaviour but would be fast when
>it worked.
>
>BSD is known to work (well, Darwin at least).

Hmmm. I'm hoping Loren can do some testing on FreeBSD. I'm expecting
FreeBSD to work, since it's Darwin + DWARF2 + ELF. Loren, any chance you
can double check this?

>> 1) What targets support PCH, and how can I identify this in autoconf?
>> I'm assuming that PCH should not be flipped on for everybody, and that
>> maybe an --enable flag will be needed, with hosts that support it
>> getting it automagically fipped on?
>
>If you did want to check PCH support with autoconf, I'd suggest trying
>to build a PCH file and trying to use it.

Yep. I suppose this is what needs to happen. So either the generation
fails with -Winvalid-pch, or -Winvalid-pch and usage of the file will
fail? Hmmm. I guess there is no need for an --enable flag for this.

>> 3) Installing a zero-size stdc++.h file so that I can use stdc++.h.gch
>> seems weird. Is it possible to just do some kind of -include
>> /foo/stdc++.gch?
>
>You don't need to have a stdc++.h file to use stdc++.h.gch; and
>-include does work, although remember that you have to leave the .gch off.

Indeed it does. I thought it wasn't, but it seems you are correct.
Thanks!

-benjamin