Apple's implementation of precompiled headers

[Daniel Berlin]

dewar@gnat.com writes:

> <<In actuality, it's not.
> This is because expansion to rtl gets counted in the parse cost, and
> it's expensive.
> With precomp'd headers as serialized trees, you don't need to
> re-expand (assuming you serialize DECL_RTL as well).
> >>
>
> Of course you do not need to convert declarations to rtl unless they are
> used, i.e. you can do it on demand, that's what we do with Ada specs, the
> declarations are converted to rtl on demand (at least that's my understanding
> of what we do, it is not the area of GNAT I know well, and if we are not
> doing it we should be doing it :-)
Right, it's done on demand, but still done.
You can expand them and save it in the precomp, and then not have to
reexpand them at compile time, on demand.
You can acually even save the asm output, and just reoutput it.
This is what redhat's precomp'd headers did, IIRC.
--Dan



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