Re: Feature request - a macro defined for GCC

[Chris Lattner <clattner at apple dot com>]

On Jul 3, 2008, at 3:01 PM, Joseph S. Myers wrote:
> > Taking an approach reduces startup time of the preprocessor,  
> > because it
> > doesn't have to populate the identifier table with tons of  
> > predefines.
>
> I'd hope this is not a significant cost (certainly not compared to the
> thousands of built-in functions on some target), though I haven't seen
> recent figures for startup costs.

I was referring to clang startup times, not GCC.  clang registers  
builtins completely lazily, so they don't take significant time at  
startup.  Much of clang startup time is populating the predefined  
identifier table for macros.

> We have some existing practice for feature macros  
> (__GNUC_GNU_INLINE__,
> __GNUC_STDC_INLINE__, __GCC_HAVE_SYNC_COMPARE_AND_SWAP_1, ...).

Understood.  Likewise many system headers have these.  I don't think  
we can eliminate existing macros, but adding a plethora of new macros  
would be bad.

-Chris