RFC: adding knowledge of the int_fastN_t types to the compiler

[FX Coudert]

Hi all,

The Fortran 2003 standard requires that Fortran compilers be able to  
know, at compile-time, what size the various int_fastN_t types have  
on the target (for N = 8, 16, 32 and 64). I've discussed that issue  
before on this list, and was told it's a known issue, tracked as PR  
448. For 4.3, we ignored the issue; for 4.4, I'd like to move forward  
and propose some way to go. Here's the idea I've been following: it's  
not excellent, but I don't think there are many alternatives available!

I propose we implement target macros INT_FAST8_TYPE_SIZE (and so on  
for 16, 32 and 64): they would be defined to -1 in defaults.h  
(meaning that int_fastN_t types are not available), and independent  
targets can redefine them. Front-ends and the middle-end can then use  
it if they feel like it. Attached is a patch implementing this idea,  
including target definitions for linux, darwin, mingw, AIX, IRIX,  
OpenBSD, Solaris 2.10.

Comments on that first draft are welcome. I know it's a hard issue  
and most possible fixes are more hacks than fixes, but the starting  
point is that we really need it to work, and a system that covers 99%  
of cases is better than nothing.

Thanks,
FX

-- 
François-Xavier Coudert
http://www.homepages.ucl.ac.uk/~uccafco/
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