On Mar 16, 2012, at 12:02 PM, Richard Guenther wrote: > On Fri, Mar 16, 2012 at 11:39 AM, Tristan Gingold <ging...@adacore.com> wrote: >> Hi, >> >> currently sizetype precision (cf store-layout.c:initialize_sizetypes) is the >> same as size_t. >> This is an issue on VMS, where size_t is 'unsigned int', but we'd like to >> have a 64 bit sizetype >> for Ada. My understanding is that ISO-C doesn't require size_t precision to >> match the one of >> void *. >> >> We can't really lie about size_t because it is exposed in API (such as >> writev). >> >> I don't see any reason (other than historic one) to have an exact match >> between sizetype and size_t. >> So this patch adds an hook to allow targets to define sizetype. > > Well, there is at least "common sense" that couples size_t and sizetype. > As you can at most allocate size_t memory via malloc (due to its size_t > use for the size) sizes larger than what fits into size_t do not make much > sense. Thus, a sizetype larger than size_t does not make much sense.
Agreed, but malloc() is not the only way to get memory. At least on VMS, there are some syscalls to allocate memory with a 64 bit length argument. > The middle-end of course would not care much what you use for sizetype. > But be warned - if the mode for sizetype is different of ptr_mode things > are going to be interesting for you (yes, ptr_mode, not Pmode). That's the issue. POINTER_SIZE is 64 bits (when -mpointer-size=64) but size_t should always be 32 bit. >> I initially thought about using Pmode precision for sizetype precision, but >> there are a few machines >> (m32c, sh, h8300) where the precisions aren't the same. I don't know wether >> this is on purpose or >> unintentional. > > At least for m32c it is IIRC because 24bit computations are soo expensive > on that target, so HImode is chosen for sizetype. That's a good reason! > So - why do you need a 64bit sizetype again? ;) > > Can it be that you don't really need 64bit sizes but you hit issues with > sizetype != ptr_mode size? I don't have an urgent need for 64bit sizes (although would be nice to have them). I remember that the first build with sizetype=32 but ptr_mode =DImode was a failure. Maybe I should first investigate this path, as m32c could use "unsigned int" (16 bits) for size_type alongside 32 for POINTER_SIZE ? > Btw, while we are transitioning to target hooks in this case I'd prefer > a target macro alongside the existing SIZE_TYPE, etc. ones. Ok. Tristan.
