On Fri, Mar 16, 2012 at 12:33 PM, Tristan Gingold <ging...@adacore.com> wrote: > > 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.
Ok. >>> 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 ? Well, this setup is not well supported by the middle-end (and indeed m32c has existing issues with that). So in your case decoupling sizetype from size_t sounds like the more appropriate solution. >> 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. I'd choose SIZETYPE (for confusion, heh), defaulting to SIZE_TYPE. Richard. > Tristan. >
