On Mon, 19 Mar 2012, Eric Botcazou wrote: > > I am lost here. Which targets (with ptr_mode size != Pmode size != > > sizetype size) are you referring to ? > > Targets for which sizetype mode isn't necessarily equal to ptr_mode like VMS. > Up to GCC 4.6, sizetype was Pmode in Ada, but ptr_mode in C.
It does make sense to give the target control over the mode used for sizetype. Of course a global change of the default (for example to use Pmode as Ada did) will require testing each affected target, so I think it makes sense to keep the default as-is. Btw, we still have the issue on which _precision_ we should use for sizetype -- if we expect modulo-semantics of arithmetic using it (thus basically sign-less arithmetic) then the precision has to match the expectation the C frontend (and other frontends) assume how pointer offsets are handled. Currently the C frontend gets this not correct which means negative offsets will be not correctly handled. Similar issues arise from the mode/precision chosen for the bitsize types. We choose a way to wide precision for them, so the modulo-semantics assumption does not usually hold for bitsize quantities. Richard.
