On 5 April 2014 20:38, Iain Buclaw <ibuc...@gdcproject.org> wrote: > On 5 Apr 2014 21:31, "Iain Buclaw" <ibuc...@gdcproject.org> wrote: >> >> On 5 Apr 2014 19:55, "Johannes Pfau" <nos...@example.com> wrote: >> > >> > Am Sun, 6 Apr 2014 02:51:28 +1000 >> > schrieb "Daniel Murphy" <yebbliesnos...@gmail.com>: >> > >> > > "Johannes Pfau" wrote in message >> > > news:lhp8h4$2j38$1...@digitalmars.com... >> > > >> > > > But we'd want this to work/inline nevertheless, right?: >> > > > ------------ >> > > > void test(const(char)[] a) >> > > > { >> > > > } >> > > > >> > > > char[] abc; >> > > > test(abc); >> > > > ------------ >> > > > >> > > > Then we still need to tell GCC that const(char)[] is a variant of >> > > > char[] or it won't inline. >> > > >> > > Can you just strip all const/immutable/etc when the type is passed to >> > > the backend? >> > > >> > >> > This would impact debug info which is also emitted by the backend. GCC >> > supports 'variants' of types which means only different qualifiers but >> > the same apart from type qualifiers. We just need to set the variant >> > information correctly (e.g. const(char)[] should be recognized as a >> > variant of char[]) >> >> Right, and not having const applied to the type means that gcc might miss >> an optimisation opportunity. >> >> In this case however I think that parameters declared in should not be >> mapped to C-style 'const'. The 'in' keyword is close, but something other. > > FORTRAN for instance has intent attributes. > > --- > intent(in) - yes, pass by value, so changes of this are not reflected in > outside code. > > intent(out) - pass somehow by reference, in fact a return argument > > intent(inout) - pass by reference, normal in/out parameter. > --- > > These are interesting concepts that allows more aggressive optimisation than > using C/C++ const/ref type variants. I think gdc should go down this route, > but I've never experimented too much round this area.
See gimple.c: gimple_call_arg_flags for the middle-end detection and the implementation is roughly: EAF_UNUSED: Unused EAF_NOCLOBBER: Read-only EAF_NOESCAPE: Not escaping EAF_DIRECT: Only once dereferenced (*p, not **p) The 'in' attribute could be mapped to 'r', meaning read-only and not escaping. Regards Iain.
