Richard Biener <richard.guent...@gmail.com> writes: > On Wed, Jul 18, 2018 at 8:08 PM Richard Sandiford > <richard.sandif...@arm.com> wrote: >> >> This patch adds the target framework for handling the SVE ACLE, >> starting with four functions: svadd, svptrue, svsub and svsubr. >> >> The ACLE has both overloaded and non-overloaded names. Without >> the equivalent of clang's __attribute__((overloadable)), a header >> file that declared all functions would need three sets of declarations: >> >> - the non-overloaded forms (used for both C and C++) >> - _Generic-based macros to handle overloading in C >> - normal overloaded inline functions for C++ >> >> This would likely require a lot of cut-&-paste. It would probably >> also lead to poor diagnosics and be slow to parse. >> >> Another consideration is that some functions require certain arguments >> to be integer constant expressions. We can (sort of) enforce that >> for calls to built-in functions using resolve_overloaded_builtin, >> but it would be harder to enforce with inline forwarder functions. >> >> For these reasons and others, the patch takes the approach of adding >> a pragma that gets the compiler to insert the definitions itself. >> This requires a slight variation on the existing lang hooks for >> built-in functions, but otherwise it seems to just work. > > I guess you did consider auto-generating the three variants from a template?
Yeah. But that would only solve the cut-&-paste problem, not the others. It would also be quite a lot more complicated overall. E.g. scripting code to produce the right _Generics is much more complicated than just implementing the overloading using resolve_overloaded_builtin (which also produces better error messages). And even just scripting the declarations is more work: the backend has to register a built-in function either way, so getting it to register the public name is easier than having the backend register a __builtin_ function and then scripting a header file declaration with the same prototype and attributes. Thanks, Richard
