On Tue, Mar 13, 2018 at 09:24:11AM +0100, Martin Liška wrote:
> On 03/12/2018 10:39 AM, Marc Glisse wrote:
> > On Mon, 12 Mar 2018, Martin Liška wrote:
> >
> > > This is fix for the PR that introduces a new target macro. Using the macro
> > > one can say that a target has a fast mempcpy and thus it's preferred to
> > > be used
> > > if possible.
> > >
> > > Patch can bootstrap on ppc64le-redhat-linux and survives regression tests.
> > > I also tested on x86_64-linux-gnu.
> > >
> > > Ready to be installed?
> > > Martin
> > >
> > > gcc/ChangeLog:
> > >
> > > 2018-03-08 Martin Liska <mli...@suse.cz>
> > >
> > > PR middle-end/81657
> > > * builtins.c (expand_builtin_memory_copy_args): Add new
> > > arguments.
> > > * config/i386/i386.h (TARGET_HAS_FAST_MEMPCPY_ROUTINE):
> > > New macro.
> >
> > Shouldn't the macro be defined in a more specific case, for instance glibc
> > on x86? Or do all known libc on x86 happen to provide a fast mempcpy?
>
> That's Marc a very good question. Do we already have a glibc-related target
> macros/hooks?
> If so, I would add this as one of these.
Yes, see e.g. TARGET_LIBC_HAS_FUNCTION target hook,
where in particular linux_libc_has_function deals with various C libraries.
Of course, in this case you need another target hook, that is dependent both
on the target backend and C library.
It would be nice to make the target hook a little bit more generic as well,
e.g. pass it enum builtin_function and query if it is fast, slow or
unknown, or even some kind of cost, where the caller could ask for cost of
BUILT_IN_MEMCPY and BUILT_IN_MEMPCPY and decide based on the relative costs.
Jakub
