PING [Patch][Middle-end]Add -fzero-call-used-regs=[skip|used-gpr|all-gpr|used|all]

[Segher Boessenkool]

On Fri, Sep 04, 2020 at 11:52:13AM -0700, H.J. Lu wrote:
> On Fri, Sep 4, 2020 at 11:09 AM Segher Boessenkool
> <segher@kernel.crashing.org> wrote:
> > On Fri, Sep 04, 2020 at 10:34:23AM -0700, H.J. Lu wrote:
> > > > You probably have to do this for every target separately?  But it is not
> > > > enough to handle it in the epilogue, you also need to make sure it is
> > > > done on every path that returns *without* epilogue.
> > >
> > > This feature is designed for normal return with epilogue.
> >
> > Very many normal returns do *not* pass through an epilogue, but are
> > simple_return.  Disabling that is *much* more expensive than that 2%.
> 
> Sibcall isn't covered.  What other cases don't have an epilogue?

Shrink-wrapped stuff.  Quite important for performance.  Not something
you can throw away.


Segher