[Bug target/100152] [10/11/12 Regression] used caller-saved register not preserved across a call.

["rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100152

--- Comment #34 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #33)
> (In reply to Iain Sandoe from comment #32)
> > (In reply to Iain Sandoe from comment #31)
> > > (In reply to Richard Biener from comment #30)
> > > > (In reply to Iain Sandoe from comment #29)
> > > > > what is also somewhat peculiar is that replacing the first function in the
> > > > > reduced test case with "extern void ___UTF_8_put(char *a, int b);" changes
> > > > > the code-gen for the second function.
> > > > 
> > > > That might hint at IPA RA which you can try disabling via -fno-ipa-ra which
> > > > in turn hints at a target issue.  
> > > 
> > > yeah, it does switch back to using rbx, at least on the reduced test case.
> > 
> > (also on the original).
> > 
> > I wonder if the problem is that IPA can't "see" the lazy symbol resolver, so
> > it just sees a call to ___UTF_8_put and doesn't know that this will be
> > resolved indirectly.
> > 
> > .. but something similar must apply to PLT and targets with linker veneers ?
> 
> I don't know how IPA RA works in detail but obviously the target has to
> expose this detail.  It looks like IPA RA causes us to add some notes to
> call insns which are supposed to describe those details and there's
> collect_fn_hard_reg_usage which looks at the target function (but likely
> does not include the ABI details of the call itself, in this case the
> resolver).

@deftypevr {Target Hook} bool TARGET_CALL_FUSAGE_CONTAINS_NON_CALLEE_CLOBBERS
Set to true if each call that binds to a local definition explicitly
clobbers or sets all non-fixed registers modified by performing the call.
That is, by the call pattern itself, or by code that might be inserted by the
linker (e.g.@: stubs, veneers, branch islands), but not including those
modifiable by the callee.  The affected registers may be mentioned explicitly
in the call pattern, or included as clobbers in CALL_INSN_FUNCTION_USAGE.
The default version of this hook is set to false.  The purpose of this hook
is to enable the fipa-ra optimization.
@end deftypevr

might be relevant - though when compiling for a shared library the call
to ___UTF_8_put does not bind locally (but then IPA RA shouldn't apply
either I guess).  So, does ___UTF_8_put bind locally?