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Re: [PATCH] Convert SPARC to LRA


On Sun, 2015-09-27 at 19:29 -0600, Jeff Law wrote:
> On 09/27/2015 01:57 PM, Hans-Peter Nilsson wrote:
> > On Wed, 9 Sep 2015, Mike Stump wrote:
> >
> >> On Sep 8, 2015, at 9:41 PM, David Miller <davem@davemloft.net> wrote:
> >>> +#define TARGET_LRA_P hook_bool_void_true
> >>
> >> Are we at the point there this should be the default, and old
> >> ports should just define to false, if they really need to?
> >
> > I think no.  For one, we don't have proper target documentation
> > updates for LRA.  What does it need?  What is outdated?
> >
> > Also, give ample time for gcc releases of odd ports with LRA to
> > get into the public and cover most of the inevitable remaining
> > bugs.  Not even sh has moved over due to remaining issues.  Let
> > the reports come in - and be fixed.  Let's revisit in a year or
> > two.
> I don't think we're there yet either -- many ports still require some 
> guidance from Vlad to get working with LRA.
> 
> It *may* be time to decree that any new ports must use the LRA path 
> rather than reload.  I'm still on the fence with that.

LRA on SH seems to work without GCC test suite failures.  However, I'd
expect that there still hidden bugs not covered by the test suite.  SH's
R0 spill failures are greatly reduced with LRA, although some hacks had
to be added to the SH backend to make it work at all.  Despite that, we
see quite some significant code size increases compared to reload.  If
the difference wasn't that big, we'd probably turn LRA on by default for
SH in GCC 6...

Cheers,
Oleg


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