[Patch,AVR] Fix PR46278, Take #3

[Georg-Johann Lay]

Denis Chertykov schrieb:
> Georg-Johann Lay :
>> Weddington, Eric schrieb:
>>>> This is yet another attempt to fix PR46278 (fake X addressing).
>>>>
>>>> After the previous clean-ups it is just a small change.
>>>>
>>>> caller-saves.c tries to eliminate call-clobbered hard-regs allocated to
>>>> pseudos around function calls and that leads to situations that reload is
>>>> no more capable to perform all requested spills because of the very few
>>>> AVR's address registers.
>>>>
>>>> Thus, the patch adds a new target option -mstrict-X so that the user can
>>>> turn that option if he like to do so, and then -fcaller-save is disabled.
>>>>
>>>> The patch passes the testsuite without regressions. Moreover, the
>>>> testsuite passes without regressions if all test cases are run with
>>>> -mstrict-X and all libraries (libgcc, avr-libc) are built with the new
>>>> option turned on.
>>> Hi Johann,
>>>
>>> Sorry, I haven't been keeping up with the discussion on this PR.
>>>
>>> But if all test cases pass with running -mstrict-X and everything built with
>>> that option on, then why is this even an option? Is it because that it may
>>> not always reduce code size?...
>> An alternative would be to set -mstrict-X per default if -O or higher.
>> Let's see what Denis thinks.
> 
> I think that it's just a great results.
> I vote for committing this patch.

So I will proceed and commit this patch if there are no objections or
propositions to improve it.

> About "to set -mstrict-X per default": if it's possible to print
> something like "Please use -mno-strict-X" instead of "Spill error
> failure...." then we can use -mstrict-X by default.

I don't see a way to hook in spill_failure or find_reload_regs or have backend
target specific customization of diagnostics.

Except someone experienced in that field recommends, say, hooking into
diagnostic printer somehow.  If so, I'd prefer to do that in a separate patch.

> i.e. how user can get a knowledge about a correlation between "Spill
> error..." and -mstrict-X

...or between "spill error" and -fcaller-saves...

Johann

> Denis.