Re: [committed] Convert xstormy16 to LRA

[Paul Koning <paulkoning@comcast.net>]

> On May 2, 2023, at 9:18 AM, Roger Sayle <roger@nextmovesoftware.com> wrote:
> 
> 
> On 02 May 2023 13:40, Paul Koning wrote:
>>> On May 1, 2023, at 7:37 PM, Roger Sayle <roger@nextmovesoftware.com>
>> wrote:
>>> 
>>> ...
>>> The shiftsi.cc regression on xstormy16 is fixed by adding
>>> -fno-split-wide-types.
>>> In fact, if all the regression tests pass, I'd suggest that
>>> flag_split_wide-types = false should be the default on xstormy16 now
>>> that we've moved to LRA.  And if this works for xstormy16, it might be
>>> useful to other targets for the LRA transition; it's a difference in
>>> behaviour between reload and LRA that could potentially affect
>>> multiple targets.
>> 
>> Is there documentation for that flag?
> 
> Yes, see the section -fsplit-wide-types in
> https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html

Thanks.  So I'm wondering why that would be a problem.

The obvious question is whether it interacts badly with MD file entries that describe wide operations, perhaps with constraints that require things like odd/even register pairs.  But I would assume all that gets handled.

Along the same lines, why would a target, or a user, not do early wide splitting all the time?  The documentation for that option gives no clue why it would ever be bad.

	paul