Re: [committed] Convert xstormy16 to LRA

[Hans-Peter Nilsson <hp@axis.com>]

> From: "Roger Sayle" <roger@nextmovesoftware.com>
> Date: Fri, 12 May 2023 15:04:03 +0100

> Hi H-P,
> This patch should now already be on trunk:
> https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=d8a6945c6ea22efa4d5e42fe1922d2
> b27953c8cd
> Many thanks to Jeff for the review/approval.
> There have been no reported adverse effects so far.
> Please let me/us know if this has helped CRIS.

TL;DR:
It sure helped for the big offender; arith-rand-ll with LRA
is now 1.3% faster!  Not everything is rosy though.

It's not a complete win for CRIS with LRA, as other of my
mini-regression tests (like, a trivial loop with 0<=i<=10
fprintf (f, "%s: %d\n", "Hello, world", i); with newlib),
where it got 0.04% larger.  On average though, 0.5% smaller.
Actually, it's more accurate to state it in terms of the
code that changed: newlib's _vfprintf_r improved slightly
performance-wise on some paths (1 cycle per call), but
regressed on others (7 cycles per call).  It got 0.2%
bigger.  Libgcc's __moddi3 regressed slightly (1 cycle per
11 calls) but stayed the same size.  The main function in
arith-rand-ll (where I guess all small functions got
inlined) improved 3% by size, performance as above.

Those clobbers must have helped reload, because with reload
there was a 0.15% performance regression for arith-rand-ll
(and 0.2% by size because main got 1.6% larger) with this
patch.  But size was smaller or equal for all other tests
using reload with this patch, if only by 0.04% on average.
 Or in other numbers: _vfprintf_r got 4 cycles faster per
call on some paths and 2 on others.  It got 0.05% bigger.  A
similar function, __vfiprintf_r, shrank by 0.5%.  Go figure.
For all but arith-rand-ll, this patch was a wash for reload.
 (Yes: the case with reload is now artificial; for that, I
was using master before Jeff's commit and added my own
commits since then, to keep track of my fight against LRA
regressions; the current score is that code is still 0.34%
slower and 0.17% larger with this applied just for LRA.)

Can we ask Vladimir for a statement; perhaps LRA could just
have handled those clobbers better (referring to the commit)?

brgds, H-P