loop-iv: Fix up bounds computation

loop-iv: Fix up bounds computation

On Thu, Apr 13, 2023 at 06:35:07AM -0600, Jeff Law wrote:
> Bootstrap was successful with v3, but there's hundreds of testsuite failures
> due to the simplify-rtx hunk.  compile/20070520-1.c for example when
> compiled with:  -O3 -funroll-loops -march=rv64gc -mabi=lp64d
>
> Thursdays are my hell day.  It's unlikely I'd be able to look at this at all
> today.

So, seems to me this is because loop-iv.cc asks for invalid RTL to be
simplified, it calls simplify_gen_binary (AND, SImode,
(subreg:SI (plus:DI (reg:DI 289 [ ivtmp_312 ])
        (const_int 4294967295 [0xffffffff])) 0),
(const_int 4294967295 [0xffffffff]))
but 0xffffffff is not valid SImode CONST_INT, and unlike previously
we no longer on WORD_REGISTER_OPERATIONS targets which have DImode
word_mode optimize that into the op0, so the invalid constant is emitted
into the IL and checking fails.

The following patch fixes that (and we optimize that & -1 away even earlier
with that).

2023-04-14  Jakub Jelinek  <jakub@redhat.com>

	* loop-iv.cc (iv_number_of_iterations): Use gen_int_mode instead
	of GEN_INT.