arc: emit clobber of CC for -mcpu=em x >> 31

arc: emit clobber of CC for -mcpu=em x >> 31

Address PR target/120375

Devices without a barrel shifter end up using a sequence of
instructions. These can use the condition codes and/or loop count
register, so those need to be marked as 'clobbered'. These clobbers were
previously added only after split1, which is too late. This patch adds
these clobbers from the beginning, in the define_expand.

Previously, define_insn_and_split *<insn>si3_nobs would match any shift or
rotate instruction and would generate the necessary patterns to emulate a
barrel shifter, but it did not have any output assembly for itself.
In many cases this would create a loop with parallel clobbers. This pattern
is then matched by the <insn>si3_loop pattern.

In the no-barrel-shifter.c test tree code:

;; no-barrel-shifter.c:9:     int sign = (x >> 31) & 1;
_2 = x.0_1 >> 31;

in the expand pass becomes the following pattern that matches *lshrsi3_nobs:

(insn 18 17 19 4 (set (reg:SI 153 [ _2 ])
        (lshiftrt:SI (reg/v:SI 156 [ x ])
            (const_int 31 [0x1f]))) "test2.c":9:24 -1
     (nil))

This pattern misses the necessary clobbers and remains untouched until the
split1 pass. Together with the later branch it becomes

;; no-barrel-shifter.c:9:     int sign = (x >> 31) & 1;
	add.f	0,r0,r0
;; no-barrel-shifter.c:14:     if (mag == 0x7f800000)
	beq.d	.L8
;; no-barrel-shifter.c:9:     int sign = (x >> 31) & 1;
	rlc	r0,0

Leading to an issue: the add.f instructions overwrites CC but beq expects
CC to contain an earlier value indicating mag == 0x7f800000.

Now, these are combined in define_insn_and_split <insn>si3_loop that is
explicitly emitted in the define_expand and already contains the clobbers.
This can then be split into another pattern or remain the loop pattern.

In the expand pass, the same example now becomes:

(insn 18 17 19 4 (parallel [
            (set (reg:SI 153 [ _2 ])
                (lshiftrt:SI (reg/v:SI 156 [ x ])
                    (const_int 31 [0x1f])))
            (clobber (reg:SI 60 lp_count))
            (clobber (reg:CC 61 cc))
        ]) "test2.c":9:24 -1
     (nil))

Because the correct clobbers are now taken into account, the branch condition
is reevaluated by using breq instead of br.

;; no-barrel-shifter.c:9:     int sign = (x >> 31) & 1;
	add.f	0,r0,r0
	rlc	r0,0
;; no-barrel-shifter.c:14:     if (mag == 0x7f800000)
	breq	r2,2139095040,.L8

Regtested for arc.

	PR target/120375

gcc/ChangeLog:

	* config/arc/arc.md (*<insn>si3_nobs): merged with <insn>si3_loop.
	(<insn>si3_loop): splits to relevant pattern or emits loop assembly.
	(<insn>si3_cnt1_clobber): Removes clobber for shift or rotate by
	const1.

gcc/testsuite/ChangeLog:

	* gcc.target/arc/no-barrel-shifter.c: New test.

Co-authored-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Loeka Rogge <loeka@synopsys.com>