arm: Fix ICE caused by arm_gen_dicompare_reg [PR94292]

arm: Fix ICE caused by arm_gen_dicompare_reg [PR94292]

The following testcase ICEs, because arm_gen_dicompare_reg creates invalid
RTL which then propagates into DEBUG_INSNs and ICEs while handling them.
The problem is that this function emits
(insn 18 17 19 2 (set (reg:CC_DNE 100 cc)
        (compare (ior:SI (ne:SI (subreg:SI (reg:DI 129) 0)
                    (subreg:SI (reg:DI 114 [ _2 ]) 0))
                (ne:SI (subreg:SI (reg:DI 129) 4)
                    (subreg:SI (reg:DI 114 [ _2 ]) 4)))
            (const_int 0 [0]))) "pr94292.c":7:11 325 {*cmp_ior}
     (nil))
and the invalid thing is that the COMPARE has VOIDmode.  Setting a
non-VOIDmode SET_DEST to VOIDmode SET_SRC is only valid if the SET_SRC is
CONST_INT/CONST_DOUBLE.
The following patch fixes it by giving the COMPARE the same mode as it gives
to the SET_DEST cc register.

2020-03-25  Jakub Jelinek  <jakub@redhat.com>

	PR target/94292
	* config/arm/arm.c (arm_gen_dicompare_reg): Set mode of COMPARE to
	mode rather than VOIDmode.

	* gcc.dg/pr94292.c: New test.