[ARM] Fix an internal error

[Bernd Schmidt]

This fixes a crash while compiling a customer testcase (which I don't
know yet whether it can be posted) for ARM.  Going into combine, we have

(insn 166 165 167 20 10208.c:22 (set (reg:CC 24 cc)
        (compare:CC (reg:SI 141 [ D.2039 ])
            (const_int 78 [0x4e])))

(insn 167 166 169 20 10208.c:22 (set (reg:SI 276)
        (eq:SI (reg:CC 24 cc)
            (const_int 0 [0x0])))

(insn 169 167 170 20 10208.c:22 (set (reg:CC 24 cc)
        (compare:CC (reg:SI 141 [ D.2039 ])
            (const_int 110 [0x6e])))

(insn 170 169 172 20 10208.c:22 (set (reg:SI 278)
        (eq:SI (reg:CC 24 cc)
            (const_int 0 [0x0])))

(insn 172 170 173 20 10208.c:22 (set (reg:SI 279)
        (ior:SI (reg:SI 276)
            (reg:SI 278)))

(insn 173 172 174 20 10208.c:14 (set (reg/v:SI 136 [ cur_k ])
        (and:SI (reg:SI 279)
            (const_int 255 [0xff])))

(insn 174 173 175 20 10208.c:28 (set (reg:CC 24 cc)
        (compare:CC (reg/v:SI 136 [ cur_k ])
            (const_int 0 [0x0])))

(jump_insn 175 174 192 20 10208.c:28 (set (pc)
        (if_then_else (le (reg:CC 24 cc)
                (const_int 0 [0x0]))
            (label_ref 180)
            (pc)))

All this gets combined so that we finally end up with the following
pattern, i3 == insn 174:

(set (reg:CC 24 cc)
    (compare:CC (ior:SI (eq:SI (reg:SI 141 [ D.2039 ])
                (const_int 78 [0x4e]))
            (eq:SI (reg:SI 141 [ D.2039 ])
                (const_int 110 [0x6e])))
        (const_int 0 [0x0])))

We call arm_select_cc_mode, it returns CC_DEQmode, and we later crash in
get_arm_condition_code because we don't expect to see a LE comparison
with that mode.

Fixed with the following patch. The comment at the top of
arm_select_dominance_cc_mode states that "in all cases OP will be EQ or
NE", which matches the assert in get_arm_condition_code, but the caller
does not ensure it.

This looks suspiciously like we have a missed-optimization bug as well,
but I did not investigate it. In the following gimple, the
compare-and-jump ought to be optimized away.

  D.2040_26 = D.2039_25 == 110;
  D.2041_27 = D.2039_25 == 78;
  D.2042_28 = D.2041_27 | D.2040_26;
  cur_k_11 = (int) D.2042_28;
  if (cur_k_11 > 0)
    goto <bb 17>;
  else
    goto <bb 18>;

Ok?


Bernd
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