RFA: small patch to fix IRA crash of m68k compiler

[Jeff Law]

Vladimir Makarov wrote:
> Andreas Schwab wrote:
>> Vladimir Makarov <vmakarov@redhat.com> writes:
>>
>>  
>>> Andreas Schwab wrote:
>>>    
>>>> Vladimir Makarov <vmakarov@redhat.com> writes:
>>>>
>>>>        
>>>>> Index: ira-conflicts.c
>>>>> ===================================================================
>>>>> --- ira-conflicts.c    (revision 140014)
>>>>> +++ ira-conflicts.c    (working copy)
>>>>> @@ -366,6 +366,9 @@ process_regs_for_copy (rtx reg1, rtx reg
>>>>>      }
>>>>>    else
>>>>>      return false;
>>>>> +  if (hard_regno < 0)
>>>>> +    /* Can not be tied.  */
>>>>> +    return false;
>>>>>             
>>>> IMHO this is just papering over the bug.  Please explain the 
>>>> meaning of
>>>> the expressions for hard_rego.  What is the significance of an 
>>>> unrelated
>>>> register wrt. this insn for the function?
>>>>
>>>>         
>>> I don't think that is just papering of the bug.
>>>
>>> (insn 22 17 28 4 /cvs/gcc/libgcc/../gcc/libgcc2.c:169 (set (reg/i:SI 
>>> 0 %d0)
>>>         (subreg:SI (reg/v:DI 30 [ w ]) 4)) 36 {*movsi_m68k2} 
>>> (expr_list:REG_DEAD (reg/v:DI 30 [ w ])
>>>         (nil)))
>>>
>>> Hard_regno here means hard register preference for pseudo#30 to 
>>> remove the
>>> insn.  It is not possible in this case.  It would be possible if the
>>> destination register would be >= 1.
>>>     
>>
>> Thanks for the explanation.  Isn't it also possible that hard_regno
>> becomes too big (>= FIRST_PSEUDO_REGISTER)?
>>   
> Yes, you are right.  I missed this.  It should be
>
> 2008-09-08  Vladimir Makarov  <vmakarov@redhat.com>
>
>    * ira-conflicts.c (process_regs_for_copy): Check that the hard
>    regno is in the right range.
>
OK.  Please install if you haven't already.

Based on Andreas's comment, can you also add a quick comment documenting 
the meaning of hard_regno and how it relates to offset1 & offset2.  
Consider that comment patch pre-approved.

Jeff