Re: [patch] More thorough checking in reg_fits_class_p

[Richard Earnshaw <rearnsha at arm dot com>]

On 02/05/12 14:00, Richard Sandiford wrote:
> Jim MacArthur <jim.macarthur@arm.com> writes:
>> New Changelog text:
>>
>> 2012-05-02 Jim MacArthur<jim.macarthur@arm.com>
>> * recog.c (reg_fits_class_p): Check both regno and regno + offset are
>> hard registers.
> 
> Thanks.  I still think the final:
> 
>> +	  && HARD_REGISTER_NUM_P (end_hard_regno (regno + offset, mode))
> 
> check belongs in in_hard_reg_set_p, since most callers don't (and IMO
> shouldn't need to) check this.  The idea behind adding these functions
> was to commonise various bits of code that were doing the same checks
> in slightly different ways.  Requiring each caller to check the end
> register would go against that to some extent.
> 

If you're going to do that (which is fine, BTW), I think
in_hard_reg_set_p should gcc_assert() that regno is a valid hard reg.

> E.g. the code could be:
> 
>   end_regno = end_hard_regno (mode, regno);
>   if (!HARD_REGISTER_NUM_P (end_regno))
>     return false;
> 
>   while (++regno < end_regno)
>     if (!TEST_HARD_REG_BIT (regs, regno))
>       return false;
> 
> Or alternatively we could change hard-reg-set.h so that HARD_REG_SET
> is big enough to store a bit for FIRST_PSEUDO_REGISTER.  I don't mind
> which, but others might.

I'd prefer the test to be explicit.  The buffer overrun check might be a
tad more efficient in some cases, but someday someone will manage to
find a way of directly going 2 regs beyond the end...

> 
> Looks good otherwise.  And for the record, I can't approve this anyway. :-)
> 
> Richard
>