[PATCH] Add a character size parameter to c_strlen/get_range_strlen

[Jeff Law]

On 08/17/2018 12:23 PM, Martin Sebor wrote:
> On 08/17/2018 06:14 AM, Joseph Myers wrote:
>> On Fri, 17 Aug 2018, Jeff Law wrote:
>>
>>> On 08/16/2018 05:01 PM, Joseph Myers wrote:
>>>> On Thu, 16 Aug 2018, Jeff Law wrote:
>>>>
>>>>> restores previous behavior.  The sprintf bits want to count element
>>>>> sized chunks, which for wchars is 4 bytes (that count will then be
>>>>
>>>>>    /* Compute the range the argument's length can be in.  */
>>>>> -Â  fmtresult slen = get_string_length (arg);
>>>>> +Â  int count_by = dir.specifier == 'S' || dir.modifier == FMT_LEN_l
>>>>> ? 4 : 1;
>>>>
>>>> I don't see how a hardcoded 4 is correct here.  Surely you need to
>>>> example
>>>> wchar_type_node to determine its actual size for this target.
>>> We did kick this around a little.  IIRC Martin didn't think that it was
>>> worth handling the 2 byte wchar case.
> 
> Sorry, I think we may have miscommunicated -- I didn't think it
> was useful to pass a size of the character type to the function.
> I agree that passing in a hardcoded constant doesn't seem right
> (even if GCC's wchar_t were always 4 bytes wide).
> 
> I'm still not sure I see the benefit of passing in the expected
> element size given that the patch causes c_strlen() fail when
> the actual element size doesn't match ELTSIZE.  If the caller
> asks for the number of bytes in a const wchar_t array it should
> get back the number bytes.  (I could see it fail if the caller
> asked for the number of words in a char array whose size was
> not evenly divisible by wordsize.)
Interestingly enough that check failing was instrumental in debugging a
failing testcase when I was poking a bit at Bernd's patch.  I probably
would have found the issue without that check, but it was pretty obvious
as I stepped through c_strlen.

I don't have a strong opinion on the check (keep vs drop).  I do think
that passing in the size makes more sense than trying to determine it
within c_strlen.  The latter is going to stumble over the C vs GIMPLE
semantics issues we've discussed elsewhere.

Jeff