On 08/02/18 22:34, Martin Sebor wrote:
> On 08/02/2018 12:56 PM, Bernd Edlinger wrote:
>> On 08/02/18 15:26, Bernd Edlinger wrote:
>>>>
>>>> /* If the length can be computed at compile-time, return it. */
>>>> - len = c_strlen (src, 0);
>>>> + tree array;
>>>> + tree len = c_strlen (src, 0, &array);
>>>
>>> You know the c_strlen tries to compute wide character sizes,
>>> but strlen does not do that, strlen (L"abc") should give 1
>>> (or 0 on a BE machine)
>>> I wonder if that is correct.
>>>
>> [snip]
>>>>
>>>> static tree
>>>> -fold_builtin_strlen (location_t loc, tree type, tree arg)
>>>> +fold_builtin_strlen (location_t loc, tree fndecl, tree type, tree arg)
>>>> {
>>>> if (!validate_arg (arg, POINTER_TYPE))
>>>> return NULL_TREE;
>>>> else
>>>> {
>>>> - tree len = c_strlen (arg, 0);
>>>> -
>>>> + tree arr = NULL_TREE;
>>>> + tree len = c_strlen (arg, 0, &arr);
>>>
>>> Is it possible to write a test case where strlen(L"test") reaches this
>>> point?
>>> what will c_strlen return then?
>>>
>>
>> Yes, of course it is:
>>
>> $ cat y.c
>> int f(char *x)
>> {
>> return __builtin_strlen(x);
>> }
>>
>> int main ()
>> {
>> return f((char*)&L"abcdef"[0]);
>> }
>> $ gcc -O3 -S y.c
>> $ cat y.s
>> main:
>> .LFB1:
>> .cfi_startproc
>> movl $6, %eax
>> ret
>> .cfi_endproc
>>
>> The reason is that c_strlen tries to fold wide chars at all.
>> I do not know when that was introduced, was that already before your last
>> patches?
>
> The function itself was introduced in 1992 if not earlier,
> before wide strings even existed. AFAICS, it has always
> accepted strings of all widths. Until r241489 (in GCC 7)
> it computed their length in bytes, not characters. I don't
> know if that was on purpose or if it was just never changed
> to compute the length in characters when wide strings were
> first introduced. From the name I assume it's the latter.
> The difference wasn't detected until sprintf tests were added
> for wide string directives. The ChangeLog description for
> the change reads: Correctly handle wide strings. I didn't
> consider pathological cases like strlen (L"abc"). It
> shouldn't be difficult to change to fix this case.
>
Oh, oh, oh....
$ cat y3.c
int main ()
{
char c[100];
int x = __builtin_sprintf (c, "%S", L"\uFFFF");
__builtin_printf("%d %ld\n", x,__builtin_strlen(c));
}
$ gcc-4.8 -O3 -std=c99 y3.c
$ ./a.out
-1 0
$ gcc -O3 y3.c
$ ./a.out
1 0
$ echo $LANG
de_DE.UTF-8
I would have expected L"\uFFFF" to converted to UTF-8
or another encoding, so the return value if sprintf is
far from obvious, and probably language dependent.
Why do you think it is a good idea to use really every
opportunity to optimize totally unnecessary things like
using the return value from the sprintf function as it is?
Did you never think this adds a significant maintenance
burden on the rest of us as well?
Bernd.
