Re: [Tinycc-devel] _Generic or __builtin_choose_expr

[uso ewin]

On Tue, Jul 4, 2017 at 5:59 PM, uso ewin <address@hidden> wrote:
> Hi
>
> I've push a new version that use skip_or_save_block from mob:
> https://github.com/cosmo-ray/tcc/commits/mob
> I've let the patch that change ex1.c that I used as testing so you can
> see my ugly tests.
>
> On Tue, Jul 4, 2017 at 4:46 PM, Michael Matz <address@hidden> wrote:
>> Hi,
>>
>> On Tue, 4 Jul 2017, Michael Matz wrote:
>>
>>> Ugh, you're right.  Indeed the standard doesn't mandate a const char[]
>>> type for string literals (I was confused because it does say that
>>> modification of string literals is undefined, i.e. that's an extension).
>>> Let me work on this a bit.
>>
>> Actually, not much need for work.  I've checked GCC sources and, even
>> though it wonders in a comment if it's a good idea to change expression
>> types with warning flags, it indeed does so; so if for nothing else than
>> compatibility I've reverted the patch.
>>
>> The hack in the current patch for _Generic (to regard string literals as
>> const char* always) isn't needed.  GCC indeed differs in behaviour
>> depending on the warning flag, also in _Generic:
>>
>> -----------------------
>> extern int printf(const char *,...);
>> int main()
>> {
>>   const char *msg;
>>   msg = _Generic("foo", const char *:"const char*", char*:"char *",
>> default:"something else");
>>   printf ("type \"foo\" = %s\n", msg);
>>   return 0;
>> }
>> -----------------------
>> % gcc-6 -Wwrite-strings x.c && ./a.out
>> type "foo" = const char*
>> % gcc-6 -Wno-write-strings x.c && ./a.out
>> type "foo" = char*
>>
>> So, thanks for checking after me ;)
>>
>
> Well, I've just test
> int main()
>  {
>    const char *msg;
>
>    msg = _Generic("foo", const char *:"const char*", char*:"char *",
>  default:"something else");
>    printf ("type \"foo\" = %s\n", msg);
>    return 0;
> }
oops, I've just type a bad shortcut on google,
and apparently unexpectedly send the mail before finish typing... sorry

So it appear than gcc remove const from variable:
so
const int a;

i = _Generic(a, int: 10, const int: 20);
printf("%d\n", i);

will print 10...

But as your example show early with  -Wwrite-strings gcc let the const....


I've made some code that remove each const,
and change array to pointer on my branch,
but I'm not sure of the idea