Implement -Wimplicit-fallthrough (take 2): the rest

[Jeff Law]

On 08/04/2016 06:36 AM, Michael Matz wrote:
> Hi,
>
> On Wed, 27 Jul 2016, Marek Polacek wrote:
>
>> And this is the rest.  Either I just adjusted a falls through comment,
>> or I added __builtin_fallthrough ().  These were the cases where I was
>> fairly sure that the fall through is intentional.
>
> I saw one case where I think the warning is a bit over-active:
>
> @@ -42072,6 +42089,7 @@ rdseed_step:
>      case IX86_BUILTIN_ADDCARRYX64:
>        icode = CODE_FOR_addcarrydi;
>        mode0 = DImode;
> +      gcc_fallthrough ();
>
>      handlecarry:
>        arg0 = CALL_EXPR_ARG (exp, 0); /* unsigned char c_in.  */
>
> I.e. it also warns if the following label is not a case label but a normal
> one.  I don't think this counts as a classical fall-through and it IMHO
> should not be warned about nor should it be marked.
It's probably the same underlying issue I saw with a false-positive in 
one of the other patches.

jeff