-Wimplicit-fallthrough broken?

[Georg-Johann Lay]

Mason schrieb:
> On 19/07/2017 22:18, Georg-Johann Lay wrote:
> 
>> Hi, with the following small small test I am getting these warnings:
>>
>> void test1 (unsigned char c)
>> {
>>      switch (c)
>>      {
>>          case 1: c++; // fallthrough
>>          case 2: c--; // FALLTHRU
>>          case 3: c++; // FALLTHROUGH
>>          case 4: z = c; break;
>>      }
>> }
>>
>> void test2 (unsigned char c)
>> {
>>      switch (c)
>>      {
>>          case 1: c++;
>>          /* fallthrough */
>>          case 2: c--;
>>          /* FALLTHRU */
>>          case 3: c++;
>>          /* FALLTHROUGH */
>>          case 4: z = c; break;
>>      }
>> }
>>
>>
>>
>> simple.c: In function 'test1':
>> simple.c:7:18: warning: this statement may fall through 
>> [-Wimplicit-fallthrough=]
>>           case 1: c++; // fallthrough
>>                   ~^~
>> simple.c:8:9: note: here
>>           case 2: c--; // FALLTHRU
>>           ^~~~
>> simple.c:8:18: warning: this statement may fall through 
>> [-Wimplicit-fallthrough=]
>>           case 2: c--; // FALLTHRU
>>                   ~^~
>> simple.c:9:9: note: here
>>           case 3: c++; // FALLTHROUGH
>>           ^~~~
>> simple.c:9:18: warning: this statement may fall through 
>> [-Wimplicit-fallthrough=]
>>           case 3: c++; // FALLTHROUGH
>>                   ~^~
>> simple.c:10:9: note: here
>>           case 4: z = c; break;
>>           ^~~~
>> simple.c: In function 'test2':
>> simple.c:18:18: warning: this statement may fall through 
>> [-Wimplicit-fallthrough=]
>>           case 1: c++;
>>                   ~^~
>> simple.c:20:9: note: here
>>           case 2: c--;
>>           ^~~~
>> simple.c:20:18: warning: this statement may fall through 
>> [-Wimplicit-fallthrough=]
>>           case 2: c--;
>>                   ~^~
>> simple.c:22:9: note: here
>>           case 3: c++;
>>           ^~~~
>> simple.c:22:18: warning: this statement may fall through 
>> [-Wimplicit-fallthrough=]
>>           case 3: c++;
>>                   ~^~
>> simple.c:24:9: note: here
>>           case 4: z = c; break;
>>           ^~~~
>>
>>
>> How do I have to formulate these comments?  It's under mingw32, may that 
>> be a problem?
> 
> There are a few important pieces missing from your message.
> 
> - The version of gcc you're using

trunk (future v8)

> - The exact command-line you used (flags, C vs C++ mode, etc)

gcc simple.c -S -W -save-temps

(cross compilation actually, but the target really should not matter)

> - What you expected vs what happened

I am expecting that the comments are silencing the warnings.  What
actually happened can be admired above.

> You seem to be looking for a way to silence the warning for specific
> instances. Have a look here:

According to the documentation, these magic comments should work and
quiet the warnings.

Johann