Re: -Wimplicit-fallthrough broken?

[Georg-Johann Lay <avr@xxxxxxxx>]

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