[Bug c/79152] New: -Wimplicit-fallthrough false positive triggered by goto statements

[sirl at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79152

            Bug ID: 79152
           Summary: -Wimplicit-fallthrough false positive triggered by
                    goto statements
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: sirl at gcc dot gnu.org
  Target Milestone: ---

This strange creduce'd testcase warns with current trunk:

typedef struct {
    char *       bs;
} xstruct;

void test (char ch, long handle) {
    switch (ch)             {
    case 1:
        goto label1;
        goto label;
        (ch) = *(((xstruct *) (handle))->bs++);
label:
label1:
        ((xstruct *) handle)->bs ;
    }
}

# gcc-trunk -c -Wimplicit-fallthrough testcase.c
testcase.c: In function 'test':
testcase.c:10:14: warning: this statement may fall through
[-Wimplicit-fallthrough=]
         (ch) = *(((xstruct *) (handle))->bs++);
         ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
testcase.c:11:1: note: here
 label:
 ^~~~~

I believe this is a false positive. I hope the creduce'd testcase is enough to
highlight the problem.