[Bug other/87371] New: Spurious -Wreturn-type warning with "pathological" for

[mwoehlke.floss at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87371

            Bug ID: 87371
           Summary: Spurious -Wreturn-type warning with "pathological" for
           Product: gcc
           Version: 8.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: other
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mwoehlke.floss at gmail dot com
  Target Milestone: ---

Consider the following code:

    int foo()
    {
        for (int y = 0; !y;)
            for (/*decl*/; !y; ++y)
                return 1;
    }

This generates a -Wreturn-type warning, despite that the inner loop body will
*always* execute. Moreover, with optimization enabled, the compiler does (as
expected) successfully remove the loops entirely.

(This is a simplified version of a pre-C++17 `with` statement. The purpose of
this code, which is usually a macro, is to look like the opening statement of a
block, where `/*decl*/` — omitted in this example — is in scope only until the
end of the block. FWIW, the C++17 form, `if (/*decl*/; true)` does not exhibit
the problem.)


Live example: https://godbolt.org/g/5xM6C3. Possibly related to #67629 and/or
#85914.