[Bug c++/67693] New: Spurious warning: control reaches end of non-void function [-Wreturn-type]

["larsch at belunktum dot dk" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67693

            Bug ID: 67693
           Summary: Spurious warning: control reaches end of non-void
                    function [-Wreturn-type]
           Product: gcc
           Version: 5.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: larsch at belunktum dot dk
  Target Milestone: ---

gcc 4.5.3 through to 5.2.0 all warn about reaching end of non-void function on
this code:

  struct foo { ~foo(); };
  int f(int n, int m) {
    foo x; // Remove this to get rid of warning
    switch (n) {
    case 0:
      if (n == 4)
        return 1;
      else
        return 2;
      break; // Or remove this
    default:
      return 0;
    }
  }

Output:

  source.cpp: In function 'int f(int, int)':
  14 : warning: control reaches end of non-void function [-Wreturn-type]

Command line: 

  gcc -Wall -O0 source.cpp

Platforms: x86/arm/arm64.

Other info:

Removing the variable 'x' gets rid of the warning. So does removing the
(unnecessary, but valid) 'break' statement. Adding optimization (-O1 or more)
eliminates the warning.