[Bug c++/87515] "no return statement in function returning non-void" miscompiles with optimizations

[Bug c++/87515] "no return statement in function returning non-void" miscompiles with optimizations

[ipelupes at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87515

ipelupes <ipelupes at hotmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ipelupes at hotmail dot com

--- Comment #4 from ipelupes <ipelupes at hotmail dot com> ---
I think the warning is not enough, because the resulting behaviour is quite
hard to debug, affecting the program flow, eg the following:

include <stdio.h>

int f()
{
}

int main()
{
  printf("calling returnless nonvoid\n");
  f();
  return 0;
}

compiled with g++  -O2 test.C

prints out "calling returnless nonvoid" for a few thousand times before seg
faulting on my machine (gcc 9.3.1). I would not be helped by the warning in
tracking this down in a large project (often lots of warnings are present).

also: adding __builtin_unreachable(); hides the warning making it even harder
to find

[Bug c++/87515] "no return statement in function returning non-void" miscompiles with optimizations

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87515

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
You can always use -Werror=return-type, or -fsanitize=undefined which will
diagnose it at runtime.

[Bug c++/87515] "no return statement in function returning non-void" miscompiles with optimizations

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87515

--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to ipelupes from comment #4)
> also: adding __builtin_unreachable(); hides the warning making it even
> harder to find

Don't do that then :)

Adding that promises the compiler your program will never reach that line of
the function, so it doesn't bother warning you. If you lie to the compiler, it
will get its revenge.

Adding __builtin_trap() instead will terminate the program if that line is
reached, which might be what you're looking for.

[Bug c++/87515] "no return statement in function returning non-void" miscompiles with optimizations

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87515

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|INVALID                     |DUPLICATE

--- Comment #7 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
.

*** This bug has been marked as a duplicate of bug 86761 ***