https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87950
Eric Gallager <egallager at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
See Also| |https://gcc.gnu.org/bugzill
| |a/show_bug.cgi?id=61864
--- Comment #15 from Eric Gallager <egallager at gcc dot gnu.org> ---
(In reply to Martin Sebor from comment #12)
> I do agree there is room for improvement here. Consider the following test
> case:
>
> $ cat t.c && gcc -O2 -S -Wall -Wextra -Wpedantic -Wswitch-enum
> -fdump-tree-optimized=/dev/stdout t.c
>
> enum E { e0 } e;
>
> int f (void)
> {
> switch (e)
> case e0: return 0;
> }
> t.c: In function âfâ:
> t.c:7:1: warning: control reaches end of non-void function [-Wreturn-type]
> 7 | }
> | ^
>
> ;; Function f (f, funcdef_no=0, decl_uid=1909, cgraph_uid=1,
> symbol_order=1)
>
> f ()
> {
> E e.0_1;
>
> <bb 2> [local count: 1073741824]:
> e.0_1 = e;
> if (e.0_1 == 0)
> goto <bb 3>; [50.00%]
> else
> goto <bb 4>; [50.00%]
>
> <bb 3> [local count: 536870913]:
> return 0;
>
> <bb 4> [local count: 536870913]:
> return;
>
> }
>
> The -Wswitch-enum option doesn't warn about the switch statement not
> handling switch values that don't correspond to any of the enumerators. To
> have it diagnosed the -Wswitch-default option has to be explicitly specified
> (it's off by default).
>
> Given that, I believe the same logic should apply to the -Wreturn-type
> warning: it should not trigger for the snippet above or for the test case in
> comment #0 unless explicitly requested somehow (perhaps it should consider
> -Wswitch-default).
kinda related here (w.r.t. other warnings considering whether -Wswitch-default
is on or not): bug 61864
>
> In addition, note the comparison to zero in the optimized GIMPLE. It's
> unnecessary because the function returns no value when the value of e is
> non-zero. Clang notices that and avoids the comparison. But perhaps a
> better example to illustrate the missed optimization opportunity than the
> contrived test case above is this:
>
> enum E { e0, e1, e2 } e;
>
> int f (void)
> {
> switch (e)
> {
> case e0: return 1;
> case e1: return 2;
> case e2: return 3;
> }
> }
>
> Here, GCC also emits the same pointless comparison/branch:
>
> f:
> movl e(%rip), %eax
> cmpl $2, %eax
> ja .L2
> addl $1, %eax
> ret
> .L2:
> ret
