[Bug c++/58192] G++ emits incorrect code when passing enum classes as function parameters

["jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58192

--- Comment #10 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
When I compile:
#ifdef CHAR
typedef unsigned char Foo;
#else
enum class Foo : unsigned char { FOO };
#endif
unsigned int v1, v2;

__attribute__((noinline, noclone)) static void
foo (Foo a)
{
  v1 = (unsigned int) a;
}

__attribute__((noinline, noclone)) void
bar (Foo a)
{
  v2 = (unsigned int) a;
}

void
baz (unsigned int a)
{
  foo ((Foo) a);
  bar ((Foo) a);
}

with -DCHAR vs. -UCHAR, there is a difference visible already in *.original
dump:
 <<cleanup_point <<< Unknown tree: expr_stmt
-  foo ((int) (Foo) a) >>>>>;
+  foo ((Foo) a) >>>>>;
 <<cleanup_point <<< Unknown tree: expr_stmt
-  bar ((int) (Foo) a) >>>>>;
+  bar ((Foo) a) >>>>>;
i.e. there is explicit zero-extension for integral types smaller than int in
the IL (i.e. for the -DCHAR) case, but nothing like that for the enum class
with underlying type smaller than int.  And presumably the middle-end and
backends rely on this.