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Add and use SDL_FALLTHROUGH for fallthroughs

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Case fallthrough warnings can be suppressed using the __fallthrough__
compiler attribute. Unfortunately, not all compilers have this
attribute, or even have __has_attribute to check if they have the
__fallthrough__ attribute. [[fallthrough]] is also available in C++17
and the next C2x, but not everyone uses C++17 or C2x.

So define the SDL_FALLTHROUGH macro to deal with those problems - if we
are using C++17 or C2x, it expands to [[fallthrough]]; else if the
compiler has __has_attribute and has the __fallthrough__ attribute, then
it expands to __attribute__((__fallthrough__)); else it expands to an
empty statement, with a /* fallthrough */ comment (it's a do {} while
(0) statement, because users of this macro need to use a semicolon,
because [[fallthrough]] and __attribute__((__fallthrough__)) require a
semicolon).

Applications using SDL are also free to use this macro (because it is
defined in begin_code.h).

All existing /* fallthrough */ comments have been replaced with this
macro. Some of them were unnecessary because they were the last case in
a switch; using SDL_FALLTHROUGH in those cases would result in a compile
error on compilers that support __fallthrough__, for having a
__attribute__((__fallthrough__)) statement that didn't immediately
precede a case label.
This commit is contained in:
Misa 2021-09-27 14:38:12 -07:00 • committed by Sam Lantinga
parent 828a0a4a10
commit 66a08aa391
15 changed files with 63 additions and 55 deletions
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20
include/SDL_stdinc.h
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@ -496,25 +496,13 @@ SDL_FORCE_INLINE void SDL_memset4(void *dst, Uint32 val, size_t dwords)
if (dwords == 0) {
return;
}
/* !!! FIXME: there are better ways to do this, but this is just to clean this up for now. */
#ifdef __clang__
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wimplicit-fallthrough"
#endif
switch (dwords % 4) {
case 0: do { *_p++ = _val; /* fallthrough */
case 3: *_p++ = _val; /* fallthrough */
case 2: *_p++ = _val; /* fallthrough */
case 1: *_p++ = _val; /* fallthrough */
case 0: do { *_p++ = _val; SDL_FALLTHROUGH;
case 3: *_p++ = _val; SDL_FALLTHROUGH;
case 2: *_p++ = _val; SDL_FALLTHROUGH;
case 1: *_p++ = _val;
} while ( --_n );
}
#ifdef __clang__
#pragma clang diagnostic pop
#endif
#endif
}