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c74531b1d2
Summary:
Example:
```
cache/clock_cache.cc:56:7: error: fallthrough annotation in unreachable code [-Werror,-Wimplicit-fallthrough]
FALLTHROUGH_INTENDED;
^
./port/lang.h:10:30: note: expanded from macro 'FALLTHROUGH_INTENDED'
^
```
In clang < 14, this is annoyingly generated from -Wimplicit-fallthrough, but was changed to -Wunreachable-code-fallthrough (implied by -Wunreachable-code) in clang 14. See https://reviews.llvm.org/D107933 for how this nuisance pattern generated false positives similar to ours in the Linux kernel.
Just to underscore the ridiculousness of this warning, here an error is reported on the annotation, not the call to do_something(), depending on the constexpr value (https://godbolt.org/z/EvxqdPTdr):
```
#include <atomic>
void do_something();
void test(int v) {
switch (v) {
case 1:
if constexpr (std::atomic<long>::is_always_lock_free) {
return;
} else {
do_something();
[[fallthrough]];
}
case 2:
return;
}
}
```
Pull Request resolved: https://github.com/facebook/rocksdb/pull/12144
Test Plan: Added the warning to our Makefile for USE_CLANG, which reproduced the warning-as-error as shown above, but is now fixed.
Reviewed By: jaykorean
Differential Revision: D52139615
Pulled By: pdillinger
fbshipit-source-id: ba967ae700c0916d1a478bc465cf917633e337d9