Certain instrumentations set the !nosanitize metadata for inserted
instructions, which are generally not interested for sanitizers. Skip
tsan instrumentation like we do for asan (D126294)/msan/hwasan.
-fprofile-arcs instrumentation has data race unless
-fprofile-update=atomic is specified. Let's remove the the `__llvm_gcov`
special case from commit 0222adbcd2 (2016)
as the racy instructions have the !nosanitize metadata.
(-fprofile-arcs instrumentation does not use `__llvm_gcda` as global variables.)
```
std::atomic<int> c;
void foo() { c++; }
int main() {
std::thread th(foo);
c++;
th.join();
}
```
Tested that `clang++ --coverage -fsanitize=thread a.cc && ./a.out` does
not report spurious tsan errors.
Also remove the default CC1 option -fprofile-update=atomic for
-fsanitize=thread to make options more orthogonal.
Reviewed By: Enna1
Differential Revision: https://reviews.llvm.org/D158385
5624e86ae0