These tests are marked XFAIL or UNSUPPORTED because either the tests:
require libc annotation, require Mach-O support, don't recognize calls to
swift-autolink-extract, requires porting alongside Linux, or rely on simd
which is not present.
Additionally, explicit REQUIRES for tsan/asan/fuzzer are added to some
tests, since OpenBSD does not support these sanitizers or fuzzers, since
it's nicer to mark that with REQUIRES rather than XFAIL.
When rebuilding a .o file, we hash the IR generated by IRGen and compare it to a hash embedded in the .o file. If they match, we simply skip asking LLVM to optimize and generate code. Certain flags that control our LLVM configuration are mixed into the hash, but the -profile-generate flag was not one of them. This usually wouldn’t matter because profiling would insert additional code into the IR, but in edge cases like empty files or files containing only protocol declarations, it could cause linker errors when profiling was turned off.
This change adds the `GenerateProfile` flag into the IR hash, ensuring that we always recompile, even if the IR was identical.
Fixes rdar://problem/54126622.
Only re-generate an object file if the llvm IR (after IRGen) changed.
The check is done based on a MD5 hash of the llvm IR which is stored in a special section in the object file.
This reduces compilation time for multi-threaded whole module compilation if only a small number of files are changed.
The incremental compilation also works for compilations with a single output file. In this case it's all-or-nothing.
