Modify IRGen to emit builtin access markers with an error flag in
Swift 3 mode.
KeyPath enforcement is required by user code in Swift 4+ mode, but is
implemented within the standard library. A [builtin] flag marks the
special case for access generated by Builtins so that they are
always enforced as an error regardless of the language mode.
This is necessary for Swift 4.2 because the standard library continues
to build in Swift 3 mode. Once the standard library build migrates,
this is all irrelevant.
This does not actually affect existing Swift 3 code, since the KeyPath
feature wasn't introduced until Swift 4.
<rdar://problem/40115738> [Exclusivity] Enforce Keypath access as an error, not a warning in 4.2.
Use begin_unpaired_access [no_nested_conflict] for
Builtin.performInstantaneousReadAccess. This can't be optimized away
and is the proper marker to use when the access scope is unknown.
Drop the requirement that
_semantics("optimize.sil.preserve_exclusivity") be @inline(never). We
actually want theses inlined into user code. Verify that the
@_semantic functions are not inlined or otherwise tampered with prior
to serialization.
Make *no* change to propagate @inline(__always) into LLVM. This no longer has
any relationship to this PR and can be investigated seperately.
This is a special @_semantics attribute that preserves exclusivity even if we
are eliminating exclusivity in other parts of a module in release mode. This is
done by:
1. Teaching the Access Marker Elimination pass to skip any function with the
semantics tag.
2. Requiring all functions with the semantics tag to be noinline. This ensures
that the SIL level inliner will not inline these functions into any callers
without the protection of the semantics tag. This is enforced in IRGenPrepare
and ensures that our access markers will live to IRGen time.
3. In IRGenPrepare, we convert these functions from noinline to always
inline. After IRGen this then allows for the LLVM inliner to inline these
trivial functions that just perform the exclusivity checks ensuring that we do
not have extra calls in the fast path.
This ensures that we can fix the keypaths exclusivity issue without having to
enable exclusivity across the entire stdlib and deal with any of the potential
performance issues therein.
rdar://39335800
