The devirtualizer performs two optimizations:
- If a value is known to have an exact class type, ie it is the result of an alloc_ref, we can devirtualize calls of *non-final* methods, because we know we’re calling that specific method and not an override.
- If a method is known to be “effectively final” (it is not open, and there are no overrides inside the module) we can devirtualize it.
However the second optimization needs to be disabled if a function is inlinable (F->getResilienceExpansion() == ResilienceExpansion::Minimal).
This is technically a source break, but the @_fixed_layout attribute
is not official yet. If anyone really cares, we can make this
conditional on -swift-version 5 later, but I'd rather not.
This change is necessary so that we can give property initializers
non-public linkage. Currently they are public, because they can be
referenced from inlinable initializers.
Now that property initializers inside a @_fixed_layout type can
only reference public symbols, they no longer have to be public,
but making that change requires a bit more work.
In 74d979f0ac, the policy was changed
so that only value type accessors are ever marked transparent, and
not class accessors.
This was intended to fix a bug where inlining an accessor of an
Objective-C-derived class across module boundaries caused a linker
failure because the accessor referenced a field offset variable,
which has hidden visibility.
However, this also caused a performance regression for Swift native
classes. Bring back the old behavior for Swift native classes in
non-resilient modules.
Fixes <rdar://problem/29884727>.
This will allow for modules to be split from the command line using a script.
The one thing that is missing from this still is that it does not handle shared
functions in IMO a satisfactory way. Given that we are splitting a module, my
feeling that the correct way to do this is to create a public shim for the
shared function in the module that the shared function gets put in and let all
other users use that entry point.
But I need to think about this a bit more.
