This is the last part of SILGen conditionalized on EnableSILOwnership being
set. It also (as you can tell from the diff) eliminates a bunch of code from the
tests.
rdar://29791263
This does not eliminate the entrypoints on SILBuilder yet. I want to do this in
two parts so that it is functionally easier to disentangle changing the APIs
above SILBuilder and changing the underlying instruction itself.
rdar://33440767
ConvertFunction and reabstraction thunks need this attribute. Otherwise,
there is no way to identify that withoutActuallyEscaping was used
to explicitly perform a conversion.
The destination of a [without_actually_escaping] conversion always has
an escaping function type. The source may have either an escaping or
@noescape function type. The conversion itself may be a nop, and there
is nothing distinctive about it. The thing that is special about these
conversions is that the source function type may have unboxed
captures. i.e. they have @inout_aliasable parameters. Exclusivity
requires that the compiler enforce a SIL data flow invariant that
nonescaping closures with unboxed captures can never be stored or
passed as an @escaping function argument. Adding this attribute allows
the compiler to enforce the invariant in general with an escape hatch
for withoutActuallyEscaping.
The SILGen testsuite consists of valid Swift code covering most language
features. We use these tests to verify that no unknown nodes are in the
file's libSyntax tree. That way we will (hopefully) catch any future
changes or additions to the language which are not implemented in
libSyntax.
