Rather than just on or off, I've changed it to allow "off", "fast",
or "full". "fast" means that we'll do symbol lookup, but we won't
try to find inline frames and we won't run line number programs
(those are the things that are taking considerable time in some
cases).
rdar://122302117
The other new runtime functions appear to have a leading underscore.
It makes sense in this case because we don't expect anything to call
this directly (other than the unwinder).
rdar://120952971
The previous approach was effectively to catch the exception and then
run a trap instruction. That has the unfortunate feature that we end
up with a crash at the catch site, not at the throw site, which leaves
us with very little information about which exception was thrown or
where from.
(Strictly we do have the exception pointer and could obtain exception
information, but it still won't tell us what threw it.)
Instead of that, set a personality function for Swift functions that
call potentially throwing code, and have that personality function
trap the exception during phase 1 (i.e. *before* the original stack
has been unwound).
rdar://120952971
`swift_willThrow` is called with an error right before it is thrown.
This existing entrypoint requires an already-boxed error existential;
with typed errors, we don't have the error existential on hand, so we
would need to allocate the box to throw a typed error. That's not okay.
Introduce a new `swift_willThrowTypedImpl` entry point into the runtime
that will first check for the presence of an error handler and, if one
is present, box the error to provide to the error handler. This
maintains the no-allocations path for typed errors while still
allowing existing error handlers to work.
This new entrypoint isn't available on older Swift runtimes, so create
a back-deployable shim called by the compiler. On new-enough platforms,
this will call through to `swift_willThrowTypedImpl`. On older
platforms, we drop the error and don't call the registered will-throw
handler at all. This is a compromise that avoids boxing when throwing
typed errors, at the cost of a slightly different experience for this
new feature on older runtimes.
Fixes rdar://119828459.
Symbolication can take some time, depending on the binaries involved.
In certain contexts it's better for the backtrace to finish quickly,
and then symbolication could be done offline.
rdar://122302117
When the Swift module is not available, we'll synthesize the
Copyable/Escapable decls into the Builtin module.
In the future, it might be nice to just do this always, and define
typealiases for those types in the stdlib to refer to the ones in the
builtin module.
The install target is sometimes the `None` target, which doesn't
actually exist. This should perhaps be spelled `never_install` instead,
but given that these are random names, we should protect the
`add_dependencies` calls to only accept install components that actually
exist.
rdar://117083470
An existential can contain a different type than the one that is being assigned, so we have to check the types and handle the values accordingly.
These functions were the odd ones out in not using `encoding` for this parameter label. Harmonizing this term will also make the documentation more consistent.
