Make _MagicMirrorData @_fixed_layout, but not the concrete mirror
implementations.
To make the calling convention work in resilient builds, make the
runtime entry points into top-level functions that take a
_MagicMirrorData, instead of adding @_silgen_name attributes on
methods.
This involves changing the convention on the 'owner' parameter
from +0 to +1.
Also, there was a memory leak in the old enum code that I noticed
by inspection. We would copy the enum value into a box, strip
the enum tag bits, take the box contents but never free the box
itself.
The fix isn't very satisfying either -- we have to modify the
source enum in-place to strip tag bits, then we copy it into a
box having the right payload type, and add the tag bits back.
At least this way, we can free the box after.
This is a staging attribute that will eventually mean "fixed-contents"
for structs and "closed" for enums, as described in
docs/LibraryEvolution.rst.
This is pretty much the minimal set of types that must be fixed-layout,
because SILGen makes assumptions about their lowering.
If desired, some SILGen refactoring can allow some of these to be
resilient. For example, bridging value types could be made to work
with resilient types.
It is a hint to the optimizer that the code, where this builtin is called, is on the fast path.
Specifically, the inliner takes it into account and increases the assumed benefit for code where the builtin is located.
Compared to the fastPath/slowPath builtins, this builtin can be placed into plain linear code and doesn't need to be used in conditions.
Compared to the @inline(__always) attribute, this builtin has also an effect on the caller function. Let's assume
foo() calls bar() contains onFastPath
and both foo and bar are small functions. Then if bar gets inlined into foo, the builtin also increases the chances that foo gets inlined.
This would not be the case if @inline(__always) is used just for bar.
This is more or less a workaround for some optimizations (mainly ARC opt) to avoid performance degradation with the upcoming inliner changes
In some situations it makes a big difference for ARC opt if a function is inlined or not, althought this shouldn't be the case.
This is an internal method that will go away in the future.
Get the value of the unmanaged referenced as a managed reference without
consuming an unbalanced retain of it and pass it to the closure. Asserts
that there is some other reference ('the owning reference') to the
unmanaged reference that guarantees the lifetime of the unmanaged reference
for the duration of the '_withUnsafeGuaranteedRef' call.
var owningReference = Instance()
...
withExtendedLifetime(owningReference) {
let u = Unmanaged.passUnretained(owningReference)
for i in 0 ..< 100 {
// Assert that the reference in 'u' is kept alive by another storage
// location or value that holds the same reference.
u._withUnsafeGuaranteedRef {
$0.doSomething()
}
}
} // owningReference's lifetime (reference count > 0) is guaranteed
// for this scope.
rdar://25129935
