This is safe because the closure is not allowed to capture the array according
to the documentation of 'withUnsafeMutableBuffer' and the current implementation
makes sure that any such capture would observe an empty array by swapping self
with an empty array.
Users will get "almost guaranteed" stack promotion for small arrays by writing
something like:
func testStackAllocation(p: Proto) {
var a = [p, p, p]
a.withUnsafeMutableBufferPointer {
let array = $0
work(array)
}
}
It is "almost guaranteed" because we need to statically be able to tell the size
required for the array (no unspecialized generics) and the total buffer size
must not exceed 1K.
We were giving special handling to ApplyInst when we were attempting to use
getMemoryBehavior(). This commit changes the special handling to work on all
full apply sites instead of just AI. Additionally, we look through partial
applies and thin to thick functions.
I also added a dumper called BasicInstructionPropertyDumper that just dumps the
results of SILInstruction::get{Memory,Releasing}Behavior() for all instructions
in order to verify this behavior.
Currently the array.get_element calls return the element as indirect result.
The generic specializer will change so that the element can be returned as direct result.
As there are no instructions left which produce multiple result values, this is a NFC regarding the generated SIL and generated code.
Although this commit is large, most changes are straightforward adoptions to the changes in the ValueBase and SILValue classes.
This is something that we have wanted for a long time and will enable us to
remove some hacks from the compiler (i.e. how we determine in the ARC optimizer
that we have "fatalError" like function) and also express new things like
"noarc".
(libraries now)
It has been generally agreed that we need to do this reorg, and now
seems like the perfect time. Some major pass reorganization is in the
works.
This does not have to be the final word on the matter. The consensus
among those working on the code is that it's much better than what we
had and a better starting point for future bike shedding.
Note that the previous organization was designed to allow separate
analysis and optimization libraries. It turns out this is an
artificial distinction and not an important goal.
