[SR-14982] UnsafeMutableRawBufferPointer.initialize(as:from: ) has no fast path for contiguous Collections

[glessard]

Previous ID	SR-14982
Radar	rdar://problem/81168547
Original Reporter	@glessard
Type	Improvement

Additional Detail from JIRA

Votes	0
Component/s	Standard Library
Labels	Improvement, Performance
Assignee	@glessard
Priority	Medium

md5: 604b61efa14e93fd1f56dd2bcf00a48f

Issue Description:

UMRBP.initializeMemory<T,S>(as type: T.Type, from source: S) takes a Sequence and and initializes an UMRBP element-by-element (see here). Note that the closest equivalent function on UnsafeMutableRawPointer is the most likely way to add a fast-path for this, by using withContiguousStorageIfAvailable on source.

Adding a fast path may require adding an overload.

[glessard]

UMRP isn't the only way to fast-path this: UMBP<T>.initialize(from: ) is also viable, and might work for more Collection types.

[glessard]

@swift-ci create

[glessard]

(this is thematically related to [SR-14886| https://bugs.swift.org/browse/SR-14886])

[glessard]

#38817