[SR-12148] Make differentiation work with class types

[rxwei]

Previous ID	SR-12148
Radar	rdar://problem/59278218
Original Reporter	@rxwei
Type	New Feature
Status	In Progress
Resolution

Additional Detail from JIRA

Votes	0
Component/s
Labels	New Feature
Assignee	@dan-zheng
Priority	Medium

md5: a71ffde72bc884ae0041737d20f410bc

Sub-Tasks:

• [SR-12175] Fix forward-mode class differentiation crash #54600
• [SR-12149] [Sema] Enable Differentiable derived conformances for class types #53442
• [SR-12150] Enable differentiation of class methods #53443
• [SR-12152] Handle differentiation of ref_element_addr #53486
• [SR-12151] Enable differentiation of class initializers #53546
• [SR-12153] Handle differentiation of casting instructions #53489
• [SR-12154] Fix vtable entry type mismatch verification error for @differentiable(wrt: self) #53490
• [SR-12155] Allow @derivative attribute to specify original function from superclass #53512
• [SR-12156] Make @differentiable attribute on class methods more fine-grained #54336
• [SR-12157] Use Differentiable-conforming class types in swift-apis #53444

blocks:

• TF-641 [AD] Handle TangentVector classes in differentiation transform

relates to:

• TF-38 KeyPathIterable derivation: Should work on classes
• TF-481 Support mutable layers

Issue Description:

Differentiation should work with class types. This enables use cases like "mutable layers", which can be neatly defined as Differentiable-conforming classes with a func callAsFunction method.

[rxwei]

@swift-ci create