Introduce the notion of "semantic result parameter". Handle differentiation of inouts via semantic result parameter abstraction. Do not consider non-wrt semantic result parameters as semantic results
Fixes#67174
1. When calculating the differential type of an original function with an inout parameter and when the inout parameter has a type parameter, the inout parameter should get a generic parameter in the subst generic signature of the differential but it currently doesn't. This causes SILGen to attempt to reabstract the differential value in the JVP protocol witness thunk, whilst the generic signature is lacking requirements, leading to a requirement machine error. This patch fixes the calculation so that the JVP's result type (the differential type) always matches the witness thunk's result type.
Wrong type:
```swift
sil private [transparent] [thunk] [ossa] @... <τ_0_0 where τ_0_0 : Differentiable> (...) -> @owned @callee_guaranteed @substituted <τ_0_0, τ_0_1> (@in_guaranteed τ_0_0) -> @out τ_0_1 for <τ_0_0.TangentVector, τ_0_0.TangentVector> {
%6 = differentiable_function_extract [jvp] %5 : $@differentiable(reverse) @convention(method) <τ_0_0 where τ_0_0 : Differentiable> (@in_guaranteed τ_0_0, @noDerivative @inout τ_0_0, @noDerivative SR_13305_Struct) -> () // user: %7
HERE ====> %7 = apply %6<τ_0_0>(%0, %1, %3) : $@convention(method) <τ_0_0 where τ_0_0 : Differentiable> (@in_guaranteed τ_0_0, @inout τ_0_0, SR_13305_Struct) -> @owned @callee_guaranteed @substituted <τ_0_0> (@in_guaranteed τ_0_0) -> @out τ_0_0 for <τ_0_0.TangentVector>
```
Should be:
```swift
%7 = apply %6<τ_0_0>(%0, %1, %3) : $@convention(method) <τ_0_0 where τ_0_0 : Differentiable> (@in_guaranteed τ_0_0, @inout τ_0_0, SR_13305_Struct) -> @owned @callee_guaranteed @substituted <τ_0_0, τ_0_1> (@in_guaranteed τ_0_0) -> @out τ_0_1 for <τ_0_0.TangentVector, τ_0_0.TangentVector>
```
2. `TypeConverter::makeConstantInterfaceType` is not passing down the derivative generic signature to `SILFunctionType::getAutoDiffDerivativeFunctionType` for class methods, and this was caught by RequirementMachine during vtable emission. This patch fixes that.
Partially resolves rdar://82549134. The only remaining tests that require `-requirement-machine=off` are SILOptimizer/semantic_member_accessors_sil.swift and SILOptimizer/differentiation_diagnostics.swift which I will fix next. Then I'll do a proper fix for workaround #39416.
The SIL type lowering logic for AutoDiff gets the substituted generic signature
mixed up with the invocation generic signature, so it tries to ask questions
about DependentMemberTypes in a signature with no requirements. This triggers
assertions when the requirement machine is enabled.
Disable the requirement machine until this is fixed.
Compiler:
- Add `Forward` and `Reverse` to `DifferentiabilityKind`.
- Expand `DifferentiabilityMask` in `ExtInfo` to 3 bits so that it now holds all 4 cases of `DifferentiabilityKind`.
- Parse `@differentiable(reverse)` and `@differentiable(_forward)` declaration attributes and type attributes.
- Emit a warning for `@differentiable` without `reverse`.
- Emit an error for `@differentiable(_forward)`.
- Rename `@differentiable(linear)` to `@differentiable(_linear)`.
- Make `@differentiable(reverse)` type lowering go through today's `@differentiable` code path. We will specialize it to reverse-mode in a follow-up patch.
ABI:
- Add `Forward` and `Reverse` to `FunctionMetadataDifferentiabilityKind`.
- Extend `TargetFunctionTypeFlags` by 1 bit to store the highest bit of differentiability kind (linear). Note that there is a 2-bit gap in `DifferentiabilityMask` which is reserved for `AsyncMask` and `ConcurrentMask`; `AsyncMask` is ABI-stable so we cannot change that.
_Differentiation module:
- Replace all occurrences of `@differentiable` with `@differentiable(reverse)`.
- Delete `_transpose(of:)`.
Resolves rdar://69980056.
Enable `@differentiable` attribute on setters of properties and
subscripts in `Differentiable`-conforming types.
Add automatically-differentiated `@differentiable` setter test.
Resolves TF-1166.
Fix SIL differential function type calculation to handle non-wrt `inout`
parameters.
Patch `SILFunctionType::getDifferentiabilityResultIndices` to prevent returning
empty result indices for `@differentiable` function types with no formal results
where all `inout` parameters are `@noDerivative`. TF-1305 tracks a robust fix.
Resolves SR-13305.
Exposes TF-1305: parameter/result differentiability hole for `inout` parameters.
