This currently fails when run on the macOS 10.14.4 stdlib:
```
[ RUN ] FunctionTypeMetadata.Reflect differentiable function type
stdout>>> check failed at /Users/buildslave/jenkins/workspace/fs-swift-main-tools_RA-stdlib_RA-macOS-swift-in-OS-10.14.4/swift/test/AutoDiff/validation-test/function_type_metadata.swift, line 10
stdout>>> expected: "@differentiable(reverse) (Swift.Float) -> Swift.Float" (of type Swift.String)
stdout>>> actual: "-3.8442426e-13" (of type Swift.String)
stderr>>> CRASHED: SIGSEGV
the test crashed unexpectedly
[ FAIL ] FunctionTypeMetadata.Reflect differentiable function type
```
rdar://76039256
* Move differentiability kinds from target function type metadata to trailing objects so that we don't exhaust all remaining bits of function type metadata.
* Differentiability kind is now stored in a tail-allocated word when function type flags say it's differentiable, located immediately after the normal function type metadata's contents (with proper alignment in between).
* Add new runtime function `swift_getFunctionTypeMetadataDifferentiable` which handles differentiable function types.
* Fix mangling of different differentiability kinds in function types. Mangle it like `ConcurrentFunctionType` so that we can drop special cases for escaping functions.
```
function-signature ::= params-type params-type async? sendable? throws? differentiable? // results and parameters
...
differentiable ::= 'jf' // @differentiable(_forward) on function type
differentiable ::= 'jr' // @differentiable(reverse) on function type
differentiable ::= 'jd' // @differentiable on function type
differentiable ::= 'jl' // @differentiable(_linear) on function type
```
Resolves rdar://75240064.
Tests for false positive precondition triggered by a .zero gradient, i.e. empty [] array, back-propagated through concatenation and move methods
Implements a simplified reproducer of SR-14297
'AnyDifferentiable' and 'AnyDerivative' should conform to 'CustomReflectable' to prevent leaking implementation details. The mirror should reflect its underlying value directly.
Resolves rdar://75496334.
Improved diagnostic for when the registered derivative function and
the function it derivates (the original) differ in terms of
`static` declaration modifier usage. Suggesting as well a fix-it,
to either remove or add the `static` keyword.
The registered derivative needs to be marked as `static` in two cases:
1. When the original function is a constructor.
2. When the original function is static as well.
When the original function is an instance method, the registered derivative must be as well.
Resolves [SR-13152](https://bugs.swift.org/browse/SR-13152).
Do not mark synthesized `TangentVector` members as synthesized so that the type checker won't sort them. We would like tangent vector members to have the same order as the properties in the parent declaration.
Also add `typealias TangentVector = Self` to the synthesized `TangentVector` so that it will not need its own `Differentiable` conformance derivation.
Resolves SR-14241 / rdar://74659803.
Rename `move(along:)` to `move(by:)` based on the proposal feedback. The main argument for the change is that tangent vectors specify both a direction and a magnitude, whereas `along:` does not indicate that `self` is being moved by the specified magnitude.
- Properly clone and use debug scopes for all instructions in pullback functions.
- Emit `debug_value` instructions for adjoint values.
- Add debug locations and variable info to adjoint buffer allocations.
- Add `TangentBuilder` (a `SILBuilder` subclass) to unify and simplify special emitter utilities for tangent vector code generation. More simplifications to come.
Pullback variable inspection example:
```console
(lldb) n
Process 50984 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = step over
frame #0: 0x0000000100003497 main`pullback of foo(x=0) at main.swift:12:11
9 import _Differentiation
10
11 func foo(_ x: Float) -> Float {
-> 12 let y = sin(x)
13 let z = cos(y)
14 let k = tanh(z) + cos(y)
15 return k
Target 0: (main) stopped.
(lldb) fr v
(Float) x = 0
(Float) k = 1
(Float) z = 0.495846391
(Float) y = -0.689988375
```
Resolves rdar://68616528 / SR-13535.
Add the following new mangling rules.
```
global ::= from-type to-type 'TJO' AUTODIFF-FUNCTION-KIND // autodiff self-reordering reabstraction thunk
global ::= from-type 'TJS' AUTODIFF-FUNCTION-KIND INDEX-SUBSET 'p' INDEX-SUBSET 'r' INDEX-SUBSET 'P' // autodiff linear map subset parameters thunk
global ::= global to-type 'TJS' AUTODIFF-FUNCTION-KIND INDEX-SUBSET 'p' INDEX-SUBSET 'r' INDEX-SUBSET 'P' // autodiff derivative function subset parameters thunk
```
Example:
```console
$s13TangentVector16_Differentiation14DifferentiablePQzAaDQy_SdAFIegnnnr_TJSdSSSpSrSUSP ---> autodiff subset parameters thunk for differential from @escaping @callee_guaranteed (@in_guaranteed A._Differentiation.Differentiable.TangentVector, @in_guaranteed B._Differentiation.Differentiable.TangentVector, @in_guaranteed Swift.Double) -> (@out B._Differentiation.Differentiable.TangentVector) with respect to parameters {0, 1, 2} and results {0} to parameters {0, 2}
$sS2f8mangling3FooV13TangentVectorVIegydd_SfAESfIegydd_TJOp ---> autodiff self-reordering reabstraction thunk for pullback from @escaping @callee_guaranteed (@unowned Swift.Float) -> (@unowned Swift.Float, @unowned mangling.Foo.TangentVector) to @escaping @callee_guaranteed (@unowned Swift.Float) -> (@unowned mangling.Foo.TangentVector, @unowned Swift.Float)
```
Resolves rdar://72666310 / SR-13508.
Also fix a bug in `AutoDiffFunction` mangling where the original may be a global that contains more than 1 node (rdar://74151229 / SR-14106).
- Set the builder's debug scope to the remapped debug scope in the overriden visiters.
- In trampoline blocks where we build predecessor enums, make the trampoline builder inherit the original terminator's remapped debug scope.
Resolves rdar://74087329.
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.
- Add `DispatchThunkDerivative` and `MethodDescriptorDerivative` as link entities. The derivative functions of initializers, subscripts, properties, and methods are **all methods**, so we don't need other link entities for this purpose.
- Mangle dispatch thunks and method descriptors. Make `AutoDiffFunction` a context node since it can be nested.
Resolves SR-13866 (rdar://71318828) and SR-13125 (rdar://65240599).
-enable-subst-sil-function-types-for-function-values
-enable-large-loadable-types
These defaulted to on, and there were no corresponding flags for
turning them off, so the flags had no effect.
`valueWithDerivative(of:)` and `valueWithGradient(of:)` are the curried version of `valueWithDerivative(at:in:)` and `valueWithGradient(at:in:)`, respectively. They are not included the proposal and are not being used by any client that I know of. This patch removes them.
This disables 4 tests:
- DerivativeRegistrationTests.NonCanonicalizedGenericSignatureComparison
- Reabstraction.diff param generic => concrete
- Reabstraction.diff param and nondiff param generic => concrete
- Reabstraction.result generic => concrete
Simultaneously, enable the remainder of the auto-diff test suite on
Windows. These tests fail on Windows due to an invalid parameter during
the reabstraction of the generic differentiable parameters. The
remainder of the auto-differentiation tests pass on all the platforms.
- `Mangle::ASTMangler::mangleAutoDiffDerivativeFunction()` and `Mangle::ASTMangler::mangleAutoDiffLinearMap()` accept original function declarations and return a mangled name for a derivative function or linear map. This is called during SILGen and TBDGen.
- `Mangle::DifferentiationMangler` handles differentiation function mangling in the differentiation transform. This part is necessary because we need to perform demangling on the original function and remangle it as part of a differentiation function mangling tree in order to get the correct substitutions in the mangled derivative generic signature.
A mangled differentiation function name includes:
- The original function.
- The differentiation function kind.
- The parameter indices for differentiation.
- The result indices for differentiation.
- The derivative generic signature.
`differentiability_function_extract` instruction has an optional explicit
extractee type. This is currently used by TypeSubstCloner and the
LoadableByAddress transform to rewrite `differentiability_function_extract`
instructions while preserving `@differentiable` function type invariants.
There is an assertion that `differentiability_function_extract` instructions do
not have explicit extractee types outside of canonical/lowered SIL. However,
this does not handle the SIL deserialization case above: when a function
containing a `differentiable_function_extract` instruction with an explicit type
is deserialized into a raw SIL module (which happens when optimizations are
enabled).
Removing the assertion unblocks this encountered use case.
A more robust longer-term solution may be to change SIL `@differentiable`
function types to explicitly store component original/JVP/VJP function types.
Also fix `differentiable_function_extract` extractee type serialization.
Resolves SR-14004.
