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
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.
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.
Fixes foward-mode crashed related to:
- Missing tangent buffers for non-wrt `inout` parameters.
- Tangent buffers not being initialized due to the corresponding original
buffer intialization instructions being non-active.
- Non-varied indirect results not being initialized.
- `emitDestroyValue` crashes due to `TangentVector` value category mismatch.
Resolves TF-984 and SR-13447.
Co-authored-by: Dan Zheng <danielzheng@google.com>
Adds forward mode support for `apply` instruction with `inout` arguments.
Example of supported code:
```
func add(_ x: inout Float, _ y: inout Float) -> Float {
var result = x
result += y
return result
}
print(differential(at: 1, 1, in: add)(1, 1)) // prints "2"
```
Use TangentStoredPropertyRequest in differentiation transform.
Improve non-differentiability diagnostics regarding invalid stored
property projection instructions:
`struct_extract`, `struct_element_addr`, `ref_element_addr`.
Diagnose the following cases:
- Original property's type does not conform to `Differentiable`.
- Base type's `TangentVector` is not a struct.
- Tangent property not found: base type's `TangentVector` does not have a
stored property with the same name as the original property.
- Tangent property's type is not equal to the original property's
`TangentVector` type.
- Tangent property is not a stored property.
Resolves TF-969 and TF-970.
