In `TangentBuilder` temporary allocations are emitted in order to make generic calls to `AdditiveArithmetic.zero` and `AdditiveArithmetic.+`. When we perform accumulation of two adjoint values that correspond to a lexical value in the original function, the stack allocations require a debug variable, as we use the original instruction's location. However such a debug variable wouldn't really make sense as these temporary allocations do not represent the original variable's adjoint. With lexical borrow scopes, we hit a crasher when creating temporary allocations when accumulating adjoints for lexical `begin_borrow` instructions.
This PR makes `TangentBuilder`'s temporary allocations use an auto-generated location. The existing debug info emission behavior is not changed, as we still emit `debug_value` when materializing an `AdjointValue` after any necessary adjoint accumulation.
The effect of passing -enable-copy-propagation is both to enable the
CopyPropagation pass to shorten object lifetimes and also to enable
lexical lifetimes to ensure that object lifetimes aren't shortened while
a variable is still in scope and used.
Add a new flag, -enable-lexical-borrow-scopes=true to override
-enable-copy-propagation's effect (setting it to ::ExperimentalLate) on
SILOptions::LexicalLifetimes that sets it to ::Early even in the face of
-enable-copy-propagation. The old flag -disable-lexical-lifetimes is
renamed to -enable-lexical-borrow-scopes=false but continues to set that
option to ::Off even when -enable-copy-propagation is passed.
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.
Fix SIL pullback function type calculation: remap original `unowned` results to
the correct pullback parameter convention depending on the `TangentVector` type
lowering.
Make `PullbackCloner` visitors for the following instructions check and handle
tangent value categories: `struct`, `struct_extract`, `tuple`, `destructure_tuple`.
Add differentiation tests for `Optional` struct and class stored properties,
exercising the instruction visitors above.
Resolves SR-13430.
Add differentiation support for non-active `try_apply` SIL instructions.
Notable pullback generation changes:
* Original basic blocks are now visited in a different order:
* starting from the original basic block, all its predecessors
* are visited in a breadth-first search order. This ensures that
* all successors of any block are visited before the block itself.
Resolves TF-433.
Fix `Optional` differentiation crash for non-resilient `Wrapped` reference type.
Add `NonresilientTracked` type to `DifferentiationUnittest` for testing.
Resolves SR-13377.
Pullback generation now supports `switch_enum` and `switch_enum_addr`
instructions for `Optional`-typed operands.
Currently, the logic is special-cased to `Optional`, but may be generalized in
the future to support enums following general rules.
