[AutoDiff][test] Ensure if `@differentiable` function SILGen thunking is fixed

[kovdan01]

Description

In test/AutoDiff/SILOptimizer/generics.swift, we have the following comment:

TODO(TF-851): Uncomment the tests below after `@differentiable` function SILGen thunking is fixed.

After uncommented the corresponding piece of test, it's still passing.

Need to ensure if the issue which was the root cause of commenting the test initially is actually fixed (or if we have a case when the original issue becomes "hidden" for this particular test case due to other change, but is still relevant).

Additional information

No response

[kovdan01]

Tagging @asl @JaapWijnen

[asl]

@kovdan01 Will you please post the reproducer / test here?

[kovdan01]

@kovdan01 Will you please post the reproducer / test here?

@asl Sure. When stripping irrelevant parts from test/AutoDiff/SILOptimizer/generics.swift, we get this. After uncommenting disabled pieces of the test, it still passes.

// RUN: %target-swift-emit-sil -verify %s

import _Differentiation

// The layout requirement directly involves `T`, the differentiable function
// parameter/result type.
// TODO(TF-851): Uncomment the tests below after `@differentiable` function
// SILGen thunking is fixed.
/*
struct LayoutRequirement<T: AnyObject & Differentiable> {
  var stored: T
}
extension LayoutRequirement {
  func test(_ x: T) {
    let _: @differentiable(reverse) (T) -> T = { _ in self.stored }
    let _: @differentiable(reverse) (T) -> T = { $0 }
  }
}
*/

// Test superclass requirements.

class Super: Differentiable {}

// The superclass requirement is "contextual": the requirement is not on `T`,
// the differentiable function parameter/result type.
struct ContextualSuperclassRequirement<T: Differentiable, U: Super> {
  var stored: T
}
extension ContextualSuperclassRequirement {
  func test(_ x: T) {
    let _: @differentiable(reverse) (T) -> T = { _ in self.stored }
    let _: @differentiable(reverse) (T) -> T = { $0 }
  }
}

// The superclass requirement directly involves `T`, the differentiable
// function parameter/result type.
// TODO(TF-851): Uncomment the tests below after `@differentiable` function
// SILGen thunking is fixed.
/*
struct SuperclassRequirement<T: Super & Differentiable> {
  var stored: T
}
extension SuperclassRequirement {
  func test(_ x: T) {
    let _: @differentiable(reverse) (T) -> T = { _ in self.stored }
    let _: @differentiable(reverse) (T) -> T = { $0 }
  }
}
*/

[asl]

@kovdan01 Thanks. Have you checked that corresponding thunks were generated? We might probably need some CHECK lines added, no?

[kovdan01]

Have you checked that corresponding thunks were generated? We might probably need some CHECK lines added, no?

@asl That's what I've created the issue for :) I've checked that derivatives are generated for @differentiable(reverse) closures from LayoutRequirement.test and SuperclassRequirement.test. But I'm not sure, what particularly is meant by '@differentiable function SILGen thunking is fixed' in the TODOs (e.g. what particularly was broken and needed to be fixed, was it a crash or incorrect codegen, and if latter, what particularly was generated incorrectly).