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[AutoDiff] Check @noDerivative for function type comparison #67121

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Merged
merged 2 commits into from
Jul 6, 2023
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[AutoDiff] Check @noDerivative for function type comparison #67121

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[AutoDiff] Check @noDerivative for function type comparison
asavonic Jul 5, 2023
017368a
Add Float -> @noDerivative Float case to differentiation_diagnostics.…
asavonic Jul 6, 2023
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7 changes: 7 additions & 0 deletions lib/Sema/CSSimplify.cpp
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Expand Up @@ -3505,6 +3505,13 @@ ConstraintSystem::matchFunctionTypes(FunctionType *func1, FunctionType *func2,
return getTypeMatchFailure(argumentLocator);
}

// If functions are differentiable, ensure that @noDerivative is not
// discarded.
if (func1->isDifferentiable() && func2->isDifferentiable() &&
func1Param.isNoDerivative() && !func2Param.isNoDerivative()) {
return getTypeMatchFailure(argumentLocator);
}

// FIXME: We should check value ownership too, but it's not completely
// trivial because of inout-to-pointer conversions.

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3 changes: 2 additions & 1 deletion test/AutoDiff/SILOptimizer/differentiation_diagnostics.swift
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Expand Up @@ -741,7 +741,8 @@ struct TF_675 : Differentiable {
let _: @differentiable(reverse) (Float) -> Float = TF_675().method

// TF-918: Test parameter subset thunk + partially-applied original function.
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I can no longer find TF-918... Is there a GitHub issue for it?

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@asl asl Jul 5, 2023 •
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I'm afraid all TF issues gone long time ago. And if they were not converted to normal Swift JIRA issues, then they cannot be found anywhere...

@shahmishal will you please confirm?

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We should probably go over all TF- bugs in comments and remove them.

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And rewrite to present issues when the issue was migrated (there are few of them IIRC). Some of the TF's refer to some design decisions made in the past. It would be good to document them somehow while there are some memories on them :) I'll check what are the most important / interesting ones

let _: @differentiable(reverse) (Float, Float) -> Float = (+) as @differentiable(reverse) (Float, @noDerivative Float) -> Float
let _: @differentiable(reverse) (Float, @noDerivative Float) -> Float = (+) as @differentiable(reverse) (Float, Float) -> Float
let _: @differentiable(reverse) (Float, @noDerivative Float) -> Float = (+) as @differentiable(reverse) (Float, @noDerivative Float) -> Float
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I'm surprised this test was there! Maybe it was meant to test function conversions to a function with more @noDerivative. That should be possible with "subset parameter thunks".

let _: @differentiable(reverse) (Float, @noDerivative Float) -> Float = (+) as @differentiable(reverse) (Float, Float) -> Float

Is the above possible today?

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Yes, the above example is also possible. I think it is the same as test1 in the new LIT test, but we can add it to differentiation_diagnostics.swift as well.

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Does it actually work in a runtime test?


//===----------------------------------------------------------------------===//
// Differentiation in fragile functions
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25 changes: 25 additions & 0 deletions test/Constraints/noderivative.swift
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@@ -0,0 +1,25 @@
// RUN: %target-typecheck-verify-swift

import _Differentiation
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Because the test is not in the test/AutoDiff folder, it needs REQUIRES: differentiable_programming or people that build without that feature will fail this test.

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@asavonic Please submit a follow-up PR

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I'm sorry for causing this issue. I've submitted a PR to fix it: #67190


// Allow Type -> @noDerivative Type
//
func test1(_ foo: @escaping @differentiable(reverse) (Float, Float) -> Float) {
let fn: @differentiable(reverse) (Float, @noDerivative Float) -> Float = foo
_ = fn(0, 0)
}

// Allow @noDerivative Type -> Type when LHS function is not differentiable
//
func test2(_ foo: @escaping @differentiable(reverse) (Float, @noDerivative Float) -> Float) {
let fn: (Float, Float) -> Float = foo
_ = fn(0, 0)
}

// Disallow @noDerivative Type -> Type when LHS function is also differentiable
//
func test3(_ foo: @escaping @differentiable(reverse) (Float, @noDerivative Float) -> Float) {
// expected-error @+1 {{cannot convert value of type '@differentiable(reverse) (Float, @noDerivative Float) -> Float' to specified type '@differentiable(reverse) (Float, Float) -> Float'}}
let fn: @differentiable(reverse) (Float, Float) -> Float = foo
_ = fn(0, 0)
}