Fix incorrect derivative (#41423)

philipturner · web-flow · commit c74cbce95a55 · 2022-05-24T23:32:04.000-07:00
diff --git a/stdlib/public/Differentiation/FloatingPointDifferentiation.swift.gyb b/stdlib/public/Differentiation/FloatingPointDifferentiation.swift.gyb
@@ -268,7 +268,7 @@ where
   func _vjpAddingProduct(
     _ lhs: Self, _ rhs: Self
   ) -> (value: Self, pullback: (Self) -> (Self, Self, Self)) {
-    return (addingProduct(lhs, rhs), { _ in (1, rhs, lhs) })
+    return (addingProduct(lhs, rhs), { v in (v, v * rhs, v * lhs) })
   }
 
   @inlinable // FIXME(sil-serialize-all)
diff --git a/test/AutoDiff/stdlib/floating_point.swift.gyb b/test/AutoDiff/stdlib/floating_point.swift.gyb
@@ -81,6 +81,7 @@ FloatingPointDerivativeTests.test("${Self}.squareRoot") {
 
 FloatingPointDerivativeTests.test("${Self}.addingProduct") {
   expectEqual((1, 2, 3), gradient(at: ${Self}(10), 3, 2, of: { $0.addingProduct($1, $2) }))
+  expectEqual((2, 4, 6), pullback(at: ${Self}(10), 3, 2, of: { $0.addingProduct($1, $2) })(2))
 }
 
 FloatingPointDerivativeTests.test("${Self}.minimum") {

Original file line number	Diff line number	Diff line change
`@@ -268,7 +268,7 @@ where`
`268`	`268`	`func _vjpAddingProduct(`
`269`	`269`	`_ lhs: Self, _ rhs: Self`
`270`	`270`	`) -> (value: Self, pullback: (Self) -> (Self, Self, Self)) {`
`271`		`- return (addingProduct(lhs, rhs), { _ in (1, rhs, lhs) })`
	`271`	`+ return (addingProduct(lhs, rhs), { v in (v, v * rhs, v * lhs) })`
`272`	`272`	`}`
`273`	`273`
`274`	`274`	`@inlinable // FIXME(sil-serialize-all)`
Original file line number	Diff line number	Diff line change
`@@ -81,6 +81,7 @@ FloatingPointDerivativeTests.test("${Self}.squareRoot") {`
`81`	`81`
`82`	`82`	`FloatingPointDerivativeTests.test("${Self}.addingProduct") {`
`83`	`83`	`expectEqual((1, 2, 3), gradient(at: ${Self}(10), 3, 2, of: { $0.addingProduct($1, $2) }))`
	`84`	`+ expectEqual((2, 4, 6), pullback(at: ${Self}(10), 3, 2, of: { $0.addingProduct($1, $2) })(2))`
`84`	`85`	`}`
`85`	`86`
`86`	`87`	`FloatingPointDerivativeTests.test("${Self}.minimum") {`