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2734f3ca05
In theory this is a source break if someone had a weird custom
conforming type, but I suspect in practice conformances to
this protocol are never defined.
The reason we want this requirement is that often you will see
code like the following:
protocol Point {
associatedtype Scalar: SIMDScalar
associatedtype Vector: SIMD where Vector.Scalar == Scalar
}
extension Point where Vector == SIMD2<Scalar> { ... }
When `Vector` is equated with `SIMD2<Scalar>`, we get an infinite
sequence of implied same-type requirements:
Vector.MaskStorage == SIMD2<Scalar.MaskScalar>
Vector.MaskStorage.MaskStorage == SIMD2<Scalar.MaskScalar.MaskScalar>
...
The protocol fails to typecheck with an error because the requirement
machine cannot build a rewrite system.
If SIMDScalar requires that MaskScalar.MaskScalar == MaskScalar, then
we instead get
Vector.MaskStorage == SIMD2<Scalar.MaskScalar>
Vector.MaskStorage.MaskStorage == SIMD2<Scalar.MaskScalar>
Vector.MaskStorage.MaskStorage == Vector.MaskStorage
...
Which ties off the recursion.
In theory, a more advanced implementation could represent this kind of
infinite recursion in 'closed form', but we don't have that yet, and I
believe adding this same-type requirement makes sense anyway.
Fixes rdar://problem/95075552.
33 lines
1.3 KiB
Swift
33 lines
1.3 KiB
Swift
// RUN: %target-swift-frontend -typecheck %s -debug-generic-signatures 2>&1 | %FileCheck %s
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// CHECK-LABEL: .Tree@
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// CHECK-NEXT: Requirement signature: <Self where Self.[Tree]Distance : FloatingPoint, Self.[Tree]Distance : SIMDScalar, Self.[Tree]Distance == Self.[Tree]Point.[SIMDStorage]Scalar, Self.[Tree]Point : SIMD>
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protocol Tree {
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associatedtype Distance: FloatingPoint & SIMDScalar
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associatedtype Point: SIMD where Point.Scalar == Distance
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}
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// CHECK-LABEL: .QuadTree@
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// CHECK-NEXT: Requirement signature: <Self where Self : Tree, Self.[Tree]Point == SIMD2<Self.[Tree]Distance>>
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protocol QuadTree : Tree where Point == SIMD2<Distance> {}
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// CHECK-LABEL: .OctTree@
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// CHECK-NEXT: Requirement signature: <Self where Self : Tree, Self.[Tree]Point == SIMD3<Self.[Tree]Distance>>
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protocol OctTree : Tree where Point == SIMD3<Distance> {}
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func sameType<T>(_: T.Type, _: T.Type) {}
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extension QuadTree {
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func foo() {
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sameType(Point.MaskStorage.self, SIMD2<Distance.SIMDMaskScalar>.self)
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sameType(Point.MaskStorage.MaskStorage.self, SIMD2<Distance.SIMDMaskScalar>.self)
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}
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}
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extension OctTree {
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func foo() {
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sameType(Point.MaskStorage.self, SIMD3<Distance.SIMDMaskScalar>.self)
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sameType(Point.MaskStorage.MaskStorage.self, SIMD3<Distance.SIMDMaskScalar>.self)
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}
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}
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