[6.0] Devirtualizer: fix a crash due to a not supported bitcast of ABI compatible types #74653
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…ut is dependent on its generic parameters
This is usually the case. Some examples, where they layout is _not_ dependent:
```
struct S<T> {
var x: Int // no members which depend on T
}
struct S<T> {
var c: SomeClass<T> // a class reference does not depend on the layout of the class
}
```
…atible types
When devirtualizing witness method calls, it can happen that we need a cast between ABI compatible return types.
We were missing supporting type casts between nominal types which are ABI compatible.
This comes from whole-module reasoning of protocol conformances.
If a protocol only has a single conformance where the associated type (`ID`) is some concrete type (e.g. `Int`), then the devirtualizer knows that `p.get()` can only return an `Int`:
```
public struct X2<ID> {
let p: any P2<ID>
public func testit(i: ID, x: ID) -> S2<ID> {
return p.get(x: x)
}
}
```
and after devirtualizing the `get` function, its result must be cast from `Int` to `ID`.
The `layoutIsTypeDependent` utility is basically only used here to assert that this cast can only happen between layout compatible types.
rdar://129004015
|
@swift-ci test |
tbkka
approved these changes
Jun 24, 2024
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When devirtualizing witness method calls, it can happen that we need a cast between ABI compatible return types.
We were missing supporting type casts between nominal types which are ABI compatible.
This comes from whole-module reasoning of protocol conformances.
If a protocol only has a single conformance where the associated type (
ID) is some concrete type (e.g.Int), then the devirtualizer knows thatp.get()can only return anInt:and after devirtualizing the
getfunction, its result must be cast fromInttoID.