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const prop nonsense eliminated

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This commit is contained in:
Oli Scherer 2024-01-05 17:31:38 +00:00
parent 6ecb2aa580
commit 1f398abcb6
6 changed files with 32 additions and 58 deletions
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49
compiler/rustc_const_eval/src/interpret/projection.rs
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@ -153,11 +153,7 @@ where
// Offset may need adjustment for unsized fields.
let (meta, offset) = if field_layout.is_unsized() {
if base.layout().is_sized() {
// An unsized field of a sized type? Sure...
// But const-prop actually feeds us such nonsense MIR! (see test `const_prop/issue-86351.rs`)
throw_inval!(ConstPropNonsense);
}
assert!(!base.layout().is_sized());
let base_meta = base.meta();
// Re-use parent metadata to determine dynamic field layout.
// With custom DSTS, this *will* execute user-defined code, but the same
@ -205,29 +201,26 @@ where
// see https://github.com/rust-lang/rust/issues/93688#issuecomment-1032929496.)
// So we just "offset" by 0.
let layout = base.layout().for_variant(self, variant);
if layout.abi.is_uninhabited() {
// `read_discriminant` should have excluded uninhabited variants... but ConstProp calls
// us on dead code.
// In the future we might want to allow this to permit code like this:
// (this is a Rust/MIR pseudocode mix)
// ```
// enum Option2 {
// Some(i32, !),
// None,
// }
//
// fn panic() -> ! { panic!() }
//
// let x: Option2;
// x.Some.0 = 42;
// x.Some.1 = panic();
// SetDiscriminant(x, Some);
// ```
// However, for now we don't generate such MIR, and this check here *has* found real
// bugs (see https://github.com/rust-lang/rust/issues/115145), so we will keep rejecting
// it.
throw_inval!(ConstPropNonsense)
}
// In the future we might want to allow this to permit code like this:
// (this is a Rust/MIR pseudocode mix)
// ```
// enum Option2 {
// Some(i32, !),
// None,
// }
//
// fn panic() -> ! { panic!() }
//
// let x: Option2;
// x.Some.0 = 42;
// x.Some.1 = panic();
// SetDiscriminant(x, Some);
// ```
// However, for now we don't generate such MIR, and this check here *has* found real
// bugs (see https://github.com/rust-lang/rust/issues/115145), so we will keep rejecting
// it.
assert!(!layout.abi.is_uninhabited());
// This cannot be `transmute` as variants *can* have a smaller size than the entire enum.
base.offset(Size::ZERO, layout, self)
}