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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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7
compiler/rustc_const_eval/src/errors.rs
View File

@ -860,9 +860,6 @@ impl<'tcx> ReportErrorExt for InvalidProgramInfo<'tcx> {
InvalidProgramInfo::FnAbiAdjustForForeignAbi(_) => {
rustc_middle::error::middle_adjust_for_foreign_abi_error
}
InvalidProgramInfo::ConstPropNonsense => {
panic!("We had const-prop nonsense, this should never be printed")
}
}
}
fn add_args<G: EmissionGuarantee>(
@ -871,9 +868,7 @@ impl<'tcx> ReportErrorExt for InvalidProgramInfo<'tcx> {
builder: &mut DiagnosticBuilder<'_, G>,
) {
match self {
InvalidProgramInfo::TooGeneric
| InvalidProgramInfo::AlreadyReported(_)
| InvalidProgramInfo::ConstPropNonsense => {}
InvalidProgramInfo::TooGeneric | InvalidProgramInfo::AlreadyReported(_) => {}
InvalidProgramInfo::Layout(e) => {
// The level doesn't matter, `diag` is consumed without it being used.
let dummy_level = Level::Bug;

6
compiler/rustc_const_eval/src/interpret/operand.rs
View File

@ -643,11 +643,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
let layout = self.layout_of_local(frame, local, layout)?;
let op = *frame.locals[local].access()?;
if matches!(op, Operand::Immediate(_)) {
if layout.is_unsized() {
// ConstProp marks *all* locals as `Immediate::Uninit` since it cannot
// efficiently check whether they are sized. We have to catch that case here.
throw_inval!(ConstPropNonsense);
}
assert!(!layout.is_unsized());
}
Ok(OpTy { op, layout })
}

19
compiler/rustc_const_eval/src/interpret/place.rs
View File

@ -519,11 +519,7 @@ where
} else {
// Unsized `Local` isn't okay (we cannot store the metadata).
match frame_ref.locals[local].access()? {
Operand::Immediate(_) => {
// ConstProp marks *all* locals as `Immediate::Uninit` since it cannot
// efficiently check whether they are sized. We have to catch that case here.
throw_inval!(ConstPropNonsense);
}
Operand::Immediate(_) => bug!(),
Operand::Indirect(mplace) => Place::Ptr(*mplace),
}
};
@ -816,17 +812,8 @@ where
// avoid force_allocation.
let src = match self.read_immediate_raw(src)? {
Right(src_val) => {
// FIXME(const_prop): Const-prop can possibly evaluate an
// unsized copy operation when it thinks that the type is
// actually sized, due to a trivially false where-clause
// predicate like `where Self: Sized` with `Self = dyn Trait`.
// See #102553 for an example of such a predicate.
if src.layout().is_unsized() {
throw_inval!(ConstPropNonsense);
}
if dest.layout().is_unsized() {
throw_inval!(ConstPropNonsense);
}
assert!(!src.layout().is_unsized());
assert!(!dest.layout().is_unsized());
assert_eq!(src.layout().size, dest.layout().size);
// Yay, we got a value that we can write directly.
return if layout_compat {

49
compiler/rustc_const_eval/src/interpret/projection.rs
View File

@ -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)
}

2
compiler/rustc_middle/src/mir/interpret/error.rs
View File

@ -200,8 +200,6 @@ pub enum InvalidProgramInfo<'tcx> {
/// (which unfortunately typeck does not reject).
/// Not using `FnAbiError` as that contains a nested `LayoutError`.
FnAbiAdjustForForeignAbi(call::AdjustForForeignAbiError),
/// We are runnning into a nonsense situation due to ConstProp violating our invariants.
ConstPropNonsense,
}
/// Details of why a pointer had to be in-bounds.

7
compiler/rustc_mir_transform/src/dataflow_const_prop.rs
View File

@ -403,7 +403,12 @@ impl<'a, 'tcx> ConstAnalysis<'a, 'tcx> {
operand,
&mut |elem, op| match elem {
TrackElem::Field(idx) => self.ecx.project_field(op, idx.as_usize()).ok(),
TrackElem::Variant(idx) => self.ecx.project_downcast(op, idx).ok(),
TrackElem::Variant(idx) => {
if op.layout.for_variant(&self.ecx, idx).abi.is_uninhabited() {
return None;
}
self.ecx.project_downcast(op, idx).ok()
}
TrackElem::Discriminant => {
let variant = self.ecx.read_discriminant(op).ok()?;
let discr_value =