const-eval interner: from-scratch rewrite using mutability information from provenance rather than types

Author: RalfJung

compiler/rustc_const_eval/messages.ftl

@@ -46,8 +46,8 @@ const_eval_dangling_int_pointer =
     {$bad_pointer_message}: {$pointer} is a dangling pointer (it has no provenance)
 const_eval_dangling_null_pointer =
     {$bad_pointer_message}: null pointer is a dangling pointer (it has no provenance)
-const_eval_dangling_ptr_in_final = encountered dangling pointer in final constant
 
+const_eval_dangling_ptr_in_final = encountered dangling pointer in final value of {const_eval_intern_kind}
 const_eval_dead_local =
     accessing a dead local variable
 const_eval_dealloc_immutable =
@@ -134,6 +134,14 @@ const_eval_interior_mutable_data_refer =
         This would make multiple uses of a constant to be able to see different values and allow circumventing
         the `Send` and `Sync` requirements for shared mutable data, which is unsound.
 
+const_eval_intern_kind = {$kind ->
+    [static] static
+    [static_mut] mutable static
+    [const] constant
+    [promoted] promoted
+    *[other] {""}
+}
+
 const_eval_invalid_align =
     align has to be a power of 2
 
@@ -205,6 +213,8 @@ const_eval_modified_global =
 const_eval_mut_deref =
     mutation through a reference is not allowed in {const_eval_const_context}s
 
+const_eval_mutable_ptr_in_final = encountered mutable pointer in final value of {const_eval_intern_kind}
+
 const_eval_non_const_fmt_macro_call =
     cannot call non-const formatting macro in {const_eval_const_context}s
 
@@ -392,9 +402,6 @@ const_eval_unstable_in_stable =
     .unstable_sugg = if it is not part of the public API, make this function unstably const
     .bypass_sugg = otherwise `#[rustc_allow_const_fn_unstable]` can be used to bypass stability checks
 
-const_eval_unsupported_untyped_pointer = unsupported untyped pointer in constant
-    .note = memory only reachable via raw pointers is not supported
-
 const_eval_unterminated_c_string =
     reading a null-terminated string starting at {$pointer} with no null found before end of allocation
 
@@ -406,7 +413,6 @@ const_eval_upcast_mismatch =
 
 ## The `front_matter`s here refer to either `const_eval_front_matter_invalid_value` or `const_eval_front_matter_invalid_value_with_path`.
 ## (We'd love to sort this differently to make that more clear but tidy won't let us...)
-const_eval_validation_box_to_mut = {$front_matter}: encountered a box pointing to mutable memory in a constant
 const_eval_validation_box_to_static = {$front_matter}: encountered a box pointing to a static variable in a constant
 const_eval_validation_box_to_uninhabited = {$front_matter}: encountered a box pointing to uninhabited type {$ty}
 const_eval_validation_dangling_box_no_provenance = {$front_matter}: encountered a dangling box ({$pointer} has no provenance)
@@ -441,7 +447,8 @@ const_eval_validation_invalid_fn_ptr = {$front_matter}: encountered {$value}, bu
 const_eval_validation_invalid_ref_meta = {$front_matter}: encountered invalid reference metadata: total size is bigger than largest supported object
 const_eval_validation_invalid_ref_slice_meta = {$front_matter}: encountered invalid reference metadata: slice is bigger than largest supported object
 const_eval_validation_invalid_vtable_ptr = {$front_matter}: encountered {$value}, but expected a vtable pointer
-const_eval_validation_mutable_ref_in_const = {$front_matter}: encountered mutable reference in a `const`
+const_eval_validation_mutable_ref_in_const = {$front_matter}: encountered mutable reference in a `const` or `static`
+const_eval_validation_mutable_ref_to_immutable = {$front_matter}: encountered mutable reference or box pointing to read-only memory
 const_eval_validation_never_val = {$front_matter}: encountered a value of the never type `!`
 const_eval_validation_null_box = {$front_matter}: encountered a null box
 const_eval_validation_null_fn_ptr = {$front_matter}: encountered a null function pointer
@@ -451,15 +458,14 @@ const_eval_validation_out_of_range = {$front_matter}: encountered {$value}, but
 const_eval_validation_partial_pointer = {$front_matter}: encountered a partial pointer or a mix of pointers
 const_eval_validation_pointer_as_int = {$front_matter}: encountered a pointer, but {$expected}
 const_eval_validation_ptr_out_of_range = {$front_matter}: encountered a pointer, but expected something that cannot possibly fail to be {$in_range}
-const_eval_validation_ref_to_mut = {$front_matter}: encountered a reference pointing to mutable memory in a constant
 const_eval_validation_ref_to_static = {$front_matter}: encountered a reference pointing to a static variable in a constant
 const_eval_validation_ref_to_uninhabited = {$front_matter}: encountered a reference pointing to uninhabited type {$ty}
 const_eval_validation_unaligned_box = {$front_matter}: encountered an unaligned box (required {$required_bytes} byte alignment but found {$found_bytes})
 const_eval_validation_unaligned_ref = {$front_matter}: encountered an unaligned reference (required {$required_bytes} byte alignment but found {$found_bytes})
 const_eval_validation_uninhabited_enum_variant = {$front_matter}: encountered an uninhabited enum variant
 const_eval_validation_uninhabited_val = {$front_matter}: encountered a value of uninhabited type `{$ty}`
 const_eval_validation_uninit = {$front_matter}: encountered uninitialized memory, but {$expected}
-const_eval_validation_unsafe_cell = {$front_matter}: encountered `UnsafeCell` in a `const`
+const_eval_validation_unsafe_cell = {$front_matter}: encountered `UnsafeCell` in read-only memory
 
 const_eval_write_through_immutable_pointer =
     writing through a pointer that was derived from a shared (immutable) reference

compiler/rustc_const_eval/src/const_eval/eval_queries.rs

@@ -293,6 +293,9 @@ pub fn eval_in_interpreter<'mir, 'tcx>(
     cid: GlobalId<'tcx>,
     is_static: bool,
 ) -> ::rustc_middle::mir::interpret::EvalToAllocationRawResult<'tcx> {
+    // `is_static` just means "in static", it could still be a promoted!
+    debug_assert_eq!(is_static, ecx.tcx.static_mutability(cid.instance.def_id()).is_some());
+
     let res = ecx.load_mir(cid.instance.def, cid.promoted);
     match res.and_then(|body| eval_body_using_ecx(&mut ecx, cid, body)) {
         Err(error) => {
@@ -330,8 +333,7 @@ pub fn eval_in_interpreter<'mir, 'tcx>(
         Ok(mplace) => {
             // Since evaluation had no errors, validate the resulting constant.
             // This is a separate `try` block to provide more targeted error reporting.
-            let validation =
-                const_validate_mplace(&ecx, &mplace, is_static, cid.promoted.is_some());
+            let validation = const_validate_mplace(&ecx, &mplace, cid);
 
             let alloc_id = mplace.ptr().provenance.unwrap().alloc_id();
 
@@ -350,22 +352,26 @@ pub fn eval_in_interpreter<'mir, 'tcx>(
 pub fn const_validate_mplace<'mir, 'tcx>(
     ecx: &InterpCx<'mir, 'tcx, CompileTimeInterpreter<'mir, 'tcx>>,
     mplace: &MPlaceTy<'tcx>,
-    is_static: bool,
-    is_promoted: bool,
+    cid: GlobalId<'tcx>,
 ) -> InterpResult<'tcx> {
     let mut ref_tracking = RefTracking::new(mplace.clone());
     let mut inner = false;
     while let Some((mplace, path)) = ref_tracking.todo.pop() {
-        let mode = if is_static {
-            if is_promoted {
-                // Promoteds in statics are allowed to point to statics.
-                CtfeValidationMode::Const { inner, allow_static_ptrs: true }
-            } else {
-                // a `static`
-                CtfeValidationMode::Regular
+        let mode = match ecx.tcx.static_mutability(cid.instance.def_id()) {
+            Some(_) if cid.promoted.is_some() => {
+                // Promoteds in statics are consts that re allowed to point to statics.
+                CtfeValidationMode::Const {
+                    allow_immutable_unsafe_cell: false,
+                    allow_static_ptrs: true,
+                }
+            }
+            Some(mutbl) => CtfeValidationMode::Static { mutbl }, // a `static`
+            None => {
+                // In normal `const` (not promoted), the outermost allocation is always only copied,
+                // so having `UnsafeCell` in there is okay despite them being in immutable memory.
+                let allow_immutable_unsafe_cell = cid.promoted.is_none() && !inner;
+                CtfeValidationMode::Const { allow_immutable_unsafe_cell, allow_static_ptrs: false }
             }
-        } else {
-            CtfeValidationMode::Const { inner, allow_static_ptrs: false }
         };
         ecx.const_validate_operand(&mplace.into(), path, &mut ref_tracking, mode)?;
         inner = true;

compiler/rustc_const_eval/src/const_eval/machine.rs

@@ -723,7 +723,7 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
             && ty.is_freeze(*ecx.tcx, ecx.param_env)
         {
             let place = ecx.ref_to_mplace(val)?;
-            let new_place = place.map_provenance(|p| p.map(CtfeProvenance::as_immutable));
+            let new_place = place.map_provenance(CtfeProvenance::as_immutable);
             Ok(ImmTy::from_immediate(new_place.to_ref(ecx), val.layout))
         } else {
             Ok(val.clone())

compiler/rustc_const_eval/src/errors.rs

@@ -1,3 +1,5 @@
+use std::borrow::Cow;
+
 use rustc_errors::{
     DiagCtxt, DiagnosticArgValue, DiagnosticBuilder, DiagnosticMessage, EmissionGuarantee,
     IntoDiagnostic, Level,
@@ -13,12 +15,24 @@ use rustc_middle::ty::{self, Ty};
 use rustc_span::Span;
 use rustc_target::abi::call::AdjustForForeignAbiError;
 use rustc_target::abi::{Size, WrappingRange};
+use rustc_type_ir::Mutability;
+
+use crate::interpret::InternKind;
 
 #[derive(Diagnostic)]
 #[diag(const_eval_dangling_ptr_in_final)]
 pub(crate) struct DanglingPtrInFinal {
     #[primary_span]
     pub span: Span,
+    pub kind: InternKind,
+}
+
+#[derive(Diagnostic)]
+#[diag(const_eval_mutable_ptr_in_final)]
+pub(crate) struct MutablePtrInFinal {
+    #[primary_span]
+    pub span: Span,
+    pub kind: InternKind,
 }
 
 #[derive(Diagnostic)]
@@ -194,14 +208,6 @@ pub(crate) struct UnallowedInlineAsm {
     pub kind: ConstContext,
 }
 
-#[derive(Diagnostic)]
-#[diag(const_eval_unsupported_untyped_pointer)]
-#[note]
-pub(crate) struct UnsupportedUntypedPointer {
-    #[primary_span]
-    pub span: Span,
-}
-
 #[derive(Diagnostic)]
 #[diag(const_eval_interior_mutable_data_refer, code = "E0492")]
 pub(crate) struct InteriorMutableDataRefer {
@@ -615,18 +621,16 @@ impl<'tcx> ReportErrorExt for ValidationErrorInfo<'tcx> {
             PtrToStatic { ptr_kind: PointerKind::Box } => const_eval_validation_box_to_static,
             PtrToStatic { ptr_kind: PointerKind::Ref } => const_eval_validation_ref_to_static,
 
-            PtrToMut { ptr_kind: PointerKind::Box } => const_eval_validation_box_to_mut,
-            PtrToMut { ptr_kind: PointerKind::Ref } => const_eval_validation_ref_to_mut,
-
             PointerAsInt { .. } => const_eval_validation_pointer_as_int,
             PartialPointer => const_eval_validation_partial_pointer,
             MutableRefInConst => const_eval_validation_mutable_ref_in_const,
+            MutableRefToImmutable => const_eval_validation_mutable_ref_to_immutable,
             NullFnPtr => const_eval_validation_null_fn_ptr,
             NeverVal => const_eval_validation_never_val,
             NullablePtrOutOfRange { .. } => const_eval_validation_nullable_ptr_out_of_range,
             PtrOutOfRange { .. } => const_eval_validation_ptr_out_of_range,
             OutOfRange { .. } => const_eval_validation_out_of_range,
-            UnsafeCell => const_eval_validation_unsafe_cell,
+            UnsafeCellInImmutable => const_eval_validation_unsafe_cell,
             UninhabitedVal { .. } => const_eval_validation_uninhabited_val,
             InvalidEnumTag { .. } => const_eval_validation_invalid_enum_tag,
             UninhabitedEnumVariant => const_eval_validation_uninhabited_enum_variant,
@@ -772,11 +776,11 @@ impl<'tcx> ReportErrorExt for ValidationErrorInfo<'tcx> {
             }
             NullPtr { .. }
             | PtrToStatic { .. }
-            | PtrToMut { .. }
             | MutableRefInConst
+            | MutableRefToImmutable
             | NullFnPtr
             | NeverVal
-            | UnsafeCell
+            | UnsafeCellInImmutable
             | InvalidMetaSliceTooLarge { .. }
             | InvalidMetaTooLarge { .. }
             | DanglingPtrUseAfterFree { .. }
@@ -905,3 +909,14 @@ impl ReportErrorExt for ResourceExhaustionInfo {
     }
     fn add_args<G: EmissionGuarantee>(self, _: &DiagCtxt, _: &mut DiagnosticBuilder<'_, G>) {}
 }
+
+impl rustc_errors::IntoDiagnosticArg for InternKind {
+    fn into_diagnostic_arg(self) -> DiagnosticArgValue<'static> {
+        DiagnosticArgValue::Str(Cow::Borrowed(match self {
+            InternKind::Static(Mutability::Not) => "static",
+            InternKind::Static(Mutability::Mut) => "static_mut",
+            InternKind::Constant => "const",
+            InternKind::Promoted => "promoted",
+        }))
+    }
+}