Rollup of 10 pull requests

compiler/rustc_codegen_cranelift/src/constant.rs

@@ -71,7 +71,7 @@ pub(crate) fn eval_mir_constant<'tcx>(
     // This cannot fail because we checked all required_consts in advance.
     let val = cv
         .eval(fx.tcx, ty::ParamEnv::reveal_all(), Some(constant.span))
-        .expect("erroneous constant not captured by required_consts");
+        .expect("erroneous constant missed by mono item collection");
     (val, cv.ty())
 }
 

compiler/rustc_codegen_ssa/src/mir/constant.rs

@@ -21,11 +21,11 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
     }
 
     pub fn eval_mir_constant(&self, constant: &mir::ConstOperand<'tcx>) -> mir::ConstValue<'tcx> {
-        // `MirUsedCollector` visited all constants before codegen began, so if we got here there
-        // can be no more constants that fail to evaluate.
+        // `MirUsedCollector` visited all required_consts before codegen began, so if we got here
+        // there can be no more constants that fail to evaluate.
         self.monomorphize(constant.const_)
             .eval(self.cx.tcx(), ty::ParamEnv::reveal_all(), Some(constant.span))
-            .expect("erroneous constant not captured by required_consts")
+            .expect("erroneous constant missed by mono item collection")
     }
 
     /// This is a convenience helper for `simd_shuffle_indices`. It has the precondition

compiler/rustc_codegen_ssa/src/mir/mod.rs

@@ -211,7 +211,8 @@ pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
 
     // It may seem like we should iterate over `required_consts` to ensure they all successfully
     // evaluate; however, the `MirUsedCollector` already did that during the collection phase of
-    // monomorphization so we don't have to do it again.
+    // monomorphization, and if there is an error during collection then codegen never starts -- so
+    // we don't have to do it again.
 
     fx.per_local_var_debug_info = fx.compute_per_local_var_debug_info(&mut start_bx);
 

compiler/rustc_const_eval/messages.ftl

@@ -374,12 +374,6 @@ const_eval_unallowed_op_in_const_context =
 const_eval_unavailable_target_features_for_fn =
     calling a function that requires unavailable target features: {$unavailable_feats}
 
-const_eval_undefined_behavior =
-    it is undefined behavior to use this value
-
-const_eval_undefined_behavior_note =
-    The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-
 const_eval_uninhabited_enum_variant_read =
     read discriminant of an uninhabited enum variant
 const_eval_uninhabited_enum_variant_written =
@@ -434,6 +428,12 @@ const_eval_validation_expected_raw_ptr = expected a raw pointer
 const_eval_validation_expected_ref = expected a reference
 const_eval_validation_expected_str = expected a string
 
+const_eval_validation_failure =
+    it is undefined behavior to use this value
+
+const_eval_validation_failure_note =
+    The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
+
 const_eval_validation_front_matter_invalid_value = constructing invalid value
 const_eval_validation_front_matter_invalid_value_with_path = constructing invalid value at {$path}
 

compiler/rustc_const_eval/src/const_eval/error.rs

@@ -2,15 +2,16 @@ use std::mem;
 
 use rustc_errors::{DiagArgName, DiagArgValue, DiagMessage, Diagnostic, IntoDiagArg};
 use rustc_hir::CRATE_HIR_ID;
+use rustc_middle::mir::interpret::Provenance;
 use rustc_middle::mir::AssertKind;
 use rustc_middle::query::TyCtxtAt;
 use rustc_middle::ty::TyCtxt;
 use rustc_middle::ty::{layout::LayoutError, ConstInt};
 use rustc_span::{Span, Symbol, DUMMY_SP};
 
-use super::{CompileTimeInterpreter, InterpCx};
+use super::CompileTimeInterpreter;
 use crate::errors::{self, FrameNote, ReportErrorExt};
-use crate::interpret::{ErrorHandled, InterpError, InterpErrorInfo, MachineStopType};
+use crate::interpret::{ErrorHandled, Frame, InterpError, InterpErrorInfo, MachineStopType};
 
 /// The CTFE machine has some custom error kinds.
 #[derive(Clone, Debug)]
@@ -58,15 +59,12 @@ impl<'tcx> Into<InterpErrorInfo<'tcx>> for ConstEvalErrKind {
 
 pub fn get_span_and_frames<'tcx, 'mir>(
     tcx: TyCtxtAt<'tcx>,
-    machine: &CompileTimeInterpreter<'mir, 'tcx>,
+    stack: &[Frame<'mir, 'tcx, impl Provenance, impl Sized>],
 ) -> (Span, Vec<errors::FrameNote>)
 where
     'tcx: 'mir,
 {
-    let mut stacktrace =
-        InterpCx::<CompileTimeInterpreter<'mir, 'tcx>>::generate_stacktrace_from_stack(
-            &machine.stack,
-        );
+    let mut stacktrace = Frame::generate_stacktrace_from_stack(stack);
     // Filter out `requires_caller_location` frames.
     stacktrace.retain(|frame| !frame.instance.def.requires_caller_location(*tcx));
     let span = stacktrace.first().map(|f| f.span).unwrap_or(tcx.span);
@@ -170,7 +168,7 @@ pub(super) fn lint<'tcx, 'mir, L>(
 ) where
     L: for<'a> rustc_errors::LintDiagnostic<'a, ()>,
 {
-    let (span, frames) = get_span_and_frames(tcx, machine);
+    let (span, frames) = get_span_and_frames(tcx, &machine.stack);
 
     tcx.emit_node_span_lint(
         lint,

compiler/rustc_const_eval/src/const_eval/eval_queries.rs

@@ -18,18 +18,18 @@ use crate::errors;
 use crate::errors::ConstEvalError;
 use crate::interpret::eval_nullary_intrinsic;
 use crate::interpret::{
-    create_static_alloc, intern_const_alloc_recursive, take_static_root_alloc, CtfeValidationMode,
-    GlobalId, Immediate, InternKind, InterpCx, InterpError, InterpResult, MPlaceTy, MemoryKind,
-    OpTy, RefTracking, StackPopCleanup,
+    create_static_alloc, intern_const_alloc_recursive, CtfeValidationMode, GlobalId, Immediate,
+    InternKind, InterpCx, InterpError, InterpResult, MPlaceTy, MemoryKind, OpTy, RefTracking,
+    StackPopCleanup,
 };
 
 // Returns a pointer to where the result lives
-#[instrument(level = "trace", skip(ecx, body), ret)]
-fn eval_body_using_ecx<'mir, 'tcx>(
+#[instrument(level = "trace", skip(ecx, body))]
+fn eval_body_using_ecx<'mir, 'tcx, R: InterpretationResult<'tcx>>(
     ecx: &mut CompileTimeEvalContext<'mir, 'tcx>,
     cid: GlobalId<'tcx>,
     body: &'mir mir::Body<'tcx>,
-) -> InterpResult<'tcx, MPlaceTy<'tcx>> {
+) -> InterpResult<'tcx, R> {
     trace!(?ecx.param_env);
     let tcx = *ecx.tcx;
     assert!(
@@ -84,7 +84,10 @@ fn eval_body_using_ecx<'mir, 'tcx>(
     // Intern the result
     intern_const_alloc_recursive(ecx, intern_kind, &ret)?;
 
-    Ok(ret)
+    // Since evaluation had no errors, validate the resulting constant.
+    const_validate_mplace(&ecx, &ret, cid)?;
+
+    Ok(R::make_result(ret, ecx))
 }
 
 /// The `InterpCx` is only meant to be used to do field and index projections into constants for
@@ -282,18 +285,26 @@ pub fn eval_static_initializer_provider<'tcx>(
 
     let instance = ty::Instance::mono(tcx, def_id.to_def_id());
     let cid = rustc_middle::mir::interpret::GlobalId { instance, promoted: None };
-    let mut ecx = InterpCx::new(
-        tcx,
-        tcx.def_span(def_id),
-        ty::ParamEnv::reveal_all(),
-        // Statics (and promoteds inside statics) may access other statics, because unlike consts
-        // they do not have to behave "as if" they were evaluated at runtime.
-        CompileTimeInterpreter::new(CanAccessMutGlobal::Yes, CheckAlignment::Error),
-    );
-    let alloc_id = eval_in_interpreter(&mut ecx, cid, true)?.alloc_id;
-    let alloc = take_static_root_alloc(&mut ecx, alloc_id);
-    let alloc = tcx.mk_const_alloc(alloc);
-    Ok(alloc)
+    eval_in_interpreter(tcx, cid, ty::ParamEnv::reveal_all())
+}
+
+pub trait InterpretationResult<'tcx> {
+    /// This function takes the place where the result of the evaluation is stored
+    /// and prepares it for returning it in the appropriate format needed by the specific
+    /// evaluation query.
+    fn make_result<'mir>(
+        mplace: MPlaceTy<'tcx>,
+        ecx: &mut InterpCx<'mir, 'tcx, CompileTimeInterpreter<'mir, 'tcx>>,
+    ) -> Self;
+}
+
+impl<'tcx> InterpretationResult<'tcx> for ConstAlloc<'tcx> {
+    fn make_result<'mir>(
+        mplace: MPlaceTy<'tcx>,
+        _ecx: &mut InterpCx<'mir, 'tcx, CompileTimeInterpreter<'mir, 'tcx>>,
+    ) -> Self {
+        ConstAlloc { alloc_id: mplace.ptr().provenance.unwrap().alloc_id(), ty: mplace.layout.ty }
+    }
 }
 
 #[instrument(skip(tcx), level = "debug")]
@@ -319,92 +330,64 @@ pub fn eval_to_allocation_raw_provider<'tcx>(
         trace!("const eval: {:?} ({})", key, instance);
     }
 
-    let cid = key.value;
+    eval_in_interpreter(tcx, key.value, key.param_env)
+}
+
+fn eval_in_interpreter<'tcx, R: InterpretationResult<'tcx>>(
+    tcx: TyCtxt<'tcx>,
+    cid: GlobalId<'tcx>,
+    param_env: ty::ParamEnv<'tcx>,
+) -> Result<R, ErrorHandled> {
     let def = cid.instance.def.def_id();
     let is_static = tcx.is_static(def);
 
     let mut ecx = InterpCx::new(
         tcx,
         tcx.def_span(def),
-        key.param_env,
+        param_env,
         // Statics (and promoteds inside statics) may access mutable global memory, because unlike consts
         // they do not have to behave "as if" they were evaluated at runtime.
         // For consts however we want to ensure they behave "as if" they were evaluated at runtime,
         // so we have to reject reading mutable global memory.
         CompileTimeInterpreter::new(CanAccessMutGlobal::from(is_static), CheckAlignment::Error),
     );
-    eval_in_interpreter(&mut ecx, cid, is_static)
-}
-
-pub fn eval_in_interpreter<'mir, 'tcx>(
-    ecx: &mut InterpCx<'mir, 'tcx, CompileTimeInterpreter<'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(ecx, cid, body)) {
-        Err(error) => {
-            let (error, backtrace) = error.into_parts();
-            backtrace.print_backtrace();
-
-            let (kind, instance) = if is_static {
-                ("static", String::new())
-            } else {
-                // If the current item has generics, we'd like to enrich the message with the
-                // instance and its args: to show the actual compile-time values, in addition to
-                // the expression, leading to the const eval error.
-                let instance = &cid.instance;
-                if !instance.args.is_empty() {
-                    let instance = with_no_trimmed_paths!(instance.to_string());
-                    ("const_with_path", instance)
-                } else {
-                    ("const", String::new())
-                }
-            };
-
-            Err(super::report(
-                *ecx.tcx,
-                error,
-                None,
-                || super::get_span_and_frames(ecx.tcx, &ecx.machine),
-                |span, frames| ConstEvalError {
-                    span,
-                    error_kind: kind,
-                    instance,
-                    frame_notes: frames,
-                },
-            ))
-        }
-        Ok(mplace) => {
-            // Since evaluation had no errors, validate the resulting constant.
-
-            // Temporarily allow access to the static_root_ids for the purpose of validation.
-            let static_root_ids = ecx.machine.static_root_ids.take();
-            let res = const_validate_mplace(&ecx, &mplace, cid);
-            ecx.machine.static_root_ids = static_root_ids;
-
-            let alloc_id = mplace.ptr().provenance.unwrap().alloc_id();
-
-            // Validation failed, report an error.
-            if let Err(error) = res {
-                Err(const_report_error(&ecx, error, alloc_id))
+    res.and_then(|body| eval_body_using_ecx(&mut ecx, cid, body)).map_err(|error| {
+        let (error, backtrace) = error.into_parts();
+        backtrace.print_backtrace();
+
+        let (kind, instance) = if ecx.tcx.is_static(cid.instance.def_id()) {
+            ("static", String::new())
+        } else {
+            // If the current item has generics, we'd like to enrich the message with the
+            // instance and its args: to show the actual compile-time values, in addition to
+            // the expression, leading to the const eval error.
+            let instance = &cid.instance;
+            if !instance.args.is_empty() {
+                let instance = with_no_trimmed_paths!(instance.to_string());
+                ("const_with_path", instance)
             } else {
-                // Convert to raw constant
-                Ok(ConstAlloc { alloc_id, ty: mplace.layout.ty })
+                ("const", String::new())
             }
-        }
-    }
+        };
+
+        super::report(
+            *ecx.tcx,
+            error,
+            None,
+            || super::get_span_and_frames(ecx.tcx, ecx.stack()),
+            |span, frames| ConstEvalError { span, error_kind: kind, instance, frame_notes: frames },
+        )
+    })
 }
 
 #[inline(always)]
-pub fn const_validate_mplace<'mir, 'tcx>(
+fn const_validate_mplace<'mir, 'tcx>(
     ecx: &InterpCx<'mir, 'tcx, CompileTimeInterpreter<'mir, 'tcx>>,
     mplace: &MPlaceTy<'tcx>,
     cid: GlobalId<'tcx>,
-) -> InterpResult<'tcx> {
+) -> Result<(), ErrorHandled> {
+    let alloc_id = mplace.ptr().provenance.unwrap().alloc_id();
     let mut ref_tracking = RefTracking::new(mplace.clone());
     let mut inner = false;
     while let Some((mplace, path)) = ref_tracking.todo.pop() {
@@ -418,15 +401,18 @@ pub fn const_validate_mplace<'mir, 'tcx>(
                 CtfeValidationMode::Const { allow_immutable_unsafe_cell: !inner }
             }
         };
-        ecx.const_validate_operand(&mplace.into(), path, &mut ref_tracking, mode)?;
+        ecx.const_validate_operand(&mplace.into(), path, &mut ref_tracking, mode)
+            // Instead of just reporting the `InterpError` via the usual machinery, we give a more targetted
+            // error about the validation failure.
+            .map_err(|error| report_validation_error(&ecx, error, alloc_id))?;
         inner = true;
     }
 
     Ok(())
 }
 
 #[inline(always)]
-pub fn const_report_error<'mir, 'tcx>(
+fn report_validation_error<'mir, 'tcx>(
     ecx: &InterpCx<'mir, 'tcx, CompileTimeInterpreter<'mir, 'tcx>>,
     error: InterpErrorInfo<'tcx>,
     alloc_id: AllocId,
@@ -444,7 +430,7 @@ pub fn const_report_error<'mir, 'tcx>(
         *ecx.tcx,
         error,
         None,
-        || crate::const_eval::get_span_and_frames(ecx.tcx, &ecx.machine),
-        move |span, frames| errors::UndefinedBehavior { span, ub_note, frames, raw_bytes },
+        || crate::const_eval::get_span_and_frames(ecx.tcx, ecx.stack()),
+        move |span, frames| errors::ValidationFailure { span, ub_note, frames, raw_bytes },
     )
 }

compiler/rustc_const_eval/src/const_eval/mod.rs

@@ -5,7 +5,7 @@ use rustc_middle::mir::interpret::InterpErrorInfo;
 use rustc_middle::query::TyCtxtAt;
 use rustc_middle::ty::{self, Ty};
 
-use crate::interpret::{format_interp_error, InterpCx};
+use crate::interpret::format_interp_error;
 
 mod error;
 mod eval_queries;

compiler/rustc_const_eval/src/errors.rs

@@ -412,11 +412,11 @@ pub struct NullaryIntrinsicError {
 }
 
 #[derive(Diagnostic)]
-#[diag(const_eval_undefined_behavior, code = E0080)]
-pub struct UndefinedBehavior {
+#[diag(const_eval_validation_failure, code = E0080)]
+pub struct ValidationFailure {
     #[primary_span]
     pub span: Span,
-    #[note(const_eval_undefined_behavior_note)]
+    #[note(const_eval_validation_failure_note)]
     pub ub_note: Option<()>,
     #[subdiagnostic]
     pub frames: Vec<FrameNote>,