Miri: avoid tracking current location three times

src/librustc_middle/ty/util.rs

@@ -705,6 +705,7 @@ impl<'tcx> ty::TyS<'tcx> {
     /// optimization as well as the rules around static values. Note
     /// that the `Freeze` trait is not exposed to end users and is
     /// effectively an implementation detail.
+    // FIXME: use `TyCtxtAt` instead of separate `Span`.
     pub fn is_freeze(
         &'tcx self,
         tcx: TyCtxt<'tcx>,

src/librustc_mir/const_eval/error.rs

@@ -2,7 +2,7 @@ use std::error::Error;
 use std::fmt;
 
 use rustc_middle::mir::AssertKind;
-use rustc_span::Symbol;
+use rustc_span::{Span, Symbol};
 
 use super::InterpCx;
 use crate::interpret::{ConstEvalErr, InterpErrorInfo, Machine};
@@ -53,8 +53,9 @@ impl Error for ConstEvalErrKind {}
 pub fn error_to_const_error<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>>(
     ecx: &InterpCx<'mir, 'tcx, M>,
     error: InterpErrorInfo<'tcx>,
+    span: Option<Span>,
 ) -> ConstEvalErr<'tcx> {
     error.print_backtrace();
     let stacktrace = ecx.generate_stacktrace();
-    ConstEvalErr { error: error.kind, stacktrace, span: ecx.tcx.span }
+    ConstEvalErr { error: error.kind, stacktrace, span: span.unwrap_or_else(|| ecx.cur_span()) }
 }

src/librustc_mir/const_eval/eval_queries.rs

@@ -27,7 +27,7 @@ fn eval_body_using_ecx<'mir, 'tcx>(
     body: &'mir mir::Body<'tcx>,
 ) -> InterpResult<'tcx, MPlaceTy<'tcx>> {
     debug!("eval_body_using_ecx: {:?}, {:?}", cid, ecx.param_env);
-    let tcx = ecx.tcx.tcx;
+    let tcx = ecx.tcx;
     let layout = ecx.layout_of(body.return_ty().subst(tcx, cid.instance.substs))?;
     assert!(!layout.is_unsized());
     let ret = ecx.allocate(layout, MemoryKind::Stack);
@@ -81,13 +81,14 @@ fn eval_body_using_ecx<'mir, 'tcx>(
 /// parameter. These bounds are passed to `mk_eval_cx` via the `ParamEnv` argument.
 pub(super) fn mk_eval_cx<'mir, 'tcx>(
     tcx: TyCtxt<'tcx>,
-    span: Span,
+    root_span: Span,
     param_env: ty::ParamEnv<'tcx>,
     can_access_statics: bool,
 ) -> CompileTimeEvalContext<'mir, 'tcx> {
     debug!("mk_eval_cx: {:?}", param_env);
     InterpCx::new(
-        tcx.at(span),
+        tcx,
+        root_span,
         param_env,
         CompileTimeInterpreter::new(tcx.sess.const_eval_limit()),
         MemoryExtra { can_access_statics },
@@ -163,7 +164,7 @@ pub(super) fn op_to_const<'tcx>(
                         0,
                     ),
                 };
-                let len = b.to_machine_usize(&ecx.tcx.tcx).unwrap();
+                let len = b.to_machine_usize(ecx).unwrap();
                 let start = start.try_into().unwrap();
                 let len: usize = len.try_into().unwrap();
                 ConstValue::Slice { data, start, end: start + len }
@@ -212,8 +213,8 @@ fn validate_and_turn_into_const<'tcx>(
     })();
 
     val.map_err(|error| {
-        let err = error_to_const_error(&ecx, error);
-        err.struct_error(ecx.tcx, "it is undefined behavior to use this value", |mut diag| {
+        let err = error_to_const_error(&ecx, error, None);
+        err.struct_error(ecx.tcx_at(), "it is undefined behavior to use this value", |mut diag| {
             diag.note(note_on_undefined_behavior_error());
             diag.emit();
         })
@@ -299,9 +300,9 @@ pub fn const_eval_raw_provider<'tcx>(
 
     let is_static = tcx.is_static(def_id);
 
-    let span = tcx.def_span(cid.instance.def_id());
     let mut ecx = InterpCx::new(
-        tcx.at(span),
+        tcx,
+        tcx.def_span(cid.instance.def_id()),
         key.param_env,
         CompileTimeInterpreter::new(tcx.sess.const_eval_limit()),
         MemoryExtra { can_access_statics: is_static },
@@ -311,12 +312,15 @@ pub fn const_eval_raw_provider<'tcx>(
     res.and_then(|body| eval_body_using_ecx(&mut ecx, cid, &body))
         .map(|place| RawConst { alloc_id: place.ptr.assert_ptr().alloc_id, ty: place.layout.ty })
         .map_err(|error| {
-            let err = error_to_const_error(&ecx, error);
+            let err = error_to_const_error(&ecx, error, None);
             // errors in statics are always emitted as fatal errors
             if is_static {
                 // Ensure that if the above error was either `TooGeneric` or `Reported`
                 // an error must be reported.
-                let v = err.report_as_error(ecx.tcx, "could not evaluate static initializer");
+                let v = err.report_as_error(
+                    ecx.tcx.at(ecx.cur_span()),
+                    "could not evaluate static initializer",
+                );
 
                 // If this is `Reveal:All`, then we need to make sure an error is reported but if
                 // this is `Reveal::UserFacing`, then it's expected that we could get a
@@ -372,13 +376,16 @@ pub fn const_eval_raw_provider<'tcx>(
                         // anything else (array lengths, enum initializers, constant patterns) are
                         // reported as hard errors
                         } else {
-                            err.report_as_error(ecx.tcx, "evaluation of constant value failed")
+                            err.report_as_error(
+                                ecx.tcx.at(ecx.cur_span()),
+                                "evaluation of constant value failed",
+                            )
                         }
                     }
                 }
             } else {
                 // use of broken constant from other crate
-                err.report_as_error(ecx.tcx, "could not evaluate constant")
+                err.report_as_error(ecx.tcx.at(ecx.cur_span()), "could not evaluate constant")
             }
         })
 }

src/librustc_mir/interpret/cast.rs

@@ -56,7 +56,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                         }
 
                         let instance = ty::Instance::resolve_for_fn_ptr(
-                            *self.tcx,
+                            self.tcx,
                             self.param_env,
                             def_id,
                             substs,
@@ -91,7 +91,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                         }
 
                         let instance = ty::Instance::resolve_closure(
-                            *self.tcx,
+                            self.tcx,
                             def_id,
                             substs,
                             ty::ClosureKind::FnOnce,
@@ -140,7 +140,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         // Handle cast from a univariant (ZST) enum.
         match src.layout.variants {
             Variants::Single { index } => {
-                if let Some(discr) = src.layout.ty.discriminant_for_variant(*self.tcx, index) {
+                if let Some(discr) = src.layout.ty.discriminant_for_variant(self.tcx, index) {
                     assert!(src.layout.is_zst());
                     let discr_layout = self.layout_of(discr.ty)?;
                     return Ok(self.cast_from_scalar(discr.val, discr_layout, cast_ty).into());
@@ -268,11 +268,8 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             (&ty::Array(_, length), &ty::Slice(_)) => {
                 let ptr = self.read_immediate(src)?.to_scalar()?;
                 // u64 cast is from usize to u64, which is always good
-                let val = Immediate::new_slice(
-                    ptr,
-                    length.eval_usize(self.tcx.tcx, self.param_env),
-                    self,
-                );
+                let val =
+                    Immediate::new_slice(ptr, length.eval_usize(self.tcx, self.param_env), self);
                 self.write_immediate(val, dest)
             }
             (&ty::Dynamic(..), &ty::Dynamic(..)) => {

src/librustc_mir/interpret/eval_context.rs

@@ -33,7 +33,11 @@ pub struct InterpCx<'mir, 'tcx, M: Machine<'mir, 'tcx>> {
     pub machine: M,
 
     /// The results of the type checker, from rustc.
-    pub tcx: TyCtxtAt<'tcx>,
+    pub tcx: TyCtxt<'tcx>,
+
+    /// The span of the "root" of the evaluation, i.e., the const
+    /// we are evaluating (if this is CTFE).
+    pub(super) root_span: Span,
 
     /// Bounds in scope for polymorphic evaluations.
     pub(crate) param_env: ty::ParamEnv<'tcx>,
@@ -196,7 +200,7 @@ where
 {
     #[inline]
     fn tcx(&self) -> TyCtxt<'tcx> {
-        *self.tcx
+        self.tcx
     }
 }
 
@@ -209,13 +213,13 @@ where
     }
 }
 
-impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> LayoutOf for InterpCx<'mir, 'tcx, M> {
+impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> LayoutOf for InterpCx<'mir, 'tcx, M> {
     type Ty = Ty<'tcx>;
     type TyAndLayout = InterpResult<'tcx, TyAndLayout<'tcx>>;
 
     #[inline]
     fn layout_of(&self, ty: Ty<'tcx>) -> Self::TyAndLayout {
-        self.tcx
+        self.tcx_at()
             .layout_of(self.param_env.and(ty))
             .map_err(|layout| err_inval!(Layout(layout)).into())
     }
@@ -292,24 +296,36 @@ pub(super) fn from_known_layout<'tcx>(
 
 impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
     pub fn new(
-        tcx: TyCtxtAt<'tcx>,
+        tcx: TyCtxt<'tcx>,
+        root_span: Span,
         param_env: ty::ParamEnv<'tcx>,
         machine: M,
         memory_extra: M::MemoryExtra,
     ) -> Self {
         InterpCx {
             machine,
             tcx,
+            root_span,
             param_env,
             memory: Memory::new(tcx, memory_extra),
             vtables: FxHashMap::default(),
         }
     }
 
     #[inline(always)]
-    pub fn set_span(&mut self, span: Span) {
-        self.tcx.span = span;
-        self.memory.tcx.span = span;
+    pub fn cur_span(&self) -> Span {
+        self.stack()
+            .last()
+            .and_then(|f| f.current_source_info())
+            .map(|si| si.span)
+            .unwrap_or(self.root_span)
+    }
+
+    #[inline(always)]
+    pub fn tcx_at(&self) -> TyCtxtAt<'tcx> {
+        // Computing the current span has a non-trivial cost, and for cycle errors
+        // the "root span" is good enough.
+        self.tcx.at(self.root_span)
     }
 
     #[inline(always)]
@@ -387,12 +403,12 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
 
     #[inline]
     pub fn type_is_sized(&self, ty: Ty<'tcx>) -> bool {
-        ty.is_sized(self.tcx, self.param_env)
+        ty.is_sized(self.tcx_at(), self.param_env)
     }
 
     #[inline]
     pub fn type_is_freeze(&self, ty: Ty<'tcx>) -> bool {
-        ty.is_freeze(*self.tcx, self.param_env, DUMMY_SP)
+        ty.is_freeze(self.tcx, self.param_env, self.root_span)
     }
 
     pub fn load_mir(
@@ -403,20 +419,21 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         // do not continue if typeck errors occurred (can only occur in local crate)
         let did = instance.def_id();
         if let Some(did) = did.as_local() {
-            if self.tcx.has_typeck_tables(did) {
-                if let Some(error_reported) = self.tcx.typeck_tables_of(did).tainted_by_errors {
+            if self.tcx_at().has_typeck_tables(did) {
+                if let Some(error_reported) = self.tcx_at().typeck_tables_of(did).tainted_by_errors
+                {
                     throw_inval!(TypeckError(error_reported))
                 }
             }
         }
         trace!("load mir(instance={:?}, promoted={:?})", instance, promoted);
         if let Some(promoted) = promoted {
-            return Ok(&self.tcx.promoted_mir(did)[promoted]);
+            return Ok(&self.tcx_at().promoted_mir(did)[promoted]);
         }
         match instance {
             ty::InstanceDef::Item(def_id) => {
-                if self.tcx.is_mir_available(did) {
-                    Ok(self.tcx.optimized_mir(did))
+                if self.tcx_at().is_mir_available(did) {
+                    Ok(self.tcx_at().optimized_mir(did))
                 } else {
                     throw_unsup!(NoMirFor(def_id))
                 }
@@ -457,7 +474,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         trace!("resolve: {:?}, {:#?}", def_id, substs);
         trace!("param_env: {:#?}", self.param_env);
         trace!("substs: {:#?}", substs);
-        match ty::Instance::resolve(*self.tcx, self.param_env, def_id, substs) {
+        match ty::Instance::resolve(self.tcx, self.param_env, def_id, substs) {
             Ok(Some(instance)) => Ok(instance),
             Ok(None) => throw_inval!(TooGeneric),
 
@@ -476,7 +493,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         // have to support that case (mostly by skipping all caching).
         match frame.locals.get(local).and_then(|state| state.layout.get()) {
             None => {
-                let layout = from_known_layout(self.tcx, layout, || {
+                let layout = from_known_layout(self.tcx_at(), layout, || {
                     let local_ty = frame.body.local_decls[local].ty;
                     let local_ty =
                         self.subst_from_frame_and_normalize_erasing_regions(frame, local_ty);
@@ -561,7 +578,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 let size = size.align_to(align);
 
                 // Check if this brought us over the size limit.
-                if size.bytes() >= self.tcx.data_layout().obj_size_bound() {
+                if size.bytes() >= self.tcx.data_layout.obj_size_bound() {
                     throw_ub!(InvalidMeta("total size is bigger than largest supported object"));
                 }
                 Ok(Some((size, align)))
@@ -577,7 +594,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 let elem = layout.field(self, 0)?;
 
                 // Make sure the slice is not too big.
-                let size = elem.size.checked_mul(len, &*self.tcx).ok_or_else(|| {
+                let size = elem.size.checked_mul(len, self).ok_or_else(|| {
                     err_ub!(InvalidMeta("slice is bigger than largest supported object"))
                 })?;
                 Ok(Some((size, elem.align.abi)))
@@ -628,7 +645,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         let mut locals = IndexVec::from_elem(dummy, &body.local_decls);
 
         // Now mark those locals as dead that we do not want to initialize
-        match self.tcx.def_kind(instance.def_id()) {
+        match self.tcx_at().def_kind(instance.def_id()) {
             // statics and constants don't have `Storage*` statements, no need to look for them
             //
             // FIXME: The above is likely untrue. See
@@ -843,7 +860,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         } else {
             self.param_env
         };
-        let val = self.tcx.const_eval_global_id(param_env, gid, Some(self.tcx.span))?;
+        let val = self.tcx.const_eval_global_id(param_env, gid, Some(self.cur_span()))?;
 
         // Even though `ecx.const_eval` is called from `eval_const_to_op` we can never have a
         // recursion deeper than one level, because the `tcx.const_eval` above is guaranteed to not
@@ -874,7 +891,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         // FIXME: We can hit delay_span_bug if this is an invalid const, interning finds
         // that problem, but we never run validation to show an error. Can we ensure
         // this does not happen?
-        let val = self.tcx.const_eval_raw(param_env.and(gid))?;
+        let val = self.tcx.at(self.cur_span()).const_eval_raw(param_env.and(gid))?;
         self.raw_const_to_mplace(val)
     }