Rollup merge of #71198 - oli-obk:const_check_cleanup, r=RalfJung

Const check/promotion cleanup and sanity assertion

r? @RalfJung

This is just the part of https://github.com/rust-lang/rust/pull/70042#issuecomment-614592765 that does not change behaviour

src/librustc_mir/borrow_check/type_check/mod.rs

@@ -42,7 +42,10 @@ use rustc_trait_selection::traits::{self, ObligationCause, PredicateObligations}
 use crate::dataflow::move_paths::MoveData;
 use crate::dataflow::MaybeInitializedPlaces;
 use crate::dataflow::ResultsCursor;
-use crate::transform::promote_consts::should_suggest_const_in_array_repeat_expressions_attribute;
+use crate::transform::{
+    check_consts::ConstCx,
+    promote_consts::should_suggest_const_in_array_repeat_expressions_attribute,
+};
 
 use crate::borrow_check::{
     borrow_set::BorrowSet,
@@ -1984,14 +1987,17 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                         let span = body.source_info(location).span;
                         let ty = operand.ty(body, tcx);
                         if !self.infcx.type_is_copy_modulo_regions(self.param_env, ty, span) {
+                            let ccx = ConstCx::new_with_param_env(
+                                tcx,
+                                self.mir_def_id,
+                                body,
+                                self.param_env,
+                            );
                             // To determine if `const_in_array_repeat_expressions` feature gate should
                             // be mentioned, need to check if the rvalue is promotable.
                             let should_suggest =
                                 should_suggest_const_in_array_repeat_expressions_attribute(
-                                    tcx,
-                                    self.mir_def_id,
-                                    body,
-                                    operand,
+                                    &ccx, operand,
                                 );
                             debug!("check_rvalue: should_suggest={:?}", should_suggest);
 

src/librustc_mir/transform/check_consts/mod.rs

@@ -20,7 +20,7 @@ pub mod validation;
 
 /// Information about the item currently being const-checked, as well as a reference to the global
 /// context.
-pub struct Item<'mir, 'tcx> {
+pub struct ConstCx<'mir, 'tcx> {
     pub body: &'mir mir::Body<'tcx>,
     pub tcx: TyCtxt<'tcx>,
     pub def_id: DefId,
@@ -28,12 +28,21 @@ pub struct Item<'mir, 'tcx> {
     pub const_kind: Option<ConstKind>,
 }
 
-impl Item<'mir, 'tcx> {
+impl ConstCx<'mir, 'tcx> {
     pub fn new(tcx: TyCtxt<'tcx>, def_id: DefId, body: &'mir mir::Body<'tcx>) -> Self {
         let param_env = tcx.param_env(def_id);
+        Self::new_with_param_env(tcx, def_id, body, param_env)
+    }
+
+    pub fn new_with_param_env(
+        tcx: TyCtxt<'tcx>,
+        def_id: DefId,
+        body: &'mir mir::Body<'tcx>,
+        param_env: ty::ParamEnv<'tcx>,
+    ) -> Self {
         let const_kind = ConstKind::for_item(tcx, def_id);
 
-        Item { body, tcx, def_id, param_env, const_kind }
+        ConstCx { body, tcx, def_id, param_env, const_kind }
     }
 
     /// Returns the kind of const context this `Item` represents (`const`, `static`, etc.).

src/librustc_mir/transform/check_consts/ops.rs

@@ -7,7 +7,7 @@ use rustc_session::parse::feature_err;
 use rustc_span::symbol::sym;
 use rustc_span::{Span, Symbol};
 
-use super::{ConstKind, Item};
+use super::{ConstCx, ConstKind};
 
 /// An operation that is not *always* allowed in a const context.
 pub trait NonConstOp: std::fmt::Debug {
@@ -27,19 +27,19 @@ pub trait NonConstOp: std::fmt::Debug {
     ///
     /// By default, it returns `true` if and only if this operation has a corresponding feature
     /// gate and that gate is enabled.
-    fn is_allowed_in_item(&self, item: &Item<'_, '_>) -> bool {
-        Self::feature_gate().map_or(false, |gate| item.tcx.features().enabled(gate))
+    fn is_allowed_in_item(&self, ccx: &ConstCx<'_, '_>) -> bool {
+        Self::feature_gate().map_or(false, |gate| ccx.tcx.features().enabled(gate))
     }
 
-    fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
+    fn emit_error(&self, ccx: &ConstCx<'_, '_>, span: Span) {
         let mut err = struct_span_err!(
-            item.tcx.sess,
+            ccx.tcx.sess,
             span,
             E0019,
             "{} contains unimplemented expression type",
-            item.const_kind()
+            ccx.const_kind()
         );
-        if item.tcx.sess.teach(&err.get_code().unwrap()) {
+        if ccx.tcx.sess.teach(&err.get_code().unwrap()) {
             err.note(
                 "A function call isn't allowed in the const's initialization expression \
                       because the expression's value must be known at compile-time.",
@@ -66,9 +66,9 @@ impl NonConstOp for Downcast {
 #[derive(Debug)]
 pub struct FnCallIndirect;
 impl NonConstOp for FnCallIndirect {
-    fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
+    fn emit_error(&self, ccx: &ConstCx<'_, '_>, span: Span) {
         let mut err =
-            item.tcx.sess.struct_span_err(span, "function pointers are not allowed in const fn");
+            ccx.tcx.sess.struct_span_err(span, "function pointers are not allowed in const fn");
         err.emit();
     }
 }
@@ -77,14 +77,14 @@ impl NonConstOp for FnCallIndirect {
 #[derive(Debug)]
 pub struct FnCallNonConst(pub DefId);
 impl NonConstOp for FnCallNonConst {
-    fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
+    fn emit_error(&self, ccx: &ConstCx<'_, '_>, span: Span) {
         let mut err = struct_span_err!(
-            item.tcx.sess,
+            ccx.tcx.sess,
             span,
             E0015,
             "calls in {}s are limited to constant functions, \
              tuple structs and tuple variants",
-            item.const_kind(),
+            ccx.const_kind(),
         );
         err.emit();
     }
@@ -96,12 +96,12 @@ impl NonConstOp for FnCallNonConst {
 #[derive(Debug)]
 pub struct FnCallUnstable(pub DefId, pub Symbol);
 impl NonConstOp for FnCallUnstable {
-    fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
+    fn emit_error(&self, ccx: &ConstCx<'_, '_>, span: Span) {
         let FnCallUnstable(def_id, feature) = *self;
 
-        let mut err = item.tcx.sess.struct_span_err(
+        let mut err = ccx.tcx.sess.struct_span_err(
             span,
-            &format!("`{}` is not yet stable as a const fn", item.tcx.def_path_str(def_id)),
+            &format!("`{}` is not yet stable as a const fn", ccx.tcx.def_path_str(def_id)),
         );
         if nightly_options::is_nightly_build() {
             err.help(&format!("add `#![feature({})]` to the crate attributes to enable", feature));
@@ -113,16 +113,16 @@ impl NonConstOp for FnCallUnstable {
 #[derive(Debug)]
 pub struct HeapAllocation;
 impl NonConstOp for HeapAllocation {
-    fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
+    fn emit_error(&self, ccx: &ConstCx<'_, '_>, span: Span) {
         let mut err = struct_span_err!(
-            item.tcx.sess,
+            ccx.tcx.sess,
             span,
             E0010,
             "allocations are not allowed in {}s",
-            item.const_kind()
+            ccx.const_kind()
         );
-        err.span_label(span, format!("allocation not allowed in {}s", item.const_kind()));
-        if item.tcx.sess.teach(&err.get_code().unwrap()) {
+        err.span_label(span, format!("allocation not allowed in {}s", ccx.const_kind()));
+        if ccx.tcx.sess.teach(&err.get_code().unwrap()) {
             err.note(
                 "The value of statics and constants must be known at compile time, \
                  and they live for the entire lifetime of a program. Creating a boxed \
@@ -141,9 +141,9 @@ impl NonConstOp for IfOrMatch {
         Some(sym::const_if_match)
     }
 
-    fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
+    fn emit_error(&self, ccx: &ConstCx<'_, '_>, span: Span) {
         // This should be caught by the HIR const-checker.
-        item.tcx.sess.delay_span_bug(span, "complex control flow is forbidden in a const context");
+        ccx.tcx.sess.delay_span_bug(span, "complex control flow is forbidden in a const context");
     }
 }
 
@@ -154,14 +154,14 @@ impl NonConstOp for InlineAsm {}
 #[derive(Debug)]
 pub struct LiveDrop;
 impl NonConstOp for LiveDrop {
-    fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
+    fn emit_error(&self, ccx: &ConstCx<'_, '_>, span: Span) {
         struct_span_err!(
-            item.tcx.sess,
+            ccx.tcx.sess,
             span,
             E0493,
             "destructors cannot be evaluated at compile-time"
         )
-        .span_label(span, format!("{}s cannot evaluate destructors", item.const_kind()))
+        .span_label(span, format!("{}s cannot evaluate destructors", ccx.const_kind()))
         .emit();
     }
 }
@@ -173,18 +173,18 @@ impl NonConstOp for Loop {
         Some(sym::const_loop)
     }
 
-    fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
+    fn emit_error(&self, ccx: &ConstCx<'_, '_>, span: Span) {
         // This should be caught by the HIR const-checker.
-        item.tcx.sess.delay_span_bug(span, "complex control flow is forbidden in a const context");
+        ccx.tcx.sess.delay_span_bug(span, "complex control flow is forbidden in a const context");
     }
 }
 
 #[derive(Debug)]
 pub struct CellBorrow;
 impl NonConstOp for CellBorrow {
-    fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
+    fn emit_error(&self, ccx: &ConstCx<'_, '_>, span: Span) {
         struct_span_err!(
-            item.tcx.sess,
+            ccx.tcx.sess,
             span,
             E0492,
             "cannot borrow a constant which may contain \
@@ -201,19 +201,19 @@ impl NonConstOp for MutBorrow {
         Some(sym::const_mut_refs)
     }
 
-    fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
+    fn emit_error(&self, ccx: &ConstCx<'_, '_>, span: Span) {
         let mut err = feature_err(
-            &item.tcx.sess.parse_sess,
+            &ccx.tcx.sess.parse_sess,
             sym::const_mut_refs,
             span,
             &format!(
                 "references in {}s may only refer \
                       to immutable values",
-                item.const_kind()
+                ccx.const_kind()
             ),
         );
-        err.span_label(span, format!("{}s require immutable values", item.const_kind()));
-        if item.tcx.sess.teach(&err.get_code().unwrap()) {
+        err.span_label(span, format!("{}s require immutable values", ccx.const_kind()));
+        if ccx.tcx.sess.teach(&err.get_code().unwrap()) {
             err.note(
                 "References in statics and constants may only refer \
                       to immutable values.\n\n\
@@ -236,12 +236,12 @@ impl NonConstOp for MutAddressOf {
         Some(sym::const_mut_refs)
     }
 
-    fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
+    fn emit_error(&self, ccx: &ConstCx<'_, '_>, span: Span) {
         feature_err(
-            &item.tcx.sess.parse_sess,
+            &ccx.tcx.sess.parse_sess,
             sym::const_mut_refs,
             span,
-            &format!("`&raw mut` is not allowed in {}s", item.const_kind()),
+            &format!("`&raw mut` is not allowed in {}s", ccx.const_kind()),
         )
         .emit();
     }
@@ -262,12 +262,12 @@ impl NonConstOp for Panic {
         Some(sym::const_panic)
     }
 
-    fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
+    fn emit_error(&self, ccx: &ConstCx<'_, '_>, span: Span) {
         feature_err(
-            &item.tcx.sess.parse_sess,
+            &ccx.tcx.sess.parse_sess,
             sym::const_panic,
             span,
-            &format!("panicking in {}s is unstable", item.const_kind()),
+            &format!("panicking in {}s is unstable", ccx.const_kind()),
         )
         .emit();
     }
@@ -280,12 +280,12 @@ impl NonConstOp for RawPtrComparison {
         Some(sym::const_compare_raw_pointers)
     }
 
-    fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
+    fn emit_error(&self, ccx: &ConstCx<'_, '_>, span: Span) {
         feature_err(
-            &item.tcx.sess.parse_sess,
+            &ccx.tcx.sess.parse_sess,
             sym::const_compare_raw_pointers,
             span,
-            &format!("comparing raw pointers inside {}", item.const_kind()),
+            &format!("comparing raw pointers inside {}", ccx.const_kind()),
         )
         .emit();
     }
@@ -298,12 +298,12 @@ impl NonConstOp for RawPtrDeref {
         Some(sym::const_raw_ptr_deref)
     }
 
-    fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
+    fn emit_error(&self, ccx: &ConstCx<'_, '_>, span: Span) {
         feature_err(
-            &item.tcx.sess.parse_sess,
+            &ccx.tcx.sess.parse_sess,
             sym::const_raw_ptr_deref,
             span,
-            &format!("dereferencing raw pointers in {}s is unstable", item.const_kind(),),
+            &format!("dereferencing raw pointers in {}s is unstable", ccx.const_kind(),),
         )
         .emit();
     }
@@ -316,12 +316,12 @@ impl NonConstOp for RawPtrToIntCast {
         Some(sym::const_raw_ptr_to_usize_cast)
     }
 
-    fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
+    fn emit_error(&self, ccx: &ConstCx<'_, '_>, span: Span) {
         feature_err(
-            &item.tcx.sess.parse_sess,
+            &ccx.tcx.sess.parse_sess,
             sym::const_raw_ptr_to_usize_cast,
             span,
-            &format!("casting pointers to integers in {}s is unstable", item.const_kind(),),
+            &format!("casting pointers to integers in {}s is unstable", ccx.const_kind(),),
         )
         .emit();
     }
@@ -331,22 +331,22 @@ impl NonConstOp for RawPtrToIntCast {
 #[derive(Debug)]
 pub struct StaticAccess;
 impl NonConstOp for StaticAccess {
-    fn is_allowed_in_item(&self, item: &Item<'_, '_>) -> bool {
-        item.const_kind().is_static()
+    fn is_allowed_in_item(&self, ccx: &ConstCx<'_, '_>) -> bool {
+        ccx.const_kind().is_static()
     }
 
-    fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
+    fn emit_error(&self, ccx: &ConstCx<'_, '_>, span: Span) {
         let mut err = struct_span_err!(
-            item.tcx.sess,
+            ccx.tcx.sess,
             span,
             E0013,
             "{}s cannot refer to statics",
-            item.const_kind()
+            ccx.const_kind()
         );
         err.help(
             "consider extracting the value of the `static` to a `const`, and referring to that",
         );
-        if item.tcx.sess.teach(&err.get_code().unwrap()) {
+        if ccx.tcx.sess.teach(&err.get_code().unwrap()) {
             err.note(
                 "`static` and `const` variables can refer to other `const` variables. \
                     A `const` variable, however, cannot refer to a `static` variable.",
@@ -363,9 +363,9 @@ pub struct ThreadLocalAccess;
 impl NonConstOp for ThreadLocalAccess {
     const IS_SUPPORTED_IN_MIRI: bool = false;
 
-    fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
+    fn emit_error(&self, ccx: &ConstCx<'_, '_>, span: Span) {
         struct_span_err!(
-            item.tcx.sess,
+            ccx.tcx.sess,
             span,
             E0625,
             "thread-local statics cannot be \
@@ -378,19 +378,19 @@ impl NonConstOp for ThreadLocalAccess {
 #[derive(Debug)]
 pub struct UnionAccess;
 impl NonConstOp for UnionAccess {
-    fn is_allowed_in_item(&self, item: &Item<'_, '_>) -> bool {
+    fn is_allowed_in_item(&self, ccx: &ConstCx<'_, '_>) -> bool {
         // Union accesses are stable in all contexts except `const fn`.
-        item.const_kind() != ConstKind::ConstFn
-            || item.tcx.features().enabled(Self::feature_gate().unwrap())
+        ccx.const_kind() != ConstKind::ConstFn
+            || ccx.tcx.features().enabled(Self::feature_gate().unwrap())
     }
 
     fn feature_gate() -> Option<Symbol> {
         Some(sym::const_fn_union)
     }
 
-    fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
+    fn emit_error(&self, ccx: &ConstCx<'_, '_>, span: Span) {
         feature_err(
-            &item.tcx.sess.parse_sess,
+            &ccx.tcx.sess.parse_sess,
             sym::const_fn_union,
             span,
             "unions in const fn are unstable",

src/librustc_mir/transform/check_consts/qualifs.rs

@@ -6,7 +6,7 @@ use rustc_middle::mir::*;
 use rustc_middle::ty::{self, AdtDef, Ty};
 use rustc_span::DUMMY_SP;
 
-use super::Item as ConstCx;
+use super::ConstCx;
 
 pub fn in_any_value_of_ty(cx: &ConstCx<'_, 'tcx>, ty: Ty<'tcx>) -> ConstQualifs {
     ConstQualifs {

src/librustc_mir/transform/check_consts/resolver.rs

@@ -8,7 +8,7 @@ use rustc_middle::mir::{self, BasicBlock, Local, Location};
 
 use std::marker::PhantomData;
 
-use super::{qualifs, Item, Qualif};
+use super::{qualifs, ConstCx, Qualif};
 use crate::dataflow;
 
 /// A `Visitor` that propagates qualifs between locals. This defines the transfer function of
@@ -18,7 +18,7 @@ use crate::dataflow;
 /// the `MaybeMutBorrowedLocals` dataflow pass to see if a `Local` may have become qualified via
 /// an indirect assignment or function call.
 struct TransferFunction<'a, 'mir, 'tcx, Q> {
-    item: &'a Item<'mir, 'tcx>,
+    ccx: &'a ConstCx<'mir, 'tcx>,
     qualifs_per_local: &'a mut BitSet<Local>,
 
     _qualif: PhantomData<Q>,
@@ -28,16 +28,16 @@ impl<Q> TransferFunction<'a, 'mir, 'tcx, Q>
 where
     Q: Qualif,
 {
-    fn new(item: &'a Item<'mir, 'tcx>, qualifs_per_local: &'a mut BitSet<Local>) -> Self {
-        TransferFunction { item, qualifs_per_local, _qualif: PhantomData }
+    fn new(ccx: &'a ConstCx<'mir, 'tcx>, qualifs_per_local: &'a mut BitSet<Local>) -> Self {
+        TransferFunction { ccx, qualifs_per_local, _qualif: PhantomData }
     }
 
     fn initialize_state(&mut self) {
         self.qualifs_per_local.clear();
 
-        for arg in self.item.body.args_iter() {
-            let arg_ty = self.item.body.local_decls[arg].ty;
-            if Q::in_any_value_of_ty(self.item, arg_ty) {
+        for arg in self.ccx.body.args_iter() {
+            let arg_ty = self.ccx.body.local_decls[arg].ty;
+            if Q::in_any_value_of_ty(self.ccx, arg_ty) {
                 self.qualifs_per_local.insert(arg);
             }
         }
@@ -72,8 +72,8 @@ where
     ) {
         // We cannot reason about another function's internals, so use conservative type-based
         // qualification for the result of a function call.
-        let return_ty = return_place.ty(self.item.body, self.item.tcx).ty;
-        let qualif = Q::in_any_value_of_ty(self.item, return_ty);
+        let return_ty = return_place.ty(self.ccx.body, self.ccx.tcx).ty;
+        let qualif = Q::in_any_value_of_ty(self.ccx, return_ty);
 
         if !return_place.is_indirect() {
             self.assign_qualif_direct(&return_place, qualif);
@@ -108,7 +108,7 @@ where
         location: Location,
     ) {
         let qualif = qualifs::in_rvalue::<Q, _>(
-            self.item,
+            self.ccx,
             &mut |l| self.qualifs_per_local.contains(l),
             rvalue,
         );
@@ -127,7 +127,7 @@ where
 
         if let mir::TerminatorKind::DropAndReplace { value, location: dest, .. } = kind {
             let qualif = qualifs::in_operand::<Q, _>(
-                self.item,
+                self.ccx,
                 &mut |l| self.qualifs_per_local.contains(l),
                 value,
             );
@@ -145,7 +145,7 @@ where
 
 /// The dataflow analysis used to propagate qualifs on arbitrary CFGs.
 pub(super) struct FlowSensitiveAnalysis<'a, 'mir, 'tcx, Q> {
-    item: &'a Item<'mir, 'tcx>,
+    ccx: &'a ConstCx<'mir, 'tcx>,
     _qualif: PhantomData<Q>,
 }
 
@@ -153,15 +153,15 @@ impl<'a, 'mir, 'tcx, Q> FlowSensitiveAnalysis<'a, 'mir, 'tcx, Q>
 where
     Q: Qualif,
 {
-    pub(super) fn new(_: Q, item: &'a Item<'mir, 'tcx>) -> Self {
-        FlowSensitiveAnalysis { item, _qualif: PhantomData }
+    pub(super) fn new(_: Q, ccx: &'a ConstCx<'mir, 'tcx>) -> Self {
+        FlowSensitiveAnalysis { ccx, _qualif: PhantomData }
     }
 
     fn transfer_function(
         &self,
         state: &'a mut BitSet<Local>,
     ) -> TransferFunction<'a, 'mir, 'tcx, Q> {
-        TransferFunction::<Q>::new(self.item, state)
+        TransferFunction::<Q>::new(self.ccx, state)
     }
 }
 

src/librustc_mir/transform/check_consts/validation.rs

@@ -20,7 +20,7 @@ use std::ops::Deref;
 use super::ops::{self, NonConstOp};
 use super::qualifs::{self, HasMutInterior, NeedsDrop};
 use super::resolver::FlowSensitiveAnalysis;
-use super::{is_lang_panic_fn, ConstKind, Item, Qualif};
+use super::{is_lang_panic_fn, ConstCx, ConstKind, Qualif};
 use crate::const_eval::{is_const_fn, is_unstable_const_fn};
 use crate::dataflow::MaybeMutBorrowedLocals;
 use crate::dataflow::{self, Analysis};
@@ -37,15 +37,15 @@ struct QualifCursor<'a, 'mir, 'tcx, Q: Qualif> {
 }
 
 impl<Q: Qualif> QualifCursor<'a, 'mir, 'tcx, Q> {
-    pub fn new(q: Q, item: &'a Item<'mir, 'tcx>) -> Self {
-        let cursor = FlowSensitiveAnalysis::new(q, item)
-            .into_engine(item.tcx, item.body, item.def_id)
+    pub fn new(q: Q, ccx: &'a ConstCx<'mir, 'tcx>) -> Self {
+        let cursor = FlowSensitiveAnalysis::new(q, ccx)
+            .into_engine(ccx.tcx, ccx.body, ccx.def_id)
             .iterate_to_fixpoint()
-            .into_results_cursor(item.body);
+            .into_results_cursor(ccx.body);
 
-        let mut in_any_value_of_ty = BitSet::new_empty(item.body.local_decls.len());
-        for (local, decl) in item.body.local_decls.iter_enumerated() {
-            if Q::in_any_value_of_ty(item, decl.ty) {
+        let mut in_any_value_of_ty = BitSet::new_empty(ccx.body.local_decls.len());
+        for (local, decl) in ccx.body.local_decls.iter_enumerated() {
+            if Q::in_any_value_of_ty(ccx, decl.ty) {
                 in_any_value_of_ty.insert(local);
             }
         }
@@ -91,12 +91,12 @@ impl Qualifs<'a, 'mir, 'tcx> {
             || self.indirectly_mutable(local, location)
     }
 
-    fn in_return_place(&mut self, item: &Item<'_, 'tcx>) -> ConstQualifs {
+    fn in_return_place(&mut self, ccx: &ConstCx<'_, 'tcx>) -> ConstQualifs {
         // Find the `Return` terminator if one exists.
         //
         // If no `Return` terminator exists, this MIR is divergent. Just return the conservative
         // qualifs for the return type.
-        let return_block = item
+        let return_block = ccx
             .body
             .basic_blocks()
             .iter_enumerated()
@@ -107,11 +107,11 @@ impl Qualifs<'a, 'mir, 'tcx> {
             .map(|(bb, _)| bb);
 
         let return_block = match return_block {
-            None => return qualifs::in_any_value_of_ty(item, item.body.return_ty()),
+            None => return qualifs::in_any_value_of_ty(ccx, ccx.body.return_ty()),
             Some(bb) => bb,
         };
 
-        let return_loc = item.body.terminator_loc(return_block);
+        let return_loc = ccx.body.terminator_loc(return_block);
 
         ConstQualifs {
             needs_drop: self.needs_drop(RETURN_PLACE, return_loc),
@@ -121,7 +121,7 @@ impl Qualifs<'a, 'mir, 'tcx> {
 }
 
 pub struct Validator<'a, 'mir, 'tcx> {
-    item: &'a Item<'mir, 'tcx>,
+    ccx: &'a ConstCx<'mir, 'tcx>,
     qualifs: Qualifs<'a, 'mir, 'tcx>,
 
     /// The span of the current statement.
@@ -129,19 +129,19 @@ pub struct Validator<'a, 'mir, 'tcx> {
 }
 
 impl Deref for Validator<'_, 'mir, 'tcx> {
-    type Target = Item<'mir, 'tcx>;
+    type Target = ConstCx<'mir, 'tcx>;
 
     fn deref(&self) -> &Self::Target {
-        &self.item
+        &self.ccx
     }
 }
 
 impl Validator<'a, 'mir, 'tcx> {
-    pub fn new(item: &'a Item<'mir, 'tcx>) -> Self {
-        let Item { tcx, body, def_id, param_env, .. } = *item;
+    pub fn new(ccx: &'a ConstCx<'mir, 'tcx>) -> Self {
+        let ConstCx { tcx, body, def_id, param_env, .. } = *ccx;
 
-        let needs_drop = QualifCursor::new(NeedsDrop, item);
-        let has_mut_interior = QualifCursor::new(HasMutInterior, item);
+        let needs_drop = QualifCursor::new(NeedsDrop, ccx);
+        let has_mut_interior = QualifCursor::new(HasMutInterior, ccx);
 
         // We can use `unsound_ignore_borrow_on_drop` here because custom drop impls are not
         // allowed in a const.
@@ -156,11 +156,11 @@ impl Validator<'a, 'mir, 'tcx> {
 
         let qualifs = Qualifs { needs_drop, has_mut_interior, indirectly_mutable };
 
-        Validator { span: item.body.span, item, qualifs }
+        Validator { span: ccx.body.span, ccx, qualifs }
     }
 
     pub fn check_body(&mut self) {
-        let Item { tcx, body, def_id, const_kind, .. } = *self.item;
+        let ConstCx { tcx, body, def_id, const_kind, .. } = *self.ccx;
 
         let use_min_const_fn_checks = (const_kind == Some(ConstKind::ConstFn)
             && crate::const_eval::is_min_const_fn(tcx, def_id))
@@ -175,7 +175,7 @@ impl Validator<'a, 'mir, 'tcx> {
             }
         }
 
-        check_short_circuiting_in_const_local(self.item);
+        check_short_circuiting_in_const_local(self.ccx);
 
         if body.is_cfg_cyclic() {
             // We can't provide a good span for the error here, but this should be caught by the
@@ -196,7 +196,7 @@ impl Validator<'a, 'mir, 'tcx> {
     }
 
     pub fn qualifs_in_return_place(&mut self) -> ConstQualifs {
-        self.qualifs.in_return_place(self.item)
+        self.qualifs.in_return_place(self.ccx)
     }
 
     /// Emits an error at the given `span` if an expression cannot be evaluated in the current
@@ -344,7 +344,7 @@ impl Visitor<'tcx> for Validator<'_, 'mir, 'tcx> {
             Rvalue::Ref(_, BorrowKind::Shared | BorrowKind::Shallow, ref place)
             | Rvalue::AddressOf(Mutability::Not, ref place) => {
                 let borrowed_place_has_mut_interior = qualifs::in_place::<HasMutInterior, _>(
-                    &self.item,
+                    &self.ccx,
                     &mut |local| self.qualifs.has_mut_interior(local, location),
                     place.as_ref(),
                 );
@@ -608,8 +608,8 @@ fn error_min_const_fn_violation(tcx: TyCtxt<'_>, span: Span, msg: Cow<'_, str>)
         .emit();
 }
 
-fn check_short_circuiting_in_const_local(item: &Item<'_, 'tcx>) {
-    let body = item.body;
+fn check_short_circuiting_in_const_local(ccx: &ConstCx<'_, 'tcx>) {
+    let body = ccx.body;
 
     if body.control_flow_destroyed.is_empty() {
         return;
@@ -618,12 +618,12 @@ fn check_short_circuiting_in_const_local(item: &Item<'_, 'tcx>) {
     let mut locals = body.vars_iter();
     if let Some(local) = locals.next() {
         let span = body.local_decls[local].source_info.span;
-        let mut error = item.tcx.sess.struct_span_err(
+        let mut error = ccx.tcx.sess.struct_span_err(
             span,
             &format!(
                 "new features like let bindings are not permitted in {}s \
                 which also use short circuiting operators",
-                item.const_kind(),
+                ccx.const_kind(),
             ),
         );
         for (span, kind) in body.control_flow_destroyed.iter() {

src/librustc_mir/transform/mod.rs

@@ -194,10 +194,10 @@ fn mir_const_qualif(tcx: TyCtxt<'_>, def_id: DefId) -> ConstQualifs {
         return Default::default();
     }
 
-    let item =
-        check_consts::Item { body, tcx, def_id, const_kind, param_env: tcx.param_env(def_id) };
+    let ccx =
+        check_consts::ConstCx { body, tcx, def_id, const_kind, param_env: tcx.param_env(def_id) };
 
-    let mut validator = check_consts::validation::Validator::new(&item);
+    let mut validator = check_consts::validation::Validator::new(&ccx);
     validator.check_body();
 
     // We return the qualifs in the return place for every MIR body, even though it is only used

src/librustc_mir/transform/promote_consts.rs

@@ -30,7 +30,7 @@ use std::cell::Cell;
 use std::{cmp, iter, mem};
 
 use crate::const_eval::{is_const_fn, is_unstable_const_fn};
-use crate::transform::check_consts::{is_lang_panic_fn, qualifs, ConstKind, Item};
+use crate::transform::check_consts::{is_lang_panic_fn, qualifs, ConstCx, ConstKind};
 use crate::transform::{MirPass, MirSource};
 
 /// A `MirPass` for promotion.
@@ -62,9 +62,10 @@ impl<'tcx> MirPass<'tcx> for PromoteTemps<'tcx> {
         let def_id = src.def_id();
 
         let mut rpo = traversal::reverse_postorder(body);
-        let (temps, all_candidates) = collect_temps_and_candidates(tcx, body, &mut rpo);
+        let ccx = ConstCx::new(tcx, def_id, body);
+        let (temps, all_candidates) = collect_temps_and_candidates(&ccx, &mut rpo);
 
-        let promotable_candidates = validate_candidates(tcx, body, def_id, &temps, &all_candidates);
+        let promotable_candidates = validate_candidates(&ccx, &temps, &all_candidates);
 
         let promoted = promote_candidates(def_id, body, tcx, temps, promotable_candidates);
         self.promoted_fragments.set(promoted);
@@ -139,8 +140,7 @@ fn args_required_const(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Vec<usize>> {
 }
 
 struct Collector<'a, 'tcx> {
-    tcx: TyCtxt<'tcx>,
-    body: &'a Body<'tcx>,
+    ccx: &'a ConstCx<'a, 'tcx>,
     temps: IndexVec<Local, TempState>,
     candidates: Vec<Candidate>,
     span: Span,
@@ -150,7 +150,7 @@ impl<'tcx> Visitor<'tcx> for Collector<'_, 'tcx> {
     fn visit_local(&mut self, &index: &Local, context: PlaceContext, location: Location) {
         debug!("visit_local: index={:?} context={:?} location={:?}", index, context, location);
         // We're only interested in temporaries and the return place
-        match self.body.local_kind(index) {
+        match self.ccx.body.local_kind(index) {
             LocalKind::Temp | LocalKind::ReturnPointer => {}
             LocalKind::Arg | LocalKind::Var => return,
         }
@@ -203,7 +203,7 @@ impl<'tcx> Visitor<'tcx> for Collector<'_, 'tcx> {
             Rvalue::Ref(..) => {
                 self.candidates.push(Candidate::Ref(location));
             }
-            Rvalue::Repeat(..) if self.tcx.features().const_in_array_repeat_expressions => {
+            Rvalue::Repeat(..) if self.ccx.tcx.features().const_in_array_repeat_expressions => {
                 // FIXME(#49147) only promote the element when it isn't `Copy`
                 // (so that code that can copy it at runtime is unaffected).
                 self.candidates.push(Candidate::Repeat(location));
@@ -216,10 +216,10 @@ impl<'tcx> Visitor<'tcx> for Collector<'_, 'tcx> {
         self.super_terminator_kind(kind, location);
 
         if let TerminatorKind::Call { ref func, .. } = *kind {
-            if let ty::FnDef(def_id, _) = func.ty(self.body, self.tcx).kind {
-                let fn_sig = self.tcx.fn_sig(def_id);
+            if let ty::FnDef(def_id, _) = func.ty(self.ccx.body, self.ccx.tcx).kind {
+                let fn_sig = self.ccx.tcx.fn_sig(def_id);
                 if let Abi::RustIntrinsic | Abi::PlatformIntrinsic = fn_sig.abi() {
-                    let name = self.tcx.item_name(def_id);
+                    let name = self.ccx.tcx.item_name(def_id);
                     // FIXME(eddyb) use `#[rustc_args_required_const(2)]` for shuffles.
                     if name.as_str().starts_with("simd_shuffle") {
                         self.candidates.push(Candidate::Argument { bb: location.block, index: 2 });
@@ -228,7 +228,7 @@ impl<'tcx> Visitor<'tcx> for Collector<'_, 'tcx> {
                     }
                 }
 
-                if let Some(constant_args) = args_required_const(self.tcx, def_id) {
+                if let Some(constant_args) = args_required_const(self.ccx.tcx, def_id) {
                     for index in constant_args {
                         self.candidates.push(Candidate::Argument { bb: location.block, index });
                     }
@@ -243,16 +243,14 @@ impl<'tcx> Visitor<'tcx> for Collector<'_, 'tcx> {
 }
 
 pub fn collect_temps_and_candidates(
-    tcx: TyCtxt<'tcx>,
-    body: &Body<'tcx>,
+    ccx: &ConstCx<'mir, 'tcx>,
     rpo: &mut ReversePostorder<'_, 'tcx>,
 ) -> (IndexVec<Local, TempState>, Vec<Candidate>) {
     let mut collector = Collector {
-        tcx,
-        body,
-        temps: IndexVec::from_elem(TempState::Undefined, &body.local_decls),
+        temps: IndexVec::from_elem(TempState::Undefined, &ccx.body.local_decls),
         candidates: vec![],
-        span: body.span,
+        span: ccx.body.span,
+        ccx,
     };
     for (bb, data) in rpo {
         collector.visit_basic_block_data(bb, data);
@@ -264,7 +262,7 @@ pub fn collect_temps_and_candidates(
 ///
 /// This wraps an `Item`, and has access to all fields of that `Item` via `Deref` coercion.
 struct Validator<'a, 'tcx> {
-    item: Item<'a, 'tcx>,
+    ccx: &'a ConstCx<'a, 'tcx>,
     temps: &'a IndexVec<Local, TempState>,
 
     /// Explicit promotion happens e.g. for constant arguments declared via
@@ -277,10 +275,10 @@ struct Validator<'a, 'tcx> {
 }
 
 impl std::ops::Deref for Validator<'a, 'tcx> {
-    type Target = Item<'a, 'tcx>;
+    type Target = ConstCx<'a, 'tcx>;
 
     fn deref(&self) -> &Self::Target {
-        &self.item
+        &self.ccx
     }
 }
 
@@ -413,7 +411,7 @@ impl<'tcx> Validator<'_, 'tcx> {
                 let statement = &self.body[loc.block].statements[loc.statement_index];
                 match &statement.kind {
                     StatementKind::Assign(box (_, rhs)) => qualifs::in_rvalue::<Q, _>(
-                        &self.item,
+                        &self.ccx,
                         &mut |l| self.qualif_local::<Q>(l),
                         rhs,
                     ),
@@ -430,7 +428,7 @@ impl<'tcx> Validator<'_, 'tcx> {
                 match &terminator.kind {
                     TerminatorKind::Call { .. } => {
                         let return_ty = self.body.local_decls[local].ty;
-                        Q::in_any_value_of_ty(&self.item, return_ty)
+                        Q::in_any_value_of_ty(&self.ccx, return_ty)
                     }
                     kind => {
                         span_bug!(terminator.source_info.span, "{:?} not promotable", kind);
@@ -717,13 +715,11 @@ impl<'tcx> Validator<'_, 'tcx> {
 
 // FIXME(eddyb) remove the differences for promotability in `static`, `const`, `const fn`.
 pub fn validate_candidates(
-    tcx: TyCtxt<'tcx>,
-    body: &Body<'tcx>,
-    def_id: DefId,
+    ccx: &ConstCx<'_, '_>,
     temps: &IndexVec<Local, TempState>,
     candidates: &[Candidate],
 ) -> Vec<Candidate> {
-    let mut validator = Validator { item: Item::new(tcx, def_id, body), temps, explicit: false };
+    let mut validator = Validator { ccx, temps, explicit: false };
 
     candidates
         .iter()
@@ -735,11 +731,23 @@ pub fn validate_candidates(
             // and `#[rustc_args_required_const]` arguments here.
 
             let is_promotable = validator.validate_candidate(candidate).is_ok();
+
+            // If we use explicit validation, we carry the risk of turning a legitimate run-time
+            // operation into a failing compile-time operation. Make sure that does not happen
+            // by asserting that there is no possible run-time behavior here in case promotion
+            // fails.
+            if validator.explicit && !is_promotable {
+                ccx.tcx.sess.delay_span_bug(
+                    ccx.body.span,
+                    "Explicit promotion requested, but failed to promote",
+                );
+            }
+
             match candidate {
                 Candidate::Argument { bb, index } if !is_promotable => {
-                    let span = body[bb].terminator().source_info.span;
+                    let span = ccx.body[bb].terminator().source_info.span;
                     let msg = format!("argument {} is required to be a constant", index + 1);
-                    tcx.sess.span_err(span, &msg);
+                    ccx.tcx.sess.span_err(span, &msg);
                 }
                 _ => (),
             }
@@ -1147,22 +1155,19 @@ pub fn promote_candidates<'tcx>(
 /// Feature attribute should be suggested if `operand` can be promoted and the feature is not
 /// enabled.
 crate fn should_suggest_const_in_array_repeat_expressions_attribute<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    mir_def_id: DefId,
-    body: &Body<'tcx>,
+    ccx: &ConstCx<'_, 'tcx>,
     operand: &Operand<'tcx>,
 ) -> bool {
-    let mut rpo = traversal::reverse_postorder(&body);
-    let (temps, _) = collect_temps_and_candidates(tcx, &body, &mut rpo);
-    let validator =
-        Validator { item: Item::new(tcx, mir_def_id, body), temps: &temps, explicit: false };
+    let mut rpo = traversal::reverse_postorder(&ccx.body);
+    let (temps, _) = collect_temps_and_candidates(&ccx, &mut rpo);
+    let validator = Validator { ccx, temps: &temps, explicit: false };
 
     let should_promote = validator.validate_operand(operand).is_ok();
-    let feature_flag = tcx.features().const_in_array_repeat_expressions;
+    let feature_flag = validator.ccx.tcx.features().const_in_array_repeat_expressions;
     debug!(
-        "should_suggest_const_in_array_repeat_expressions_flag: mir_def_id={:?} \
+        "should_suggest_const_in_array_repeat_expressions_flag: def_id={:?} \
             should_promote={:?} feature_flag={:?}",
-        mir_def_id, should_promote, feature_flag
+        validator.ccx.def_id, should_promote, feature_flag
     );
     should_promote && !feature_flag
 }

src/tools/compiletest/src/runtest.rs

@@ -3338,6 +3338,10 @@ impl<'test> TestCx<'test> {
     }
 
     fn delete_file(&self, file: &PathBuf) {
+        if !file.exists() {
+            // Deleting a nonexistant file would error.
+            return;
+        }
         if let Err(e) = fs::remove_file(file) {
             self.fatal(&format!("failed to delete `{}`: {}", file.display(), e,));
         }
@@ -3400,7 +3404,7 @@ impl<'test> TestCx<'test> {
         let examined_content =
             self.load_expected_output_from_path(&examined_path).unwrap_or_else(|_| String::new());
 
-        if examined_path.exists() && canon_content == &examined_content {
+        if canon_content == &examined_content {
             self.delete_file(&examined_path);
         }
     }