Rollup merge of #66587 - matthewjasper:handle-static-as-const, r=oli-obk

Handle statics in MIR as const pointers

This is the first PR towards the goal of removing `PlaceBase::Static`. In this PR:

* Statics are lowered to dereferencing a const pointer.
* The temporaries holding such pointers are tracked in MIR, for the most part this is only used for diagnostics. There are two exceptions:
    * The borrow checker has some checks for thread-locals that directly use this data.
    * Const checking will suppress "cannot dereference raw pointer" diagnostics for pointers to `static mut`/`extern static`. This is to maintain the current behaviour (12 tests fail otherwise).

The following are left to future PRs (I think that @spastorino will be working on the first 3):

* Applying the same treatments to promoted statics.
* Removing `PlaceBase::Static`.
* Replacing `PlaceBase` with `Local`.
* Moving the ever growing collection of metadata that we have for diagnostics in MIR passes somewhere more appropriate.

r? @oli-obk

Author: Centril

src/librustc/mir/mod.rs

@@ -7,7 +7,7 @@
 use crate::hir::def::{CtorKind, Namespace};
 use crate::hir::def_id::DefId;
 use crate::hir;
-use crate::mir::interpret::{PanicInfo, Scalar};
+use crate::mir::interpret::{GlobalAlloc, PanicInfo, Scalar};
 use crate::mir::visit::MirVisitable;
 use crate::ty::adjustment::PointerCast;
 use crate::ty::fold::{TypeFoldable, TypeFolder, TypeVisitor};
@@ -292,7 +292,7 @@ impl<'tcx> Body<'tcx> {
     pub fn temps_iter<'a>(&'a self) -> impl Iterator<Item = Local> + 'a {
         (self.arg_count + 1..self.local_decls.len()).filter_map(move |index| {
             let local = Local::new(index);
-            if self.local_decls[local].is_user_variable.is_some() {
+            if self.local_decls[local].is_user_variable() {
                 None
             } else {
                 Some(local)
@@ -305,7 +305,7 @@ impl<'tcx> Body<'tcx> {
     pub fn vars_iter<'a>(&'a self) -> impl Iterator<Item = Local> + 'a {
         (self.arg_count + 1..self.local_decls.len()).filter_map(move |index| {
             let local = Local::new(index);
-            if self.local_decls[local].is_user_variable.is_some() {
+            if self.local_decls[local].is_user_variable() {
                 Some(local)
             } else {
                 None
@@ -319,7 +319,7 @@ impl<'tcx> Body<'tcx> {
         (self.arg_count + 1..self.local_decls.len()).filter_map(move |index| {
             let local = Local::new(index);
             let decl = &self.local_decls[local];
-            if decl.is_user_variable.is_some() && decl.mutability == Mutability::Mut {
+            if decl.is_user_variable() && decl.mutability == Mutability::Mut {
                 Some(local)
             } else {
                 None
@@ -333,7 +333,7 @@ impl<'tcx> Body<'tcx> {
         (1..self.local_decls.len()).filter_map(move |index| {
             let local = Local::new(index);
             let decl = &self.local_decls[local];
-            if (decl.is_user_variable.is_some() || index < self.arg_count + 1)
+            if (decl.is_user_variable() || index < self.arg_count + 1)
                 && decl.mutability == Mutability::Mut
             {
                 Some(local)
@@ -689,14 +689,8 @@ pub struct LocalDecl<'tcx> {
     /// Temporaries and the return place are always mutable.
     pub mutability: Mutability,
 
-    /// `Some(binding_mode)` if this corresponds to a user-declared local variable.
-    ///
-    /// This is solely used for local diagnostics when generating
-    /// warnings/errors when compiling the current crate, and
-    /// therefore it need not be visible across crates. pnkfelix
-    /// currently hypothesized we *need* to wrap this in a
-    /// `ClearCrossCrate` as long as it carries as `HirId`.
-    pub is_user_variable: Option<ClearCrossCrate<BindingForm<'tcx>>>,
+    // FIXME(matthewjasper) Don't store in this in `Body`
+    pub local_info: LocalInfo<'tcx>,
 
     /// `true` if this is an internal local.
     ///
@@ -721,6 +715,7 @@ pub struct LocalDecl<'tcx> {
     /// then it is a temporary created for evaluation of some
     /// subexpression of some block's tail expression (with no
     /// intervening statement context).
+    // FIXME(matthewjasper) Don't store in this in `Body`
     pub is_block_tail: Option<BlockTailInfo>,
 
     /// The type of this local.
@@ -730,6 +725,7 @@ pub struct LocalDecl<'tcx> {
     /// e.g., via `let x: T`, then we carry that type here. The MIR
     /// borrow checker needs this information since it can affect
     /// region inference.
+    // FIXME(matthewjasper) Don't store in this in `Body`
     pub user_ty: UserTypeProjections,
 
     /// The name of the local, used in debuginfo and pretty-printing.
@@ -824,6 +820,21 @@ pub struct LocalDecl<'tcx> {
     pub visibility_scope: SourceScope,
 }
 
+/// Extra information about a local that's used for diagnostics.
+#[derive(Clone, Debug, RustcEncodable, RustcDecodable, HashStable, TypeFoldable)]
+pub enum LocalInfo<'tcx> {
+    /// A user-defined local variable or function parameter
+    ///
+    /// The `BindingForm` is solely used for local diagnostics when generating
+    /// warnings/errors when compiling the current crate, and therefore it need
+    /// not be visible across crates.
+    User(ClearCrossCrate<BindingForm<'tcx>>),
+    /// A temporary created that references the static with the given `DefId`.
+    StaticRef { def_id: DefId, is_thread_local: bool },
+    /// Any other temporary, the return place, or an anonymous function parameter.
+    Other,
+}
+
 impl<'tcx> LocalDecl<'tcx> {
     /// Returns `true` only if local is a binding that can itself be
     /// made mutable via the addition of the `mut` keyword, namely
@@ -832,15 +843,17 @@ impl<'tcx> LocalDecl<'tcx> {
     /// - `let x = ...`,
     /// - or `match ... { C(x) => ... }`
     pub fn can_be_made_mutable(&self) -> bool {
-        match self.is_user_variable {
-            Some(ClearCrossCrate::Set(BindingForm::Var(VarBindingForm {
+        match self.local_info {
+            LocalInfo::User(ClearCrossCrate::Set(BindingForm::Var(VarBindingForm {
                 binding_mode: ty::BindingMode::BindByValue(_),
                 opt_ty_info: _,
                 opt_match_place: _,
                 pat_span: _,
             }))) => true,
 
-            Some(ClearCrossCrate::Set(BindingForm::ImplicitSelf(ImplicitSelfKind::Imm))) => true,
+            LocalInfo::User(
+                ClearCrossCrate::Set(BindingForm::ImplicitSelf(ImplicitSelfKind::Imm)),
+            ) => true,
 
             _ => false,
         }
@@ -850,26 +863,54 @@ impl<'tcx> LocalDecl<'tcx> {
     /// `ref mut ident` binding. (Such bindings cannot be made into
     /// mutable bindings, but the inverse does not necessarily hold).
     pub fn is_nonref_binding(&self) -> bool {
-        match self.is_user_variable {
-            Some(ClearCrossCrate::Set(BindingForm::Var(VarBindingForm {
+        match self.local_info {
+            LocalInfo::User(ClearCrossCrate::Set(BindingForm::Var(VarBindingForm {
                 binding_mode: ty::BindingMode::BindByValue(_),
                 opt_ty_info: _,
                 opt_match_place: _,
                 pat_span: _,
             }))) => true,
 
-            Some(ClearCrossCrate::Set(BindingForm::ImplicitSelf(_))) => true,
+            LocalInfo::User(ClearCrossCrate::Set(BindingForm::ImplicitSelf(_))) => true,
 
             _ => false,
         }
     }
 
+    /// Returns `true` if this variable is a named variable or function
+    /// parameter declared by the user.
+    #[inline]
+    pub fn is_user_variable(&self) -> bool {
+        match self.local_info {
+            LocalInfo::User(_) => true,
+            _ => false,
+        }
+    }
+
     /// Returns `true` if this is a reference to a variable bound in a `match`
     /// expression that is used to access said variable for the guard of the
     /// match arm.
     pub fn is_ref_for_guard(&self) -> bool {
-        match self.is_user_variable {
-            Some(ClearCrossCrate::Set(BindingForm::RefForGuard)) => true,
+        match self.local_info {
+            LocalInfo::User(ClearCrossCrate::Set(BindingForm::RefForGuard)) => true,
+            _ => false,
+        }
+    }
+
+    /// Returns `Some` if this is a reference to a static item that is used to
+    /// access that static
+    pub fn is_ref_to_static(&self) -> bool {
+        match self.local_info {
+            LocalInfo::StaticRef { .. } => true,
+            _ => false,
+        }
+    }
+
+    /// Returns `Some` if this is a reference to a static item that is used to
+    /// access that static
+    pub fn is_ref_to_thread_local(&self) -> bool {
+        match self.local_info {
+            LocalInfo::StaticRef { is_thread_local, .. } => is_thread_local,
             _ => false,
         }
     }
@@ -918,7 +959,7 @@ impl<'tcx> LocalDecl<'tcx> {
             source_info: SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE },
             visibility_scope: OUTERMOST_SOURCE_SCOPE,
             internal,
-            is_user_variable: None,
+            local_info: LocalInfo::Other,
             is_block_tail: None,
         }
     }
@@ -937,7 +978,7 @@ impl<'tcx> LocalDecl<'tcx> {
             internal: false,
             is_block_tail: None,
             name: None, // FIXME maybe we do want some name here?
-            is_user_variable: None,
+            local_info: LocalInfo::Other,
         }
     }
 }
@@ -2341,6 +2382,24 @@ pub struct Constant<'tcx> {
     pub literal: &'tcx ty::Const<'tcx>,
 }
 
+impl Constant<'tcx> {
+    pub fn check_static_ptr(&self, tcx: TyCtxt<'_>) -> Option<DefId> {
+        match self.literal.val.try_to_scalar() {
+            Some(Scalar::Ptr(ptr)) => match tcx.alloc_map.lock().get(ptr.alloc_id) {
+                Some(GlobalAlloc::Static(def_id)) => Some(def_id),
+                Some(_) => None,
+                None => {
+                    tcx.sess.delay_span_bug(
+                        DUMMY_SP, "MIR cannot contain dangling const pointers",
+                    );
+                    None
+                },
+            },
+            _ => None,
+        }
+    }
+}
+
 /// A collection of projections into user types.
 ///
 /// They are projections because a binding can occur a part of a

src/librustc/mir/visit.rs

@@ -691,7 +691,7 @@ macro_rules! make_mir_visitor {
                     source_info,
                     visibility_scope,
                     internal: _,
-                    is_user_variable: _,
+                    local_info: _,
                     is_block_tail: _,
                 } = local_decl;
 

src/librustc_codegen_ssa/mir/constant.rs

@@ -5,17 +5,40 @@ use rustc::ty::{self, Ty};
 use rustc::ty::layout::{self, HasTyCtxt};
 use syntax::source_map::Span;
 use crate::traits::*;
+use crate::mir::operand::OperandRef;
 
 use super::FunctionCx;
 
 impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
+    pub fn eval_mir_constant_to_operand(
+        &mut self,
+        bx: &mut Bx,
+        constant: &mir::Constant<'tcx>,
+    ) -> Result<OperandRef<'tcx, Bx::Value>, ErrorHandled> {
+        match constant.literal.val {
+            ty::ConstKind::Unevaluated(def_id, substs)
+                if self.cx.tcx().is_static(def_id) => {
+                    assert!(substs.is_empty(), "we don't support generic statics yet");
+                    let static_ = bx.get_static(def_id);
+                    // we treat operands referring to statics as if they were `&STATIC` instead
+                    let ptr_ty = self.cx.tcx().mk_mut_ptr(self.monomorphize(&constant.literal.ty));
+                    let layout = bx.layout_of(ptr_ty);
+                    Ok(OperandRef::from_immediate_or_packed_pair(bx, static_, layout))
+                }
+            _ => {
+                let val = self.eval_mir_constant(constant)?;
+                Ok(OperandRef::from_const(bx, val))
+            }
+        }
+    }
+
     pub fn eval_mir_constant(
         &mut self,
         constant: &mir::Constant<'tcx>,
     ) -> Result<&'tcx ty::Const<'tcx>, ErrorHandled> {
         match constant.literal.val {
-            ty::ConstKind::Unevaluated(def_id, ref substs) => {
-                let substs = self.monomorphize(substs);
+            ty::ConstKind::Unevaluated(def_id, substs) => {
+                let substs = self.monomorphize(&substs);
                 let instance = ty::Instance::resolve(
                     self.cx.tcx(), ty::ParamEnv::reveal_all(), def_id, substs,
                 ).unwrap();

src/librustc_codegen_ssa/mir/operand.rs

@@ -465,8 +465,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             }
 
             mir::Operand::Constant(ref constant) => {
-                self.eval_mir_constant(constant)
-                    .map(|c| OperandRef::from_const(bx, c))
+                self.eval_mir_constant_to_operand(bx, constant)
                     .unwrap_or_else(|err| {
                         match err {
                             // errored or at least linted

src/librustc_mir/borrow_check/borrow_set.rs

@@ -189,8 +189,8 @@ impl<'a, 'tcx> Visitor<'tcx> for GatherBorrows<'a, 'tcx> {
         location: mir::Location,
     ) {
         if let mir::Rvalue::Ref(region, kind, ref borrowed_place) = *rvalue {
-            if borrowed_place.ignore_borrow(
-                self.tcx, self.body, &self.locals_state_at_exit) {
+            if borrowed_place.ignore_borrow(self.tcx, self.body, &self.locals_state_at_exit) {
+                debug!("ignoring_borrow of {:?}", borrowed_place);
                 return;
             }
 

src/librustc_mir/borrow_check/conflict_errors.rs

@@ -3,8 +3,8 @@ use rustc::hir::def_id::DefId;
 use rustc::hir::{AsyncGeneratorKind, GeneratorKind};
 use rustc::mir::{
     self, AggregateKind, BindingForm, BorrowKind, ClearCrossCrate, ConstraintCategory,
-    FakeReadCause, Local, LocalDecl, LocalKind, Location, Operand, Place, PlaceBase, PlaceRef,
-    ProjectionElem, Rvalue, Statement, StatementKind, TerminatorKind, VarBindingForm,
+    FakeReadCause, Local, LocalDecl, LocalInfo, LocalKind, Location, Operand, Place, PlaceBase,
+    PlaceRef, ProjectionElem, Rvalue, Statement, StatementKind, TerminatorKind, VarBindingForm,
 };
 use rustc::ty::{self, Ty};
 use rustc_data_structures::fx::FxHashSet;
@@ -744,6 +744,17 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 projection: root_place_projection,
             }, borrow_span));
 
+        if let PlaceBase::Local(local) = borrow.borrowed_place.base {
+            if self.body.local_decls[local].is_ref_to_thread_local() {
+                let err = self.report_thread_local_value_does_not_live_long_enough(
+                    drop_span,
+                    borrow_span,
+                );
+                err.buffer(&mut self.errors_buffer);
+                return;
+            }
+        };
+
         if let StorageDeadOrDrop::Destructor(dropped_ty) =
             self.classify_drop_access_kind(borrow.borrowed_place.as_ref())
         {
@@ -770,9 +781,6 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             explanation
         );
         let err = match (place_desc, explanation) {
-            (Some(_), _) if self.is_place_thread_local(root_place) => {
-                self.report_thread_local_value_does_not_live_long_enough(drop_span, borrow_span)
-            }
             // If the outlives constraint comes from inside the closure,
             // for example:
             //
@@ -1509,19 +1517,22 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         // place being assigned later.
         let (place_description, assigned_span) = match local_decl {
             Some(LocalDecl {
-                is_user_variable: Some(ClearCrossCrate::Clear),
+                local_info: LocalInfo::User(ClearCrossCrate::Clear),
                 ..
             })
             | Some(LocalDecl {
-                is_user_variable:
-                    Some(ClearCrossCrate::Set(BindingForm::Var(VarBindingForm {
-                        opt_match_place: None,
-                        ..
-                    }))),
+                local_info: LocalInfo::User(ClearCrossCrate::Set(BindingForm::Var(VarBindingForm {
+                    opt_match_place: None,
+                    ..
+                }))),
+                ..
+            })
+            | Some(LocalDecl {
+                local_info: LocalInfo::StaticRef { .. },
                 ..
             })
             | Some(LocalDecl {
-                is_user_variable: None,
+                local_info: LocalInfo::Other,
                 ..
             })
             | None => (self.describe_place(place.as_ref()), assigned_span),