Make results immutable.

Because most of them are. The one exception is `ConstAnalysis`, which
gains a `RefCell` to provide interior mutability. This is a bit
annoying, but I think it's worth inconveniencing the one analysis that
requires mutability in exchange for making the interface simpler for all
the other analyses.

Author: nnethercote

compiler/rustc_borrowck/src/lib.rs

@@ -602,7 +602,7 @@ impl<'a, 'tcx, R> rustc_mir_dataflow::ResultsVisitor<'a, 'tcx, R>
 
     fn visit_statement_before_primary_effect(
         &mut self,
-        _results: &mut R,
+        _results: &R,
         state: &BorrowckDomain<'a, 'tcx>,
         stmt: &'a Statement<'tcx>,
         location: Location,
@@ -672,7 +672,7 @@ impl<'a, 'tcx, R> rustc_mir_dataflow::ResultsVisitor<'a, 'tcx, R>
 
     fn visit_terminator_before_primary_effect(
         &mut self,
-        _results: &mut R,
+        _results: &R,
         state: &BorrowckDomain<'a, 'tcx>,
         term: &'a Terminator<'tcx>,
         loc: Location,
@@ -785,7 +785,7 @@ impl<'a, 'tcx, R> rustc_mir_dataflow::ResultsVisitor<'a, 'tcx, R>
 
     fn visit_terminator_after_primary_effect(
         &mut self,
-        _results: &mut R,
+        _results: &R,
         state: &BorrowckDomain<'a, 'tcx>,
         term: &'a Terminator<'tcx>,
         loc: Location,

compiler/rustc_mir_dataflow/src/framework/cursor.rs

@@ -83,11 +83,6 @@ where
         &self.results
     }
 
-    /// Returns the underlying `Results`.
-    pub fn mut_results(&mut self) -> &mut Results<'tcx, A> {
-        &mut self.results
-    }
-
     /// Returns the `Analysis` used to generate the underlying `Results`.
     pub fn analysis(&self) -> &A {
         &self.results.analysis

compiler/rustc_mir_dataflow/src/framework/direction.rs

@@ -37,7 +37,7 @@ pub trait Direction {
         state: &mut D,
         block: BasicBlock,
         block_data: &'mir mir::BasicBlockData<'tcx>,
-        results: &mut R,
+        results: &R,
         vis: &mut impl ResultsVisitor<'mir, 'tcx, R, Domain = D>,
     ) where
         R: ResultsVisitable<'tcx, Domain = D>;
@@ -161,7 +161,7 @@ impl Direction for Backward {
         state: &mut D,
         block: BasicBlock,
         block_data: &'mir mir::BasicBlockData<'tcx>,
-        results: &mut R,
+        results: &R,
         vis: &mut impl ResultsVisitor<'mir, 'tcx, R, Domain = D>,
     ) where
         R: ResultsVisitable<'tcx, Domain = D>,
@@ -393,7 +393,7 @@ impl Direction for Forward {
         state: &mut F,
         block: BasicBlock,
         block_data: &'mir mir::BasicBlockData<'tcx>,
-        results: &mut R,
+        results: &R,
         vis: &mut impl ResultsVisitor<'mir, 'tcx, R, Domain = F>,
     ) where
         R: ResultsVisitable<'tcx, Domain = F>,

compiler/rustc_mir_dataflow/src/framework/engine.rs

@@ -52,7 +52,7 @@ where
     }
 
     pub fn visit_with<'mir>(
-        &mut self,
+        &self,
         body: &'mir mir::Body<'tcx>,
         blocks: impl IntoIterator<Item = BasicBlock>,
         vis: &mut impl ResultsVisitor<'mir, 'tcx, Self, Domain = A::Domain>,

compiler/rustc_mir_dataflow/src/framework/graphviz.rs

@@ -406,12 +406,8 @@ where
         w: &mut impl io::Write,
         block: BasicBlock,
     ) -> io::Result<()> {
-        let diffs = StateDiffCollector::run(
-            self.results.body(),
-            block,
-            self.results.mut_results(),
-            self.style,
-        );
+        let diffs =
+            StateDiffCollector::run(self.results.body(), block, self.results.results(), self.style);
 
         let mut diffs_before = diffs.before.map(|v| v.into_iter());
         let mut diffs_after = diffs.after.into_iter();
@@ -521,7 +517,7 @@ impl<D> StateDiffCollector<D> {
     fn run<'tcx, A>(
         body: &mir::Body<'tcx>,
         block: BasicBlock,
-        results: &mut Results<'tcx, A>,
+        results: &Results<'tcx, A>,
         style: OutputStyle,
     ) -> Self
     where
@@ -560,7 +556,7 @@ where
 
     fn visit_statement_before_primary_effect(
         &mut self,
-        results: &mut Results<'tcx, A>,
+        results: &Results<'tcx, A>,
         state: &Self::Domain,
         _statement: &mir::Statement<'tcx>,
         _location: Location,
@@ -573,7 +569,7 @@ where
 
     fn visit_statement_after_primary_effect(
         &mut self,
-        results: &mut Results<'tcx, A>,
+        results: &Results<'tcx, A>,
         state: &Self::Domain,
         _statement: &mir::Statement<'tcx>,
         _location: Location,
@@ -584,7 +580,7 @@ where
 
     fn visit_terminator_before_primary_effect(
         &mut self,
-        results: &mut Results<'tcx, A>,
+        results: &Results<'tcx, A>,
         state: &Self::Domain,
         _terminator: &mir::Terminator<'tcx>,
         _location: Location,
@@ -597,7 +593,7 @@ where
 
     fn visit_terminator_after_primary_effect(
         &mut self,
-        results: &mut Results<'tcx, A>,
+        results: &Results<'tcx, A>,
         state: &Self::Domain,
         _terminator: &mir::Terminator<'tcx>,
         _location: Location,

compiler/rustc_mir_dataflow/src/framework/visitor.rs

@@ -7,7 +7,7 @@ use super::{Analysis, Direction, Results};
 pub fn visit_results<'mir, 'tcx, D, R>(
     body: &'mir mir::Body<'tcx>,
     blocks: impl IntoIterator<Item = BasicBlock>,
-    results: &mut R,
+    results: &R,
     vis: &mut impl ResultsVisitor<'mir, 'tcx, R, Domain = D>,
 ) where
     R: ResultsVisitable<'tcx, Domain = D>,
@@ -37,7 +37,7 @@ pub trait ResultsVisitor<'mir, 'tcx, R> {
     /// its `statement_effect`.
     fn visit_statement_before_primary_effect(
         &mut self,
-        _results: &mut R,
+        _results: &R,
         _state: &Self::Domain,
         _statement: &'mir mir::Statement<'tcx>,
         _location: Location,
@@ -48,7 +48,7 @@ pub trait ResultsVisitor<'mir, 'tcx, R> {
     /// statement applied to `state`.
     fn visit_statement_after_primary_effect(
         &mut self,
-        _results: &mut R,
+        _results: &R,
         _state: &Self::Domain,
         _statement: &'mir mir::Statement<'tcx>,
         _location: Location,
@@ -59,7 +59,7 @@ pub trait ResultsVisitor<'mir, 'tcx, R> {
     /// its `terminator_effect`.
     fn visit_terminator_before_primary_effect(
         &mut self,
-        _results: &mut R,
+        _results: &R,
         _state: &Self::Domain,
         _terminator: &'mir mir::Terminator<'tcx>,
         _location: Location,
@@ -72,7 +72,7 @@ pub trait ResultsVisitor<'mir, 'tcx, R> {
     /// The `call_return_effect` (if one exists) will *not* be applied to `state`.
     fn visit_terminator_after_primary_effect(
         &mut self,
-        _results: &mut R,
+        _results: &R,
         _state: &Self::Domain,
         _terminator: &'mir mir::Terminator<'tcx>,
         _location: Location,

compiler/rustc_mir_dataflow/src/points.rs

@@ -128,7 +128,7 @@ where
 
     fn visit_statement_after_primary_effect(
         &mut self,
-        _results: &mut R,
+        _results: &R,
         state: &Self::Domain,
         _statement: &'mir mir::Statement<'tcx>,
         location: Location,
@@ -142,7 +142,7 @@ where
 
     fn visit_terminator_after_primary_effect(
         &mut self,
-        _results: &mut R,
+        _results: &R,
         state: &Self::Domain,
         _terminator: &'mir mir::Terminator<'tcx>,
         location: Location,

compiler/rustc_mir_transform/src/coroutine.rs

@@ -888,7 +888,7 @@ impl<'a, 'tcx, R> rustc_mir_dataflow::ResultsVisitor<'a, 'tcx, R>
 
     fn visit_statement_before_primary_effect(
         &mut self,
-        _results: &mut R,
+        _results: &R,
         state: &Self::Domain,
         _statement: &'a Statement<'tcx>,
         loc: Location,
@@ -898,7 +898,7 @@ impl<'a, 'tcx, R> rustc_mir_dataflow::ResultsVisitor<'a, 'tcx, R>
 
     fn visit_terminator_before_primary_effect(
         &mut self,
-        _results: &mut R,
+        _results: &R,
         state: &Self::Domain,
         _terminator: &'a Terminator<'tcx>,
         loc: Location,