Separate `Analysis` and `Results`.

`Results` contains and `Analysis` and an `EntryStates`. The unfortunate
thing about this is that the analysis needs to be mutable everywhere
(`&mut Analysis`) which forces the `Results` to be mutable everywhere,
even though `EntryStates` is immutable everywhere.

To fix this, this commit renames `Results` as `AnalysisAndResults`,
renames `EntryStates` as `Results`, and separates the analysis and
results as much as possible. (`AnalysisAndResults` doesn't get much use,
it's mostly there to facilitate method chaining of
`iterate_to_fixpoint`.)

`Results` is immutable everywhere, which:
- is a bit clearer on how the data is used,
- avoids an unnecessary clone of entry states in
  `locals_live_across_suspend_points`, and
- moves the results outside the `RefCell` in Formatter.

The commit also reformulates `ResultsHandle` as the generic `CowMut`,
which is simpler than `ResultsHandle` because it doesn't need the
`'tcx` lifetime and the trait bounds. It also which sits nicely
alongside the new use of `Cow` in `ResultsCursor`.

1 files changed, 13 insertions, 17 deletions

diff --git a/compiler/rustc_mir_dataflow/src/framework/mod.rs b/compiler/rustc_mir_dataflow/src/framework/mod.rs
index 09f6cdb5c4a..9cadec100b5 100644
--- a/compiler/rustc_mir_dataflow/src/framework/mod.rs
+++ b/compiler/rustc_mir_dataflow/src/framework/mod.rs
@@ -58,8 +58,9 @@ mod visitor;
 pub use self::cursor::ResultsCursor;
 pub use self::direction::{Backward, Direction, Forward};
 pub use self::lattice::{JoinSemiLattice, MaybeReachable};
-pub use self::results::{EntryStates, Results};
-pub use self::visitor::{ResultsVisitor, visit_results};
+pub(crate) use self::results::AnalysisAndResults;
+pub use self::results::Results;
+pub use self::visitor::{ResultsVisitor, visit_reachable_results, visit_results};
 
 /// Analysis domains are all bitsets of various kinds. This trait holds
 /// operations needed by all of them.
@@ -247,17 +248,15 @@ pub trait Analysis<'tcx> {
         tcx: TyCtxt<'tcx>,
         body: &'mir mir::Body<'tcx>,
         pass_name: Option<&'static str>,
-    ) -> Results<'tcx, Self>
+    ) -> AnalysisAndResults<'tcx, Self>
     where
         Self: Sized,
         Self::Domain: DebugWithContext<Self>,
     {
-        let mut entry_states =
-            IndexVec::from_fn_n(|_| self.bottom_value(body), body.basic_blocks.len());
-        self.initialize_start_block(body, &mut entry_states[mir::START_BLOCK]);
+        let mut results = IndexVec::from_fn_n(|_| self.bottom_value(body), body.basic_blocks.len());
+        self.initialize_start_block(body, &mut results[mir::START_BLOCK]);
 
-        if Self::Direction::IS_BACKWARD && entry_states[mir::START_BLOCK] != self.bottom_value(body)
-        {
+        if Self::Direction::IS_BACKWARD && results[mir::START_BLOCK] != self.bottom_value(body) {
             bug!("`initialize_start_block` is not yet supported for backward dataflow analyses");
         }
 
@@ -280,10 +279,9 @@ pub trait Analysis<'tcx> {
         // every iteration.
         let mut state = self.bottom_value(body);
         while let Some(bb) = dirty_queue.pop() {
-            // Set the state to the entry state of the block.
-            // This is equivalent to `state = entry_states[bb].clone()`,
-            // but it saves an allocation, thus improving compile times.
-            state.clone_from(&entry_states[bb]);
+            // Set the state to the entry state of the block. This is equivalent to `state =
+            // results[bb].clone()`, but it saves an allocation, thus improving compile times.
+            state.clone_from(&results[bb]);
 
             Self::Direction::apply_effects_in_block(
                 &mut self,
@@ -292,7 +290,7 @@ pub trait Analysis<'tcx> {
                 bb,
                 &body[bb],
                 |target: BasicBlock, state: &Self::Domain| {
-                    let set_changed = entry_states[target].join(state);
+                    let set_changed = results[target].join(state);
                     if set_changed {
                         dirty_queue.insert(target);
                     }
@@ -300,16 +298,14 @@ pub trait Analysis<'tcx> {
             );
         }
 
-        let mut results = Results { analysis: self, entry_states };
-
         if tcx.sess.opts.unstable_opts.dump_mir_dataflow {
-            let res = write_graphviz_results(tcx, body, &mut results, pass_name);
+            let res = write_graphviz_results(tcx, body, &mut self, &results, pass_name);
             if let Err(e) = res {
                 error!("Failed to write graphviz dataflow results: {}", e);
             }
         }
 
-        results
+        AnalysisAndResults { analysis: self, results }
     }
 }