Make MIR basic blocks field public

This makes it possible to mutably borrow different fields of the MIR
body without resorting to methods like `basic_blocks_local_decls_mut_and_var_debug_info`.

To preserve validity of control flow graph caches in the presence of
modifications, a new struct `BasicBlocks` wraps together basic blocks
and control flow graph caches.

The `BasicBlocks` dereferences to `IndexVec<BasicBlock, BasicBlockData>`.
On the other hand a mutable access requires explicit `as_mut()` call.

3 files changed, 4 insertions, 2 deletions

diff --git a/compiler/rustc_mir_transform/src/coverage/graph.rs b/compiler/rustc_mir_transform/src/coverage/graph.rs
index 510f1e64ed1..47f851c9709 100644
--- a/compiler/rustc_mir_transform/src/coverage/graph.rs
+++ b/compiler/rustc_mir_transform/src/coverage/graph.rs
@@ -80,7 +80,7 @@ impl CoverageGraph {
         IndexVec<BasicCoverageBlock, BasicCoverageBlockData>,
         IndexVec<BasicBlock, Option<BasicCoverageBlock>>,
     ) {
-        let num_basic_blocks = mir_body.num_nodes();
+        let num_basic_blocks = mir_body.basic_blocks.len();
         let mut bcbs = IndexVec::with_capacity(num_basic_blocks);
         let mut bb_to_bcb = IndexVec::from_elem_n(None, num_basic_blocks);
 
diff --git a/compiler/rustc_mir_transform/src/coverage/spans.rs b/compiler/rustc_mir_transform/src/coverage/spans.rs
index 82070b90325..423e78317aa 100644
--- a/compiler/rustc_mir_transform/src/coverage/spans.rs
+++ b/compiler/rustc_mir_transform/src/coverage/spans.rs
@@ -321,7 +321,8 @@ impl<'a, 'tcx> CoverageSpans<'a, 'tcx> {
     }
 
     fn mir_to_initial_sorted_coverage_spans(&self) -> Vec<CoverageSpan> {
-        let mut initial_spans = Vec::<CoverageSpan>::with_capacity(self.mir_body.num_nodes() * 2);
+        let mut initial_spans =
+            Vec::<CoverageSpan>::with_capacity(self.mir_body.basic_blocks.len() * 2);
         for (bcb, bcb_data) in self.basic_coverage_blocks.iter_enumerated() {
             initial_spans.extend(self.bcb_to_initial_coverage_spans(bcb, bcb_data));
         }
diff --git a/compiler/rustc_mir_transform/src/coverage/tests.rs b/compiler/rustc_mir_transform/src/coverage/tests.rs
index 213bb6608e1..6380f03528a 100644
--- a/compiler/rustc_mir_transform/src/coverage/tests.rs
+++ b/compiler/rustc_mir_transform/src/coverage/tests.rs
@@ -222,6 +222,7 @@ fn print_mir_graphviz(name: &str, mir_body: &Body<'_>) {
                         bb,
                         debug::term_type(&data.terminator().kind),
                         mir_body
+                            .basic_blocks
                             .successors(bb)
                             .map(|successor| { format!("    {:?} -> {:?};", bb, successor) })
                             .join("\n")