Rollup merge of #98930 - tmiasko:pub-basic-blocks, r=oli-obk

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.

Author: Dylan-DPC

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -1628,7 +1628,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             location: Location,
         ) -> impl Iterator<Item = Location> + Captures<'tcx> + 'a {
             if location.statement_index == 0 {
-                let predecessors = body.predecessors()[location.block].to_vec();
+                let predecessors = body.basic_blocks.predecessors()[location.block].to_vec();
                 Either::Left(predecessors.into_iter().map(move |bb| body.terminator_loc(bb)))
             } else {
                 Either::Right(std::iter::once(Location {

compiler/rustc_borrowck/src/invalidation.rs

@@ -26,7 +26,7 @@ pub(super) fn generate_invalidates<'tcx>(
 
     if let Some(all_facts) = all_facts {
         let _prof_timer = tcx.prof.generic_activity("polonius_fact_generation");
-        let dominators = body.dominators();
+        let dominators = body.basic_blocks.dominators();
         let mut ig = InvalidationGenerator {
             all_facts,
             borrow_set,

compiler/rustc_borrowck/src/lib.rs

@@ -334,7 +334,7 @@ fn do_mir_borrowck<'a, 'tcx>(
         };
     }
 
-    let dominators = body.dominators();
+    let dominators = body.basic_blocks.dominators();
 
     let mut mbcx = MirBorrowckCtxt {
         infcx,

compiler/rustc_borrowck/src/type_check/liveness/trace.rs

@@ -258,7 +258,7 @@ impl<'me, 'typeck, 'flow, 'tcx> LivenessResults<'me, 'typeck, 'flow, 'tcx> {
 
                 let block = self.cx.elements.to_location(block_start).block;
                 self.stack.extend(
-                    self.cx.body.predecessors()[block]
+                    self.cx.body.basic_blocks.predecessors()[block]
                         .iter()
                         .map(|&pred_bb| self.cx.body.terminator_loc(pred_bb))
                         .map(|pred_loc| self.cx.elements.point_from_location(pred_loc)),
@@ -354,7 +354,7 @@ impl<'me, 'typeck, 'flow, 'tcx> LivenessResults<'me, 'typeck, 'flow, 'tcx> {
         }
 
         let body = self.cx.body;
-        for &pred_block in body.predecessors()[block].iter() {
+        for &pred_block in body.basic_blocks.predecessors()[block].iter() {
             debug!("compute_drop_live_points_for_block: pred_block = {:?}", pred_block,);
 
             // Check whether the variable is (at least partially)

compiler/rustc_codegen_ssa/src/mir/analyze.rs

@@ -15,7 +15,7 @@ pub fn non_ssa_locals<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
     fx: &FunctionCx<'a, 'tcx, Bx>,
 ) -> BitSet<mir::Local> {
     let mir = fx.mir;
-    let dominators = mir.dominators();
+    let dominators = mir.basic_blocks.dominators();
     let locals = mir
         .local_decls
         .iter()

compiler/rustc_const_eval/src/transform/promote_consts.rs

@@ -856,7 +856,8 @@ impl<'a, 'tcx> Promoter<'a, 'tcx> {
                     literal: ConstantKind::from_const(_const, tcx),
                 }))
             };
-            let (blocks, local_decls) = self.source.basic_blocks_and_local_decls_mut();
+            let blocks = self.source.basic_blocks.as_mut();
+            let local_decls = &mut self.source.local_decls;
             let loc = candidate.location;
             let statement = &mut blocks[loc.block].statements[loc.statement_index];
             match statement.kind {
@@ -865,7 +866,7 @@ impl<'a, 'tcx> Promoter<'a, 'tcx> {
                     Rvalue::Ref(ref mut region, borrow_kind, ref mut place),
                 )) => {
                     // Use the underlying local for this (necessarily interior) borrow.
-                    let ty = local_decls.local_decls()[place.local].ty;
+                    let ty = local_decls[place.local].ty;
                     let span = statement.source_info.span;
 
                     let ref_ty = tcx.mk_ref(

compiler/rustc_middle/src/mir/basic_blocks.rs

@@ -0,0 +1,147 @@
+use crate::mir::graph_cyclic_cache::GraphIsCyclicCache;
+use crate::mir::predecessors::{PredecessorCache, Predecessors};
+use crate::mir::switch_sources::{SwitchSourceCache, SwitchSources};
+use crate::mir::traversal::PostorderCache;
+use crate::mir::{BasicBlock, BasicBlockData, Successors, START_BLOCK};
+
+use rustc_data_structures::graph;
+use rustc_data_structures::graph::dominators::{dominators, Dominators};
+use rustc_index::vec::IndexVec;
+
+#[derive(Clone, TyEncodable, TyDecodable, Debug, HashStable, TypeFoldable, TypeVisitable)]
+pub struct BasicBlocks<'tcx> {
+    basic_blocks: IndexVec<BasicBlock, BasicBlockData<'tcx>>,
+    predecessor_cache: PredecessorCache,
+    switch_source_cache: SwitchSourceCache,
+    is_cyclic: GraphIsCyclicCache,
+    postorder_cache: PostorderCache,
+}
+
+impl<'tcx> BasicBlocks<'tcx> {
+    #[inline]
+    pub fn new(basic_blocks: IndexVec<BasicBlock, BasicBlockData<'tcx>>) -> Self {
+        BasicBlocks {
+            basic_blocks,
+            predecessor_cache: PredecessorCache::new(),
+            switch_source_cache: SwitchSourceCache::new(),
+            is_cyclic: GraphIsCyclicCache::new(),
+            postorder_cache: PostorderCache::new(),
+        }
+    }
+
+    /// Returns true if control-flow graph contains a cycle reachable from the `START_BLOCK`.
+    #[inline]
+    pub fn is_cfg_cyclic(&self) -> bool {
+        self.is_cyclic.is_cyclic(self)
+    }
+
+    #[inline]
+    pub fn dominators(&self) -> Dominators<BasicBlock> {
+        dominators(&self)
+    }
+
+    /// Returns predecessors for each basic block.
+    #[inline]
+    pub fn predecessors(&self) -> &Predecessors {
+        self.predecessor_cache.compute(&self.basic_blocks)
+    }
+
+    /// Returns basic blocks in a postorder.
+    #[inline]
+    pub fn postorder(&self) -> &[BasicBlock] {
+        self.postorder_cache.compute(&self.basic_blocks)
+    }
+
+    /// `switch_sources()[&(target, switch)]` returns a list of switch
+    /// values that lead to a `target` block from a `switch` block.
+    #[inline]
+    pub fn switch_sources(&self) -> &SwitchSources {
+        self.switch_source_cache.compute(&self.basic_blocks)
+    }
+
+    /// Returns mutable reference to basic blocks. Invalidates CFG cache.
+    #[inline]
+    pub fn as_mut(&mut self) -> &mut IndexVec<BasicBlock, BasicBlockData<'tcx>> {
+        self.invalidate_cfg_cache();
+        &mut self.basic_blocks
+    }
+
+    /// Get mutable access to basic blocks without invalidating the CFG cache.
+    ///
+    /// By calling this method instead of e.g. [`BasicBlocks::as_mut`] you promise not to change
+    /// the CFG. This means that
+    ///
+    ///  1) The number of basic blocks remains unchanged
+    ///  2) The set of successors of each terminator remains unchanged.
+    ///  3) For each `TerminatorKind::SwitchInt`, the `targets` remains the same and the terminator
+    ///     kind is not changed.
+    ///
+    /// If any of these conditions cannot be upheld, you should call [`BasicBlocks::invalidate_cfg_cache`].
+    #[inline]
+    pub fn as_mut_preserves_cfg(&mut self) -> &mut IndexVec<BasicBlock, BasicBlockData<'tcx>> {
+        &mut self.basic_blocks
+    }
+
+    /// Invalidates cached information about the CFG.
+    ///
+    /// You will only ever need this if you have also called [`BasicBlocks::as_mut_preserves_cfg`].
+    /// All other methods that allow you to mutate the basic blocks also call this method
+    /// themselves, thereby avoiding any risk of accidentaly cache invalidation.
+    pub fn invalidate_cfg_cache(&mut self) {
+        self.predecessor_cache.invalidate();
+        self.switch_source_cache.invalidate();
+        self.is_cyclic.invalidate();
+        self.postorder_cache.invalidate();
+    }
+}
+
+impl<'tcx> std::ops::Deref for BasicBlocks<'tcx> {
+    type Target = IndexVec<BasicBlock, BasicBlockData<'tcx>>;
+
+    #[inline]
+    fn deref(&self) -> &IndexVec<BasicBlock, BasicBlockData<'tcx>> {
+        &self.basic_blocks
+    }
+}
+
+impl<'tcx> graph::DirectedGraph for BasicBlocks<'tcx> {
+    type Node = BasicBlock;
+}
+
+impl<'tcx> graph::WithNumNodes for BasicBlocks<'tcx> {
+    #[inline]
+    fn num_nodes(&self) -> usize {
+        self.basic_blocks.len()
+    }
+}
+
+impl<'tcx> graph::WithStartNode for BasicBlocks<'tcx> {
+    #[inline]
+    fn start_node(&self) -> Self::Node {
+        START_BLOCK
+    }
+}
+
+impl<'tcx> graph::WithSuccessors for BasicBlocks<'tcx> {
+    #[inline]
+    fn successors(&self, node: Self::Node) -> <Self as graph::GraphSuccessors<'_>>::Iter {
+        self.basic_blocks[node].terminator().successors()
+    }
+}
+
+impl<'a, 'b> graph::GraphSuccessors<'b> for BasicBlocks<'a> {
+    type Item = BasicBlock;
+    type Iter = Successors<'b>;
+}
+
+impl<'tcx, 'graph> graph::GraphPredecessors<'graph> for BasicBlocks<'tcx> {
+    type Item = BasicBlock;
+    type Iter = std::iter::Copied<std::slice::Iter<'graph, BasicBlock>>;
+}
+
+impl<'tcx> graph::WithPredecessors for BasicBlocks<'tcx> {
+    #[inline]
+    fn predecessors(&self, node: Self::Node) -> <Self as graph::GraphPredecessors<'_>>::Iter {
+        self.predecessors()[node].iter().copied()
+    }
+}

compiler/rustc_middle/src/mir/mod.rs

@@ -5,7 +5,6 @@
 use crate::mir::interpret::{
     AllocRange, ConstAllocation, ConstValue, GlobalAlloc, LitToConstInput, Scalar,
 };
-use crate::mir::traversal::PostorderCache;
 use crate::mir::visit::MirVisitable;
 use crate::ty::codec::{TyDecoder, TyEncoder};
 use crate::ty::fold::{FallibleTypeFolder, TypeFoldable, TypeSuperFoldable};
@@ -27,8 +26,7 @@ use rustc_target::abi::{Size, VariantIdx};
 use polonius_engine::Atom;
 pub use rustc_ast::Mutability;
 use rustc_data_structures::fx::FxHashSet;
-use rustc_data_structures::graph::dominators::{dominators, Dominators};
-use rustc_data_structures::graph::{self, GraphSuccessors};
+use rustc_data_structures::graph::dominators::Dominators;
 use rustc_index::bit_set::BitMatrix;
 use rustc_index::vec::{Idx, IndexVec};
 use rustc_serialize::{Decodable, Encodable};
@@ -43,11 +41,10 @@ use std::fmt::{self, Debug, Display, Formatter, Write};
 use std::ops::{ControlFlow, Index, IndexMut};
 use std::{iter, mem};
 
-use self::graph_cyclic_cache::GraphIsCyclicCache;
-use self::predecessors::{PredecessorCache, Predecessors};
 pub use self::query::*;
-use self::switch_sources::{SwitchSourceCache, SwitchSources};
+pub use basic_blocks::BasicBlocks;
 
+mod basic_blocks;
 pub mod coverage;
 mod generic_graph;
 pub mod generic_graphviz;
@@ -189,7 +186,7 @@ pub struct GeneratorInfo<'tcx> {
 pub struct Body<'tcx> {
     /// A list of basic blocks. References to basic block use a newtyped index type [`BasicBlock`]
     /// that indexes into this vector.
-    basic_blocks: IndexVec<BasicBlock, BasicBlockData<'tcx>>,
+    pub basic_blocks: BasicBlocks<'tcx>,
 
     /// Records how far through the "desugaring and optimization" process this particular
     /// MIR has traversed. This is particularly useful when inlining, since in that context
@@ -257,11 +254,6 @@ pub struct Body<'tcx> {
     /// potentially allow things like `[u8; std::mem::size_of::<T>() * 0]` due to this.
     pub is_polymorphic: bool,
 
-    predecessor_cache: PredecessorCache,
-    switch_source_cache: SwitchSourceCache,
-    is_cyclic: GraphIsCyclicCache,
-    postorder_cache: PostorderCache,
-
     pub tainted_by_errors: Option<ErrorGuaranteed>,
 }
 
@@ -289,7 +281,7 @@ impl<'tcx> Body<'tcx> {
         let mut body = Body {
             phase: MirPhase::Built,
             source,
-            basic_blocks,
+            basic_blocks: BasicBlocks::new(basic_blocks),
             source_scopes,
             generator: generator_kind.map(|generator_kind| {
                 Box::new(GeneratorInfo {
@@ -307,10 +299,6 @@ impl<'tcx> Body<'tcx> {
             span,
             required_consts: Vec::new(),
             is_polymorphic: false,
-            predecessor_cache: PredecessorCache::new(),
-            switch_source_cache: SwitchSourceCache::new(),
-            is_cyclic: GraphIsCyclicCache::new(),
-            postorder_cache: PostorderCache::new(),
             tainted_by_errors,
         };
         body.is_polymorphic = body.has_param_types_or_consts();
@@ -326,7 +314,7 @@ impl<'tcx> Body<'tcx> {
         let mut body = Body {
             phase: MirPhase::Built,
             source: MirSource::item(CRATE_DEF_ID.to_def_id()),
-            basic_blocks,
+            basic_blocks: BasicBlocks::new(basic_blocks),
             source_scopes: IndexVec::new(),
             generator: None,
             local_decls: IndexVec::new(),
@@ -337,10 +325,6 @@ impl<'tcx> Body<'tcx> {
             required_consts: Vec::new(),
             var_debug_info: Vec::new(),
             is_polymorphic: false,
-            predecessor_cache: PredecessorCache::new(),
-            switch_source_cache: SwitchSourceCache::new(),
-            is_cyclic: GraphIsCyclicCache::new(),
-            postorder_cache: PostorderCache::new(),
             tainted_by_errors: None,
         };
         body.is_polymorphic = body.has_param_types_or_consts();
@@ -354,74 +338,7 @@ impl<'tcx> Body<'tcx> {
 
     #[inline]
     pub fn basic_blocks_mut(&mut self) -> &mut IndexVec<BasicBlock, BasicBlockData<'tcx>> {
-        // Because the user could mutate basic block terminators via this reference, we need to
-        // invalidate the caches.
-        //
-        // FIXME: Use a finer-grained API for this, so only transformations that alter terminators
-        // invalidate the caches.
-        self.invalidate_cfg_cache();
-        &mut self.basic_blocks
-    }
-
-    #[inline]
-    pub fn basic_blocks_and_local_decls_mut(
-        &mut self,
-    ) -> (&mut IndexVec<BasicBlock, BasicBlockData<'tcx>>, &mut LocalDecls<'tcx>) {
-        self.invalidate_cfg_cache();
-        (&mut self.basic_blocks, &mut self.local_decls)
-    }
-
-    #[inline]
-    pub fn basic_blocks_local_decls_mut_and_var_debug_info(
-        &mut self,
-    ) -> (
-        &mut IndexVec<BasicBlock, BasicBlockData<'tcx>>,
-        &mut LocalDecls<'tcx>,
-        &mut Vec<VarDebugInfo<'tcx>>,
-    ) {
-        self.invalidate_cfg_cache();
-        (&mut self.basic_blocks, &mut self.local_decls, &mut self.var_debug_info)
-    }
-
-    /// Get mutable access to parts of the Body without invalidating the CFG cache.
-    ///
-    /// By calling this method instead of eg [`Body::basic_blocks_mut`], you promise not to change
-    /// the CFG. This means that
-    ///
-    ///  1) The number of basic blocks remains unchanged
-    ///  2) The set of successors of each terminator remains unchanged.
-    ///  3) For each `TerminatorKind::SwitchInt`, the `targets` remains the same and the terminator
-    ///     kind is not changed.
-    ///
-    /// If any of these conditions cannot be upheld, you should call [`Body::invalidate_cfg_cache`].
-    #[inline]
-    pub fn basic_blocks_local_decls_mut_and_var_debug_info_no_invalidate(
-        &mut self,
-    ) -> (
-        &mut IndexVec<BasicBlock, BasicBlockData<'tcx>>,
-        &mut LocalDecls<'tcx>,
-        &mut Vec<VarDebugInfo<'tcx>>,
-    ) {
-        (&mut self.basic_blocks, &mut self.local_decls, &mut self.var_debug_info)
-    }
-
-    /// Invalidates cached information about the CFG.
-    ///
-    /// You will only ever need this if you have also called
-    /// [`Body::basic_blocks_local_decls_mut_and_var_debug_info_no_invalidate`]. All other methods
-    /// that allow you to mutate the body also call this method themselves, thereby avoiding any
-    /// risk of accidentaly cache invalidation.
-    pub fn invalidate_cfg_cache(&mut self) {
-        self.predecessor_cache.invalidate();
-        self.switch_source_cache.invalidate();
-        self.is_cyclic.invalidate();
-        self.postorder_cache.invalidate();
-    }
-
-    /// Returns `true` if a cycle exists in the control-flow graph that is reachable from the
-    /// `START_BLOCK`.
-    pub fn is_cfg_cyclic(&self) -> bool {
-        self.is_cyclic.is_cyclic(self)
+        self.basic_blocks.as_mut()
     }
 
     #[inline]
@@ -495,14 +412,6 @@ impl<'tcx> Body<'tcx> {
         self.local_decls.drain(self.arg_count + 1..)
     }
 
-    /// Changes a statement to a nop. This is both faster than deleting instructions and avoids
-    /// invalidating statement indices in `Location`s.
-    pub fn make_statement_nop(&mut self, location: Location) {
-        let block = &mut self.basic_blocks[location.block];
-        debug_assert!(location.statement_index < block.statements.len());
-        block.statements[location.statement_index].make_nop()
-    }
-
     /// Returns the source info associated with `location`.
     pub fn source_info(&self, location: Location) -> &SourceInfo {
         let block = &self[location.block];
@@ -538,23 +447,6 @@ impl<'tcx> Body<'tcx> {
             .unwrap_or_else(|| Either::Right(block_data.terminator()))
     }
 
-    #[inline]
-    pub fn predecessors(&self) -> &Predecessors {
-        self.predecessor_cache.compute(&self.basic_blocks)
-    }
-
-    /// `body.switch_sources()[&(target, switch)]` returns a list of switch
-    /// values that lead to a `target` block from a `switch` block.
-    #[inline]
-    pub fn switch_sources(&self) -> &SwitchSources {
-        self.switch_source_cache.compute(&self.basic_blocks)
-    }
-
-    #[inline]
-    pub fn dominators(&self) -> Dominators<BasicBlock> {
-        dominators(self)
-    }
-
     #[inline]
     pub fn yield_ty(&self) -> Option<Ty<'tcx>> {
         self.generator.as_ref().and_then(|generator| generator.yield_ty)
@@ -599,7 +491,7 @@ impl<'tcx> Index<BasicBlock> for Body<'tcx> {
 impl<'tcx> IndexMut<BasicBlock> for Body<'tcx> {
     #[inline]
     fn index_mut(&mut self, index: BasicBlock) -> &mut BasicBlockData<'tcx> {
-        &mut self.basic_blocks_mut()[index]
+        &mut self.basic_blocks.as_mut()[index]
     }
 }
 
@@ -2890,48 +2782,6 @@ fn pretty_print_const_value<'tcx>(
     })
 }
 
-impl<'tcx> graph::DirectedGraph for Body<'tcx> {
-    type Node = BasicBlock;
-}
-
-impl<'tcx> graph::WithNumNodes for Body<'tcx> {
-    #[inline]
-    fn num_nodes(&self) -> usize {
-        self.basic_blocks.len()
-    }
-}
-
-impl<'tcx> graph::WithStartNode for Body<'tcx> {
-    #[inline]
-    fn start_node(&self) -> Self::Node {
-        START_BLOCK
-    }
-}
-
-impl<'tcx> graph::WithSuccessors for Body<'tcx> {
-    #[inline]
-    fn successors(&self, node: Self::Node) -> <Self as GraphSuccessors<'_>>::Iter {
-        self.basic_blocks[node].terminator().successors()
-    }
-}
-
-impl<'a, 'b> graph::GraphSuccessors<'b> for Body<'a> {
-    type Item = BasicBlock;
-    type Iter = Successors<'b>;
-}
-
-impl<'tcx, 'graph> graph::GraphPredecessors<'graph> for Body<'tcx> {
-    type Item = BasicBlock;
-    type Iter = std::iter::Copied<std::slice::Iter<'graph, BasicBlock>>;
-}
-
-impl<'tcx> graph::WithPredecessors for Body<'tcx> {
-    #[inline]
-    fn predecessors(&self, node: Self::Node) -> <Self as graph::GraphPredecessors<'_>>::Iter {
-        self.predecessors()[node].iter().copied()
-    }
-}
-
 /// `Location` represents the position of the start of the statement; or, if
 /// `statement_index` equals the number of statements, then the start of the
 /// terminator.
@@ -2968,7 +2818,7 @@ impl Location {
             return true;
         }
 
-        let predecessors = body.predecessors();
+        let predecessors = body.basic_blocks.predecessors();
 
         // If we're in another block, then we want to check that block is a predecessor of `other`.
         let mut queue: Vec<BasicBlock> = predecessors[other.block].to_vec();

compiler/rustc_middle/src/mir/traversal.rs

@@ -104,22 +104,25 @@ impl<'a, 'tcx> Iterator for Preorder<'a, 'tcx> {
 ///
 /// A Postorder traversal of this graph is `D B C A` or `D C B A`
 pub struct Postorder<'a, 'tcx> {
-    body: &'a Body<'tcx>,
+    basic_blocks: &'a IndexVec<BasicBlock, BasicBlockData<'tcx>>,
     visited: BitSet<BasicBlock>,
     visit_stack: Vec<(BasicBlock, Successors<'a>)>,
     root_is_start_block: bool,
 }
 
 impl<'a, 'tcx> Postorder<'a, 'tcx> {
-    pub fn new(body: &'a Body<'tcx>, root: BasicBlock) -> Postorder<'a, 'tcx> {
+    pub fn new(
+        basic_blocks: &'a IndexVec<BasicBlock, BasicBlockData<'tcx>>,
+        root: BasicBlock,
+    ) -> Postorder<'a, 'tcx> {
         let mut po = Postorder {
-            body,
-            visited: BitSet::new_empty(body.basic_blocks().len()),
+            basic_blocks,
+            visited: BitSet::new_empty(basic_blocks.len()),
             visit_stack: Vec::new(),
             root_is_start_block: root == START_BLOCK,
         };
 
-        let data = &po.body[root];
+        let data = &po.basic_blocks[root];
 
         if let Some(ref term) = data.terminator {
             po.visited.insert(root);
@@ -190,7 +193,7 @@ impl<'a, 'tcx> Postorder<'a, 'tcx> {
             };
 
             if self.visited.insert(bb) {
-                if let Some(term) = &self.body[bb].terminator {
+                if let Some(term) = &self.basic_blocks[bb].terminator {
                     self.visit_stack.push((bb, term.successors()));
                 }
             }
@@ -199,7 +202,7 @@ impl<'a, 'tcx> Postorder<'a, 'tcx> {
 }
 
 pub fn postorder<'a, 'tcx>(body: &'a Body<'tcx>) -> Postorder<'a, 'tcx> {
-    Postorder::new(body, START_BLOCK)
+    Postorder::new(&body.basic_blocks, START_BLOCK)
 }
 
 impl<'a, 'tcx> Iterator for Postorder<'a, 'tcx> {
@@ -211,12 +214,12 @@ impl<'a, 'tcx> Iterator for Postorder<'a, 'tcx> {
             self.traverse_successor();
         }
 
-        next.map(|(bb, _)| (bb, &self.body[bb]))
+        next.map(|(bb, _)| (bb, &self.basic_blocks[bb]))
     }
 
     fn size_hint(&self) -> (usize, Option<usize>) {
         // All the blocks, minus the number of blocks we've visited.
-        let upper = self.body.basic_blocks().len() - self.visited.count();
+        let upper = self.basic_blocks.len() - self.visited.count();
 
         let lower = if self.root_is_start_block {
             // We will visit all remaining blocks exactly once.
@@ -263,10 +266,8 @@ pub struct ReversePostorder<'a, 'tcx> {
 
 impl<'a, 'tcx> ReversePostorder<'a, 'tcx> {
     pub fn new(body: &'a Body<'tcx>, root: BasicBlock) -> ReversePostorder<'a, 'tcx> {
-        let blocks: Vec<_> = Postorder::new(body, root).map(|(bb, _)| bb).collect();
-
+        let blocks: Vec<_> = Postorder::new(&body.basic_blocks, root).map(|(bb, _)| bb).collect();
         let len = blocks.len();
-
         ReversePostorder { body, blocks, idx: len }
     }
 }
@@ -334,10 +335,8 @@ impl<'a, 'tcx> Iterator for ReversePostorderIter<'a, 'tcx> {
 impl<'a, 'tcx> ExactSizeIterator for ReversePostorderIter<'a, 'tcx> {}
 
 pub fn reverse_postorder<'a, 'tcx>(body: &'a Body<'tcx>) -> ReversePostorderIter<'a, 'tcx> {
-    let blocks = body.postorder_cache.compute(body);
-
+    let blocks = body.basic_blocks.postorder();
     let len = blocks.len();
-
     ReversePostorderIter { body, blocks, idx: len }
 }
 
@@ -360,7 +359,7 @@ impl PostorderCache {
 
     /// Returns the `&[BasicBlocks]` represents the postorder graph for this MIR.
     #[inline]
-    pub(super) fn compute(&self, body: &Body<'_>) -> &[BasicBlock] {
+    pub(super) fn compute(&self, body: &IndexVec<BasicBlock, BasicBlockData<'_>>) -> &[BasicBlock] {
         self.cache.get_or_init(|| Postorder::new(body, START_BLOCK).map(|(bb, _)| bb).collect())
     }
 }

compiler/rustc_mir_build/src/lints.rs

@@ -2,7 +2,7 @@ use rustc_data_structures::graph::iterate::{
     NodeStatus, TriColorDepthFirstSearch, TriColorVisitor,
 };
 use rustc_hir::intravisit::FnKind;
-use rustc_middle::mir::{BasicBlock, Body, Operand, TerminatorKind};
+use rustc_middle::mir::{BasicBlock, BasicBlocks, Body, Operand, TerminatorKind};
 use rustc_middle::ty::subst::{GenericArg, InternalSubsts};
 use rustc_middle::ty::{self, AssocItem, AssocItemContainer, Instance, TyCtxt};
 use rustc_session::lint::builtin::UNCONDITIONAL_RECURSION;
@@ -30,7 +30,9 @@ pub(crate) fn check<'tcx>(tcx: TyCtxt<'tcx>, body: &Body<'tcx>) {
         };
 
         let mut vis = Search { tcx, body, reachable_recursive_calls: vec![], trait_substs };
-        if let Some(NonRecursive) = TriColorDepthFirstSearch::new(&body).run_from_start(&mut vis) {
+        if let Some(NonRecursive) =
+            TriColorDepthFirstSearch::new(&body.basic_blocks).run_from_start(&mut vis)
+        {
             return;
         }
         if vis.reachable_recursive_calls.is_empty() {
@@ -101,7 +103,7 @@ impl<'mir, 'tcx> Search<'mir, 'tcx> {
     }
 }
 
-impl<'mir, 'tcx> TriColorVisitor<&'mir Body<'tcx>> for Search<'mir, 'tcx> {
+impl<'mir, 'tcx> TriColorVisitor<BasicBlocks<'tcx>> for Search<'mir, 'tcx> {
     type BreakVal = NonRecursive;
 
     fn node_examined(

compiler/rustc_mir_dataflow/src/framework/direction.rs

@@ -228,7 +228,7 @@ impl Direction for Backward {
     ) where
         A: Analysis<'tcx>,
     {
-        for pred in body.predecessors()[bb].iter().copied() {
+        for pred in body.basic_blocks.predecessors()[bb].iter().copied() {
             match body[pred].terminator().kind {
                 // Apply terminator-specific edge effects.
                 //
@@ -316,7 +316,7 @@ where
     fn apply(&mut self, mut apply_edge_effect: impl FnMut(&mut D, SwitchIntTarget)) {
         assert!(!self.effects_applied);
 
-        let values = &self.body.switch_sources()[&(self.bb, self.pred)];
+        let values = &self.body.basic_blocks.switch_sources()[&(self.bb, self.pred)];
         let targets = values.iter().map(|&value| SwitchIntTarget { value, target: self.bb });
 
         let mut tmp = None;

compiler/rustc_mir_dataflow/src/framework/engine.rs

@@ -101,7 +101,7 @@ where
         // transfer function for each block exactly once (assuming that we process blocks in RPO).
         //
         // In this case, there's no need to compute the block transfer functions ahead of time.
-        if !body.is_cfg_cyclic() {
+        if !body.basic_blocks.is_cfg_cyclic() {
             return Self::new(tcx, body, analysis, None);
         }
 

compiler/rustc_mir_transform/src/add_call_guards.rs

@@ -39,7 +39,7 @@ impl<'tcx> MirPass<'tcx> for AddCallGuards {
 impl AddCallGuards {
     pub fn add_call_guards(&self, body: &mut Body<'_>) {
         let mut pred_count: IndexVec<_, _> =
-            body.predecessors().iter().map(|ps| ps.len()).collect();
+            body.basic_blocks.predecessors().iter().map(|ps| ps.len()).collect();
         pred_count[START_BLOCK] += 1;
 
         // We need a place to store the new blocks generated

compiler/rustc_mir_transform/src/add_retag.rs

@@ -91,7 +91,8 @@ impl<'tcx> MirPass<'tcx> for AddRetag {
         super::add_call_guards::AllCallEdges.run_pass(tcx, body);
 
         let (span, arg_count) = (body.span, body.arg_count);
-        let (basic_blocks, local_decls) = body.basic_blocks_and_local_decls_mut();
+        let basic_blocks = body.basic_blocks.as_mut();
+        let local_decls = &body.local_decls;
         let needs_retag = |place: &Place<'tcx>| {
             // FIXME: Instead of giving up for unstable places, we should introduce
             // a temporary and retag on that.

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);
 
@@ -95,7 +95,7 @@ impl CoverageGraph {
         let mut basic_blocks = Vec::new();
         for (bb, data) in mir_cfg_without_unwind {
             if let Some(last) = basic_blocks.last() {
-                let predecessors = &mir_body.predecessors()[bb];
+                let predecessors = &mir_body.basic_blocks.predecessors()[bb];
                 if predecessors.len() > 1 || !predecessors.contains(last) {
                     // The `bb` has more than one _incoming_ edge, and should start its own
                     // `BasicCoverageBlockData`. (Note, the `basic_blocks` vector does not yet

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));
         }

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")

compiler/rustc_mir_transform/src/dead_store_elimination.rs

@@ -66,7 +66,7 @@ pub fn eliminate<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>, borrowed: &BitS
         return;
     }
 
-    let bbs = body.basic_blocks_local_decls_mut_and_var_debug_info_no_invalidate().0;
+    let bbs = body.basic_blocks.as_mut_preserves_cfg();
     for Location { block, statement_index } in patch {
         bbs[block].statements[statement_index].make_nop();
     }

compiler/rustc_mir_transform/src/deaggregator.rs

@@ -11,9 +11,7 @@ impl<'tcx> MirPass<'tcx> for Deaggregator {
     }
 
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
-        let (basic_blocks, local_decls, _) =
-            body.basic_blocks_local_decls_mut_and_var_debug_info_no_invalidate();
-        let local_decls = &*local_decls;
+        let basic_blocks = body.basic_blocks.as_mut_preserves_cfg();
         for bb in basic_blocks {
             bb.expand_statements(|stmt| {
                 // FIXME(eddyb) don't match twice on `stmt.kind` (post-NLL).
@@ -38,7 +36,7 @@ impl<'tcx> MirPass<'tcx> for Deaggregator {
                 Some(expand_aggregate(
                     lhs,
                     operands.into_iter().map(|op| {
-                        let ty = op.ty(local_decls, tcx);
+                        let ty = op.ty(&body.local_decls, tcx);
                         (op, ty)
                     }),
                     *kind,

compiler/rustc_mir_transform/src/elaborate_box_derefs.rs

@@ -110,13 +110,13 @@ impl<'tcx> MirPass<'tcx> for ElaborateBoxDerefs {
 
             let patch = MirPatch::new(body);
 
-            let (basic_blocks, local_decls) = body.basic_blocks_and_local_decls_mut();
+            let local_decls = &mut body.local_decls;
 
             let mut visitor =
                 ElaborateBoxDerefVisitor { tcx, unique_did, nonnull_did, local_decls, patch };
 
             for (block, BasicBlockData { statements, terminator, .. }) in
-                basic_blocks.iter_enumerated_mut()
+                body.basic_blocks.as_mut().iter_enumerated_mut()
             {
                 let mut index = 0;
                 for statement in statements {

compiler/rustc_mir_transform/src/instcombine.rs

@@ -16,9 +16,8 @@ impl<'tcx> MirPass<'tcx> for InstCombine {
     }
 
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
-        let (basic_blocks, local_decls) = body.basic_blocks_and_local_decls_mut();
-        let ctx = InstCombineContext { tcx, local_decls };
-        for block in basic_blocks.iter_mut() {
+        let ctx = InstCombineContext { tcx, local_decls: &body.local_decls };
+        for block in body.basic_blocks.as_mut() {
             for statement in block.statements.iter_mut() {
                 match statement.kind {
                     StatementKind::Assign(box (_place, ref mut rvalue)) => {

compiler/rustc_mir_transform/src/lower_intrinsics.rs

@@ -11,8 +11,8 @@ pub struct LowerIntrinsics;
 
 impl<'tcx> MirPass<'tcx> for LowerIntrinsics {
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
-        let (basic_blocks, local_decls) = body.basic_blocks_and_local_decls_mut();
-        for block in basic_blocks {
+        let local_decls = &body.local_decls;
+        for block in body.basic_blocks.as_mut() {
             let terminator = block.terminator.as_mut().unwrap();
             if let TerminatorKind::Call { func, args, destination, target, .. } =
                 &mut terminator.kind

compiler/rustc_mir_transform/src/lower_slice_len.rs

@@ -27,12 +27,10 @@ pub fn lower_slice_len_calls<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
     };
 
     // The one successor remains unchanged, so no need to invalidate
-    let (basic_blocks, local_decls, _) =
-        body.basic_blocks_local_decls_mut_and_var_debug_info_no_invalidate();
-
+    let basic_blocks = body.basic_blocks.as_mut_preserves_cfg();
     for block in basic_blocks {
         // lower `<[_]>::len` calls
-        lower_slice_len_call(tcx, block, &*local_decls, slice_len_fn_item_def_id);
+        lower_slice_len_call(tcx, block, &body.local_decls, slice_len_fn_item_def_id);
     }
 }
 

compiler/rustc_mir_transform/src/match_branches.rs

@@ -48,7 +48,7 @@ impl<'tcx> MirPass<'tcx> for MatchBranchSimplification {
         let def_id = body.source.def_id();
         let param_env = tcx.param_env(def_id);
 
-        let (bbs, local_decls) = body.basic_blocks_and_local_decls_mut();
+        let bbs = body.basic_blocks.as_mut();
         let mut should_cleanup = false;
         'outer: for bb_idx in bbs.indices() {
             if !tcx.consider_optimizing(|| format!("MatchBranchSimplification {:?} ", def_id)) {
@@ -108,7 +108,7 @@ impl<'tcx> MirPass<'tcx> for MatchBranchSimplification {
 
             // Introduce a temporary for the discriminant value.
             let source_info = bbs[bb_idx].terminator().source_info;
-            let discr_local = local_decls.push(LocalDecl::new(switch_ty, source_info.span));
+            let discr_local = body.local_decls.push(LocalDecl::new(switch_ty, source_info.span));
 
             // We already checked that first and second are different blocks,
             // and bb_idx has a different terminator from both of them.

compiler/rustc_mir_transform/src/normalize_array_len.rs

@@ -33,8 +33,8 @@ impl<'tcx> MirPass<'tcx> for NormalizeArrayLen {
 
 pub fn normalize_array_len_calls<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
     // We don't ever touch terminators, so no need to invalidate the CFG cache
-    let (basic_blocks, local_decls, _) =
-        body.basic_blocks_local_decls_mut_and_var_debug_info_no_invalidate();
+    let basic_blocks = body.basic_blocks.as_mut_preserves_cfg();
+    let local_decls = &mut body.local_decls;
 
     // do a preliminary analysis to see if we ever have locals of type `[T;N]` or `&[T;N]`
     let mut interesting_locals = BitSet::new_empty(local_decls.len());

compiler/rustc_mir_transform/src/nrvo.rs

@@ -133,7 +133,7 @@ fn find_local_assigned_to_return_place(
             return local;
         }
 
-        match body.predecessors()[block].as_slice() {
+        match body.basic_blocks.predecessors()[block].as_slice() {
             &[pred] => block = pred,
             _ => return None,
         }

compiler/rustc_mir_transform/src/remove_storage_markers.rs

@@ -17,7 +17,7 @@ impl<'tcx> MirPass<'tcx> for RemoveStorageMarkers {
         }
 
         trace!("Running RemoveStorageMarkers on {:?}", body.source);
-        for data in body.basic_blocks_local_decls_mut_and_var_debug_info_no_invalidate().0 {
+        for data in body.basic_blocks.as_mut_preserves_cfg() {
             data.statements.retain(|statement| match statement.kind {
                 StatementKind::StorageLive(..)
                 | StatementKind::StorageDead(..)

compiler/rustc_mir_transform/src/remove_unneeded_drops.rs

@@ -20,11 +20,10 @@ impl<'tcx> MirPass<'tcx> for RemoveUnneededDrops {
         let param_env = tcx.param_env_reveal_all_normalized(did);
         let mut should_simplify = false;
 
-        let (basic_blocks, local_decls) = body.basic_blocks_and_local_decls_mut();
-        for block in basic_blocks {
+        for block in body.basic_blocks.as_mut() {
             let terminator = block.terminator_mut();
             if let TerminatorKind::Drop { place, target, .. } = terminator.kind {
-                let ty = place.ty(local_decls, tcx);
+                let ty = place.ty(&body.local_decls, tcx);
                 if ty.ty.needs_drop(tcx, param_env) {
                     continue;
                 }

compiler/rustc_mir_transform/src/remove_zsts.rs

@@ -18,9 +18,9 @@ impl<'tcx> MirPass<'tcx> for RemoveZsts {
             return;
         }
         let param_env = tcx.param_env(body.source.def_id());
-        let (basic_blocks, local_decls, _) =
-            body.basic_blocks_local_decls_mut_and_var_debug_info_no_invalidate();
-        for block in basic_blocks.iter_mut() {
+        let basic_blocks = body.basic_blocks.as_mut_preserves_cfg();
+        let local_decls = &body.local_decls;
+        for block in basic_blocks {
             for statement in block.statements.iter_mut() {
                 if let StatementKind::Assign(box (place, _)) | StatementKind::Deinit(box place) =
                     statement.kind

compiler/rustc_mir_transform/src/separate_const_switch.rs

@@ -61,7 +61,7 @@ impl<'tcx> MirPass<'tcx> for SeparateConstSwitch {
 /// Returns the amount of blocks that were duplicated
 pub fn separate_const_switch(body: &mut Body<'_>) -> usize {
     let mut new_blocks: SmallVec<[(BasicBlock, BasicBlock); 6]> = SmallVec::new();
-    let predecessors = body.predecessors();
+    let predecessors = body.basic_blocks.predecessors();
     'block_iter: for (block_id, block) in body.basic_blocks().iter_enumerated() {
         if let TerminatorKind::SwitchInt {
             discr: Operand::Copy(switch_place) | Operand::Move(switch_place),

compiler/rustc_mir_transform/src/simplify_try.rs

@@ -386,14 +386,17 @@ impl<'tcx> MirPass<'tcx> for SimplifyArmIdentity {
         trace!("running SimplifyArmIdentity on {:?}", source);
 
         let local_uses = LocalUseCounter::get_local_uses(body);
-        let (basic_blocks, local_decls, debug_info) =
-            body.basic_blocks_local_decls_mut_and_var_debug_info();
-        for bb in basic_blocks {
+        for bb in body.basic_blocks.as_mut() {
             if let Some(opt_info) =
-                get_arm_identity_info(&bb.statements, local_decls.len(), debug_info)
+                get_arm_identity_info(&bb.statements, body.local_decls.len(), &body.var_debug_info)
             {
                 trace!("got opt_info = {:#?}", opt_info);
-                if !optimization_applies(&opt_info, local_decls, &local_uses, &debug_info) {
+                if !optimization_applies(
+                    &opt_info,
+                    &body.local_decls,
+                    &local_uses,
+                    &body.var_debug_info,
+                ) {
                     debug!("optimization skipped for {:?}", source);
                     continue;
                 }
@@ -431,7 +434,7 @@ impl<'tcx> MirPass<'tcx> for SimplifyArmIdentity {
 
                 // Fix the debug info to point to the right local
                 for dbg_index in opt_info.dbg_info_to_adjust {
-                    let dbg_info = &mut debug_info[dbg_index];
+                    let dbg_info = &mut body.var_debug_info[dbg_index];
                     assert!(
                         matches!(dbg_info.value, VarDebugInfoContents::Place(_)),
                         "value was not a Place"

src/tools/clippy/clippy_lints/src/redundant_clone.rs

@@ -161,7 +161,7 @@ impl<'tcx> LateLintPass<'tcx> for RedundantClone {
                 // `arg` is a reference as it is `.deref()`ed in the previous block.
                 // Look into the predecessor block and find out the source of deref.
 
-                let ps = &mir.predecessors()[bb];
+                let ps = &mir.basic_blocks.predecessors()[bb];
                 if ps.len() != 1 {
                     continue;
                 }