Auto merge of #37764 - nnethercote:shrink-scope_auxiliary, r=nikomatsakis

Remove `scope_auxiliary`.

`scope_auxiliary` is a big part of the high memory usage in #36799. It's only used for MIR dumping. I have taken a hubristic approach: I have assumed that particular use is unimportant and removed `scope_auxiliary` and related things. This reduces peak RSS by ~10% for a cut-down version of the program in #36799.

If that assumption is wrong perhaps we can avoid building `scope_auxiliary` unless MIR dumping is enabled.

src/librustc_mir/build/block.rs

@@ -54,7 +54,7 @@ pub fn ast_block(&mut self,
                         let tcx = this.hir.tcx();
 
                         // Enter the remainder scope, i.e. the bindings' destruction scope.
-                        this.push_scope(remainder_scope, block);
+                        this.push_scope(remainder_scope);
                         let_extent_stack.push(remainder_scope);
 
                         // Declare the bindings, which may create a visibility scope.

src/librustc_mir/build/cfg.rs

@@ -40,11 +40,6 @@ pub fn push(&mut self, block: BasicBlock, statement: Statement<'tcx>) {
         self.block_data_mut(block).statements.push(statement);
     }
 
-    pub fn current_location(&mut self, block: BasicBlock) -> Location {
-        let index = self.block_data(block).statements.len();
-        Location { block: block, statement_index: index }
-    }
-
     pub fn push_assign(&mut self,
                        block: BasicBlock,
                        source_info: SourceInfo,

src/librustc_mir/build/mod.rs

@@ -36,13 +36,6 @@ pub struct Builder<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
     /// see the `scope` module for more details
     scopes: Vec<scope::Scope<'tcx>>,
 
-    ///  for each scope, a span of blocks that defines it;
-    ///  we track these for use in region and borrow checking,
-    ///  but these are liable to get out of date once optimization
-    ///  begins. They are also hopefully temporary, and will be
-    ///  no longer needed when we adopt graph-based regions.
-    scope_auxiliary: IndexVec<ScopeId, ScopeAuxiliary>,
-
     /// the current set of loops; see the `scope` module for more
     /// details
     loop_scopes: Vec<scope::LoopScope>,
@@ -82,30 +75,6 @@ fn index(self) -> usize {
     }
 }
 
-/// For each scope, we track the extent (from the HIR) and a
-/// single-entry-multiple-exit subgraph that contains all the
-/// statements/terminators within it.
-///
-/// This information is separated out from the main `ScopeData`
-/// because it is short-lived. First, the extent contains node-ids,
-/// so it cannot be saved and re-loaded. Second, any optimization will mess up
-/// the dominator/postdominator information.
-///
-/// The intention is basically to use this information to do
-/// regionck/borrowck and then throw it away once we are done.
-pub struct ScopeAuxiliary {
-    /// extent of this scope from the MIR.
-    pub extent: CodeExtent,
-
-    /// "entry point": dominator of all nodes in the scope
-    pub dom: Location,
-
-    /// "exit points": mutual postdominators of all nodes in the scope
-    pub postdoms: Vec<Location>,
-}
-
-pub type ScopeAuxiliaryVec = IndexVec<ScopeId, ScopeAuxiliary>;
-
 ///////////////////////////////////////////////////////////////////////////
 /// The `BlockAnd` "monad" packages up the new basic block along with a
 /// produced value (sometimes just unit, of course). The `unpack!`
@@ -158,7 +127,7 @@ pub fn construct_fn<'a, 'gcx, 'tcx, A>(hir: Cx<'a, 'gcx, 'tcx>,
                                        abi: Abi,
                                        return_ty: Ty<'gcx>,
                                        ast_body: &'gcx hir::Expr)
-                                       -> (Mir<'tcx>, ScopeAuxiliaryVec)
+                                       -> Mir<'tcx>
     where A: Iterator<Item=(Ty<'gcx>, Option<&'gcx hir::Pat>)>
 {
     let arguments: Vec<_> = arguments.collect();
@@ -221,15 +190,15 @@ pub fn construct_fn<'a, 'gcx, 'tcx, A>(hir: Cx<'a, 'gcx, 'tcx>,
         }).collect()
     });
 
-    let (mut mir, aux) = builder.finish(upvar_decls, return_ty);
+    let mut mir = builder.finish(upvar_decls, return_ty);
     mir.spread_arg = spread_arg;
-    (mir, aux)
+    mir
 }
 
 pub fn construct_const<'a, 'gcx, 'tcx>(hir: Cx<'a, 'gcx, 'tcx>,
                                        item_id: ast::NodeId,
                                        ast_expr: &'tcx hir::Expr)
-                                       -> (Mir<'tcx>, ScopeAuxiliaryVec) {
+                                       -> Mir<'tcx> {
     let tcx = hir.tcx();
     let ty = tcx.tables().expr_ty_adjusted(ast_expr);
     let span = tcx.map.span(item_id);
@@ -269,7 +238,6 @@ fn new(hir: Cx<'a, 'gcx, 'tcx>,
             scopes: vec![],
             visibility_scopes: IndexVec::new(),
             visibility_scope: ARGUMENT_VISIBILITY_SCOPE,
-            scope_auxiliary: IndexVec::new(),
             loop_scopes: vec![],
             local_decls: IndexVec::from_elem_n(LocalDecl::new_return_pointer(return_ty), 1),
             var_indices: NodeMap(),
@@ -288,22 +256,22 @@ fn new(hir: Cx<'a, 'gcx, 'tcx>,
     fn finish(self,
               upvar_decls: Vec<UpvarDecl>,
               return_ty: Ty<'tcx>)
-              -> (Mir<'tcx>, ScopeAuxiliaryVec) {
+              -> Mir<'tcx> {
         for (index, block) in self.cfg.basic_blocks.iter().enumerate() {
             if block.terminator.is_none() {
                 span_bug!(self.fn_span, "no terminator on block {:?}", index);
             }
         }
 
-        (Mir::new(self.cfg.basic_blocks,
-                  self.visibility_scopes,
-                  IndexVec::new(),
-                  return_ty,
-                  self.local_decls,
-                  self.arg_count,
-                  upvar_decls,
-                  self.fn_span
-        ), self.scope_auxiliary)
+        Mir::new(self.cfg.basic_blocks,
+                 self.visibility_scopes,
+                 IndexVec::new(),
+                 return_ty,
+                 self.local_decls,
+                 self.arg_count,
+                 upvar_decls,
+                 self.fn_span
+        )
     }
 
     fn args_and_body(&mut self,

src/librustc_mir/build/scope.rs

@@ -86,7 +86,7 @@
 
 */
 
-use build::{BlockAnd, BlockAndExtension, Builder, CFG, ScopeAuxiliary, ScopeId};
+use build::{BlockAnd, BlockAndExtension, Builder, CFG};
 use rustc::middle::region::{CodeExtent, CodeExtentData};
 use rustc::middle::lang_items;
 use rustc::ty::subst::{Kind, Subst};
@@ -97,14 +97,10 @@
 use rustc_data_structures::fx::FxHashMap;
 
 pub struct Scope<'tcx> {
-    /// the scope-id within the scope_auxiliary
-    id: ScopeId,
-
     /// The visibility scope this scope was created in.
     visibility_scope: VisibilityScope,
 
-    /// the extent of this scope within source code; also stored in
-    /// `ScopeAuxiliary`, but kept here for convenience
+    /// the extent of this scope within source code.
     extent: CodeExtent,
 
     /// Whether there's anything to do for the cleanup path, that is,
@@ -276,7 +272,7 @@ pub fn in_scope<F, R>(&mut self, extent: CodeExtent, mut block: BasicBlock, f: F
         where F: FnOnce(&mut Builder<'a, 'gcx, 'tcx>) -> BlockAnd<R>
     {
         debug!("in_scope(extent={:?}, block={:?})", extent, block);
-        self.push_scope(extent, block);
+        self.push_scope(extent);
         let rv = unpack!(block = f(self));
         unpack!(block = self.pop_scope(extent, block));
         debug!("in_scope: exiting extent={:?} block={:?}", extent, block);
@@ -287,12 +283,10 @@ pub fn in_scope<F, R>(&mut self, extent: CodeExtent, mut block: BasicBlock, f: F
     /// scope and call `pop_scope` afterwards. Note that these two
     /// calls must be paired; using `in_scope` as a convenience
     /// wrapper maybe preferable.
-    pub fn push_scope(&mut self, extent: CodeExtent, entry: BasicBlock) {
+    pub fn push_scope(&mut self, extent: CodeExtent) {
         debug!("push_scope({:?})", extent);
-        let id = ScopeId::new(self.scope_auxiliary.len());
         let vis_scope = self.visibility_scope;
         self.scopes.push(Scope {
-            id: id,
             visibility_scope: vis_scope,
             extent: extent,
             needs_cleanup: false,
@@ -300,11 +294,6 @@ pub fn push_scope(&mut self, extent: CodeExtent, entry: BasicBlock) {
             free: None,
             cached_exits: FxHashMap()
         });
-        self.scope_auxiliary.push(ScopeAuxiliary {
-            extent: extent,
-            dom: self.cfg.current_location(entry),
-            postdoms: vec![]
-        });
     }
 
     /// Pops a scope, which should have extent `extent`, adding any
@@ -325,9 +314,6 @@ pub fn pop_scope(&mut self,
                                           &self.scopes,
                                           block,
                                           self.arg_count));
-        self.scope_auxiliary[scope.id]
-            .postdoms
-            .push(self.cfg.current_location(block));
         block.unit()
     }
 
@@ -375,9 +361,6 @@ pub fn exit_scope(&mut self,
                 self.cfg.terminate(block, scope.source_info(span), free);
                 block = next;
             }
-            self.scope_auxiliary[scope.id]
-                .postdoms
-                .push(self.cfg.current_location(block));
         }
         }
         let scope = &self.scopes[len - scope_count];

src/librustc_mir/mir_map.rs

@@ -103,11 +103,11 @@ fn cx<'b>(&'b mut self, src: MirSource) -> CxBuilder<'b, 'gcx, 'tcx> {
 
 impl<'a, 'gcx, 'tcx> CxBuilder<'a, 'gcx, 'tcx> {
     fn build<F>(&'tcx mut self, f: F)
-        where F: for<'b> FnOnce(Cx<'b, 'gcx, 'tcx>) -> (Mir<'tcx>, build::ScopeAuxiliaryVec)
+        where F: for<'b> FnOnce(Cx<'b, 'gcx, 'tcx>) -> Mir<'tcx>
     {
         let (src, def_id) = (self.src, self.def_id);
         self.infcx.enter(|infcx| {
-            let (mut mir, scope_auxiliary) = f(Cx::new(&infcx, src));
+            let mut mir = f(Cx::new(&infcx, src));
 
             // Convert the Mir to global types.
             let tcx = infcx.tcx.global_tcx();
@@ -120,7 +120,7 @@ fn build<F>(&'tcx mut self, f: F)
                 mem::transmute::<Mir, Mir<'gcx>>(mir)
             };
 
-            pretty::dump_mir(tcx, "mir_map", &0, src, &mir, Some(&scope_auxiliary));
+            pretty::dump_mir(tcx, "mir_map", &0, src, &mir);
 
             let mir = tcx.alloc_mir(mir);
             assert!(tcx.mir_map.borrow_mut().insert(def_id, mir).is_none());

src/librustc_mir/pretty.rs

@@ -8,7 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use build::{ScopeAuxiliaryVec, ScopeId};
 use rustc::hir;
 use rustc::hir::def_id::DefId;
 use rustc::mir::*;
@@ -43,8 +42,7 @@ pub fn dump_mir<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                           pass_name: &str,
                           disambiguator: &Display,
                           src: MirSource,
-                          mir: &Mir<'tcx>,
-                          auxiliary: Option<&ScopeAuxiliaryVec>) {
+                          mir: &Mir<'tcx>) {
     let filters = match tcx.sess.opts.debugging_opts.dump_mir {
         None => return,
         Some(ref filters) => filters,
@@ -81,7 +79,7 @@ pub fn dump_mir<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
         writeln!(file, "// pass_name = {}", pass_name)?;
         writeln!(file, "// disambiguator = {}", disambiguator)?;
         writeln!(file, "")?;
-        write_mir_fn(tcx, src, mir, &mut file, auxiliary)?;
+        write_mir_fn(tcx, src, mir, &mut file)?;
         Ok(())
     });
 }
@@ -106,52 +104,24 @@ pub fn write_mir_pretty<'a, 'b, 'tcx, I>(tcx: TyCtxt<'b, 'tcx, 'tcx>,
 
         let id = tcx.map.as_local_node_id(def_id).unwrap();
         let src = MirSource::from_node(tcx, id);
-        write_mir_fn(tcx, src, mir, w, None)?;
+        write_mir_fn(tcx, src, mir, w)?;
 
         for (i, mir) in mir.promoted.iter_enumerated() {
             writeln!(w, "")?;
-            write_mir_fn(tcx, MirSource::Promoted(id, i), mir, w, None)?;
+            write_mir_fn(tcx, MirSource::Promoted(id, i), mir, w)?;
         }
     }
     Ok(())
 }
 
-enum Annotation {
-    EnterScope(ScopeId),
-    ExitScope(ScopeId),
-}
-
-fn scope_entry_exit_annotations(auxiliary: Option<&ScopeAuxiliaryVec>)
-                                -> FxHashMap<Location, Vec<Annotation>>
-{
-    // compute scope/entry exit annotations
-    let mut annotations = FxHashMap();
-    if let Some(auxiliary) = auxiliary {
-        for (scope_id, auxiliary) in auxiliary.iter_enumerated() {
-            annotations.entry(auxiliary.dom)
-                       .or_insert(vec![])
-                       .push(Annotation::EnterScope(scope_id));
-
-            for &loc in &auxiliary.postdoms {
-                annotations.entry(loc)
-                           .or_insert(vec![])
-                           .push(Annotation::ExitScope(scope_id));
-            }
-        }
-    }
-    return annotations;
-}
-
 pub fn write_mir_fn<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                               src: MirSource,
                               mir: &Mir<'tcx>,
-                              w: &mut Write,
-                              auxiliary: Option<&ScopeAuxiliaryVec>)
+                              w: &mut Write)
                               -> io::Result<()> {
-    let annotations = scope_entry_exit_annotations(auxiliary);
     write_mir_intro(tcx, src, mir, w)?;
     for block in mir.basic_blocks().indices() {
-        write_basic_block(tcx, block, mir, w, &annotations)?;
+        write_basic_block(tcx, block, mir, w)?;
         if block.index() + 1 != mir.basic_blocks().len() {
             writeln!(w, "")?;
         }
@@ -165,8 +135,7 @@ pub fn write_mir_fn<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 fn write_basic_block(tcx: TyCtxt,
                      block: BasicBlock,
                      mir: &Mir,
-                     w: &mut Write,
-                     annotations: &FxHashMap<Location, Vec<Annotation>>)
+                     w: &mut Write)
                      -> io::Result<()> {
     let data = &mir[block];
 
@@ -176,19 +145,6 @@ fn write_basic_block(tcx: TyCtxt,
     // List of statements in the middle.
     let mut current_location = Location { block: block, statement_index: 0 };
     for statement in &data.statements {
-        if let Some(ref annotations) = annotations.get(&current_location) {
-            for annotation in annotations.iter() {
-                match *annotation {
-                    Annotation::EnterScope(id) =>
-                        writeln!(w, "{0}{0}// Enter Scope({1})",
-                                 INDENT, id.index())?,
-                    Annotation::ExitScope(id) =>
-                        writeln!(w, "{0}{0}// Exit Scope({1})",
-                                 INDENT, id.index())?,
-                }
-            }
-        }
-
         let indented_mir = format!("{0}{0}{1:?};", INDENT, statement);
         writeln!(w, "{0:1$} // {2}",
                  indented_mir,

src/librustc_mir/transform/dump_mir.rs

@@ -64,8 +64,7 @@ fn on_mir_pass<'a>(
                 is_after: is_after
             },
             src,
-            mir,
-            None
+            mir
         );
     }
 }