Rollup merge of rust-lang#71942 - nnethercote:shrink-LocalDecl, r=matthewjasper

Shrink `LocalDecl`

`LocalDecl` contributes 4-8% of peak heap memory usage on a range of benchmarks. This PR reduces its size from 128 bytes to 56 bytes on 64-bit, and does some clean-ups as well.

r? @matthewjasper

Author: Dylan-DPC

src/librustc_middle/mir/mod.rs

@@ -474,6 +474,13 @@ pub struct SourceInfo {
     pub scope: SourceScope,
 }
 
+impl SourceInfo {
+    #[inline]
+    pub fn outermost(span: Span) -> Self {
+        SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE }
+    }
+}
+
 ///////////////////////////////////////////////////////////////////////////
 // Borrow kinds
 
@@ -689,7 +696,7 @@ pub struct LocalDecl<'tcx> {
     pub mutability: Mutability,
 
     // FIXME(matthewjasper) Don't store in this in `Body`
-    pub local_info: LocalInfo<'tcx>,
+    pub local_info: Option<Box<LocalInfo<'tcx>>>,
 
     /// `true` if this is an internal local.
     ///
@@ -725,7 +732,7 @@ pub struct LocalDecl<'tcx> {
     /// borrow checker needs this information since it can affect
     /// region inference.
     // FIXME(matthewjasper) Don't store in this in `Body`
-    pub user_ty: UserTypeProjections,
+    pub user_ty: Option<Box<UserTypeProjections>>,
 
     /// The *syntactic* (i.e., not visibility) source scope the local is defined
     /// in. If the local was defined in a let-statement, this
@@ -809,7 +816,13 @@ pub struct LocalDecl<'tcx> {
     pub source_info: SourceInfo,
 }
 
-/// Extra information about a local that's used for diagnostics.
+// `LocalDecl` is used a lot. Make sure it doesn't unintentionally get bigger.
+#[cfg(target_arch = "x86_64")]
+static_assert_size!(LocalDecl<'_>, 56);
+
+/// Extra information about a some locals that's used for diagnostics. (Not
+/// used for non-StaticRef temporaries, the return place, or anonymous function
+/// parameters.)
 #[derive(Clone, Debug, RustcEncodable, RustcDecodable, HashStable, TypeFoldable)]
 pub enum LocalInfo<'tcx> {
     /// A user-defined local variable or function parameter
@@ -820,8 +833,6 @@ pub enum LocalInfo<'tcx> {
     User(ClearCrossCrate<BindingForm<'tcx>>),
     /// A temporary created that references the static with the given `DefId`.
     StaticRef { def_id: DefId, is_thread_local: bool },
-    /// Any other temporary, the return place, or an anonymous function parameter.
-    Other,
 }
 
 impl<'tcx> LocalDecl<'tcx> {
@@ -833,16 +844,16 @@ impl<'tcx> LocalDecl<'tcx> {
     /// - or `match ... { C(x) => ... }`
     pub fn can_be_made_mutable(&self) -> bool {
         match self.local_info {
-            LocalInfo::User(ClearCrossCrate::Set(BindingForm::Var(VarBindingForm {
+            Some(box LocalInfo::User(ClearCrossCrate::Set(BindingForm::Var(VarBindingForm {
                 binding_mode: ty::BindingMode::BindByValue(_),
                 opt_ty_info: _,
                 opt_match_place: _,
                 pat_span: _,
-            }))) => true,
+            })))) => true,
 
-            LocalInfo::User(ClearCrossCrate::Set(BindingForm::ImplicitSelf(
+            Some(box LocalInfo::User(ClearCrossCrate::Set(BindingForm::ImplicitSelf(
                 ImplicitSelfKind::Imm,
-            ))) => true,
+            )))) => true,
 
             _ => false,
         }
@@ -853,14 +864,14 @@ impl<'tcx> LocalDecl<'tcx> {
     /// mutable bindings, but the inverse does not necessarily hold).
     pub fn is_nonref_binding(&self) -> bool {
         match self.local_info {
-            LocalInfo::User(ClearCrossCrate::Set(BindingForm::Var(VarBindingForm {
+            Some(box LocalInfo::User(ClearCrossCrate::Set(BindingForm::Var(VarBindingForm {
                 binding_mode: ty::BindingMode::BindByValue(_),
                 opt_ty_info: _,
                 opt_match_place: _,
                 pat_span: _,
-            }))) => true,
+            })))) => true,
 
-            LocalInfo::User(ClearCrossCrate::Set(BindingForm::ImplicitSelf(_))) => true,
+            Some(box LocalInfo::User(ClearCrossCrate::Set(BindingForm::ImplicitSelf(_)))) => true,
 
             _ => false,
         }
@@ -871,7 +882,7 @@ impl<'tcx> LocalDecl<'tcx> {
     #[inline]
     pub fn is_user_variable(&self) -> bool {
         match self.local_info {
-            LocalInfo::User(_) => true,
+            Some(box LocalInfo::User(_)) => true,
             _ => false,
         }
     }
@@ -881,7 +892,7 @@ impl<'tcx> LocalDecl<'tcx> {
     /// match arm.
     pub fn is_ref_for_guard(&self) -> bool {
         match self.local_info {
-            LocalInfo::User(ClearCrossCrate::Set(BindingForm::RefForGuard)) => true,
+            Some(box LocalInfo::User(ClearCrossCrate::Set(BindingForm::RefForGuard))) => true,
             _ => false,
         }
     }
@@ -890,7 +901,7 @@ impl<'tcx> LocalDecl<'tcx> {
     /// access that static
     pub fn is_ref_to_static(&self) -> bool {
         match self.local_info {
-            LocalInfo::StaticRef { .. } => true,
+            Some(box LocalInfo::StaticRef { .. }) => true,
             _ => false,
         }
     }
@@ -899,7 +910,7 @@ impl<'tcx> LocalDecl<'tcx> {
     /// access that static
     pub fn is_ref_to_thread_local(&self) -> bool {
         match self.local_info {
-            LocalInfo::StaticRef { is_thread_local, .. } => is_thread_local,
+            Some(box LocalInfo::StaticRef { is_thread_local, .. }) => is_thread_local,
             _ => false,
         }
     }
@@ -911,10 +922,31 @@ impl<'tcx> LocalDecl<'tcx> {
         self.source_info.span.desugaring_kind().is_some()
     }
 
-    /// Creates a new `LocalDecl` for a temporary.
+    /// Creates a new `LocalDecl` for a temporary: mutable, non-internal.
     #[inline]
-    pub fn new_temp(ty: Ty<'tcx>, span: Span) -> Self {
-        Self::new_local(ty, Mutability::Mut, false, span)
+    pub fn new(ty: Ty<'tcx>, span: Span) -> Self {
+        Self::with_source_info(ty, SourceInfo::outermost(span))
+    }
+
+    /// Like `LocalDecl::new`, but takes a `SourceInfo` instead of a `Span`.
+    #[inline]
+    pub fn with_source_info(ty: Ty<'tcx>, source_info: SourceInfo) -> Self {
+        LocalDecl {
+            mutability: Mutability::Mut,
+            local_info: None,
+            internal: false,
+            is_block_tail: None,
+            ty,
+            user_ty: None,
+            source_info,
+        }
+    }
+
+    /// Converts `self` into same `LocalDecl` except tagged as internal.
+    #[inline]
+    pub fn internal(mut self) -> Self {
+        self.internal = true;
+        self
     }
 
     /// Converts `self` into same `LocalDecl` except tagged as immutable.
@@ -931,41 +963,6 @@ impl<'tcx> LocalDecl<'tcx> {
         self.is_block_tail = Some(info);
         self
     }
-
-    /// Creates a new `LocalDecl` for a internal temporary.
-    #[inline]
-    pub fn new_internal(ty: Ty<'tcx>, span: Span) -> Self {
-        Self::new_local(ty, Mutability::Mut, true, span)
-    }
-
-    #[inline]
-    fn new_local(ty: Ty<'tcx>, mutability: Mutability, internal: bool, span: Span) -> Self {
-        LocalDecl {
-            mutability,
-            ty,
-            user_ty: UserTypeProjections::none(),
-            source_info: SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE },
-            internal,
-            local_info: LocalInfo::Other,
-            is_block_tail: None,
-        }
-    }
-
-    /// Builds a `LocalDecl` for the return place.
-    ///
-    /// This must be inserted into the `local_decls` list as the first local.
-    #[inline]
-    pub fn new_return_place(return_ty: Ty<'_>, span: Span) -> LocalDecl<'_> {
-        LocalDecl {
-            mutability: Mutability::Mut,
-            ty: return_ty,
-            user_ty: UserTypeProjections::none(),
-            source_info: SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE },
-            internal: false,
-            is_block_tail: None,
-            local_info: LocalInfo::Other,
-        }
-    }
 }
 
 /// Debug information pertaining to a user variable.
@@ -1406,10 +1403,7 @@ impl<'tcx> BasicBlockData<'tcx> {
         let mut gap = self.statements.len()..self.statements.len() + extra_stmts;
         self.statements.resize(
             gap.end,
-            Statement {
-                source_info: SourceInfo { span: DUMMY_SP, scope: OUTERMOST_SOURCE_SCOPE },
-                kind: StatementKind::Nop,
-            },
+            Statement { source_info: SourceInfo::outermost(DUMMY_SP), kind: StatementKind::Nop },
         );
         for (splice_start, new_stmts) in splices.into_iter().rev() {
             let splice_end = splice_start + new_stmts.size_hint().0;
@@ -2457,14 +2451,18 @@ impl Constant<'tcx> {
 /// &'static str`.
 #[derive(Clone, Debug, RustcEncodable, RustcDecodable, HashStable, TypeFoldable)]
 pub struct UserTypeProjections {
-    pub(crate) contents: Vec<(UserTypeProjection, Span)>,
+    pub contents: Vec<(UserTypeProjection, Span)>,
 }
 
 impl<'tcx> UserTypeProjections {
     pub fn none() -> Self {
         UserTypeProjections { contents: vec![] }
     }
 
+    pub fn is_empty(&self) -> bool {
+        self.contents.is_empty()
+    }
+
     pub fn from_projections(projs: impl Iterator<Item = (UserTypeProjection, Span)>) -> Self {
         UserTypeProjections { contents: projs.collect() }
     }

src/librustc_middle/mir/visit.rs

@@ -242,10 +242,10 @@ macro_rules! make_mir_visitor {
             ) {
                 let span = body.span;
                 if let Some(yield_ty) = &$($mutability)? body.yield_ty {
-                    self.visit_ty(yield_ty, TyContext::YieldTy(SourceInfo {
-                        span,
-                        scope: OUTERMOST_SOURCE_SCOPE,
-                    }));
+                    self.visit_ty(
+                        yield_ty,
+                        TyContext::YieldTy(SourceInfo::outermost(span))
+                    );
                 }
 
                 // for best performance, we want to use an iterator rather
@@ -263,10 +263,10 @@ macro_rules! make_mir_visitor {
                     self.visit_source_scope_data(scope);
                 }
 
-                self.visit_ty(&$($mutability)? body.return_ty(), TyContext::ReturnTy(SourceInfo {
-                    span: body.span,
-                    scope: OUTERMOST_SOURCE_SCOPE,
-                }));
+                self.visit_ty(
+                    &$($mutability)? body.return_ty(),
+                    TyContext::ReturnTy(SourceInfo::outermost(body.span))
+                );
 
                 for local in body.local_decls.indices() {
                     self.visit_local_decl(local, & $($mutability)? body.local_decls[local]);
@@ -715,8 +715,10 @@ macro_rules! make_mir_visitor {
                     local,
                     source_info: *source_info,
                 });
-                for (user_ty, _) in & $($mutability)? user_ty.contents {
-                    self.visit_user_type_projection(user_ty);
+                if let Some(user_ty) = user_ty {
+                    for (user_ty, _) in & $($mutability)? user_ty.contents {
+                        self.visit_user_type_projection(user_ty);
+                    }
                 }
                 self.visit_source_info(source_info);
             }

src/librustc_mir/borrow_check/diagnostics/conflict_errors.rs

@@ -1447,15 +1447,15 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         let (place_description, assigned_span) = match local_decl {
             Some(LocalDecl {
                 local_info:
-                    LocalInfo::User(
+                    Some(box LocalInfo::User(
                         ClearCrossCrate::Clear
                         | ClearCrossCrate::Set(BindingForm::Var(VarBindingForm {
                             opt_match_place: None,
                             ..
                         })),
-                    )
-                    | LocalInfo::StaticRef { .. }
-                    | LocalInfo::Other,
+                    ))
+                    | Some(box LocalInfo::StaticRef { .. })
+                    | None,
                 ..
             })
             | None => (self.describe_any_place(place.as_ref()), assigned_span),

src/librustc_mir/borrow_check/diagnostics/mod.rs

@@ -202,7 +202,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 if self.body.local_decls[local].is_ref_to_static() =>
             {
                 let local_info = &self.body.local_decls[local].local_info;
-                if let LocalInfo::StaticRef { def_id, .. } = *local_info {
+                if let Some(box LocalInfo::StaticRef { def_id, .. }) = *local_info {
                     buf.push_str(&self.infcx.tcx.item_name(def_id).as_str());
                 } else {
                     unreachable!();

src/librustc_mir/borrow_check/diagnostics/move_errors.rs

@@ -103,14 +103,14 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
                         //
                         // opt_match_place is None for let [mut] x = ... statements,
                         // whether or not the right-hand side is a place expression
-                        if let LocalInfo::User(ClearCrossCrate::Set(BindingForm::Var(
+                        if let Some(box LocalInfo::User(ClearCrossCrate::Set(BindingForm::Var(
                             VarBindingForm {
                                 opt_match_place: Some((opt_match_place, match_span)),
                                 binding_mode: _,
                                 opt_ty_info: _,
                                 pat_span: _,
                             },
-                        ))) = local_decl.local_info
+                        )))) = local_decl.local_info
                         {
                             let stmt_source_info = self.body.source_info(location);
                             self.append_binding_error(
@@ -482,10 +482,9 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
         let mut suggestions: Vec<(Span, &str, String)> = Vec::new();
         for local in binds_to {
             let bind_to = &self.body.local_decls[*local];
-            if let LocalInfo::User(ClearCrossCrate::Set(BindingForm::Var(VarBindingForm {
-                pat_span,
-                ..
-            }))) = bind_to.local_info
+            if let Some(box LocalInfo::User(ClearCrossCrate::Set(BindingForm::Var(
+                VarBindingForm { pat_span, .. },
+            )))) = bind_to.local_info
             {
                 if let Ok(pat_snippet) = self.infcx.tcx.sess.source_map().span_to_snippet(pat_span)
                 {