Shrink LocalDecl by 16 bytes.

By boxing `user_ty`.

Author: nnethercote

src/librustc_middle/mir/mod.rs

@@ -732,7 +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
@@ -818,7 +818,7 @@ pub struct LocalDecl<'tcx> {
 
 // `LocalDecl` is used a lot. Make sure it doesn't unintentionally get bigger.
 #[cfg(target_arch = "x86_64")]
-static_assert_size!(LocalDecl<'_>, 72);
+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
@@ -937,7 +937,7 @@ impl<'tcx> LocalDecl<'tcx> {
             internal: false,
             is_block_tail: None,
             ty,
-            user_ty: UserTypeProjections::none(),
+            user_ty: None,
             source_info,
         }
     }
@@ -2451,14 +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

@@ -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/move_errors.rs

@@ -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 Some(box 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)
                 {

src/librustc_mir/borrow_check/type_check/mod.rs

@@ -405,35 +405,38 @@ impl<'a, 'b, 'tcx> Visitor<'tcx> for TypeVerifier<'a, 'b, 'tcx> {
         self.super_local_decl(local, local_decl);
         self.sanitize_type(local_decl, local_decl.ty);
 
-        for (user_ty, span) in local_decl.user_ty.projections_and_spans() {
-            let ty = if !local_decl.is_nonref_binding() {
-                // If we have a binding of the form `let ref x: T = ..` then remove the outermost
-                // reference so we can check the type annotation for the remaining type.
-                if let ty::Ref(_, rty, _) = local_decl.ty.kind {
-                    rty
+        if let Some(user_ty) = &local_decl.user_ty {
+            for (user_ty, span) in user_ty.projections_and_spans() {
+                let ty = if !local_decl.is_nonref_binding() {
+                    // If we have a binding of the form `let ref x: T = ..`
+                    // then remove the outermost reference so we can check the
+                    // type annotation for the remaining type.
+                    if let ty::Ref(_, rty, _) = local_decl.ty.kind {
+                        rty
+                    } else {
+                        bug!("{:?} with ref binding has wrong type {}", local, local_decl.ty);
+                    }
                 } else {
-                    bug!("{:?} with ref binding has wrong type {}", local, local_decl.ty);
-                }
-            } else {
-                local_decl.ty
-            };
+                    local_decl.ty
+                };
 
-            if let Err(terr) = self.cx.relate_type_and_user_type(
-                ty,
-                ty::Variance::Invariant,
-                user_ty,
-                Locations::All(*span),
-                ConstraintCategory::TypeAnnotation,
-            ) {
-                span_mirbug!(
-                    self,
-                    local,
-                    "bad user type on variable {:?}: {:?} != {:?} ({:?})",
-                    local,
-                    local_decl.ty,
-                    local_decl.user_ty,
-                    terr,
-                );
+                if let Err(terr) = self.cx.relate_type_and_user_type(
+                    ty,
+                    ty::Variance::Invariant,
+                    user_ty,
+                    Locations::All(*span),
+                    ConstraintCategory::TypeAnnotation,
+                ) {
+                    span_mirbug!(
+                        self,
+                        local,
+                        "bad user type on variable {:?}: {:?} != {:?} ({:?})",
+                        local,
+                        local_decl.ty,
+                        local_decl.user_ty,
+                        terr,
+                    );
+                }
             }
         }
     }

src/librustc_mir/util/pretty.rs

@@ -472,8 +472,10 @@ fn write_scope_tree(
 
         let mut indented_decl =
             format!("{0:1$}let {2}{3:?}: {4:?}", INDENT, indent, mut_str, local, local_decl.ty);
-        for user_ty in local_decl.user_ty.projections() {
-            write!(indented_decl, " as {:?}", user_ty).unwrap();
+        if let Some(user_ty) = &local_decl.user_ty {
+            for user_ty in user_ty.projections() {
+                write!(indented_decl, " as {:?}", user_ty).unwrap();
+            }
         }
         indented_decl.push_str(";");
 

src/librustc_mir_build/build/matches/mod.rs

@@ -1949,7 +1949,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         let local = LocalDecl::<'tcx> {
             mutability,
             ty: var_ty,
-            user_ty,
+            user_ty: if user_ty.is_empty() { None } else { Some(box user_ty) },
             source_info,
             internal: false,
             is_block_tail: None,
@@ -1976,7 +1976,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 // immutable to avoid the unused mut lint.
                 mutability: Mutability::Not,
                 ty: tcx.mk_imm_ref(tcx.lifetimes.re_erased, var_ty),
-                user_ty: UserTypeProjections::none(),
+                user_ty: None,
                 source_info,
                 internal: false,
                 is_block_tail: None,