Don't include destruction scopes in THIR

They are not used by anyone, and add memory/performance overhead.

Author: matthewjasper

compiler/rustc_mir_build/src/thir/cx/expr.rs

@@ -54,7 +54,7 @@ impl<'tcx> Cx<'tcx> {
 
         trace!(?expr.ty, "after adjustments");
 
-        // Next, wrap this up in the expr's scope.
+        // Finally, wrap this up in the expr's scope.
         expr = Expr {
             temp_lifetime: expr.temp_lifetime,
             ty: expr.ty,
@@ -66,22 +66,6 @@ impl<'tcx> Cx<'tcx> {
             },
         };
 
-        // Finally, create a destruction scope, if any.
-        if let Some(region_scope) =
-            self.region_scope_tree.opt_destruction_scope(hir_expr.hir_id.local_id)
-        {
-            expr = Expr {
-                temp_lifetime: expr.temp_lifetime,
-                ty: expr.ty,
-                span: hir_expr.span,
-                kind: ExprKind::Scope {
-                    region_scope,
-                    value: self.thir.exprs.push(expr),
-                    lint_level: LintLevel::Inherited,
-                },
-            };
-        }
-
         // OK, all done!
         self.thir.exprs.push(expr)
     }

tests/ui/thir-print/thir-flat-const-variant.stdout

@@ -66,18 +66,6 @@ Thir {
             ),
             span: $DIR/thir-flat-const-variant.rs:12:23: 12:35 (#0),
         },
-        Expr {
-            kind: Scope {
-                region_scope: Destruction(3),
-                lint_level: Inherited,
-                value: e3,
-            },
-            ty: Foo,
-            temp_lifetime: Some(
-                Node(3),
-            ),
-            span: $DIR/thir-flat-const-variant.rs:12:23: 12:35 (#0),
-        },
     ],
     stmts: [],
     params: [],
@@ -151,18 +139,6 @@ Thir {
             ),
             span: $DIR/thir-flat-const-variant.rs:13:23: 13:36 (#0),
         },
-        Expr {
-            kind: Scope {
-                region_scope: Destruction(3),
-                lint_level: Inherited,
-                value: e3,
-            },
-            ty: Foo,
-            temp_lifetime: Some(
-                Node(3),
-            ),
-            span: $DIR/thir-flat-const-variant.rs:13:23: 13:36 (#0),
-        },
     ],
     stmts: [],
     params: [],
@@ -236,18 +212,6 @@ Thir {
             ),
             span: $DIR/thir-flat-const-variant.rs:14:24: 14:36 (#0),
         },
-        Expr {
-            kind: Scope {
-                region_scope: Destruction(3),
-                lint_level: Inherited,
-                value: e3,
-            },
-            ty: Foo,
-            temp_lifetime: Some(
-                Node(3),
-            ),
-            span: $DIR/thir-flat-const-variant.rs:14:24: 14:36 (#0),
-        },
     ],
     stmts: [],
     params: [],
@@ -321,18 +285,6 @@ Thir {
             ),
             span: $DIR/thir-flat-const-variant.rs:15:24: 15:37 (#0),
         },
-        Expr {
-            kind: Scope {
-                region_scope: Destruction(3),
-                lint_level: Inherited,
-                value: e3,
-            },
-            ty: Foo,
-            temp_lifetime: Some(
-                Node(3),
-            ),
-            span: $DIR/thir-flat-const-variant.rs:15:24: 15:37 (#0),
-        },
     ],
     stmts: [],
     params: [],
@@ -380,18 +332,6 @@ Thir {
             ),
             span: $DIR/thir-flat-const-variant.rs:18:11: 18:13 (#0),
         },
-        Expr {
-            kind: Scope {
-                region_scope: Destruction(2),
-                lint_level: Inherited,
-                value: e1,
-            },
-            ty: (),
-            temp_lifetime: Some(
-                Node(2),
-            ),
-            span: $DIR/thir-flat-const-variant.rs:18:11: 18:13 (#0),
-        },
     ],
     stmts: [],
     params: [],

tests/ui/thir-print/thir-flat.stdout

@@ -40,18 +40,6 @@ Thir {
             ),
             span: $DIR/thir-flat.rs:4:15: 4:17 (#0),
         },
-        Expr {
-            kind: Scope {
-                region_scope: Destruction(2),
-                lint_level: Inherited,
-                value: e1,
-            },
-            ty: (),
-            temp_lifetime: Some(
-                Node(2),
-            ),
-            span: $DIR/thir-flat.rs:4:15: 4:17 (#0),
-        },
     ],
     stmts: [],
     params: [],