Use as_temp to evaluate statement expressions

Author: matthewjasper

src/librustc_mir/build/block.rs

@@ -78,7 +78,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
 
         let source_info = this.source_info(span);
         for stmt in stmts {
-            let Stmt { kind, opt_destruction_scope, span: stmt_span } = this.hir.mirror(stmt);
+            let Stmt { kind, opt_destruction_scope } = this.hir.mirror(stmt);
             match kind {
                 StmtKind::Expr { scope, expr } => {
                     this.block_context.push(BlockFrame::Statement { ignores_expr_result: true });
@@ -87,7 +87,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                             let si = (scope, source_info);
                             this.in_scope(si, LintLevel::Inherited, |this| {
                                 let expr = this.hir.mirror(expr);
-                                this.stmt_expr(block, expr, Some(stmt_span))
+                                this.stmt_expr(block, expr, Some(scope))
                             })
                         }));
                 }

src/librustc_mir/build/expr/stmt.rs

@@ -1,21 +1,21 @@
 use crate::build::scope::BreakableScope;
 use crate::build::{BlockAnd, BlockAndExtension, BlockFrame, Builder};
 use crate::hair::*;
+use rustc::middle::region;
 use rustc::mir::*;
 
 impl<'a, 'tcx> Builder<'a, 'tcx> {
     /// Builds a block of MIR statements to evaluate the HAIR `expr`.
     /// If the original expression was an AST statement,
     /// (e.g., `some().code(&here());`) then `opt_stmt_span` is the
     /// span of that statement (including its semicolon, if any).
-    /// Diagnostics use this span (which may be larger than that of
-    /// `expr`) to identify when statement temporaries are dropped.
-    pub fn stmt_expr(&mut self,
-                     mut block: BasicBlock,
-                     expr: Expr<'tcx>,
-                     opt_stmt_span: Option<StatementSpan>)
-                     -> BlockAnd<()>
-    {
+    /// The scope is used if a statement temporary must be dropped.
+    pub fn stmt_expr(
+        &mut self,
+        mut block: BasicBlock,
+        expr: Expr<'tcx>,
+        statement_scope: Option<region::Scope>,
+    ) -> BlockAnd<()> {
         let this = self;
         let expr_span = expr.span;
         let source_info = this.source_info(expr.span);
@@ -30,7 +30,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             } => {
                 let value = this.hir.mirror(value);
                 this.in_scope((region_scope, source_info), lint_level, |this| {
-                    this.stmt_expr(block, value, opt_stmt_span)
+                    this.stmt_expr(block, value, statement_scope)
                 })
             }
             ExprKind::Assign { lhs, rhs } => {
@@ -199,7 +199,11 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 block.unit()
             }
             _ => {
-                let expr_ty = expr.ty;
+                assert!(
+                    statement_scope.is_some(),
+                    "Should not be calling `stmt_expr` on a general expression \
+                     without a statement scope",
+                );
 
                 // Issue #54382: When creating temp for the value of
                 // expression like:
@@ -208,48 +212,34 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 //
                 // it is usually better to focus on `the_value` rather
                 // than the entirety of block(s) surrounding it.
-                let mut temp_span = expr_span;
-                let mut temp_in_tail_of_block = false;
-                if let ExprKind::Block { body } = expr.kind {
-                    if let Some(tail_expr) = &body.expr {
-                        let mut expr = tail_expr;
-                        while let rustc::hir::ExprKind::Block(subblock, _label) = &expr.node {
-                            if let Some(subtail_expr) = &subblock.expr {
-                                expr = subtail_expr
-                            } else {
-                                break;
+                let adjusted_span = (|| {
+                    if let ExprKind::Block { body } = expr.kind {
+                        if let Some(tail_expr) = &body.expr {
+                            let mut expr = tail_expr;
+                            while let rustc::hir::ExprKind::Block(subblock, _label) = &expr.node {
+                                if let Some(subtail_expr) = &subblock.expr {
+                                    expr = subtail_expr
+                                } else {
+                                    break;
+                                }
                             }
-                        }
-                        temp_span = expr.span;
-                        temp_in_tail_of_block = true;
-                    }
-                }
-
-                let temp = {
-                    let mut local_decl = LocalDecl::new_temp(expr.ty.clone(), temp_span);
-                    if temp_in_tail_of_block {
-                        if this.block_context.currently_ignores_tail_results() {
-                            local_decl = local_decl.block_tail(BlockTailInfo {
+                            this.block_context.push(BlockFrame::TailExpr {
                                 tail_result_is_ignored: true
                             });
+                            return Some(expr.span);
                         }
                     }
-                    let temp = this.local_decls.push(local_decl);
-                    let place = Place::from(temp);
-                    debug!("created temp {:?} for expr {:?} in block_context: {:?}",
-                           temp, expr, this.block_context);
-                    place
-                };
-                unpack!(block = this.into(&temp, block, expr));
+                    None
+                })();
+
+                let temp = unpack!(block =
+                    this.as_temp(block, statement_scope, expr, Mutability::Not));
 
-                // Attribute drops of the statement's temps to the
-                // semicolon at the statement's end.
-                let drop_point = this.hir.tcx().sess.source_map().end_point(match opt_stmt_span {
-                    None => expr_span,
-                    Some(StatementSpan(span)) => span,
-                });
+                if let Some(span) = adjusted_span {
+                    this.local_decls[temp].source_info.span = span;
+                    this.block_context.pop();
+                }
 
-                unpack!(block = this.build_drop(block, drop_point, temp, expr_ty));
                 block.unit()
             }
         }

src/librustc_mir/build/scope.rs

@@ -805,27 +805,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         target
     }
 
-    /// Utility function for *non*-scope code to build their own drops
-    pub fn build_drop(&mut self,
-                      block: BasicBlock,
-                      span: Span,
-                      location: Place<'tcx>,
-                      ty: Ty<'tcx>) -> BlockAnd<()> {
-        if !self.hir.needs_drop(ty) {
-            return block.unit();
-        }
-        let source_info = self.source_info(span);
-        let next_target = self.cfg.start_new_block();
-        let diverge_target = self.diverge_cleanup();
-        self.cfg.terminate(block, source_info,
-                           TerminatorKind::Drop {
-                               location,
-                               target: next_target,
-                               unwind: Some(diverge_target),
-                           });
-        next_target.unit()
-    }
-
     /// Utility function for *non*-scope code to build their own drops
     pub fn build_drop_and_replace(&mut self,
                                   block: BasicBlock,

src/librustc_mir/hair/cx/block.rs

@@ -49,7 +49,6 @@ fn mirror_stmts<'a, 'tcx>(
     for (index, stmt) in stmts.iter().enumerate() {
         let hir_id = stmt.hir_id;
         let opt_dxn_ext = cx.region_scope_tree.opt_destruction_scope(hir_id.local_id);
-        let stmt_span = StatementSpan(cx.tcx.hir().span(hir_id));
         match stmt.node {
             hir::StmtKind::Expr(ref expr) |
             hir::StmtKind::Semi(ref expr) => {
@@ -62,7 +61,6 @@ fn mirror_stmts<'a, 'tcx>(
                         expr: expr.to_ref(),
                     },
                     opt_destruction_scope: opt_dxn_ext,
-                    span: stmt_span,
                 })))
             }
             hir::StmtKind::Item(..) => {
@@ -107,7 +105,6 @@ fn mirror_stmts<'a, 'tcx>(
                         lint_level: LintLevel::Explicit(local.hir_id),
                     },
                     opt_destruction_scope: opt_dxn_ext,
-                    span: stmt_span,
                 })));
             }
         }

src/librustc_mir/hair/mod.rs

@@ -55,14 +55,10 @@ pub enum StmtRef<'tcx> {
     Mirror(Box<Stmt<'tcx>>),
 }
 
-#[derive(Clone, Debug)]
-pub struct StatementSpan(pub Span);
-
 #[derive(Clone, Debug)]
 pub struct Stmt<'tcx> {
     pub kind: StmtKind<'tcx>,
     pub opt_destruction_scope: Option<region::Scope>,
-    pub span: StatementSpan,
 }
 
 #[derive(Clone, Debug)]

src/test/mir-opt/box_expr.rs

@@ -24,7 +24,7 @@ impl Drop for S {
 //     let mut _0: ();
 //     let _1: std::boxed::Box<S>;
 //     let mut _2: std::boxed::Box<S>;
-//     let mut _3: ();
+//     let _3: ();
 //     let mut _4: std::boxed::Box<S>;
 //     scope 1 {
 //     }
@@ -50,6 +50,7 @@ impl Drop for S {
 //
 //     bb4: {
 //         StorageDead(_2);
+//         StorageLive(_3);
 //         StorageLive(_4);
 //         _4 = move _1;
 //         _3 = const std::mem::drop::<std::boxed::Box<S>>(move _4) -> [return: bb5, unwind: bb7];
@@ -69,6 +70,7 @@ impl Drop for S {
 //
 //     bb8: {
 //         StorageDead(_4);
+//         StorageDead(_3);
 //         _0 = ();
 //         drop(_1) -> bb9;
 //     }

src/test/mir-opt/copy_propagation_arg.rs

@@ -61,12 +61,14 @@ fn main() {
 // END rustc.foo.CopyPropagation.after.mir
 // START rustc.bar.CopyPropagation.before.mir
 // bb0: {
+//     StorageLive(_2);
 //     StorageLive(_3);
 //     _3 = _1;
 //     _2 = const dummy(move _3) -> bb1;
 // }
 // bb1: {
 //     StorageDead(_3);
+//     StorageDead(_2);
 //     _1 = const 5u8;
 //     ...
 //     return;

src/test/mir-opt/generator-drop-cleanup.rs

@@ -18,6 +18,7 @@ fn main() {
 // }
 // bb1: {
 //     StorageDead(_3);
+//     StorageDead(_2);
 //     goto -> bb5;
 // }
 // bb2: {
@@ -36,6 +37,7 @@ fn main() {
 //     goto -> bb3;
 // }
 // bb7: {
+//     StorageLive(_2);
 //     StorageLive(_3);
 //     goto -> bb1;
 // }

src/test/mir-opt/generator-storage-dead-unwind.rs

@@ -54,6 +54,7 @@ fn main() {
 // }
 // bb2: {
 //     ...
+//     StorageLive(_6);
 //     StorageLive(_7);
 //     _7 = move _2;
 //     _6 = const take::<Foo>(move _7) -> [return: bb9, unwind: bb8];
@@ -81,23 +82,28 @@ fn main() {
 // }
 // bb8 (cleanup): {
 //     StorageDead(_7);
+//     StorageDead(_6);
 //     goto -> bb7;
 // }
 // bb9: {
 //     StorageDead(_7);
+//     StorageDead(_6);
+//     StorageLive(_8);
 //     StorageLive(_9);
 //     _9 = move _3;
 //     _8 = const take::<Bar>(move _9) -> [return: bb10, unwind: bb11];
 // }
 // bb10: {
 //     StorageDead(_9);
+//     StorageDead(_8);
 //     ...
 //     StorageDead(_3);
 //     StorageDead(_2);
 //     drop(_1) -> [return: bb12, unwind: bb1];
 // }
 // bb11 (cleanup): {
 //     StorageDead(_9);
+//     StorageDead(_8);
 //     goto -> bb7;
 // }
 // bb12: {

src/test/mir-opt/issue-38669.rs

@@ -25,6 +25,7 @@ fn main() {
 //         falseUnwind -> [real: bb3, cleanup: bb1];
 //     }
 //     bb3: {
+//         StorageLive(_3);
 //         StorageLive(_4);
 //         _4 = _1;
 //         FakeRead(ForMatchedPlace, _4);
@@ -34,13 +35,15 @@ fn main() {
 //     bb5: {
 //         _3 = ();
 //         StorageDead(_4);
+//         StorageDead(_3);
 //         _1 = const true;
 //         _2 = ();
 //         goto -> bb2;
 //     }
 //     bb6: {
 //         _0 = ();
 //         StorageDead(_4);
+//         StorageDead(_3);
 //         StorageDead(_1);
 //         return;
 //     }