src/librustc_mir/build/expr/stmt.rs

   1 // Copyright 2016 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use build::scope::BreakableScope;
  12 use build::{BlockAnd, BlockAndExtension, Builder};
  13 use hair::*;
  14 use rustc::mir::*;
  15
  16 impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
  17     pub fn stmt_expr(&mut self, mut block: BasicBlock, expr: Expr<'tcx>) -> BlockAnd<()> {
  18         let this = self;
  19         let expr_span = expr.span;
  20         let source_info = this.source_info(expr.span);
  21         // Handle a number of expressions that don't need a destination at all. This
  22         // avoids needing a mountain of temporary `()` variables.
  23         match expr.kind {
  24             ExprKind::Scope {
  25                 region_scope,
  26                 lint_level,
  27                 value,
  28             } => {
  29                 let value = this.hir.mirror(value);
  30                 this.in_scope((region_scope, source_info), lint_level, block, |this| {
  31                     this.stmt_expr(block, value)
  32                 })
  33             }
  34             ExprKind::Assign { lhs, rhs } => {
  35                 let lhs = this.hir.mirror(lhs);
  36                 let rhs = this.hir.mirror(rhs);
  37                 let lhs_span = lhs.span;
  38
  39                 // Note: we evaluate assignments right-to-left. This
  40                 // is better for borrowck interaction with overloaded
  41                 // operators like x[j] = x[i].
  42
  43                 // Generate better code for things that don't need to be
  44                 // dropped.
  45                 if this.hir.needs_drop(lhs.ty) {
  46                     let rhs = unpack!(block = this.as_local_operand(block, rhs));
  47                     let lhs = unpack!(block = this.as_place(block, lhs));
  48                     unpack!(block = this.build_drop_and_replace(block, lhs_span, lhs, rhs));
  49                     block.unit()
  50                 } else {
  51                     let rhs = unpack!(block = this.as_local_rvalue(block, rhs));
  52                     let lhs = unpack!(block = this.as_place(block, lhs));
  53                     this.cfg.push_assign(block, source_info, &lhs, rhs);
  54                     block.unit()
  55                 }
  56             }
  57             ExprKind::AssignOp { op, lhs, rhs } => {
  58                 // FIXME(#28160) there is an interesting semantics
  59                 // question raised here -- should we "freeze" the
  60                 // value of the lhs here?  I'm inclined to think not,
  61                 // since it seems closer to the semantics of the
  62                 // overloaded version, which takes `&mut self`.  This
  63                 // only affects weird things like `x += {x += 1; x}`
  64                 // -- is that equal to `x + (x + 1)` or `2*(x+1)`?
  65
  66                 let lhs = this.hir.mirror(lhs);
  67                 let lhs_ty = lhs.ty;
  68
  69                 // As above, RTL.
  70                 let rhs = unpack!(block = this.as_local_operand(block, rhs));
  71                 let lhs = unpack!(block = this.as_place(block, lhs));
  72
  73                 // we don't have to drop prior contents or anything
  74                 // because AssignOp is only legal for Copy types
  75                 // (overloaded ops should be desugared into a call).
  76                 let result = unpack!(
  77                     block = this.build_binary_op(
  78                         block,
  79                         op,
  80                         expr_span,
  81                         lhs_ty,
  82                         Operand::Copy(lhs.clone()),
  83                         rhs
  84                     )
  85                 );
  86                 this.cfg.push_assign(block, source_info, &lhs, result);
  87
  88                 block.unit()
  89             }
  90             ExprKind::Continue { label } => {
  91                 let BreakableScope {
  92                     continue_block,
  93                     region_scope,
  94                     ..
  95                 } = *this.find_breakable_scope(expr_span, label);
  96                 let continue_block = continue_block
  97                     .expect("Attempted to continue in non-continuable breakable block");
  98                 this.exit_scope(
  99                     expr_span,
 100                     (region_scope, source_info),
 101                     block,
 102                     continue_block,
 103                 );
 104                 this.cfg.start_new_block().unit()
 105             }
 106             ExprKind::Break { label, value } => {
 107                 let (break_block, region_scope, destination) = {
 108                     let BreakableScope {
 109                         break_block,
 110                         region_scope,
 111                         ref break_destination,
 112                         ..
 113                     } = *this.find_breakable_scope(expr_span, label);
 114                     (break_block, region_scope, break_destination.clone())
 115                 };
 116                 if let Some(value) = value {
 117                     unpack!(block = this.into(&destination, block, value))
 118                 } else {
 119                     this.cfg.push_assign_unit(block, source_info, &destination)
 120                 }
 121                 this.exit_scope(expr_span, (region_scope, source_info), block, break_block);
 122                 this.cfg.start_new_block().unit()
 123             }
 124             ExprKind::Return { value } => {
 125                 block = match value {
 126                     Some(value) => unpack!(this.into(&Place::Local(RETURN_PLACE), block, value)),
 127                     None => {
 128                         this.cfg
 129                             .push_assign_unit(block, source_info, &Place::Local(RETURN_PLACE));
 130                         block
 131                     }
 132                 };
 133                 let region_scope = this.region_scope_of_return_scope();
 134                 let return_block = this.return_block();
 135                 this.exit_scope(expr_span, (region_scope, source_info), block, return_block);
 136                 this.cfg.start_new_block().unit()
 137             }
 138             ExprKind::InlineAsm {
 139                 asm,
 140                 outputs,
 141                 inputs,
 142             } => {
 143                 let outputs = outputs
 144                     .into_iter()
 145                     .map(|output| unpack!(block = this.as_place(block, output)))
 146                     .collect::<Vec<_>>()
 147                     .into_boxed_slice();
 148                 let inputs = inputs
 149                     .into_iter()
 150                     .map(|input| unpack!(block = this.as_local_operand(block, input)))
 151                     .collect::<Vec<_>>()
 152                     .into_boxed_slice();
 153                 this.cfg.push(
 154                     block,
 155                     Statement {
 156                         source_info,
 157                         kind: StatementKind::InlineAsm {
 158                             asm: box asm.clone(),
 159                             outputs,
 160                             inputs,
 161                         },
 162                     },
 163                 );
 164                 block.unit()
 165             }
 166             _ => {
 167                 let expr_ty = expr.ty;
 168                 let temp = this.temp(expr.ty.clone(), expr_span);
 169                 unpack!(block = this.into(&temp, block, expr));
 170                 unpack!(block = this.build_drop(block, expr_span, temp, expr_ty));
 171                 block.unit()
 172             }
 173         }
 174     }
 175 }