diff options
Diffstat (limited to 'compiler/rustc_mir_build/src/build/expr/stmt.rs')
| -rw-r--r-- | compiler/rustc_mir_build/src/build/expr/stmt.rs | 149 |
1 files changed, 149 insertions, 0 deletions
diff --git a/compiler/rustc_mir_build/src/build/expr/stmt.rs b/compiler/rustc_mir_build/src/build/expr/stmt.rs new file mode 100644 index 000000000..a7e1331aa --- /dev/null +++ b/compiler/rustc_mir_build/src/build/expr/stmt.rs @@ -0,0 +1,149 @@ +use crate::build::scope::BreakableTarget; +use crate::build::{BlockAnd, BlockAndExtension, BlockFrame, Builder}; +use rustc_middle::middle::region; +use rustc_middle::mir::*; +use rustc_middle::thir::*; + +impl<'a, 'tcx> Builder<'a, 'tcx> { + /// Builds a block of MIR statements to evaluate the THIR `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). + /// The scope is used if a statement temporary must be dropped. + pub(crate) 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); + // Handle a number of expressions that don't need a destination at all. This + // avoids needing a mountain of temporary `()` variables. + match expr.kind { + ExprKind::Scope { region_scope, lint_level, value } => { + this.in_scope((region_scope, source_info), lint_level, |this| { + this.stmt_expr(block, &this.thir[value], statement_scope) + }) + } + ExprKind::Assign { lhs, rhs } => { + let lhs = &this.thir[lhs]; + let rhs = &this.thir[rhs]; + let lhs_span = lhs.span; + + // Note: we evaluate assignments right-to-left. This + // is better for borrowck interaction with overloaded + // operators like x[j] = x[i]. + + debug!("stmt_expr Assign block_context.push(SubExpr) : {:?}", expr); + this.block_context.push(BlockFrame::SubExpr); + + // Generate better code for things that don't need to be + // dropped. + if lhs.ty.needs_drop(this.tcx, this.param_env) { + let rhs = unpack!(block = this.as_local_operand(block, rhs)); + let lhs = unpack!(block = this.as_place(block, lhs)); + unpack!(block = this.build_drop_and_replace(block, lhs_span, lhs, rhs)); + } else { + let rhs = unpack!(block = this.as_local_rvalue(block, rhs)); + let lhs = unpack!(block = this.as_place(block, lhs)); + this.cfg.push_assign(block, source_info, lhs, rhs); + } + + this.block_context.pop(); + block.unit() + } + ExprKind::AssignOp { op, lhs, rhs } => { + // FIXME(#28160) there is an interesting semantics + // question raised here -- should we "freeze" the + // value of the lhs here? I'm inclined to think not, + // since it seems closer to the semantics of the + // overloaded version, which takes `&mut self`. This + // only affects weird things like `x += {x += 1; x}` + // -- is that equal to `x + (x + 1)` or `2*(x+1)`? + + let lhs = &this.thir[lhs]; + let rhs = &this.thir[rhs]; + let lhs_ty = lhs.ty; + + debug!("stmt_expr AssignOp block_context.push(SubExpr) : {:?}", expr); + this.block_context.push(BlockFrame::SubExpr); + + // As above, RTL. + let rhs = unpack!(block = this.as_local_operand(block, rhs)); + let lhs = unpack!(block = this.as_place(block, lhs)); + + // we don't have to drop prior contents or anything + // because AssignOp is only legal for Copy types + // (overloaded ops should be desugared into a call). + let result = unpack!( + block = + this.build_binary_op(block, op, expr_span, lhs_ty, Operand::Copy(lhs), rhs) + ); + this.cfg.push_assign(block, source_info, lhs, result); + + this.block_context.pop(); + block.unit() + } + ExprKind::Continue { label } => { + this.break_scope(block, None, BreakableTarget::Continue(label), source_info) + } + ExprKind::Break { label, value } => this.break_scope( + block, + value.map(|value| &this.thir[value]), + BreakableTarget::Break(label), + source_info, + ), + ExprKind::Return { value } => this.break_scope( + block, + value.map(|value| &this.thir[value]), + BreakableTarget::Return, + source_info, + ), + _ => { + 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: + // + // `{ side_effects(); { let l = stuff(); the_value } }` + // + // it is usually better to focus on `the_value` rather + // than the entirety of block(s) surrounding it. + let adjusted_span = (|| { + if let ExprKind::Block { body } = &expr.kind && let Some(tail_ex) = body.expr { + let mut expr = &this.thir[tail_ex]; + while let ExprKind::Block { + body: Block { expr: Some(nested_expr), .. }, + } + | ExprKind::Scope { value: nested_expr, .. } = expr.kind + { + expr = &this.thir[nested_expr]; + } + this.block_context.push(BlockFrame::TailExpr { + tail_result_is_ignored: true, + span: expr.span, + }); + return Some(expr.span); + } + None + })(); + + let temp = + unpack!(block = this.as_temp(block, statement_scope, expr, Mutability::Not)); + + if let Some(span) = adjusted_span { + this.local_decls[temp].source_info.span = span; + this.block_context.pop(); + } + + block.unit() + } + } + } +} |