diff options
| -rw-r--r-- | compiler/rustc_ast_lowering/src/expr.rs | 65 | ||||
| -rw-r--r-- | src/test/ui/drop/drop_order.rs | 64 |
2 files changed, 109 insertions, 20 deletions
diff --git a/compiler/rustc_ast_lowering/src/expr.rs b/compiler/rustc_ast_lowering/src/expr.rs index c55b4906302..ec9c3935020 100644 --- a/compiler/rustc_ast_lowering/src/expr.rs +++ b/compiler/rustc_ast_lowering/src/expr.rs @@ -387,32 +387,58 @@ impl<'hir> LoweringContext<'_, 'hir> { then: &Block, else_opt: Option<&Expr>, ) -> hir::ExprKind<'hir> { - let lowered_cond = self.lower_expr(cond); - let new_cond = self.manage_let_cond(lowered_cond); + let lowered_cond = self.lower_cond(cond); let then_expr = self.lower_block_expr(then); if let Some(rslt) = else_opt { - hir::ExprKind::If(new_cond, self.arena.alloc(then_expr), Some(self.lower_expr(rslt))) + hir::ExprKind::If( + lowered_cond, + self.arena.alloc(then_expr), + Some(self.lower_expr(rslt)), + ) } else { - hir::ExprKind::If(new_cond, self.arena.alloc(then_expr), None) + hir::ExprKind::If(lowered_cond, self.arena.alloc(then_expr), None) } } - // If `cond` kind is `let`, returns `let`. Otherwise, wraps and returns `cond` - // in a temporary block. - fn manage_let_cond(&mut self, cond: &'hir hir::Expr<'hir>) -> &'hir hir::Expr<'hir> { - fn has_let_expr<'hir>(expr: &'hir hir::Expr<'hir>) -> bool { - match expr.kind { - hir::ExprKind::Binary(_, lhs, rhs) => has_let_expr(lhs) || has_let_expr(rhs), - hir::ExprKind::Let(..) => true, + // Lowers a condition (i.e. `cond` in `if cond` or `while cond`), wrapping it in a terminating scope + // so that temporaries created in the condition don't live beyond it. + fn lower_cond(&mut self, cond: &Expr) -> &'hir hir::Expr<'hir> { + fn has_let_expr(expr: &Expr) -> bool { + match &expr.kind { + ExprKind::Binary(_, lhs, rhs) => has_let_expr(lhs) || has_let_expr(rhs), + ExprKind::Let(..) => true, _ => false, } } - if has_let_expr(cond) { - cond - } else { - let reason = DesugaringKind::CondTemporary; - let span_block = self.mark_span_with_reason(reason, cond.span, None); - self.expr_drop_temps(span_block, cond, AttrVec::new()) + + // We have to take special care for `let` exprs in the condition, e.g. in + // `if let pat = val` or `if foo && let pat = val`, as we _do_ want `val` to live beyond the + // condition in this case. + // + // In order to mantain the drop behavior for the non `let` parts of the condition, + // we still wrap them in terminating scopes, e.g. `if foo && let pat = val` essentially + // gets transformed into `if { let _t = foo; _t } && let pat = val` + match &cond.kind { + ExprKind::Binary(op @ Spanned { node: ast::BinOpKind::And, .. }, lhs, rhs) + if has_let_expr(cond) => + { + let op = self.lower_binop(*op); + let lhs = self.lower_cond(lhs); + let rhs = self.lower_cond(rhs); + + self.arena.alloc(self.expr( + cond.span, + hir::ExprKind::Binary(op, lhs, rhs), + AttrVec::new(), + )) + } + ExprKind::Let(..) => self.lower_expr(cond), + _ => { + let cond = self.lower_expr(cond); + let reason = DesugaringKind::CondTemporary; + let span_block = self.mark_span_with_reason(reason, cond.span, None); + self.expr_drop_temps(span_block, cond, AttrVec::new()) + } } } @@ -439,14 +465,13 @@ impl<'hir> LoweringContext<'_, 'hir> { body: &Block, opt_label: Option<Label>, ) -> hir::ExprKind<'hir> { - let lowered_cond = self.with_loop_condition_scope(|t| t.lower_expr(cond)); - let new_cond = self.manage_let_cond(lowered_cond); + let lowered_cond = self.with_loop_condition_scope(|t| t.lower_cond(cond)); let then = self.lower_block_expr(body); let expr_break = self.expr_break(span, AttrVec::new()); let stmt_break = self.stmt_expr(span, expr_break); let else_blk = self.block_all(span, arena_vec![self; stmt_break], None); let else_expr = self.arena.alloc(self.expr_block(else_blk, AttrVec::new())); - let if_kind = hir::ExprKind::If(new_cond, self.arena.alloc(then), Some(else_expr)); + let if_kind = hir::ExprKind::If(lowered_cond, self.arena.alloc(then), Some(else_expr)); let if_expr = self.expr(span, if_kind, AttrVec::new()); let block = self.block_expr(self.arena.alloc(if_expr)); let span = self.lower_span(span.with_hi(cond.span.hi())); diff --git a/src/test/ui/drop/drop_order.rs b/src/test/ui/drop/drop_order.rs index e42150dcc09..ba1ac53aa7c 100644 --- a/src/test/ui/drop/drop_order.rs +++ b/src/test/ui/drop/drop_order.rs @@ -1,4 +1,6 @@ // run-pass +// compile-flags: -Z validate-mir +#![feature(let_chains)] use std::cell::RefCell; use std::convert::TryInto; @@ -116,6 +118,58 @@ impl DropOrderCollector { } } + fn let_chain(&self) { + // take the "then" branch + if self.option_loud_drop(2).is_some() // 2 + && self.option_loud_drop(1).is_some() // 1 + && let Some(_d) = self.option_loud_drop(4) { // 4 + self.print(3); // 3 + } + + // take the "else" branch + if self.option_loud_drop(6).is_some() // 2 + && self.option_loud_drop(5).is_some() // 1 + && let None = self.option_loud_drop(7) { // 3 + unreachable!(); + } else { + self.print(8); // 4 + } + + // let exprs interspersed + if self.option_loud_drop(9).is_some() // 1 + && let Some(_d) = self.option_loud_drop(13) // 5 + && self.option_loud_drop(10).is_some() // 2 + && let Some(_e) = self.option_loud_drop(12) { // 4 + self.print(11); // 3 + } + + // let exprs first + if let Some(_d) = self.option_loud_drop(18) // 5 + && let Some(_e) = self.option_loud_drop(17) // 4 + && self.option_loud_drop(14).is_some() // 1 + && self.option_loud_drop(15).is_some() { // 2 + self.print(16); // 3 + } + + // let exprs last + if self.option_loud_drop(20).is_some() // 2 + && self.option_loud_drop(19).is_some() // 1 + && let Some(_d) = self.option_loud_drop(23) // 5 + && let Some(_e) = self.option_loud_drop(22) { // 4 + self.print(21); // 3 + } + } + + fn while_(&self) { + let mut v = self.option_loud_drop(4); + while let Some(_d) = v + && self.option_loud_drop(1).is_some() + && self.option_loud_drop(2).is_some() { + self.print(3); + v = None; + } + } + fn assert_sorted(self) { assert!( self.0 @@ -142,4 +196,14 @@ fn main() { let collector = DropOrderCollector::default(); collector.match_(); collector.assert_sorted(); + + println!("-- let chain --"); + let collector = DropOrderCollector::default(); + collector.let_chain(); + collector.assert_sorted(); + + println!("-- while --"); + let collector = DropOrderCollector::default(); + collector.while_(); + collector.assert_sorted(); } |