Skip to content

Commit

Permalink
Lowering: Fuse ExprKind::While logic + Cleanup.
Browse files Browse the repository at this point in the history
  • Loading branch information
@Centril
Centril committed Jul 6, 2019
1 parent 5477354 commit 26144fe
Showing 1 changed file with 54 additions and 85 deletions.
139 changes: 54 additions & 85 deletions src/librustc/hir/lowering.rs
View file
Expand Up @@ -4394,20 +4394,17 @@ impl<'a> LoweringContext<'a> {
let then_blk = self.lower_block(then, false);
let then_expr = self.expr_block(then_blk, ThinVec::new());
let (then_pats, scrutinee, desugar) = match cond.node {
// `<pat> => <then>`
// `<pat> => <then>`:
ExprKind::Let(ref pats, ref scrutinee) => {
let scrutinee = self.lower_expr(scrutinee);
let pats = pats.iter().map(|pat| self.lower_pat(pat)).collect();
let desugar = hir::MatchSource::IfLetDesugar { contains_else_clause };
(pats, scrutinee, desugar)
}
// `true => then`:
// `true => <then>`:
_ => {
// Lower condition:
let cond = self.lower_expr(cond);
// Wrap in a construct equivalent to `{ let _t = $cond; _t }`
// to preserve drop semantics since `if cond { ... }`
// don't let temporaries live outside of `cond`.
let span_block = self.mark_span_with_reason(CondTemporary, cond.span, None);
// Wrap in a construct equivalent to `{ let _t = $cond; _t }`
// to preserve drop semantics since `if cond { ... }` does not
Expand All @@ -4424,61 +4421,36 @@ impl<'a> LoweringContext<'a> {
hir::ExprKind::Match(P(scrutinee), vec![then_arm, else_arm].into(), desugar)
}
// FIXME(#53667): handle lowering of && and parens.
ExprKind::While(ref cond, ref body, opt_label) => {
// Desugar `ExprWhileLet`
// from: `[opt_ident]: while let <pat> = <sub_expr> <body>`
if let ExprKind::Let(ref pats, ref sub_expr) = cond.node {
// to:
//
// [opt_ident]: loop {
// match <sub_expr> {
// <pat> => <body>,
// _ => break
// }
// }

// Note that the block AND the condition are evaluated in the loop scope.
// This is done to allow `break` from inside the condition of the loop.
let (body, break_expr, sub_expr) = self.with_loop_scope(e.id, |this| {
(
this.lower_block(body, false),
this.expr_break(e.span, ThinVec::new()),
this.with_loop_condition_scope(|this| P(this.lower_expr(sub_expr))),
)
});
ExprKind::While(ref cond, ref body, opt_label) => self.with_loop_scope(e.id, |this| {
// Note that the block AND the condition are evaluated in the loop scope.
// This is done to allow `break` from inside the condition of the loop.

// `<pat> => <body>`
let pat_arm = {
let body_expr = P(self.expr_block(body, ThinVec::new()));
let pats = pats.iter().map(|pat| self.lower_pat(pat)).collect();
self.arm(pats, body_expr)
};

// `_ => break`
let break_arm = {
let pat_under = self.pat_wild(e.span);
self.arm(hir_vec![pat_under], break_expr)
};

// `match <sub_expr> { ... }`
let match_expr = self.expr_match(
sub_expr.span,
sub_expr,
hir_vec![pat_arm, break_arm],
hir::MatchSource::WhileLetDesugar,
);
// `_ => break`:
let else_arm = {
let else_pat = this.pat_wild(e.span);
let else_expr = this.expr_break(e.span, ThinVec::new());
this.arm(hir_vec![else_pat], else_expr)
};

// `[opt_ident]: loop { ... }`
let loop_block = P(self.block_expr(P(match_expr)));
let loop_expr = hir::ExprKind::Loop(
loop_block,
self.lower_label(opt_label),
hir::LoopSource::WhileLet,
);
// Add attributes to the outer returned expr node.
loop_expr
} else {
self.with_loop_scope(e.id, |this| {
// Handle then + scrutinee:
let then_blk = this.lower_block(body, false);
let then_expr = this.expr_block(then_blk, ThinVec::new());
let (then_pats, scrutinee, desugar, source) = match cond.node {
ExprKind::Let(ref pats, ref scrutinee) => {
// to:
//
// [opt_ident]: loop {
// match <sub_expr> {
// <pat> => <body>,
// _ => break
// }
// }
let scrutinee = this.with_loop_condition_scope(|t| t.lower_expr(scrutinee));
let pats = pats.iter().map(|pat| this.lower_pat(pat)).collect();
let desugar = hir::MatchSource::WhileLetDesugar;
(pats, scrutinee, desugar, hir::LoopSource::WhileLet)
}
_ => {
// We desugar: `'label: while $cond $body` into:
//
// ```
Expand All @@ -4490,40 +4462,37 @@ impl<'a> LoweringContext<'a> {
// }
// ```

// `true => then`:
let then_pat = this.pat_bool(e.span, true);
let then_blk = this.lower_block(body, false);
let then_expr = this.expr_block(then_blk, ThinVec::new());
let then_arm = this.arm(hir_vec![then_pat], P(then_expr));

// `_ => break`:
let else_pat = this.pat_wild(e.span);
let else_expr = this.expr_break(e.span, ThinVec::new());
let else_arm = this.arm(hir_vec![else_pat], else_expr);

// Lower condition:
let span_block = this.mark_span_with_reason(CondTemporary, cond.span, None);
let cond = this.with_loop_condition_scope(|this| this.lower_expr(cond));
let span_block = this.mark_span_with_reason(CondTemporary, cond.span, None);
// Wrap in a construct equivalent to `{ let _t = $cond; _t }`
// to preserve drop semantics since `if cond { ... }` does not
// to preserve drop semantics since `while cond { ... }` does not
// let temporaries live outside of `cond`.
let cond = this.expr_drop_temps(span_block, P(cond), ThinVec::new());

let match_expr = this.expr_match(
cond.span,
P(cond),
vec![then_arm, else_arm].into(),
hir::MatchSource::WhileDesugar,
);
let desugar = hir::MatchSource::WhileDesugar;
// `true => <then>`:
let pats = hir_vec![this.pat_bool(e.span, true)];
(pats, cond, desugar, hir::LoopSource::While)
}
};
let then_arm = this.arm(then_pats, P(then_expr));

hir::ExprKind::Loop(
P(this.block_expr(P(match_expr))),
this.lower_label(opt_label),
hir::LoopSource::While,
)
})
}
}
// `match <scrutinee> { ... }`
let match_expr = this.expr_match(
scrutinee.span,
P(scrutinee),
hir_vec![then_arm, else_arm],
desugar,
);

// `[opt_ident]: loop { ... }`
hir::ExprKind::Loop(
P(this.block_expr(P(match_expr))),
this.lower_label(opt_label),
source
)
}),
ExprKind::Loop(ref body, opt_label) => self.with_loop_scope(e.id, |this| {
hir::ExprKind::Loop(
this.lower_block(body, false),
Expand Down

0 comments on commit 26144fe

Please sign in to comment.