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ajkleinJulien Gilli
ajklein
authored and
Julien Gilli
committed
v8: fix issue with let bindings in for loops
Backport b17eaaa5755e625493c5fe537f42b58838923c52 from upstream v8. Original commit message: Fix desugaring of let bindings in for loops to handle continue properly This requires putting the original loop's body inside an inner for loop (with the same labels as the original loop) and re-binding the temp variables in its "next" expression. A second flag is added to the desugared code to ensure the loop body executes at most once per loop. BUG=v8:3683 LOG=y Review URL: https://codereview.chromium.org/720863002 Cr-Commit-Position: refs/heads/master@{#25363} Fixes #9113 and #14411.
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‎deps/v8/src/parser.cc‎

Lines changed: 129 additions & 59 deletions
Original file line numberDiff line numberDiff line change
@@ -2846,29 +2846,33 @@ Statement* Parser::DesugarLetBindingsInForStatement(
28462846
//
28472847
// We rewrite a for statement of the form
28482848
//
2849-
// for (let x = i; cond; next) body
2849+
// labels: for (let x = i; cond; next) body
28502850
//
28512851
// into
28522852
//
28532853
// {
2854-
// let x = i;
2855-
// temp_x = x;
2856-
// flag = 1;
2857-
// for (;;) {
2858-
// let x = temp_x;
2859-
// if (flag == 1) {
2860-
// flag = 0;
2861-
// } else {
2862-
// next;
2863-
// }
2854+
// let x = i;
2855+
// temp_x = x;
2856+
// first = 1;
2857+
// outer: for (;;) {
2858+
// let x = temp_x;
2859+
// if (first == 1) {
2860+
// first = 0;
2861+
// } else {
2862+
// next;
2863+
// }
2864+
// flag = 1;
2865+
// labels: for (; flag == 1; flag = 0, temp_x = x) {
28642866
// if (cond) {
2865-
// <empty>
2867+
// body
28662868
// } else {
2867-
// break;
2869+
// break outer;
28682870
// }
2869-
// b
2870-
// temp_x = x;
2871-
// }
2871+
// }
2872+
// if (flag == 1) {
2873+
// break;
2874+
// }
2875+
// }
28722876
// }
28732877

28742878
DCHECK(names->length() > 0);
@@ -2896,24 +2900,33 @@ Statement* Parser::DesugarLetBindingsInForStatement(
28962900
temps.Add(temp, zone());
28972901
}
28982902

2899-
Variable* flag = scope_->DeclarationScope()->NewTemporary(temp_name);
2900-
// Make statement: flag = 1.
2901-
{
2902-
VariableProxy* flag_proxy = factory()->NewVariableProxy(flag);
2903+
Variable* first = NULL;
2904+
// Make statement: first = 1.
2905+
if (next) {
2906+
first = scope_->DeclarationScope()->NewTemporary(temp_name);
2907+
VariableProxy* first_proxy = factory()->NewVariableProxy(first);
29032908
Expression* const1 = factory()->NewSmiLiteral(1, RelocInfo::kNoPosition);
29042909
Assignment* assignment = factory()->NewAssignment(
2905-
Token::ASSIGN, flag_proxy, const1, RelocInfo::kNoPosition);
2906-
Statement* assignment_statement = factory()->NewExpressionStatement(
2907-
assignment, RelocInfo::kNoPosition);
2910+
Token::ASSIGN, first_proxy, const1, RelocInfo::kNoPosition);
2911+
Statement* assignment_statement =
2912+
factory()->NewExpressionStatement(assignment, RelocInfo::kNoPosition);
29082913
outer_block->AddStatement(assignment_statement, zone());
29092914
}
29102915

2911-
outer_block->AddStatement(loop, zone());
2916+
// Make statement: outer: for (;;)
2917+
// Note that we don't actually create the label, or set this loop up as an
2918+
// explicit break target, instead handing it directly to those nodes that
2919+
// need to know about it. This should be safe because we don't run any code
2920+
// in this function that looks up break targets.
2921+
ForStatement* outer_loop =
2922+
factory()->NewForStatement(NULL, RelocInfo::kNoPosition);
2923+
outer_block->AddStatement(outer_loop, zone());
2924+
29122925
outer_block->set_scope(for_scope);
29132926
scope_ = inner_scope;
29142927

2915-
Block* inner_block = factory()->NewBlock(NULL, 2 * names->length() + 3,
2916-
false, RelocInfo::kNoPosition);
2928+
Block* inner_block = factory()->NewBlock(NULL, names->length() + 4, false,
2929+
RelocInfo::kNoPosition);
29172930
int pos = scanner()->location().beg_pos;
29182931
ZoneList<Variable*> inner_vars(names->length(), zone());
29192932

@@ -2935,61 +2948,118 @@ Statement* Parser::DesugarLetBindingsInForStatement(
29352948
inner_block->AddStatement(assignment_statement, zone());
29362949
}
29372950

2938-
// Make statement: if (flag == 1) { flag = 0; } else { next; }.
2951+
// Make statement: if (first == 1) { first = 0; } else { next; }
29392952
if (next) {
2953+
DCHECK(first);
29402954
Expression* compare = NULL;
2941-
// Make compare expresion: flag == 1.
2955+
// Make compare expression: first == 1.
29422956
{
29432957
Expression* const1 = factory()->NewSmiLiteral(1, RelocInfo::kNoPosition);
2944-
VariableProxy* flag_proxy = factory()->NewVariableProxy(flag);
2945-
compare = factory()->NewCompareOperation(
2946-
Token::EQ, flag_proxy, const1, pos);
2958+
VariableProxy* first_proxy = factory()->NewVariableProxy(first);
2959+
compare =
2960+
factory()->NewCompareOperation(Token::EQ, first_proxy, const1, pos);
29472961
}
2948-
Statement* clear_flag = NULL;
2949-
// Make statement: flag = 0.
2962+
Statement* clear_first = NULL;
2963+
// Make statement: first = 0.
29502964
{
2951-
VariableProxy* flag_proxy = factory()->NewVariableProxy(flag);
2965+
VariableProxy* first_proxy = factory()->NewVariableProxy(first);
29522966
Expression* const0 = factory()->NewSmiLiteral(0, RelocInfo::kNoPosition);
29532967
Assignment* assignment = factory()->NewAssignment(
2954-
Token::ASSIGN, flag_proxy, const0, RelocInfo::kNoPosition);
2955-
clear_flag = factory()->NewExpressionStatement(assignment, pos);
2968+
Token::ASSIGN, first_proxy, const0, RelocInfo::kNoPosition);
2969+
clear_first =
2970+
factory()->NewExpressionStatement(assignment, RelocInfo::kNoPosition);
29562971
}
2957-
Statement* clear_flag_or_next = factory()->NewIfStatement(
2958-
compare, clear_flag, next, RelocInfo::kNoPosition);
2959-
inner_block->AddStatement(clear_flag_or_next, zone());
2972+
Statement* clear_first_or_next = factory()->NewIfStatement(
2973+
compare, clear_first, next, RelocInfo::kNoPosition);
2974+
inner_block->AddStatement(clear_first_or_next, zone());
29602975
}
29612976

2977+
Variable* flag = scope_->DeclarationScope()->NewTemporary(temp_name);
2978+
// Make statement: flag = 1.
2979+
{
2980+
VariableProxy* flag_proxy = factory()->NewVariableProxy(flag);
2981+
Expression* const1 = factory()->NewSmiLiteral(1, RelocInfo::kNoPosition);
2982+
Assignment* assignment = factory()->NewAssignment(
2983+
Token::ASSIGN, flag_proxy, const1, RelocInfo::kNoPosition);
2984+
Statement* assignment_statement =
2985+
factory()->NewExpressionStatement(assignment, RelocInfo::kNoPosition);
2986+
inner_block->AddStatement(assignment_statement, zone());
2987+
}
2988+
2989+
// Make cond expression for main loop: flag == 1.
2990+
Expression* flag_cond = NULL;
2991+
{
2992+
Expression* const1 = factory()->NewSmiLiteral(1, RelocInfo::kNoPosition);
2993+
VariableProxy* flag_proxy = factory()->NewVariableProxy(flag);
2994+
flag_cond =
2995+
factory()->NewCompareOperation(Token::EQ, flag_proxy, const1, pos);
2996+
}
29622997

2963-
// Make statement: if (cond) { } else { break; }.
2998+
// Create chain of expressions "flag = 0, temp_x = x, ..."
2999+
Statement* compound_next_statement = NULL;
3000+
{
3001+
Expression* compound_next = NULL;
3002+
// Make expression: flag = 0.
3003+
{
3004+
VariableProxy* flag_proxy = factory()->NewVariableProxy(flag);
3005+
Expression* const0 = factory()->NewSmiLiteral(0, RelocInfo::kNoPosition);
3006+
compound_next = factory()->NewAssignment(Token::ASSIGN, flag_proxy,
3007+
const0, RelocInfo::kNoPosition);
3008+
}
3009+
3010+
// Make the comma-separated list of temp_x = x assignments.
3011+
for (int i = 0; i < names->length(); i++) {
3012+
VariableProxy* temp_proxy = factory()->NewVariableProxy(temps.at(i));
3013+
VariableProxy* proxy = factory()->NewVariableProxy(inner_vars.at(i), pos);
3014+
Assignment* assignment = factory()->NewAssignment(
3015+
Token::ASSIGN, temp_proxy, proxy, RelocInfo::kNoPosition);
3016+
compound_next = factory()->NewBinaryOperation(
3017+
Token::COMMA, compound_next, assignment, RelocInfo::kNoPosition);
3018+
}
3019+
3020+
compound_next_statement = factory()->NewExpressionStatement(
3021+
compound_next, RelocInfo::kNoPosition);
3022+
}
3023+
3024+
// Make statement: if (cond) { body; } else { break outer; }
3025+
Statement* body_or_stop = body;
29643026
if (cond) {
2965-
Statement* empty = factory()->NewEmptyStatement(RelocInfo::kNoPosition);
2966-
BreakableStatement* t = LookupBreakTarget(NULL, CHECK_OK);
2967-
Statement* stop = factory()->NewBreakStatement(t, RelocInfo::kNoPosition);
2968-
Statement* if_not_cond_break = factory()->NewIfStatement(
2969-
cond, empty, stop, cond->position());
2970-
inner_block->AddStatement(if_not_cond_break, zone());
3027+
Statement* stop =
3028+
factory()->NewBreakStatement(outer_loop, RelocInfo::kNoPosition);
3029+
body_or_stop =
3030+
factory()->NewIfStatement(cond, body, stop, cond->position());
29713031
}
29723032

2973-
inner_block->AddStatement(body, zone());
3033+
// Make statement: labels: for (; flag == 1; flag = 0, temp_x = x)
3034+
// Note that we re-use the original loop node, which retains it labels
3035+
// and ensures that any break or continue statements in body point to
3036+
// the right place.
3037+
loop->Initialize(NULL, flag_cond, compound_next_statement, body_or_stop);
3038+
inner_block->AddStatement(loop, zone());
29743039

2975-
// For each let variable x:
2976-
// make statement: temp_x = x;
2977-
for (int i = 0; i < names->length(); i++) {
2978-
VariableProxy* temp_proxy = factory()->NewVariableProxy(temps.at(i));
2979-
int pos = scanner()->location().end_pos;
2980-
VariableProxy* proxy = factory()->NewVariableProxy(inner_vars.at(i), pos);
2981-
Assignment* assignment = factory()->NewAssignment(
2982-
Token::ASSIGN, temp_proxy, proxy, RelocInfo::kNoPosition);
2983-
Statement* assignment_statement = factory()->NewExpressionStatement(
2984-
assignment, RelocInfo::kNoPosition);
2985-
inner_block->AddStatement(assignment_statement, zone());
3040+
// Make statement: if (flag == 1) { break; }
3041+
{
3042+
Expression* compare = NULL;
3043+
// Make compare expresion: flag == 1.
3044+
{
3045+
Expression* const1 = factory()->NewSmiLiteral(1, RelocInfo::kNoPosition);
3046+
VariableProxy* flag_proxy = factory()->NewVariableProxy(flag);
3047+
compare =
3048+
factory()->NewCompareOperation(Token::EQ, flag_proxy, const1, pos);
3049+
}
3050+
Statement* stop =
3051+
factory()->NewBreakStatement(outer_loop, RelocInfo::kNoPosition);
3052+
Statement* empty = factory()->NewEmptyStatement(RelocInfo::kNoPosition);
3053+
Statement* if_flag_break =
3054+
factory()->NewIfStatement(compare, stop, empty, RelocInfo::kNoPosition);
3055+
inner_block->AddStatement(if_flag_break, zone());
29863056
}
29873057

29883058
inner_scope->set_end_position(scanner()->location().end_pos);
29893059
inner_block->set_scope(inner_scope);
29903060
scope_ = for_scope;
29913061

2992-
loop->Initialize(NULL, NULL, NULL, inner_block);
3062+
outer_loop->Initialize(NULL, NULL, NULL, inner_block);
29933063
return outer_block;
29943064
}
29953065

‎deps/v8/test/mjsunit/harmony/regress/regress-3683.js‎

Lines changed: 84 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,84 @@
1+
// Copyright 2014 the V8 project authors. All rights reserved.
2+
// Use of this source code is governed by a BSD-style license that can be
3+
// found in the LICENSE file.
4+
//
5+
// Flags: --harmony-scoping
6+
7+
"use strict";
8+
9+
// Simplest case
10+
var count = 0;
11+
for (let x = 0; x < 10;) {
12+
x++;
13+
count++;
14+
continue;
15+
}
16+
assertEquals(10, count);
17+
18+
// Labeled
19+
count = 0;
20+
label: for (let x = 0; x < 10;) {
21+
while (true) {
22+
x++;
23+
count++;
24+
continue label;
25+
}
26+
}
27+
assertEquals(10, count);
28+
29+
// Simple and labeled
30+
count = 0;
31+
label: for (let x = 0; x < 10;) {
32+
x++;
33+
count++;
34+
continue label;
35+
}
36+
assertEquals(10, count);
37+
38+
// Shadowing loop variable in same scope as continue
39+
count = 0;
40+
for (let x = 0; x < 10;) {
41+
x++;
42+
count++;
43+
{
44+
let x = "hello";
45+
continue;
46+
}
47+
}
48+
assertEquals(10, count);
49+
50+
// Nested let-bound for loops, inner continue
51+
count = 0;
52+
for (let x = 0; x < 10;) {
53+
x++;
54+
for (let y = 0; y < 2;) {
55+
y++;
56+
count++;
57+
continue;
58+
}
59+
}
60+
assertEquals(20, count);
61+
62+
// Nested let-bound for loops, outer continue
63+
count = 0;
64+
for (let x = 0; x < 10;) {
65+
x++;
66+
for (let y = 0; y < 2;) {
67+
y++;
68+
count++;
69+
}
70+
continue;
71+
}
72+
assertEquals(20, count);
73+
74+
// Nested let-bound for loops, labeled continue
75+
count = 0;
76+
outer: for (let x = 0; x < 10;) {
77+
x++;
78+
for (let y = 0; y < 2;) {
79+
y++;
80+
count++;
81+
if (y == 2) continue outer;
82+
}
83+
}
84+
assertEquals(20, count);

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