src: fix performance regression in node_file.cc

[bnoordhuis]

Commits dcb6929, 4396beb and 8a96d05 turned the O(n) scan in
InternalModuleReadJSON() into an O(4n) scan. Fix the performance
regression by turning that into a linear scan again.

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/28431/

[guybedford]

Great to see this, thanks.

[devsnek]

could you use if statements here to avoid goto?

[bnoordhuis]

No, for two reasons:

1. Aesthetic. It keeps the level of indent small.
2. Performance. g++ 9.2.1 at -O3 doesn't move the block out of the way. The goto keeps the inner loop at around 80 bytes:

    10ec:       80 f9 22                cmp    $0x22,%cl
    10ef:       74 1f                   je     1110 <main+0x70>
    10f1:       80 f9 5c                cmp    $0x5c,%cl
    10f4:       75 44                   jne    113a <main+0x9a>
    10f6:       48 39 fa                cmp    %rdi,%rdx
    10f9:       73 65                   jae    1160 <main+0xc0>
    10fb:       0f b6 4e 01             movzbl 0x1(%rsi),%ecx
    10ff:       80 f9 22                cmp    $0x22,%cl
    1102:       74 7c                   je     1180 <main+0xe0>
    1104:       48 89 d6                mov    %rdx,%rsi
    1107:       48 8d 56 01             lea    0x1(%rsi),%rdx
    110b:       80 f9 22                cmp    $0x22,%cl
    110e:       75 e1                   jne    10f1 <main+0x51>
    1110:       49 8d 48 08             lea    0x8(%r8),%rcx
    1114:       49 89 10                mov    %rdx,(%r8)
    1117:       4c 39 c9                cmp    %r9,%rcx
    111a:       72 34                   jb     1150 <main+0xb0>
    111c:       48 8b 34 24             mov    (%rsp),%rsi
    1120:       48 89 f1                mov    %rsi,%rcx
    1123:       48 f7 d1                not    %rcx
    1126:       48 03 4c 24 08          add    0x8(%rsp),%rcx
    112b:       48 83 f9 04             cmp    $0x4,%rcx
    112f:       74 5f                   je     1190 <main+0xf0>
    1131:       4d 89 d0                mov    %r10,%r8
    1134:       48 83 f9 07             cmp    $0x7,%rcx
    1138:       74 76                   je     11b0 <main+0x110>
    113a:       48 39 fa                cmp    %rdi,%rdx
    113d:       73 21                   jae    1160 <main+0xc0>
    113f:       0f b6 0a                movzbl (%rdx),%ecx
    1142:       48 89 d6                mov    %rdx,%rsi
    1145:       eb a1                   jmp    10e8 <main+0x48>

(-O3 is kind of disappointing; with -Os it fits in a single cache line.)

I'll add a comment explaining why it's there.

[addaleax]

Code LGTM but the commit message should be changed to something that’s a) descriptive of what this commit actually does and b) not a wordplay on a right-wing slogan before or during merging.

[ryanmurakami]

@bnoordhuis The Moderation Team is requesting that you change the commit message and pull request title. The Moderation Team believes the similarities to an American politician's campaign slogan is not in line with the Code of Conduct's guide to use "welcoming and inclusive language". The Moderation Team is happy to provide external references should you need them.

obsolete

[bnoordhuis]

not a wordplay on a right-wing slogan before or during merging.

A play on a left-wing slogan would've been okay then? I've changed it to something more boring, PTAL.

[Trott]

not a wordplay on a right-wing slogan before or during merging.

A play on a left-wing slogan would've been okay then?

The phrase is one that provokes strong reactions. I think it is reasonable to request that it be changed in a situation like this where using the phrase is unnecessary.

But yes, the fact that the slogan is right-wing is not really the problem, per se. Had it been a play on "Read my lips: no new taxes", I don't think it would generate the same reaction.

FWIW, I can definitely think of a few left-wing slogans that would be problematic.

I've changed it to something more boring, PTAL.

Let's make it even more boring and remove all vestiges of the wordplay. src: fix performance regression in node_file.cc or maybe src: fix performance regression in InternalModuleReadJSON?

[jkrems]

LGTM with updated commit message

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/28447/

[Trott]

Landed in 6623481.

I updated the commit message on landing.