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src: fix performance regression in node_file.cc - #31343
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nodejs-github-bot
commented
Jan 13, 2020
guybedford
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Great to see this, thanks.
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could you use if statements here to avoid goto?
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No, for two reasons:
- Aesthetic. It keeps the level of indent small.
- 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:
Details
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
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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
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@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.
bnoordhuis
commented
Jan 14, 2020
A play on a left-wing slogan would've been okay then? I've changed it to something more boring, PTAL. |
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.
Let's make it even more boring and remove all vestiges of the wordplay. |
hybrist
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LGTM with updated commit message
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nodejs-github-bot
commented
Jan 15, 2020
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. PR-URL: #31343 Reviewed-By: Colin Ihrig <cjihrig@gmail.com> Reviewed-By: Guy Bedford <guybedford@gmail.com> Reviewed-By: David Carlier <devnexen@gmail.com> Reviewed-By: Anna Henningsen <anna@addaleax.net> Reviewed-By: Rich Trott <rtrott@gmail.com> Reviewed-By: Jan Krems <jan.krems@gmail.com>
Trott
commented
Jan 15, 2020
Landed in 6623481. I updated the commit message on landing. |
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. PR-URL: #31343 Reviewed-By: Colin Ihrig <cjihrig@gmail.com> Reviewed-By: Guy Bedford <guybedford@gmail.com> Reviewed-By: David Carlier <devnexen@gmail.com> Reviewed-By: Anna Henningsen <anna@addaleax.net> Reviewed-By: Rich Trott <rtrott@gmail.com> Reviewed-By: Jan Krems <jan.krems@gmail.com>
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. PR-URL: #31343 Reviewed-By: Colin Ihrig <cjihrig@gmail.com> Reviewed-By: Guy Bedford <guybedford@gmail.com> Reviewed-By: David Carlier <devnexen@gmail.com> Reviewed-By: Anna Henningsen <anna@addaleax.net> Reviewed-By: Rich Trott <rtrott@gmail.com> Reviewed-By: Jan Krems <jan.krems@gmail.com>
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. PR-URL: #31343 Reviewed-By: Colin Ihrig <cjihrig@gmail.com> Reviewed-By: Guy Bedford <guybedford@gmail.com> Reviewed-By: David Carlier <devnexen@gmail.com> Reviewed-By: Anna Henningsen <anna@addaleax.net> Reviewed-By: Rich Trott <rtrott@gmail.com> Reviewed-By: Jan Krems <jan.krems@gmail.com>
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.