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41b2fa7375
Linking clang-13 with debug info takes ~3.6 seconds on a simulated 10-core/20-threads machine. mold spends most of its time (~2.3 seconds) merging string literals in .debug_str. Input .debug_str sections contain 70 million string literals in total, which is reduced to 2 million after de-duplication. The input object files contain a lot of duplicates. clang-13 with debug info is enormous -- it is ~3.1 GiB after linking. It looks like TBB's concurrent hashmap doesn't scale well with the input. In this patch, I implemented our own concurrent hashmap. The hashmap is extremely lightweight and support only the key-value insertion operation. It doesn't even support rehashing. It aborts once the hash table becomes full. In order to know the correct size for the hashmap before inserting strings into it, I also implemented HyperLogLog algorithm in this patch. HyperLogLog is an algorithm that gives a fairly accurate estimate on the number of unique elements. With this patch, mold can link clang-13 in ~2.5 seconds, which is ~30% faster than before. https://github.com/rui314/mold/issues/73
22 lines
531 B
C++
22 lines
531 B
C++
// This file implements HyperLogLog algorithm, which estimates
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// the number of unique items in a given multiset.
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//
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// For more info, read
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// https://engineering.fb.com/2018/12/13/data-infrastructure/hyperloglog
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#include "mold.h"
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#include <cmath>
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i64 HyperLogLog::get_cardinality() const {
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double z = 0;
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for (i64 val : buckets)
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z += pow(2, -val);
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return ALPHA * NBUCKETS * NBUCKETS / z;
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}
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void HyperLogLog::merge(const HyperLogLog &other) {
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for (i64 i = 0; i < NBUCKETS; i++)
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merge_one(i, other.buckets[i]);
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}
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