Optimize ULEB decoding to improve MCCAS replay time #7952
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This function is not used anywhere and can be safely removed.
BinaryStreamReader and DataExtractor do similar things, but BinaryStreamReader can also hold a buffer that is not contiguous which comes with some performance penalties. Replacing it with DataExtractor allows us to keep the same functionality but improve MCCAS replay time.
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@swift-ci please test llvm |
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| uint64_t Data64; | ||
| if (auto Err = Reader.readULEB128(Data64)) | ||
| handleAllErrors(std::move(Err)); | ||
| DataExtractor Extractor(FormData, true, 8); |
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Do we know for sure that there will be 8 bytes available at all times?
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That is just the address size, not how many bytes are available in the buffer
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Cherry-pick PR. #7952 to stable/20230725
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MCCAS replay is slower than file based caching because it is DWARF aware. Part of parsing DWARF is decoding a lot of ULEBs. One way to quickly get the benefits is by replacing
BinaryStreamReaderwithDataExtractorWith this patch we can see that on average MCCAS replay time went from between 15-16 seconds, to between 14 and 15 seconds.
ULEB unopt numbers:
Build Num, Median Replay Time
1, 16.362477000
2, 15.626469000
3, 15.794678000
4, 15.838866000
5, 15.691996000
6, 15.206883000
7, 16.119893000
8, 15.525278000
9, 16.549542000
10, 16.782434000
ULEB Opt Numbers:
Build Num, Median Replay Time
1, 15.498433000
2, 14.566443000
3, 14.720929000
4, 14.535185000
5, 14.107377000
6, 14.132124000
7, 14.922363000
8, 14.481217000
9, 14.866581000
10, 15.974748000