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| author | Sam McCall <sam.mccall@gmail.com> | 2019-07-08 11:33:17 +0000 |
|---|---|---|
| committer | Sam McCall <sam.mccall@gmail.com> | 2019-07-08 11:33:17 +0000 |
| commit | 674d8a947c7fc323dde9dc16d22667ce30169ee7 (patch) | |
| tree | 29fc013c8b5ac4507a0477f6c9a3f1e091a3defb /clang-tools-extra/clangd/SourceCode.cpp | |
| parent | 556ec990e97c6e6bb6ef91d7bdb813b2776608f2 (diff) | |
[clangd] Use xxhash instead of SHA1 for background index file digests.
Summary:
Currently SHA1 is about 10% of our CPU, this patch reduces it to ~1%.
xxhash is a well-defined (stable) non-cryptographic hash optimized for
fast checksums (like crc32).
Collisions shouldn't be a problem, despite the reduced length:
- for actual file content (used to invalidate bg index shards), there
are only two versions that can collide (new shard and old shard).
- for file paths in bg index shard filenames, we would need 2^32 files
with the same filename to expect a collision. Imperfect hashing may
reduce this a bit but it's well beyond what's plausible.
This will invalidate shards on disk (as usual; I bumped the version),
but this time the filenames are changing so the old files will stick
around :-( So this is more expensive than the usual bump, but would be
good to land before the v9 branch when everyone will start using bg index.
Reviewers: kadircet
Subscribers: ilya-biryukov, MaskRay, jkorous, arphaman, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D64306
llvm-svn: 365311
Diffstat (limited to 'clang-tools-extra/clangd/SourceCode.cpp')
| -rw-r--r-- | clang-tools-extra/clangd/SourceCode.cpp | 9 |
1 files changed, 8 insertions, 1 deletions
diff --git a/clang-tools-extra/clangd/SourceCode.cpp b/clang-tools-extra/clangd/SourceCode.cpp index 9fcaed455194..5c715ba8df7a 100644 --- a/clang-tools-extra/clangd/SourceCode.cpp +++ b/clang-tools-extra/clangd/SourceCode.cpp @@ -25,6 +25,7 @@ #include "llvm/Support/Error.h" #include "llvm/Support/ErrorHandling.h" #include "llvm/Support/Path.h" +#include "llvm/Support/xxhash.h" #include <algorithm> namespace clang { @@ -376,7 +377,13 @@ bool isRangeConsecutive(const Range &Left, const Range &Right) { } FileDigest digest(llvm::StringRef Content) { - return llvm::SHA1::hash({(const uint8_t *)Content.data(), Content.size()}); + uint64_t Hash{llvm::xxHash64(Content)}; + FileDigest Result; + for (unsigned I = 0; I < Result.size(); ++I) { + Result[I] = uint8_t(Hash); + Hash >>= 8; + } + return Result; } llvm::Optional<FileDigest> digestFile(const SourceManager &SM, FileID FID) { |