ICU-22419 Performance improvements of collated string comparison #2505
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Checklist
Currently, collated string comparisons are optimized to find the first byte where the prefix doesn't match by performing a byte comparison.
However, a comparison of one byte at a time is used to evaluate the prefix mismatch.
Making a double word comparison to discover the prefix mismatch is one way to improve the performance. In this PR, the
double word
comparison is performed only when both strings have the same alignment:(uintptr_t)left % sizeof(uint64_t) == (uintptr_t)right % sizeof(uint64_t)
This leads to a 10x performance improvement when the strings have some binary equal prefix. Results based on google/benchmark: ICU Comparison Benchmarks
Benchmark: