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[clang][Syntax] Optimize expandedTokens for token ranges.

Authored by usaxena95 on Mar 22 2021, 7:40 AM.

Description

[clang][Syntax] Optimize expandedTokens for token ranges.

expandedTokens(SourceRange) used to do a binary search to get the
expanded tokens belonging to a source range. Each binary search uses
isBeforeInTranslationUnit to order two source locations. This is
inherently very slow.
By profiling clangd we found out that users like clangd::SelectionTree
spend 95% of time in isBeforeInTranslationUnit. Also it is worth
noting that users of expandedTokens(SourceRange) majorly use ranges
provided by AST to query this funciton. The ranges provided by AST are
token ranges (starting at the beginning of a token and ending at the
beginning of another token).

Therefore we can avoid the binary search in majority of the cases by
maintaining an index of ExpandedToken by their SourceLocations. We still
do binary search for ranges which are not token ranges but such
instances are quite low.

Performance:
~/build/bin/clangd --check=clang/lib/Serialization/ASTReader.cpp
Before: Took 2:10s to complete.
Now: Took 1:13s to complete.

Differential Revision: https://reviews.llvm.org/D99086

Details

Committed
usaxena95Mar 25 2021, 10:54 AM
Differential Revision
D99086: [clang][Syntax] Optimize expandedTokens for token ranges.
Parents
rG27899112c698: [flang] fold LOGICAL intrinsic calls
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