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LibJS: Replace source map HashMap with sorted Vector

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Bytecode source map entries are always added in order of increasing
bytecode offset, and lookups only happen during error handling (a cold
path). This makes a sorted vector with binary search a better fit than
a hash map.

This change reduces memory overhead and speeds up bytecode generation
by avoiding hash table operations during compilation. Lookups remain
fast via binary search, and since source_range_at() is only called
when generating stack traces, the O(log n) lookup is acceptable.
This commit is contained in:
Andreas Kling
2026-01-26 17:51:53 +01:00
committed by Andreas Kling
parent d488f9f12f
commit 81bee185e6
Notes: github-actions[bot] 2026-02-06 11:03:57 +00:00 
Author: https://github.com/awesomekling
Commit: https://github.com/LadybirdBrowser/ladybird/commit/81bee185e6b
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/7633
4 changed files with 23 additions and 11 deletions
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15
Libraries/LibJS/Bytecode/Executable.cpp
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@@ -4,6 +4,7 @@
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/BinarySearch.h>
#include <LibJS/Bytecode/BasicBlock.h>
#include <LibJS/Bytecode/Executable.h>
#include <LibJS/Bytecode/Instruction.h>
@@ -115,13 +116,19 @@ UnrealizedSourceRange Executable::source_range_at(size_t offset) const
return {};
auto it = InstructionStreamIterator(bytecode.span().slice(offset), this);
VERIFY(!it.at_end());
auto mapping = source_map.get(offset);
if (!mapping.has_value())
auto* entry = binary_search(source_map, offset, nullptr, [](size_t needle, SourceMapEntry const& entry) -> int {
if (needle < entry.bytecode_offset)
return -1;
if (needle > entry.bytecode_offset)
return 1;
return 0;
});
if (!entry)
return {};
return UnrealizedSourceRange {
.source_code = source_code,
.start_offset = mapping->source_start_offset,
.end_offset = mapping->source_end_offset,
.start_offset = entry->source_record.source_start_offset,
.end_offset = entry->source_record.source_end_offset,
};
}