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LibRegex: Add the literal string search optimisation

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This switches to using a simple string equality check if the regex
pattern is strictly a string literal.
Technically this optimisation can also be made on bounded literal
patterns like /[abc]def/ or /abc|def/ as well, but those are
significantly more complex to implement due to our bytecode-only
approach.
This commit is contained in:
Ali Mohammad Pur 2023-07-28 20:59:33 +03:30 • committed by Andreas Kling
parent 221c52c696
commit 18f4b6c670
6 changed files with 82 additions and 4 deletions
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51
Userland/Libraries/LibRegex/RegexOptimizer.cpp
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@ -25,9 +25,13 @@ void Regex<Parser>::run_optimization_passes()
{
parser_result.bytecode.flatten();
auto blocks = split_basic_blocks(parser_result.bytecode);
if (attempt_rewrite_entire_match_as_substring_search(blocks))
return;
// Rewrite fork loops as atomic groups
// e.g. a*b -> (ATOMIC a*)b
attempt_rewrite_loops_as_atomic_groups(split_basic_blocks(parser_result.bytecode));
attempt_rewrite_loops_as_atomic_groups(blocks);
parser_result.bytecode.flatten();
}
@ -520,6 +524,51 @@ static AtomicRewritePreconditionResult block_satisfies_atomic_rewrite_preconditi
return AtomicRewritePreconditionResult::SatisfiedWithEmptyHeader;
}
template<typename Parser>
bool Regex<Parser>::attempt_rewrite_entire_match_as_substring_search(BasicBlockList const& basic_blocks)
{
// If there's no jumps, we can probably rewrite this as a substring search (Compare { string = str }).
if (basic_blocks.size() > 1)
return false;
if (basic_blocks.is_empty()) {
parser_result.optimization_data.pure_substring_search = ""sv;
return true; // Empty regex, sure.
}
auto& bytecode = parser_result.bytecode;
auto is_unicode = parser_result.options.has_flag_set(AllFlags::Unicode);
// We have a single basic block, let's see if it's a series of character or string compares.
StringBuilder final_string;
MatchState state;
while (state.instruction_position < bytecode.size()) {
auto& opcode = bytecode.get_opcode(state);
switch (opcode.opcode_id()) {
case OpCodeId::Compare: {
auto& compare = static_cast<OpCode_Compare const&>(opcode);
for (auto& flat_compare : compare.flat_compares()) {
if (flat_compare.type != CharacterCompareType::Char)
return false;
if (is_unicode || flat_compare.value <= 0x7f)
final_string.append_code_point(flat_compare.value);
else
final_string.append(bit_cast<char>(static_cast<u8>(flat_compare.value)));
}
break;
}
default:
return false;
}
state.instruction_position += opcode.size();
}
parser_result.optimization_data.pure_substring_search = final_string.to_deprecated_string();
return true;
}
template<typename Parser>
void Regex<Parser>::attempt_rewrite_loops_as_atomic_groups(BasicBlockList const& basic_blocks)
{