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LibRegex: Add a basic optimization pass
This currently tries to convert forking loops to atomic groups, and unify the left side of alternations.
This commit is contained in:
Ali Mohammad Pur
Ali Mohammad Pur
parent
913382734c
commit
246ab432ff
9 changed files with 677 additions and 24 deletions
477
Userland/Libraries/LibRegex/RegexOptimizer.cpp
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477
Userland/Libraries/LibRegex/RegexOptimizer.cpp
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/*
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* Copyright (c) 2021, Ali Mohammad Pur <mpfard@serenityos.org>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#include <AK/QuickSort.h>
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#include <AK/RedBlackTree.h>
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#include <AK/Stack.h>
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#include <LibRegex/Regex.h>
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#include <LibRegex/RegexBytecodeStreamOptimizer.h>
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namespace regex {
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using Detail::Block;
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template<typename Parser>
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void Regex<Parser>::run_optimization_passes()
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{
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// Rewrite fork loops as atomic groups
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// e.g. a*b -> (ATOMIC a*)b
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attempt_rewrite_loops_as_atomic_groups(split_basic_blocks());
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}
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template<typename Parser>
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typename Regex<Parser>::BasicBlockList Regex<Parser>::split_basic_blocks()
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{
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BasicBlockList block_boundaries;
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auto& bytecode = parser_result.bytecode;
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size_t end_of_last_block = 0;
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MatchState state;
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state.instruction_position = 0;
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auto check_jump = [&]<typename T>(OpCode const& opcode) {
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auto& op = static_cast<T const&>(opcode);
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ssize_t jump_offset = op.size() + op.offset();
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if (jump_offset >= 0) {
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block_boundaries.append({ end_of_last_block, state.instruction_position });
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end_of_last_block = state.instruction_position + opcode.size();
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} else {
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// This op jumps back, see if that's within this "block".
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if (jump_offset + state.instruction_position > end_of_last_block) {
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// Split the block!
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block_boundaries.append({ end_of_last_block, jump_offset + state.instruction_position });
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block_boundaries.append({ jump_offset + state.instruction_position, state.instruction_position });
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end_of_last_block = state.instruction_position + opcode.size();
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} else {
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// Nope, it's just a jump to another block
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block_boundaries.append({ end_of_last_block, state.instruction_position });
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end_of_last_block = state.instruction_position + opcode.size();
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}
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}
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};
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for (;;) {
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auto& opcode = bytecode.get_opcode(state);
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switch (opcode.opcode_id()) {
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case OpCodeId::Jump:
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check_jump.template operator()<OpCode_Jump>(opcode);
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break;
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case OpCodeId::JumpNonEmpty:
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check_jump.template operator()<OpCode_JumpNonEmpty>(opcode);
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break;
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case OpCodeId::ForkJump:
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check_jump.template operator()<OpCode_ForkJump>(opcode);
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break;
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case OpCodeId::ForkStay:
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check_jump.template operator()<OpCode_ForkStay>(opcode);
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break;
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case OpCodeId::FailForks:
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block_boundaries.append({ end_of_last_block, state.instruction_position });
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end_of_last_block = state.instruction_position + opcode.size();
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break;
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case OpCodeId::Repeat: {
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// Repeat produces two blocks, one containing its repeated expr, and one after that.
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auto repeat_start = state.instruction_position - static_cast<OpCode_Repeat const&>(opcode).offset();
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if (repeat_start > end_of_last_block)
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block_boundaries.append({ end_of_last_block, repeat_start });
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block_boundaries.append({ repeat_start, state.instruction_position });
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end_of_last_block = state.instruction_position + opcode.size();
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break;
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}
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default:
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break;
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}
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auto next_ip = state.instruction_position + opcode.size();
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if (next_ip < bytecode.size())
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state.instruction_position = next_ip;
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else
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break;
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}
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if (end_of_last_block < bytecode.size())
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block_boundaries.append({ end_of_last_block, bytecode.size() });
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quick_sort(block_boundaries, [](auto& a, auto& b) { return a.start < b.start; });
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return block_boundaries;
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}
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static bool block_satisfies_atomic_rewrite_precondition(ByteCode const& bytecode, Block const& repeated_block, Block const& following_block)
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{
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Vector<Vector<CompareTypeAndValuePair>> repeated_values;
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MatchState state;
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for (state.instruction_position = repeated_block.start; state.instruction_position < repeated_block.end;) {
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auto& opcode = bytecode.get_opcode(state);
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switch (opcode.opcode_id()) {
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case OpCodeId::Compare: {
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auto compares = static_cast<OpCode_Compare const&>(opcode).flat_compares();
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if (repeated_values.is_empty() && any_of(compares, [](auto& compare) { return compare.type == CharacterCompareType::AnyChar; }))
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return false;
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repeated_values.append(move(compares));
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break;
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}
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case OpCodeId::CheckBegin:
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case OpCodeId::CheckEnd:
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if (repeated_values.is_empty())
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return true;
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break;
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case OpCodeId::CheckBoundary:
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// FIXME: What should we do with these? for now, let's fail.
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return false;
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case OpCodeId::Restore:
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case OpCodeId::GoBack:
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return false;
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default:
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break;
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}
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state.instruction_position += opcode.size();
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}
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dbgln_if(REGEX_DEBUG, "Found {} entries in reference", repeated_values.size());
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// Find the first compare in the following block, it must NOT match any of the values in `repeated_values'.
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for (state.instruction_position = following_block.start; state.instruction_position < following_block.end;) {
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auto& opcode = bytecode.get_opcode(state);
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switch (opcode.opcode_id()) {
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case OpCodeId::Compare: {
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// We found a compare, let's see what it has.
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auto compares = static_cast<OpCode_Compare const&>(opcode).flat_compares();
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if (compares.is_empty())
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break;
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// If either side can match _anything_, fail.
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if (any_of(compares, [](auto& compare) { return compare.type == CharacterCompareType::AnyChar; }))
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return false;
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for (auto& repeated_value : repeated_values) {
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// FIXME: This is too naive!
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if (any_of(repeated_value, [](auto& compare) { return compare.type == CharacterCompareType::AnyChar; }))
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return false;
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for (auto& repeated_compare : repeated_value) {
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// FIXME: This is too naive! it will miss _tons_ of cases since it doesn't check ranges!
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if (any_of(compares, [&](auto& compare) { return compare.type == repeated_compare.type && compare.value == repeated_compare.value; }))
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return false;
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}
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}
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return true;
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}
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case OpCodeId::CheckBegin:
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case OpCodeId::CheckEnd:
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return true; // Nothing can match the end!
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case OpCodeId::CheckBoundary:
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// FIXME: What should we do with these? For now, consider them a failure.
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return false;
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default:
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break;
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}
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state.instruction_position += opcode.size();
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}
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return true;
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}
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template<typename Parser>
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void Regex<Parser>::attempt_rewrite_loops_as_atomic_groups(BasicBlockList const& basic_blocks)
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{
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auto& bytecode = parser_result.bytecode;
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if constexpr (REGEX_DEBUG) {
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RegexDebug dbg;
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dbg.print_bytecode(*this);
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for (auto& block : basic_blocks)
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dbgln("block from {} to {}", block.start, block.end);
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}
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// A pattern such as:
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// bb0 | RE0
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// | ForkX bb0
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// -------------------------
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// bb1 | RE1
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// can be rewritten as:
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// loop.hdr | ForkStay bb1
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// -------------------------
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// bb0 | RE0
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// | ForkReplaceX bb0
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// -------------------------
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// bb1 | RE1
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// provided that first(RE1) not-in end(RE0), which is to say
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// that RE1 cannot start with whatever RE0 has matched (ever).
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//
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// Alternatively, a second form of this pattern can also occur:
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// bb0 | *
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// | ForkX bb2
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// ------------------------
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// bb1 | RE0
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// | Jump bb0
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// ------------------------
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// bb2 | RE1
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// which can be transformed (with the same preconditions) to:
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// bb0 | *
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// | ForkReplaceX bb2
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// ------------------------
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// bb1 | RE0
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// | Jump bb0
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// ------------------------
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// bb2 | RE1
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enum class AlternateForm {
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DirectLoopWithoutHeader, // loop without proper header, a block forking to itself. i.e. the first form.
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DirectLoopWithHeader, // loop with proper header, i.e. the second form.
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};
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struct CandidateBlock {
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Block forking_block;
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Optional<Block> new_target_block;
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AlternateForm form;
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};
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Vector<CandidateBlock> candidate_blocks;
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auto is_an_eligible_jump = [](OpCode const& opcode, size_t ip, size_t block_start, AlternateForm alternate_form) {
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switch (opcode.opcode_id()) {
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case OpCodeId::JumpNonEmpty: {
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auto& op = static_cast<OpCode_JumpNonEmpty const&>(opcode);
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auto form = op.form();
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if (form != OpCodeId::Jump && alternate_form == AlternateForm::DirectLoopWithHeader)
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return false;
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if (form != OpCodeId::ForkJump && form != OpCodeId::ForkStay && alternate_form == AlternateForm::DirectLoopWithoutHeader)
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return false;
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return op.offset() + ip + opcode.size() == block_start;
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}
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case OpCodeId::ForkJump:
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if (alternate_form == AlternateForm::DirectLoopWithHeader)
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return false;
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return static_cast<OpCode_ForkJump const&>(opcode).offset() + ip + opcode.size() == block_start;
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case OpCodeId::ForkStay:
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if (alternate_form == AlternateForm::DirectLoopWithHeader)
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return false;
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return static_cast<OpCode_ForkStay const&>(opcode).offset() + ip + opcode.size() == block_start;
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case OpCodeId::Jump:
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// Infinite loop does *not* produce forks.
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if (alternate_form == AlternateForm::DirectLoopWithoutHeader)
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return false;
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if (alternate_form == AlternateForm::DirectLoopWithHeader)
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return static_cast<OpCode_Jump const&>(opcode).offset() + ip + opcode.size() == block_start;
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VERIFY_NOT_REACHED();
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default:
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return false;
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}
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};
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for (size_t i = 0; i < basic_blocks.size(); ++i) {
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auto forking_block = basic_blocks[i];
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Optional<Block> fork_fallback_block;
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if (i + 1 < basic_blocks.size())
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fork_fallback_block = basic_blocks[i + 1];
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MatchState state;
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// Check if the last instruction in this block is a jump to the block itself:
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{
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state.instruction_position = forking_block.end;
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auto& opcode = bytecode.get_opcode(state);
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if (is_an_eligible_jump(opcode, state.instruction_position, forking_block.start, AlternateForm::DirectLoopWithoutHeader)) {
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// We've found RE0 (and RE1 is just the following block, if any), let's see if the precondition applies.
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// if RE1 is empty, there's no first(RE1), so this is an automatic pass.
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if (!fork_fallback_block.has_value() || fork_fallback_block->end == fork_fallback_block->start) {
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candidate_blocks.append({ forking_block, fork_fallback_block, AlternateForm::DirectLoopWithoutHeader });
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break;
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}
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if (block_satisfies_atomic_rewrite_precondition(bytecode, forking_block, *fork_fallback_block)) {
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candidate_blocks.append({ forking_block, fork_fallback_block, AlternateForm::DirectLoopWithoutHeader });
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break;
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}
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}
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}
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// Check if the last instruction in the last block is a direct jump to this block
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if (fork_fallback_block.has_value()) {
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state.instruction_position = fork_fallback_block->end;
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auto& opcode = bytecode.get_opcode(state);
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if (is_an_eligible_jump(opcode, state.instruction_position, forking_block.start, AlternateForm::DirectLoopWithHeader)) {
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// We've found bb1 and bb0, let's just make sure that bb0 forks to bb2.
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state.instruction_position = forking_block.end;
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auto& opcode = bytecode.get_opcode(state);
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if (opcode.opcode_id() == OpCodeId::ForkJump || opcode.opcode_id() == OpCodeId::ForkStay) {
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Optional<Block> block_following_fork_fallback;
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if (i + 2 < basic_blocks.size())
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block_following_fork_fallback = basic_blocks[i + 2];
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if (!block_following_fork_fallback.has_value() || block_satisfies_atomic_rewrite_precondition(bytecode, *fork_fallback_block, *block_following_fork_fallback)) {
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candidate_blocks.append({ forking_block, {}, AlternateForm::DirectLoopWithHeader });
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break;
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}
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}
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}
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}
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}
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dbgln_if(REGEX_DEBUG, "Found {} candidate blocks", candidate_blocks.size());
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if (candidate_blocks.is_empty()) {
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dbgln_if(REGEX_DEBUG, "Failed to find anything for {}", pattern_value);
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return;
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}
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RedBlackTree<size_t, size_t> needed_patches;
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// Reverse the blocks, so we can patch the bytecode without messing with the latter patches.
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quick_sort(candidate_blocks, [](auto& a, auto& b) { return b.forking_block.start > a.forking_block.start; });
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for (auto& candidate : candidate_blocks) {
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// Note that both forms share a ForkReplace patch in forking_block.
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// Patch the ForkX in forking_block to be a ForkReplaceX instead.
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auto& opcode_id = bytecode[candidate.forking_block.end];
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if (opcode_id == (ByteCodeValueType)OpCodeId::ForkStay) {
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opcode_id = (ByteCodeValueType)OpCodeId::ForkReplaceStay;
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} else if (opcode_id == (ByteCodeValueType)OpCodeId::ForkJump) {
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opcode_id = (ByteCodeValueType)OpCodeId::ForkReplaceJump;
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} else if (opcode_id == (ByteCodeValueType)OpCodeId::JumpNonEmpty) {
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auto& jump_opcode_id = bytecode[candidate.forking_block.end + 3];
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if (jump_opcode_id == (ByteCodeValueType)OpCodeId::ForkStay)
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jump_opcode_id = (ByteCodeValueType)OpCodeId::ForkReplaceStay;
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else if (jump_opcode_id == (ByteCodeValueType)OpCodeId::ForkJump)
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jump_opcode_id = (ByteCodeValueType)OpCodeId::ForkReplaceJump;
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else
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VERIFY_NOT_REACHED();
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} else {
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VERIFY_NOT_REACHED();
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}
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if (candidate.form == AlternateForm::DirectLoopWithoutHeader) {
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if (candidate.new_target_block.has_value()) {
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// Insert a fork-stay targeted at the second block.
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bytecode.insert(candidate.forking_block.start, (ByteCodeValueType)OpCodeId::ForkStay);
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bytecode.insert(candidate.forking_block.start + 1, candidate.new_target_block->start - candidate.forking_block.start);
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needed_patches.insert(candidate.forking_block.start, 2u);
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}
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}
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}
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if (!needed_patches.is_empty()) {
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MatchState state;
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state.instruction_position = 0;
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struct Patch {
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ssize_t value;
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size_t offset;
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bool should_negate { false };
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};
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for (;;) {
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if (state.instruction_position >= bytecode.size())
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break;
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auto& opcode = bytecode.get_opcode(state);
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Stack<Patch, 2> patch_points;
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switch (opcode.opcode_id()) {
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case OpCodeId::Jump:
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patch_points.push({ static_cast<OpCode_Jump const&>(opcode).offset(), state.instruction_position + 1 });
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break;
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case OpCodeId::JumpNonEmpty:
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patch_points.push({ static_cast<OpCode_JumpNonEmpty const&>(opcode).offset(), state.instruction_position + 1 });
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patch_points.push({ static_cast<OpCode_JumpNonEmpty const&>(opcode).checkpoint(), state.instruction_position + 2 });
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break;
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case OpCodeId::ForkJump:
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patch_points.push({ static_cast<OpCode_ForkJump const&>(opcode).offset(), state.instruction_position + 1 });
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break;
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case OpCodeId::ForkStay:
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patch_points.push({ static_cast<OpCode_ForkStay const&>(opcode).offset(), state.instruction_position + 1 });
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break;
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case OpCodeId::Repeat:
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patch_points.push({ -(ssize_t) static_cast<OpCode_Repeat const&>(opcode).offset(), state.instruction_position + 1, true });
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break;
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default:
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break;
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}
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while (!patch_points.is_empty()) {
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auto& patch_point = patch_points.top();
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auto target_offset = patch_point.value + state.instruction_position + opcode.size();
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constexpr auto do_patch = [](auto& patch_it, auto& patch_point, auto& target_offset, auto& bytecode, auto ip) {
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if (patch_it.key() == ip)
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return;
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if (patch_point.value < 0 && target_offset < patch_it.key() && ip > patch_it.key())
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bytecode[patch_point.offset] += (patch_point.should_negate ? 1 : -1) * (*patch_it);
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else if (patch_point.value > 0 && target_offset > patch_it.key() && ip < patch_it.key())
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bytecode[patch_point.offset] += (patch_point.should_negate ? -1 : 1) * (*patch_it);
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};
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if (auto patch_it = needed_patches.find_largest_not_above_iterator(target_offset); !patch_it.is_end())
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do_patch(patch_it, patch_point, target_offset, bytecode, state.instruction_position);
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else if (auto patch_it = needed_patches.find_largest_not_above_iterator(state.instruction_position); !patch_it.is_end())
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do_patch(patch_it, patch_point, target_offset, bytecode, state.instruction_position);
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patch_points.pop();
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}
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state.instruction_position += opcode.size();
|
||||
}
|
||||
}
|
||||
|
||||
if constexpr (REGEX_DEBUG) {
|
||||
warnln("Transformed to:");
|
||||
RegexDebug dbg;
|
||||
dbg.print_bytecode(*this);
|
||||
}
|
||||
}
|
||||
|
||||
void Optimizer::append_alternation(ByteCode& target, ByteCode& left, ByteCode& right)
|
||||
{
|
||||
if (left.is_empty()) {
|
||||
target.extend(right);
|
||||
return;
|
||||
}
|
||||
|
||||
if (right.is_empty()) {
|
||||
target.extend(left);
|
||||
return;
|
||||
}
|
||||
|
||||
size_t left_skip = 0;
|
||||
MatchState state;
|
||||
for (state.instruction_position = 0; state.instruction_position < left.size() && state.instruction_position < right.size();) {
|
||||
auto left_size = left.get_opcode(state).size();
|
||||
auto right_size = right.get_opcode(state).size();
|
||||
if (left_size != right_size)
|
||||
break;
|
||||
|
||||
if (left.span().slice(state.instruction_position, left_size) == right.span().slice(state.instruction_position, right_size))
|
||||
left_skip = state.instruction_position + left_size;
|
||||
else
|
||||
break;
|
||||
|
||||
state.instruction_position += left_size;
|
||||
}
|
||||
|
||||
// FIXME: Implement postfix unification too.
|
||||
size_t right_skip = 0;
|
||||
|
||||
if (left_skip)
|
||||
target.append(left.data(), left_skip);
|
||||
|
||||
dbgln_if(REGEX_DEBUG, "Skipping {}/{} bytecode entries from {}/{}", left_skip, right_skip, left.size(), right.size());
|
||||
|
||||
auto left_slice = left.span().slice(left_skip, left.size() - left_skip - right_skip);
|
||||
auto right_slice = right.span().slice(left_skip, right.size() - left_skip - right_skip);
|
||||
|
||||
target.empend(static_cast<ByteCodeValueType>(OpCodeId::ForkJump));
|
||||
target.empend(right_slice.size() + 2); // Jump to the _ALT label
|
||||
|
||||
target.append(right_slice.data(), right_slice.size());
|
||||
|
||||
if (!left_slice.is_empty()) {
|
||||
target.empend(static_cast<ByteCodeValueType>(OpCodeId::Jump));
|
||||
target.empend(left_slice.size()); // Jump to the _END label
|
||||
}
|
||||
|
||||
// LABEL _ALT = bytecode.size() + 2
|
||||
|
||||
target.append(left_slice.data(), left_slice.size());
|
||||
|
||||
// LABEL _END = alterantive_bytecode.size
|
||||
if (right_skip)
|
||||
target.append(left.span().slice_from_end(right_skip).data(), right_skip);
|
||||
}
|
||||
|
||||
template void Regex<PosixBasicParser>::run_optimization_passes();
|
||||
template void Regex<PosixExtendedParser>::run_optimization_passes();
|
||||
template void Regex<ECMA262Parser>::run_optimization_passes();
|
||||
}
|
||||
Loading…
Add table
Add a link
Reference in a new issue