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111 lines
3.2 KiB
C++
111 lines
3.2 KiB
C++
//===-- TrigramIndex.cpp - a heuristic for SpecialCaseList ----------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// TrigramIndex implements a heuristic for SpecialCaseList that allows to
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// filter out ~99% incoming queries when all regular expressions in the
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// SpecialCaseList are simple wildcards with '*' and '.'. If rules are more
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// complicated, the check is defeated and it will always pass the queries to a
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// full regex.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Support/TrigramIndex.h"
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#include "llvm/ADT/SmallVector.h"
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#include <set>
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#include <string>
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#include <unordered_map>
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using namespace llvm;
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static const char RegexAdvancedMetachars[] = "()^$|+?[]\\{}";
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static bool isAdvancedMetachar(unsigned Char) {
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return strchr(RegexAdvancedMetachars, Char) != nullptr;
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}
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void TrigramIndex::insert(std::string Regex) {
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if (Defeated) return;
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std::set<unsigned> Was;
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unsigned Cnt = 0;
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unsigned Tri = 0;
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unsigned Len = 0;
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bool Escaped = false;
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for (unsigned Char : Regex) {
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if (!Escaped) {
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// Regular expressions allow escaping symbols by preceding it with '\'.
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if (Char == '\\') {
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Escaped = true;
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continue;
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}
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if (isAdvancedMetachar(Char)) {
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// This is a more complicated regex than we can handle here.
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Defeated = true;
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return;
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}
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if (Char == '.' || Char == '*') {
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Tri = 0;
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Len = 0;
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continue;
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}
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}
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if (Escaped && Char >= '1' && Char <= '9') {
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Defeated = true;
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return;
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}
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// We have already handled escaping and can reset the flag.
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Escaped = false;
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Tri = ((Tri << 8) + Char) & 0xFFFFFF;
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Len++;
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if (Len < 3)
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continue;
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// We don't want the index to grow too much for the popular trigrams,
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// as they are weak signals. It's ok to still require them for the
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// rules we have already processed. It's just a small additional
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// computational cost.
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if (Index[Tri].size() >= 4)
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continue;
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Cnt++;
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if (!Was.count(Tri)) {
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// Adding the current rule to the index.
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Index[Tri].push_back(Counts.size());
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Was.insert(Tri);
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}
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}
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if (!Cnt) {
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// This rule does not have remarkable trigrams to rely on.
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// We have to always call the full regex chain.
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Defeated = true;
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return;
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}
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Counts.push_back(Cnt);
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}
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bool TrigramIndex::isDefinitelyOut(StringRef Query) const {
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if (Defeated)
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return false;
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std::vector<unsigned> CurCounts(Counts.size());
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unsigned Tri = 0;
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for (size_t I = 0; I < Query.size(); I++) {
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Tri = ((Tri << 8) + Query[I]) & 0xFFFFFF;
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if (I < 2)
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continue;
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const auto &II = Index.find(Tri);
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if (II == Index.end())
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continue;
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for (size_t J : II->second) {
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CurCounts[J]++;
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// If we have reached a desired limit, we have to look at the query
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// more closely by running a full regex.
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if (CurCounts[J] >= Counts[J])
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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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