LLVM  14.0.0git
TrigramIndex.cpp
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1 //===-- TrigramIndex.cpp - a heuristic for SpecialCaseList ----------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // TrigramIndex implements a heuristic for SpecialCaseList that allows to
10 // filter out ~99% incoming queries when all regular expressions in the
11 // SpecialCaseList are simple wildcards with '*' and '.'. If rules are more
12 // complicated, the check is defeated and it will always pass the queries to a
13 // full regex.
14 //
15 //===----------------------------------------------------------------------===//
16 
18 #include <set>
19 
20 using namespace llvm;
21 
22 static const char RegexAdvancedMetachars[] = "()^$|+?[]\\{}";
23 
24 static bool isAdvancedMetachar(unsigned Char) {
25  return strchr(RegexAdvancedMetachars, Char) != nullptr;
26 }
27 
28 void TrigramIndex::insert(const std::string &Regex) {
29  if (Defeated) return;
30  std::set<unsigned> Was;
31  unsigned Cnt = 0;
32  unsigned Tri = 0;
33  unsigned Len = 0;
34  bool Escaped = false;
35  for (unsigned Char : Regex) {
36  if (!Escaped) {
37  // Regular expressions allow escaping symbols by preceding it with '\'.
38  if (Char == '\\') {
39  Escaped = true;
40  continue;
41  }
42  if (isAdvancedMetachar(Char)) {
43  // This is a more complicated regex than we can handle here.
44  Defeated = true;
45  return;
46  }
47  if (Char == '.' || Char == '*') {
48  Tri = 0;
49  Len = 0;
50  continue;
51  }
52  }
53  if (Escaped && Char >= '1' && Char <= '9') {
54  Defeated = true;
55  return;
56  }
57  // We have already handled escaping and can reset the flag.
58  Escaped = false;
59  Tri = ((Tri << 8) + Char) & 0xFFFFFF;
60  Len++;
61  if (Len < 3)
62  continue;
63  // We don't want the index to grow too much for the popular trigrams,
64  // as they are weak signals. It's ok to still require them for the
65  // rules we have already processed. It's just a small additional
66  // computational cost.
67  if (Index[Tri].size() >= 4)
68  continue;
69  Cnt++;
70  if (!Was.count(Tri)) {
71  // Adding the current rule to the index.
72  Index[Tri].push_back(Counts.size());
73  Was.insert(Tri);
74  }
75  }
76  if (!Cnt) {
77  // This rule does not have remarkable trigrams to rely on.
78  // We have to always call the full regex chain.
79  Defeated = true;
80  return;
81  }
82  Counts.push_back(Cnt);
83 }
84 
86  if (Defeated)
87  return false;
88  std::vector<unsigned> CurCounts(Counts.size());
89  unsigned Tri = 0;
90  for (size_t I = 0; I < Query.size(); I++) {
91  Tri = ((Tri << 8) + Query[I]) & 0xFFFFFF;
92  if (I < 2)
93  continue;
94  const auto &II = Index.find(Tri);
95  if (II == Index.end())
96  continue;
97  for (size_t J : II->second) {
98  CurCounts[J]++;
99  // If we have reached a desired limit, we have to look at the query
100  // more closely by running a full regex.
101  if (CurCounts[J] >= Counts[J])
102  return false;
103  }
104  }
105  return true;
106 }
llvm
This is an optimization pass for GlobalISel generic memory operations.
Definition: AllocatorList.h:23
RegexAdvancedMetachars
static const char RegexAdvancedMetachars[]
Definition: TrigramIndex.cpp:22
isAdvancedMetachar
static bool isAdvancedMetachar(unsigned Char)
Definition: TrigramIndex.cpp:24
llvm::TrigramIndex::insert
void insert(const std::string &Regex)
Inserts a new Regex into the index.
Definition: TrigramIndex.cpp:28
TrigramIndex.h
I
#define I(x, y, z)
Definition: MD5.cpp:59
llvm::size
auto size(R &&Range, std::enable_if_t< std::is_base_of< std::random_access_iterator_tag, typename std::iterator_traits< decltype(Range.begin())>::iterator_category >::value, void > *=nullptr)
Get the size of a range.
Definition: STLExtras.h:1581
llvm::StringRef
StringRef - Represent a constant reference to a string, i.e.
Definition: StringRef.h:57
llvm::TrigramIndex::isDefinitelyOut
bool isDefinitelyOut(StringRef Query) const
Returns true, if special case list definitely does not have a line that matches the query.
Definition: TrigramIndex.cpp:85
llvm::Regex
Definition: Regex.h:28
llvm::StringRef::size
LLVM_NODISCARD size_t size() const
size - Get the string size.
Definition: StringRef.h:156