1//===- StringMatcher.cpp - Generate a matcher for input strings -----------===//
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// This file implements the StringMatcher class.
10//
11//===----------------------------------------------------------------------===//
12
13#include "llvm/TableGen/StringMatcher.h"
14#include "llvm/ADT/StringRef.h"
15#include "llvm/Support/raw_ostream.h"
16#include <cassert>
17#include <map>
18#include <string>
19#include <utility>
20#include <vector>
21
22using namespace llvm;
23
24/// FindFirstNonCommonLetter - Find the first character in the keys of the
25/// string pairs that is not shared across the whole set of strings.  All
26/// strings are assumed to have the same length.
27static unsigned
28FindFirstNonCommonLetter(const std::vector<const
29                              StringMatcher::StringPair*> &Matches) {
30  assert(!Matches.empty());
31  for (unsigned i = 0, e = Matches[0]->first.size(); i != e; ++i) {
32    // Check to see if letter i is the same across the set.
33    char Letter = Matches[0]->first[i];
34
35    for (unsigned str = 0, e = Matches.size(); str != e; ++str)
36      if (Matches[str]->first[i] != Letter)
37        return i;
38  }
39
40  return Matches[0]->first.size();
41}
42
43/// EmitStringMatcherForChar - Given a set of strings that are known to be the
44/// same length and whose characters leading up to CharNo are the same, emit
45/// code to verify that CharNo and later are the same.
46///
47/// \return - True if control can leave the emitted code fragment.
48bool StringMatcher::EmitStringMatcherForChar(
49    const std::vector<const StringPair *> &Matches, unsigned CharNo,
50    unsigned IndentCount, bool IgnoreDuplicates) const {
51  assert(!Matches.empty() && "Must have at least one string to match!");
52  std::string Indent(IndentCount * 2 + 4, ' ');
53
54  // If we have verified that the entire string matches, we're done: output the
55  // matching code.
56  if (CharNo == Matches[0]->first.size()) {
57    if (Matches.size() > 1 && !IgnoreDuplicates)
58      report_fatal_error("Had duplicate keys to match on");
59
60    // If the to-execute code has \n's in it, indent each subsequent line.
61    StringRef Code = Matches[0]->second;
62
63    std::pair<StringRef, StringRef> Split = Code.split('\n');
64    OS << Indent << Split.first << "\t // \"" << Matches[0]->first << "\"\n";
65
66    Code = Split.second;
67    while (!Code.empty()) {
68      Split = Code.split('\n');
69      OS << Indent << Split.first << "\n";
70      Code = Split.second;
71    }
72    return false;
73  }
74
75  // Bucket the matches by the character we are comparing.
76  std::map<char, std::vector<const StringPair*>> MatchesByLetter;
77
78  for (unsigned i = 0, e = Matches.size(); i != e; ++i)
79    MatchesByLetter[Matches[i]->first[CharNo]].push_back(Matches[i]);
80
81
82  // If we have exactly one bucket to match, see how many characters are common
83  // across the whole set and match all of them at once.
84  if (MatchesByLetter.size() == 1) {
85    unsigned FirstNonCommonLetter = FindFirstNonCommonLetter(Matches);
86    unsigned NumChars = FirstNonCommonLetter-CharNo;
87
88    // Emit code to break out if the prefix doesn't match.
89    if (NumChars == 1) {
90      // Do the comparison with if (Str[1] != 'f')
91      // FIXME: Need to escape general characters.
92      OS << Indent << "if (" << StrVariableName << "[" << CharNo << "] != '"
93      << Matches[0]->first[CharNo] << "')\n";
94      OS << Indent << "  break;\n";
95    } else {
96      // Do the comparison with if memcmp(Str.data()+1, "foo", 3).
97      // FIXME: Need to escape general strings.
98      OS << Indent << "if (memcmp(" << StrVariableName << ".data()+" << CharNo
99         << ", \"" << Matches[0]->first.substr(CharNo, NumChars) << "\", "
100         << NumChars << ") != 0)\n";
101      OS << Indent << "  break;\n";
102    }
103
104    return EmitStringMatcherForChar(Matches, FirstNonCommonLetter, IndentCount,
105                                    IgnoreDuplicates);
106  }
107
108  // Otherwise, we have multiple possible things, emit a switch on the
109  // character.
110  OS << Indent << "switch (" << StrVariableName << "[" << CharNo << "]) {\n";
111  OS << Indent << "default: break;\n";
112
113  for (std::map<char, std::vector<const StringPair*>>::iterator LI =
114       MatchesByLetter.begin(), E = MatchesByLetter.end(); LI != E; ++LI) {
115    // TODO: escape hard stuff (like \n) if we ever care about it.
116    OS << Indent << "case '" << LI->first << "':\t // "
117       << LI->second.size() << " string";
118    if (LI->second.size() != 1) OS << 's';
119    OS << " to match.\n";
120    if (EmitStringMatcherForChar(LI->second, CharNo + 1, IndentCount + 1,
121                                 IgnoreDuplicates))
122      OS << Indent << "  break;\n";
123  }
124
125  OS << Indent << "}\n";
126  return true;
127}
128
129/// Emit - Top level entry point.
130///
131void StringMatcher::Emit(unsigned Indent, bool IgnoreDuplicates) const {
132  // If nothing to match, just fall through.
133  if (Matches.empty()) return;
134
135  // First level categorization: group strings by length.
136  std::map<unsigned, std::vector<const StringPair*>> MatchesByLength;
137
138  for (unsigned i = 0, e = Matches.size(); i != e; ++i)
139    MatchesByLength[Matches[i].first.size()].push_back(&Matches[i]);
140
141  // Output a switch statement on length and categorize the elements within each
142  // bin.
143  OS.indent(Indent*2+2) << "switch (" << StrVariableName << ".size()) {\n";
144  OS.indent(Indent*2+2) << "default: break;\n";
145
146  for (std::map<unsigned, std::vector<const StringPair*>>::iterator LI =
147       MatchesByLength.begin(), E = MatchesByLength.end(); LI != E; ++LI) {
148    OS.indent(Indent*2+2) << "case " << LI->first << ":\t // "
149       << LI->second.size()
150       << " string" << (LI->second.size() == 1 ? "" : "s") << " to match.\n";
151    if (EmitStringMatcherForChar(LI->second, 0, Indent, IgnoreDuplicates))
152      OS.indent(Indent*2+4) << "break;\n";
153  }
154
155  OS.indent(Indent*2+2) << "}\n";
156}
157