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 
22 using 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.
27 static unsigned
28 FindFirstNonCommonLetter(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.
48 bool 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 (const auto &LI : MatchesByLetter) {
114     // TODO: escape hard stuff (like \n) if we ever care about it.
115     OS << Indent << "case '" << LI.first << "':\t // " << LI.second.size()
116        << " string";
117     if (LI.second.size() != 1)
118       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 ///
131 void 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 (const auto &LI : MatchesByLength) {
147     OS.indent(Indent * 2 + 2)
148         << "case " << LI.first << ":\t // " << LI.second.size() << " string"
149         << (LI.second.size() == 1 ? "" : "s") << " to match.\n";
150     if (EmitStringMatcherForChar(LI.second, 0, Indent, IgnoreDuplicates))
151       OS.indent(Indent*2+4) << "break;\n";
152   }
153 
154   OS.indent(Indent*2+2) << "}\n";
155 }
156