1 //===- StringMatcher.cpp - Generate a matcher for input strings -----------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file implements the StringMatcher class.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "llvm/TableGen/StringMatcher.h"
15 #include "llvm/ADT/StringRef.h"
16 #include "llvm/Support/raw_ostream.h"
17 #include <cassert>
18 #include <map>
19 #include <string>
20 #include <utility>
21 #include <vector>
22 
23 using namespace llvm;
24 
25 /// FindFirstNonCommonLetter - Find the first character in the keys of the
26 /// string pairs that is not shared across the whole set of strings.  All
27 /// strings are assumed to have the same length.
28 static unsigned
29 FindFirstNonCommonLetter(const std::vector<const
30                               StringMatcher::StringPair*> &Matches) {
31   assert(!Matches.empty());
32   for (unsigned i = 0, e = Matches[0]->first.size(); i != e; ++i) {
33     // Check to see if letter i is the same across the set.
34     char Letter = Matches[0]->first[i];
35 
36     for (unsigned str = 0, e = Matches.size(); str != e; ++str)
37       if (Matches[str]->first[i] != Letter)
38         return i;
39   }
40 
41   return Matches[0]->first.size();
42 }
43 
44 /// EmitStringMatcherForChar - Given a set of strings that are known to be the
45 /// same length and whose characters leading up to CharNo are the same, emit
46 /// code to verify that CharNo and later are the same.
47 ///
48 /// \return - True if control can leave the emitted code fragment.
49 bool StringMatcher::EmitStringMatcherForChar(
50     const std::vector<const StringPair *> &Matches, unsigned CharNo,
51     unsigned IndentCount, bool IgnoreDuplicates) const {
52   assert(!Matches.empty() && "Must have at least one string to match!");
53   std::string Indent(IndentCount * 2 + 4, ' ');
54 
55   // If we have verified that the entire string matches, we're done: output the
56   // matching code.
57   if (CharNo == Matches[0]->first.size()) {
58     if (Matches.size() > 1 && !IgnoreDuplicates)
59       report_fatal_error("Had duplicate keys to match on");
60 
61     // If the to-execute code has \n's in it, indent each subsequent line.
62     StringRef Code = Matches[0]->second;
63 
64     std::pair<StringRef, StringRef> Split = Code.split('\n');
65     OS << Indent << Split.first << "\t // \"" << Matches[0]->first << "\"\n";
66 
67     Code = Split.second;
68     while (!Code.empty()) {
69       Split = Code.split('\n');
70       OS << Indent << Split.first << "\n";
71       Code = Split.second;
72     }
73     return false;
74   }
75 
76   // Bucket the matches by the character we are comparing.
77   std::map<char, std::vector<const StringPair*>> MatchesByLetter;
78 
79   for (unsigned i = 0, e = Matches.size(); i != e; ++i)
80     MatchesByLetter[Matches[i]->first[CharNo]].push_back(Matches[i]);
81 
82 
83   // If we have exactly one bucket to match, see how many characters are common
84   // across the whole set and match all of them at once.
85   if (MatchesByLetter.size() == 1) {
86     unsigned FirstNonCommonLetter = FindFirstNonCommonLetter(Matches);
87     unsigned NumChars = FirstNonCommonLetter-CharNo;
88 
89     // Emit code to break out if the prefix doesn't match.
90     if (NumChars == 1) {
91       // Do the comparison with if (Str[1] != 'f')
92       // FIXME: Need to escape general characters.
93       OS << Indent << "if (" << StrVariableName << "[" << CharNo << "] != '"
94       << Matches[0]->first[CharNo] << "')\n";
95       OS << Indent << "  break;\n";
96     } else {
97       // Do the comparison with if memcmp(Str.data()+1, "foo", 3).
98       // FIXME: Need to escape general strings.
99       OS << Indent << "if (memcmp(" << StrVariableName << ".data()+" << CharNo
100          << ", \"" << Matches[0]->first.substr(CharNo, NumChars) << "\", "
101          << NumChars << ") != 0)\n";
102       OS << Indent << "  break;\n";
103     }
104 
105     return EmitStringMatcherForChar(Matches, FirstNonCommonLetter, IndentCount,
106                                     IgnoreDuplicates);
107   }
108 
109   // Otherwise, we have multiple possible things, emit a switch on the
110   // character.
111   OS << Indent << "switch (" << StrVariableName << "[" << CharNo << "]) {\n";
112   OS << Indent << "default: break;\n";
113 
114   for (std::map<char, std::vector<const StringPair*>>::iterator LI =
115        MatchesByLetter.begin(), E = MatchesByLetter.end(); LI != E; ++LI) {
116     // TODO: escape hard stuff (like \n) if we ever care about it.
117     OS << Indent << "case '" << LI->first << "':\t // "
118        << LI->second.size() << " string";
119     if (LI->second.size() != 1) OS << 's';
120     OS << " to match.\n";
121     if (EmitStringMatcherForChar(LI->second, CharNo + 1, IndentCount + 1,
122                                  IgnoreDuplicates))
123       OS << Indent << "  break;\n";
124   }
125 
126   OS << Indent << "}\n";
127   return true;
128 }
129 
130 /// Emit - Top level entry point.
131 ///
132 void StringMatcher::Emit(unsigned Indent, bool IgnoreDuplicates) const {
133   // If nothing to match, just fall through.
134   if (Matches.empty()) return;
135 
136   // First level categorization: group strings by length.
137   std::map<unsigned, std::vector<const StringPair*>> MatchesByLength;
138 
139   for (unsigned i = 0, e = Matches.size(); i != e; ++i)
140     MatchesByLength[Matches[i].first.size()].push_back(&Matches[i]);
141 
142   // Output a switch statement on length and categorize the elements within each
143   // bin.
144   OS.indent(Indent*2+2) << "switch (" << StrVariableName << ".size()) {\n";
145   OS.indent(Indent*2+2) << "default: break;\n";
146 
147   for (std::map<unsigned, std::vector<const StringPair*>>::iterator LI =
148        MatchesByLength.begin(), E = MatchesByLength.end(); LI != E; ++LI) {
149     OS.indent(Indent*2+2) << "case " << LI->first << ":\t // "
150        << LI->second.size()
151        << " string" << (LI->second.size() == 1 ? "" : "s") << " to match.\n";
152     if (EmitStringMatcherForChar(LI->second, 0, Indent, IgnoreDuplicates))
153       OS.indent(Indent*2+4) << "break;\n";
154   }
155 
156   OS.indent(Indent*2+2) << "}\n";
157 }
158