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/Support/raw_ostream.h"
16 #include <map>
17 using namespace llvm;
18
19 /// FindFirstNonCommonLetter - Find the first character in the keys of the
20 /// string pairs that is not shared across the whole set of strings. All
21 /// strings are assumed to have the same length.
22 static unsigned
FindFirstNonCommonLetter(const std::vector<const StringMatcher::StringPair * > & Matches)23 FindFirstNonCommonLetter(const std::vector<const
24 StringMatcher::StringPair*> &Matches) {
25 assert(!Matches.empty());
26 for (unsigned i = 0, e = Matches[0]->first.size(); i != e; ++i) {
27 // Check to see if letter i is the same across the set.
28 char Letter = Matches[0]->first[i];
29
30 for (unsigned str = 0, e = Matches.size(); str != e; ++str)
31 if (Matches[str]->first[i] != Letter)
32 return i;
33 }
34
35 return Matches[0]->first.size();
36 }
37
38 /// EmitStringMatcherForChar - Given a set of strings that are known to be the
39 /// same length and whose characters leading up to CharNo are the same, emit
40 /// code to verify that CharNo and later are the same.
41 ///
42 /// \return - True if control can leave the emitted code fragment.
43 bool StringMatcher::
EmitStringMatcherForChar(const std::vector<const StringPair * > & Matches,unsigned CharNo,unsigned IndentCount) const44 EmitStringMatcherForChar(const std::vector<const StringPair*> &Matches,
45 unsigned CharNo, unsigned IndentCount) const {
46 assert(!Matches.empty() && "Must have at least one string to match!");
47 std::string Indent(IndentCount*2+4, ' ');
48
49 // If we have verified that the entire string matches, we're done: output the
50 // matching code.
51 if (CharNo == Matches[0]->first.size()) {
52 assert(Matches.size() == 1 && "Had duplicate keys to match on");
53
54 // If the to-execute code has \n's in it, indent each subsequent line.
55 StringRef Code = Matches[0]->second;
56
57 std::pair<StringRef, StringRef> Split = Code.split('\n');
58 OS << Indent << Split.first << "\t // \"" << Matches[0]->first << "\"\n";
59
60 Code = Split.second;
61 while (!Code.empty()) {
62 Split = Code.split('\n');
63 OS << Indent << Split.first << "\n";
64 Code = Split.second;
65 }
66 return false;
67 }
68
69 // Bucket the matches by the character we are comparing.
70 std::map<char, std::vector<const StringPair*> > MatchesByLetter;
71
72 for (unsigned i = 0, e = Matches.size(); i != e; ++i)
73 MatchesByLetter[Matches[i]->first[CharNo]].push_back(Matches[i]);
74
75
76 // If we have exactly one bucket to match, see how many characters are common
77 // across the whole set and match all of them at once.
78 if (MatchesByLetter.size() == 1) {
79 unsigned FirstNonCommonLetter = FindFirstNonCommonLetter(Matches);
80 unsigned NumChars = FirstNonCommonLetter-CharNo;
81
82 // Emit code to break out if the prefix doesn't match.
83 if (NumChars == 1) {
84 // Do the comparison with if (Str[1] != 'f')
85 // FIXME: Need to escape general characters.
86 OS << Indent << "if (" << StrVariableName << "[" << CharNo << "] != '"
87 << Matches[0]->first[CharNo] << "')\n";
88 OS << Indent << " break;\n";
89 } else {
90 // Do the comparison with if memcmp(Str.data()+1, "foo", 3).
91 // FIXME: Need to escape general strings.
92 OS << Indent << "if (memcmp(" << StrVariableName << ".data()+" << CharNo
93 << ", \"" << Matches[0]->first.substr(CharNo, NumChars) << "\", "
94 << NumChars << "))\n";
95 OS << Indent << " break;\n";
96 }
97
98 return EmitStringMatcherForChar(Matches, FirstNonCommonLetter, IndentCount);
99 }
100
101 // Otherwise, we have multiple possible things, emit a switch on the
102 // character.
103 OS << Indent << "switch (" << StrVariableName << "[" << CharNo << "]) {\n";
104 OS << Indent << "default: break;\n";
105
106 for (std::map<char, std::vector<const StringPair*> >::iterator LI =
107 MatchesByLetter.begin(), E = MatchesByLetter.end(); LI != E; ++LI) {
108 // TODO: escape hard stuff (like \n) if we ever care about it.
109 OS << Indent << "case '" << LI->first << "':\t // "
110 << LI->second.size() << " string";
111 if (LI->second.size() != 1) OS << 's';
112 OS << " to match.\n";
113 if (EmitStringMatcherForChar(LI->second, CharNo+1, IndentCount+1))
114 OS << Indent << " break;\n";
115 }
116
117 OS << Indent << "}\n";
118 return true;
119 }
120
121
122 /// Emit - Top level entry point.
123 ///
Emit(unsigned Indent) const124 void StringMatcher::Emit(unsigned Indent) const {
125 // If nothing to match, just fall through.
126 if (Matches.empty()) return;
127
128 // First level categorization: group strings by length.
129 std::map<unsigned, std::vector<const StringPair*> > MatchesByLength;
130
131 for (unsigned i = 0, e = Matches.size(); i != e; ++i)
132 MatchesByLength[Matches[i].first.size()].push_back(&Matches[i]);
133
134 // Output a switch statement on length and categorize the elements within each
135 // bin.
136 OS.indent(Indent*2+2) << "switch (" << StrVariableName << ".size()) {\n";
137 OS.indent(Indent*2+2) << "default: break;\n";
138
139 for (std::map<unsigned, std::vector<const StringPair*> >::iterator LI =
140 MatchesByLength.begin(), E = MatchesByLength.end(); LI != E; ++LI) {
141 OS.indent(Indent*2+2) << "case " << LI->first << ":\t // "
142 << LI->second.size()
143 << " string" << (LI->second.size() == 1 ? "" : "s") << " to match.\n";
144 if (EmitStringMatcherForChar(LI->second, 0, Indent))
145 OS.indent(Indent*2+4) << "break;\n";
146 }
147
148 OS.indent(Indent*2+2) << "}\n";
149 }
150