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/ErrorHandling.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
FindFirstNonCommonLetter(const std::vector<const StringMatcher::StringPair * > & Matches)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 (const StringMatcher::StringPair *Match : Matches)
37 if (Match->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.
EmitStringMatcherForChar(const std::vector<const StringPair * > & Matches,unsigned CharNo,unsigned IndentCount,bool IgnoreDuplicates) const49 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 (const StringPair *Match : Matches)
80 MatchesByLetter[Match->first[CharNo]].push_back(Match);
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 ///
Emit(unsigned Indent,bool IgnoreDuplicates) const131 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 (const StringPair &Match : Matches)
139 MatchesByLength[Match.first.size()].push_back(&Match);
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