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 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. 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 (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 /// 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 (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