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 (std::map<char, std::vector<const StringPair*>>::iterator LI = 114 MatchesByLetter.begin(), E = MatchesByLetter.end(); LI != E; ++LI) { 115 // TODO: escape hard stuff (like \n) if we ever care about it. 116 OS << Indent << "case '" << LI->first << "':\t // " 117 << LI->second.size() << " string"; 118 if (LI->second.size() != 1) 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 (std::map<unsigned, std::vector<const StringPair*>>::iterator LI = 147 MatchesByLength.begin(), E = MatchesByLength.end(); LI != E; ++LI) { 148 OS.indent(Indent*2+2) << "case " << LI->first << ":\t // " 149 << LI->second.size() 150 << " string" << (LI->second.size() == 1 ? "" : "s") << " to match.\n"; 151 if (EmitStringMatcherForChar(LI->second, 0, Indent, IgnoreDuplicates)) 152 OS.indent(Indent*2+4) << "break;\n"; 153 } 154 155 OS.indent(Indent*2+2) << "}\n"; 156 } 157