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/STLExtras.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(ArrayRef<const StringMatcher::StringPair *> Matches) { 30 assert(!Matches.empty()); 31 for (auto [Idx, Letter] : enumerate(Matches[0]->first)) { 32 // Check to see if `Letter` is the same across the set. Since the letter is 33 // from `Matches[0]`, we can skip `Matches[0]` in the loop below. 34 for (const StringMatcher::StringPair *Match : Matches.drop_front()) 35 if (Match->first[Idx] != Letter) 36 return Idx; 37 } 38 39 return Matches[0]->first.size(); 40 } 41 42 /// EmitStringMatcherForChar - Given a set of strings that are known to be the 43 /// same length and whose characters leading up to CharNo are the same, emit 44 /// code to verify that CharNo and later are the same. 45 /// 46 /// \return - True if control can leave the emitted code fragment. 47 bool StringMatcher::EmitStringMatcherForChar( 48 ArrayRef<const StringPair *> Matches, unsigned CharNo, unsigned IndentCount, 49 bool IgnoreDuplicates) const { 50 assert(!Matches.empty() && "Must have at least one string to match!"); 51 std::string Indent(IndentCount * 2 + 4, ' '); 52 53 // If we have verified that the entire string matches, we're done: output the 54 // matching code. 55 if (CharNo == Matches[0]->first.size()) { 56 if (Matches.size() > 1 && !IgnoreDuplicates) 57 report_fatal_error("Had duplicate keys to match on"); 58 59 // If the to-execute code has \n's in it, indent each subsequent line. 60 StringRef Code = Matches[0]->second; 61 62 std::pair<StringRef, StringRef> Split = Code.split('\n'); 63 OS << Indent << Split.first << "\t // \"" << Matches[0]->first << "\"\n"; 64 65 Code = Split.second; 66 while (!Code.empty()) { 67 Split = Code.split('\n'); 68 OS << Indent << Split.first << "\n"; 69 Code = Split.second; 70 } 71 return false; 72 } 73 74 // Bucket the matches by the character we are comparing. 75 std::map<char, std::vector<const StringPair*>> MatchesByLetter; 76 77 for (const StringPair *Match : Matches) 78 MatchesByLetter[Match->first[CharNo]].push_back(Match); 79 80 // If we have exactly one bucket to match, see how many characters are common 81 // across the whole set and match all of them at once. 82 if (MatchesByLetter.size() == 1) { 83 unsigned FirstNonCommonLetter = FindFirstNonCommonLetter(Matches); 84 unsigned NumChars = FirstNonCommonLetter-CharNo; 85 86 // Emit code to break out if the prefix doesn't match. 87 if (NumChars == 1) { 88 // Do the comparison with if (Str[1] != 'f') 89 // FIXME: Need to escape general characters. 90 OS << Indent << "if (" << StrVariableName << "[" << CharNo << "] != '" 91 << Matches[0]->first[CharNo] << "')\n"; 92 OS << Indent << " break;\n"; 93 } else { 94 // Do the comparison with if memcmp(Str.data()+1, "foo", 3). 95 // FIXME: Need to escape general strings. 96 OS << Indent << "if (memcmp(" << StrVariableName << ".data()+" << CharNo 97 << ", \"" << Matches[0]->first.substr(CharNo, NumChars) << "\", " 98 << NumChars << ") != 0)\n"; 99 OS << Indent << " break;\n"; 100 } 101 102 return EmitStringMatcherForChar(Matches, FirstNonCommonLetter, IndentCount, 103 IgnoreDuplicates); 104 } 105 106 // Otherwise, we have multiple possible things, emit a switch on the 107 // character. 108 OS << Indent << "switch (" << StrVariableName << "[" << CharNo << "]) {\n"; 109 OS << Indent << "default: break;\n"; 110 111 for (const auto &[Letter, Matches] : MatchesByLetter) { 112 // TODO: escape hard stuff (like \n) if we ever care about it. 113 OS << Indent << "case '" << Letter << "':\t // " << Matches.size() 114 << " string"; 115 if (Matches.size() != 1) 116 OS << 's'; 117 OS << " to match.\n"; 118 if (EmitStringMatcherForChar(Matches, CharNo + 1, IndentCount + 1, 119 IgnoreDuplicates)) 120 OS << Indent << " break;\n"; 121 } 122 123 OS << Indent << "}\n"; 124 return true; 125 } 126 127 /// Emit - Top level entry point. 128 /// 129 void StringMatcher::Emit(unsigned Indent, bool IgnoreDuplicates) const { 130 // If nothing to match, just fall through. 131 if (Matches.empty()) return; 132 133 // First level categorization: group strings by length. 134 std::map<unsigned, std::vector<const StringPair*>> MatchesByLength; 135 136 for (const StringPair &Match : Matches) 137 MatchesByLength[Match.first.size()].push_back(&Match); 138 139 // Output a switch statement on length and categorize the elements within each 140 // bin. 141 OS.indent(Indent*2+2) << "switch (" << StrVariableName << ".size()) {\n"; 142 OS.indent(Indent*2+2) << "default: break;\n"; 143 144 for (const auto &[Length, Matches] : MatchesByLength) { 145 OS.indent(Indent * 2 + 2) 146 << "case " << Length << ":\t // " << Matches.size() << " string" 147 << (Matches.size() == 1 ? "" : "s") << " to match.\n"; 148 if (EmitStringMatcherForChar(Matches, 0, Indent, IgnoreDuplicates)) 149 OS.indent(Indent*2+4) << "break;\n"; 150 } 151 152 OS.indent(Indent*2+2) << "}\n"; 153 } 154