llvm/lib/TableGen/StringMatcher.cpp

   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 (const StringMatcher::StringPair *Match : Matches)
  36       if (Match->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 (const StringPair *Match : Matches)
  79     MatchesByLetter[Match->first[CharNo]].push_back(Match);
  80
  81   // If we have exactly one bucket to match, see how many characters are common
  82   // across the whole set and match all of them at once.
  83   if (MatchesByLetter.size() == 1) {
  84     unsigned FirstNonCommonLetter = FindFirstNonCommonLetter(Matches);
  85     unsigned NumChars = FirstNonCommonLetter-CharNo;
  86
  87     // Emit code to break out if the prefix doesn't match.
  88     if (NumChars == 1) {
  89       // Do the comparison with if (Str[1] != 'f')
  90       // FIXME: Need to escape general characters.
  91       OS << Indent << "if (" << StrVariableName << "[" << CharNo << "] != '"
  92       << Matches[0]->first[CharNo] << "')\n";
  93       OS << Indent << "  break;\n";
  94     } else {
  95       // Do the comparison with if memcmp(Str.data()+1, "foo", 3).
  96       // FIXME: Need to escape general strings.
  97       OS << Indent << "if (memcmp(" << StrVariableName << ".data()+" << CharNo
  98          << ", \"" << Matches[0]->first.substr(CharNo, NumChars) << "\", "
  99          << NumChars << ") != 0)\n";
 100       OS << Indent << "  break;\n";
 101     }
 102
 103     return EmitStringMatcherForChar(Matches, FirstNonCommonLetter, IndentCount,
 104                                     IgnoreDuplicates);
 105   }
 106
 107   // Otherwise, we have multiple possible things, emit a switch on the
 108   // character.
 109   OS << Indent << "switch (" << StrVariableName << "[" << CharNo << "]) {\n";
 110   OS << Indent << "default: break;\n";
 111
 112   for (const auto &LI : MatchesByLetter) {
 113     // TODO: escape hard stuff (like \n) if we ever care about it.
 114     OS << Indent << "case '" << LI.first << "':\t // " << LI.second.size()
 115        << " string";
 116     if (LI.second.size() != 1)
 117       OS << 's';
 118     OS << " to match.\n";
 119     if (EmitStringMatcherForChar(LI.second, CharNo + 1, IndentCount + 1,
 120                                  IgnoreDuplicates))
 121       OS << Indent << "  break;\n";
 122   }
 123
 124   OS << Indent << "}\n";
 125   return true;
 126 }
 127
 128 /// Emit - Top level entry point.
 129 ///
 130 void StringMatcher::Emit(unsigned Indent, bool IgnoreDuplicates) const {
 131   // If nothing to match, just fall through.
 132   if (Matches.empty()) return;
 133
 134   // First level categorization: group strings by length.
 135   std::map<unsigned, std::vector<const StringPair*>> MatchesByLength;
 136
 137   for (const StringPair &Match : Matches)
 138     MatchesByLength[Match.first.size()].push_back(&Match);
 139
 140   // Output a switch statement on length and categorize the elements within each
 141   // bin.
 142   OS.indent(Indent*2+2) << "switch (" << StrVariableName << ".size()) {\n";
 143   OS.indent(Indent*2+2) << "default: break;\n";
 144
 145   for (const auto &LI : MatchesByLength) {
 146     OS.indent(Indent * 2 + 2)
 147         << "case " << LI.first << ":\t // " << LI.second.size() << " string"
 148         << (LI.second.size() == 1 ? "" : "s") << " to match.\n";
 149     if (EmitStringMatcherForChar(LI.second, 0, Indent, IgnoreDuplicates))
 150       OS.indent(Indent*2+4) << "break;\n";
 151   }
 152
 153   OS.indent(Indent*2+2) << "}\n";
 154 }