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 (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 }