utils/TableGen/StringMatcher.cpp

   1 //===- StringMatcher.cpp - Generate a matcher for input strings -----------===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // This file implements the StringMatcher class.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "StringMatcher.h"
  15 #include "llvm/Support/raw_ostream.h"
  16 #include <map>
  17 using namespace llvm;
  18
  19 /// FindFirstNonCommonLetter - Find the first character in the keys of the
  20 /// string pairs that is not shared across the whole set of strings.  All
  21 /// strings are assumed to have the same length.
  22 static unsigned
  23 FindFirstNonCommonLetter(const std::vector<const
  24                               StringMatcher::StringPair*> &Matches) {
  25   assert(!Matches.empty());
  26   for (unsigned i = 0, e = Matches[0]->first.size(); i != e; ++i) {
  27     // Check to see if letter i is the same across the set.
  28     char Letter = Matches[0]->first[i];
  29
  30     for (unsigned str = 0, e = Matches.size(); str != e; ++str)
  31       if (Matches[str]->first[i] != Letter)
  32         return i;
  33   }
  34
  35   return Matches[0]->first.size();
  36 }
  37
  38 /// EmitStringMatcherForChar - Given a set of strings that are known to be the
  39 /// same length and whose characters leading up to CharNo are the same, emit
  40 /// code to verify that CharNo and later are the same.
  41 ///
  42 /// \return - True if control can leave the emitted code fragment.
  43 bool StringMatcher::
  44 EmitStringMatcherForChar(const std::vector<const StringPair*> &Matches,
  45                          unsigned CharNo, unsigned IndentCount) const {
  46   assert(!Matches.empty() && "Must have at least one string to match!");
  47   std::string Indent(IndentCount*2+4, ' ');
  48
  49   // If we have verified that the entire string matches, we're done: output the
  50   // matching code.
  51   if (CharNo == Matches[0]->first.size()) {
  52     assert(Matches.size() == 1 && "Had duplicate keys to match on");
  53
  54     // If the to-execute code has \n's in it, indent each subsequent line.
  55     StringRef Code = Matches[0]->second;
  56
  57     std::pair<StringRef, StringRef> Split = Code.split('\n');
  58     OS << Indent << Split.first << "\t // \"" << Matches[0]->first << "\"\n";
  59
  60     Code = Split.second;
  61     while (!Code.empty()) {
  62       Split = Code.split('\n');
  63       OS << Indent << Split.first << "\n";
  64       Code = Split.second;
  65     }
  66     return false;
  67   }
  68
  69   // Bucket the matches by the character we are comparing.
  70   std::map<char, std::vector<const StringPair*> > MatchesByLetter;
  71
  72   for (unsigned i = 0, e = Matches.size(); i != e; ++i)
  73     MatchesByLetter[Matches[i]->first[CharNo]].push_back(Matches[i]);
  74
  75
  76   // If we have exactly one bucket to match, see how many characters are common
  77   // across the whole set and match all of them at once.
  78   if (MatchesByLetter.size() == 1) {
  79     unsigned FirstNonCommonLetter = FindFirstNonCommonLetter(Matches);
  80     unsigned NumChars = FirstNonCommonLetter-CharNo;
  81
  82     // Emit code to break out if the prefix doesn't match.
  83     if (NumChars == 1) {
  84       // Do the comparison with if (Str[1] != 'f')
  85       // FIXME: Need to escape general characters.
  86       OS << Indent << "if (" << StrVariableName << "[" << CharNo << "] != '"
  87       << Matches[0]->first[CharNo] << "')\n";
  88       OS << Indent << "  break;\n";
  89     } else {
  90       // Do the comparison with if (Str.substr(1, 3) != "foo").
  91       // FIXME: Need to escape general strings.
  92       OS << Indent << "if (" << StrVariableName << ".substr(" << CharNo << ", "
  93       << NumChars << ") != \"";
  94       OS << Matches[0]->first.substr(CharNo, NumChars) << "\")\n";
  95       OS << Indent << "  break;\n";
  96     }
  97
  98     return EmitStringMatcherForChar(Matches, FirstNonCommonLetter, IndentCount);
  99   }
 100
 101   // Otherwise, we have multiple possible things, emit a switch on the
 102   // character.
 103   OS << Indent << "switch (" << StrVariableName << "[" << CharNo << "]) {\n";
 104   OS << Indent << "default: break;\n";
 105
 106   for (std::map<char, std::vector<const StringPair*> >::iterator LI =
 107        MatchesByLetter.begin(), E = MatchesByLetter.end(); LI != E; ++LI) {
 108     // TODO: escape hard stuff (like \n) if we ever care about it.
 109     OS << Indent << "case '" << LI->first << "':\t // "
 110        << LI->second.size() << " string";
 111     if (LI->second.size() != 1) OS << 's';
 112     OS << " to match.\n";
 113     if (EmitStringMatcherForChar(LI->second, CharNo+1, IndentCount+1))
 114       OS << Indent << "  break;\n";
 115   }
 116
 117   OS << Indent << "}\n";
 118   return true;
 119 }
 120
 121
 122 /// Emit - Top level entry point.
 123 ///
 124 void StringMatcher::Emit(unsigned Indent) const {
 125   // If nothing to match, just fall through.
 126   if (Matches.empty()) return;
 127
 128   // First level categorization: group strings by length.
 129   std::map<unsigned, std::vector<const StringPair*> > MatchesByLength;
 130
 131   for (unsigned i = 0, e = Matches.size(); i != e; ++i)
 132     MatchesByLength[Matches[i].first.size()].push_back(&Matches[i]);
 133
 134   // Output a switch statement on length and categorize the elements within each
 135   // bin.
 136   OS.indent(Indent*2+2) << "switch (" << StrVariableName << ".size()) {\n";
 137   OS.indent(Indent*2+2) << "default: break;\n";
 138
 139   for (std::map<unsigned, std::vector<const StringPair*> >::iterator LI =
 140        MatchesByLength.begin(), E = MatchesByLength.end(); LI != E; ++LI) {
 141     OS.indent(Indent*2+2) << "case " << LI->first << ":\t // "
 142        << LI->second.size()
 143        << " string" << (LI->second.size() == 1 ? "" : "s") << " to match.\n";
 144     if (EmitStringMatcherForChar(LI->second, 0, Indent))
 145       OS.indent(Indent*2+4) << "break;\n";
 146   }
 147
 148   OS.indent(Indent*2+2) << "}\n";
 149 }