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      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 }
    150