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/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(const std::vector<const
  30                               StringMatcher::StringPair*> &Matches) {
  31   assert(!Matches.empty());
  32   for (unsigned i = 0, e = Matches[0]->first.size(); i != e; ++i) {
  33     // Check to see if letter i is the same across the set.
  34     char Letter = Matches[0]->first[i];
  35
  36     for (const StringMatcher::StringPair *Match : Matches)
  37       if (Match->first[i] != Letter)
  38         return i;
  39   }
  40
  41   return Matches[0]->first.size();
  42 }
  43
  44 /// EmitStringMatcherForChar - Given a set of strings that are known to be the
  45 /// same length and whose characters leading up to CharNo are the same, emit
  46 /// code to verify that CharNo and later are the same.
  47 ///
  48 /// \return - True if control can leave the emitted code fragment.
  49 bool StringMatcher::EmitStringMatcherForChar(
  50     const std::vector<const StringPair *> &Matches, unsigned CharNo,
  51     unsigned IndentCount, bool IgnoreDuplicates) const {
  52   assert(!Matches.empty() && "Must have at least one string to match!");
  53   std::string Indent(IndentCount * 2 + 4, ' ');
  54
  55   // If we have verified that the entire string matches, we're done: output the
  56   // matching code.
  57   if (CharNo == Matches[0]->first.size()) {
  58     if (Matches.size() > 1 && !IgnoreDuplicates)
  59       report_fatal_error("Had duplicate keys to match on");
  60
  61     // If the to-execute code has \n's in it, indent each subsequent line.
  62     StringRef Code = Matches[0]->second;
  63
  64     std::pair<StringRef, StringRef> Split = Code.split('\n');
  65     OS << Indent << Split.first << "\t // \"" << Matches[0]->first << "\"\n";
  66
  67     Code = Split.second;
  68     while (!Code.empty()) {
  69       Split = Code.split('\n');
  70       OS << Indent << Split.first << "\n";
  71       Code = Split.second;
  72     }
  73     return false;
  74   }
  75
  76   // Bucket the matches by the character we are comparing.
  77   std::map<char, std::vector<const StringPair*>> MatchesByLetter;
  78
  79   for (const StringPair *Match : Matches)
  80     MatchesByLetter[Match->first[CharNo]].push_back(Match);
  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 (const auto &LI : MatchesByLetter) {
 114     // TODO: escape hard stuff (like \n) if we ever care about it.
 115     OS << Indent << "case '" << LI.first << "':\t // " << LI.second.size()
 116        << " string";
 117     if (LI.second.size() != 1)
 118       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 (const StringPair &Match : Matches)
 139     MatchesByLength[Match.first.size()].push_back(&Match);
 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 (const auto &LI : MatchesByLength) {
 147     OS.indent(Indent * 2 + 2)
 148         << "case " << LI.first << ":\t // " << LI.second.size() << " string"
 149         << (LI.second.size() == 1 ? "" : "s") << " to match.\n";
 150     if (EmitStringMatcherForChar(LI.second, 0, Indent, IgnoreDuplicates))
 151       OS.indent(Indent*2+4) << "break;\n";
 152   }
 153
 154   OS.indent(Indent*2+2) << "}\n";
 155 }