add a little function to do arbitrary string pattern matching in a

much more efficient way than a sequence of if's.  Switch MatchRegisterName
to use it.  It would be nice if someone could factor this out to a shared
place in tblgen :)


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@78492 91177308-0d34-0410-b5e6-96231b3b80d8

utils/TableGen/AsmMatcherEmitter.cpp

@@ -709,6 +709,8 @@ static void EmitMatchTokenString(CodeGenTarget &Target,
   OS << "}\n\n";
 }
 
+
+
 /// EmitClassifyOperand - Emit the function to classify an operand.
 static void EmitClassifyOperand(CodeGenTarget &Target,
                                 std::vector<ClassInfo*> &Infos,
@@ -730,6 +732,135 @@ static void EmitClassifyOperand(CodeGenTarget &Target,
   OS << "}\n\n";
 }
 
+typedef std::pair<std::string, std::string> StringPair;
+
+/// FindFirstNonCommonLetter - Find the first character in the keys of the
+/// string pairs that is not shared across the whole set of strings.  All
+/// strings are assumed to have the same length.
+static unsigned 
+FindFirstNonCommonLetter(const std::vector<const StringPair*> &Matches) {
+  assert(!Matches.empty());
+  for (unsigned i = 0, e = Matches[0]->first.size(); i != e; ++i) {
+    // Check to see if letter i is the same across the set.
+    char Letter = Matches[0]->first[i];
+    
+    for (unsigned str = 0, e = Matches.size(); str != e; ++str)
+      if (Matches[str]->first[i] != Letter)
+        return i;
+  }
+  
+  return Matches[0]->first.size();
+}
+
+/// EmitStringMatcherForChar - Given a set of strings that are known to be the
+/// same length and whose characters leading up to CharNo are the same, emit
+/// code to verify that CharNo and later are the same.
+static void EmitStringMatcherForChar(const std::string &StrVariableName,
+                                  const std::vector<const StringPair*> &Matches,
+                                     unsigned CharNo, unsigned IndentCount,
+                                     raw_ostream &OS) {
+  assert(!Matches.empty() && "Must have at least one string to match!");
+  std::string Indent(IndentCount*2+4, ' ');
+
+  // If we have verified that the entire string matches, we're done: output the
+  // matching code.
+  if (CharNo == Matches[0]->first.size()) {
+    assert(Matches.size() == 1 && "Had duplicate keys to match on");
+    
+    // FIXME: If Matches[0].first has embeded \n, this will be bad.
+    OS << Indent << Matches[0]->second << "\t // \"" << Matches[0]->first
+       << "\"\n";
+    return;
+  }
+  
+  // Bucket the matches by the character we are comparing.
+  std::map<char, std::vector<const StringPair*> > MatchesByLetter;
+  
+  for (unsigned i = 0, e = Matches.size(); i != e; ++i)
+    MatchesByLetter[Matches[i]->first[CharNo]].push_back(Matches[i]);
+  
+
+  // If we have exactly one bucket to match, see how many characters are common
+  // across the whole set and match all of them at once.
+  // length, just verify the rest of it with one if.
+  if (MatchesByLetter.size() == 1) {
+    unsigned FirstNonCommonLetter = FindFirstNonCommonLetter(Matches);
+    unsigned NumChars = FirstNonCommonLetter-CharNo;
+    
+    if (NumChars == 1) {
+      // Do the comparison with if (Str[1] == 'f')
+      // FIXME: Need to escape general characters.
+      OS << Indent << "if (" << StrVariableName << "[" << CharNo << "] == '"
+         << Matches[0]->first[CharNo] << "') {\n";
+    } else {
+      // Do the comparison with if (Str.substr(1,3) == "foo").
+      OS << Indent << "if (" << StrVariableName << ".substr(" << CharNo << ","
+         << NumChars << ") == \"";
+    
+      // FIXME: Need to escape general strings.
+      OS << Matches[0]->first.substr(CharNo, NumChars) << "\") {\n";
+    }
+    
+    EmitStringMatcherForChar(StrVariableName, Matches, FirstNonCommonLetter,
+                             IndentCount+1, OS);
+    OS << Indent << "}\n";
+    return;
+  }
+  
+  // Otherwise, we have multiple possible things, emit a switch on the
+  // character.
+  OS << Indent << "switch (" << StrVariableName << "[" << CharNo << "]) {\n";
+  OS << Indent << "default: break;\n";
+  
+  for (std::map<char, std::vector<const StringPair*> >::iterator LI = 
+       MatchesByLetter.begin(), E = MatchesByLetter.end(); LI != E; ++LI) {
+    // TODO: escape hard stuff (like \n) if we ever care about it.
+    OS << Indent << "case '" << LI->first << "':\t // "
+       << LI->second.size() << " strings to match.\n";
+    EmitStringMatcherForChar(StrVariableName, LI->second, CharNo+1,
+                             IndentCount+1, OS);
+    OS << Indent << "  break;\n";
+  }
+  
+  OS << Indent << "}\n";
+  
+}
+
+
+/// EmitStringMatcher - Given a list of strings and code to execute when they
+/// match, output a simple switch tree to classify the input string.  If a
+/// match is found, the code in Vals[i].second is executed.  This code should do
+/// a return to avoid falling through.  If nothing matches, execution falls
+/// through.  StrVariableName is the name of teh variable to test.
+static void EmitStringMatcher(const std::string &StrVariableName,
+                              const std::vector<StringPair> &Matches,
+                              raw_ostream &OS) {
+  // First level categorization: group strings by length.
+  std::map<unsigned, std::vector<const StringPair*> > MatchesByLength;
+  
+  for (unsigned i = 0, e = Matches.size(); i != e; ++i)
+    MatchesByLength[Matches[i].first.size()].push_back(&Matches[i]);
+  
+  // Output a switch statement on length and categorize the elements within each
+  // bin.
+  OS << "  switch (" << StrVariableName << ".size()) {\n";
+  OS << "  default: break;\n";
+  
+  
+  for (std::map<unsigned, std::vector<const StringPair*> >::iterator LI =
+       MatchesByLength.begin(), E = MatchesByLength.end(); LI != E; ++LI) {
+    OS << "  case " << LI->first << ":\t // " << LI->second.size()
+       << " strings to match.\n";
+    EmitStringMatcherForChar(StrVariableName, LI->second, 0, 0, OS);
+    OS << "    break;\n";
+  }
+  
+  
+  OS << "  }\n";
+}
+
+
+
 /// EmitMatchRegisterName - Emit the function to match a string to the target
 /// specific register enum.
 static void EmitMatchRegisterName(CodeGenTarget &Target, Record *AsmParser,
@@ -740,16 +871,20 @@ static void EmitMatchRegisterName(CodeGenTarget &Target, Record *AsmParser,
      << AsmParser->getValueAsString("AsmParserClassName")
      << "::MatchRegisterName(const StringRef &Name, unsigned &RegNo) {\n";
 
+  std::vector<StringPair> Matches;
+  
   // FIXME: TableGen should have a fast string matcher generator.
   for (unsigned i = 0, e = Registers.size(); i != e; ++i) {
     const CodeGenRegister &Reg = Registers[i];
     if (Reg.TheDef->getValueAsString("AsmName").empty())
       continue;
 
-    OS << "  if (Name == \"" 
-       << Reg.TheDef->getValueAsString("AsmName") << "\")\n"
-       << "    return RegNo=" << i + 1 << ", false;\n";
+    Matches.push_back(StringPair(Reg.TheDef->getValueAsString("AsmName"),
+                                 "RegNo=" + utostr(i + 1) + "; return false;"));
   }
+  
+  EmitStringMatcher("Name", Matches, OS);
+  
   OS << "  return true;\n";
   OS << "}\n\n";
 }