factor the snazzy string matcher code that Daniel hates

out of AsmMatcherEmitter.cpp into its own class.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@113137 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 134 insertions, 0 deletions

diff --git a/utils/TableGen/StringMatcher.cpp b/utils/TableGen/StringMatcher.cpp
new file mode 100644
index 0000000000..2d2f773578
--- /dev/null
+++ b/utils/TableGen/StringMatcher.cpp
@@ -0,0 +1,134 @@
+//===- StringMatcher.cpp - Generate a matcher for input strings -----------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the StringMatcher class.
+//
+//===----------------------------------------------------------------------===//
+
+#include "StringMatcher.h"
+#include "llvm/Support/raw_ostream.h"
+#include <map>
+using namespace llvm;
+
+/// 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
+                              StringMatcher::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.
+///
+/// \return - True if control can leave the emitted code fragment.
+bool StringMatcher::
+EmitStringMatcherForChar(const std::vector<const StringPair*> &Matches,
+                         unsigned CharNo, unsigned IndentCount) const {
+  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 false;
+  }
+  
+  // 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.
+  if (MatchesByLetter.size() == 1) {
+    unsigned FirstNonCommonLetter = FindFirstNonCommonLetter(Matches);
+    unsigned NumChars = FirstNonCommonLetter-CharNo;
+    
+    // Emit code to break out if the prefix doesn't match.
+    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";
+      OS << Indent << "  break;\n";
+    } else {
+      // Do the comparison with if (Str.substr(1,3) != "foo").    
+      // FIXME: Need to escape general strings.
+      OS << Indent << "if (" << StrVariableName << ".substr(" << CharNo << ","
+      << NumChars << ") != \"";
+      OS << Matches[0]->first.substr(CharNo, NumChars) << "\")\n";
+      OS << Indent << "  break;\n";
+    }
+    
+    return EmitStringMatcherForChar(Matches, FirstNonCommonLetter, IndentCount);
+  }
+  
+  // 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";
+    if (EmitStringMatcherForChar(LI->second, CharNo+1, IndentCount+1))
+      OS << Indent << "  break;\n";
+  }
+  
+  OS << Indent << "}\n";
+  return true;
+}
+
+
+/// Emit - Top level entry point.
+///
+void StringMatcher::Emit() const {
+  // 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";
+    if (EmitStringMatcherForChar(LI->second, 0, 0))
+      OS << "    break;\n";
+  }
+  
+  OS << "  }\n";
+}