150 lines
5.6 KiB
C++
150 lines
5.6 KiB
C++
//===- StringMatcher.cpp - Generate a matcher for input strings -----------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements the StringMatcher class.
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//
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//===----------------------------------------------------------------------===//
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#include "StringMatcher.h"
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#include "llvm/Support/raw_ostream.h"
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#include <map>
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using namespace llvm;
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/// FindFirstNonCommonLetter - Find the first character in the keys of the
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/// string pairs that is not shared across the whole set of strings. All
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/// strings are assumed to have the same length.
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static unsigned
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FindFirstNonCommonLetter(const std::vector<const
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StringMatcher::StringPair*> &Matches) {
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assert(!Matches.empty());
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for (unsigned i = 0, e = Matches[0]->first.size(); i != e; ++i) {
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// Check to see if letter i is the same across the set.
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char Letter = Matches[0]->first[i];
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for (unsigned str = 0, e = Matches.size(); str != e; ++str)
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if (Matches[str]->first[i] != Letter)
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return i;
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}
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return Matches[0]->first.size();
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}
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/// EmitStringMatcherForChar - Given a set of strings that are known to be the
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/// same length and whose characters leading up to CharNo are the same, emit
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/// code to verify that CharNo and later are the same.
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///
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/// \return - True if control can leave the emitted code fragment.
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bool StringMatcher::
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EmitStringMatcherForChar(const std::vector<const StringPair*> &Matches,
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unsigned CharNo, unsigned IndentCount) const {
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assert(!Matches.empty() && "Must have at least one string to match!");
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std::string Indent(IndentCount*2+4, ' ');
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// If we have verified that the entire string matches, we're done: output the
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// matching code.
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if (CharNo == Matches[0]->first.size()) {
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assert(Matches.size() == 1 && "Had duplicate keys to match on");
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// If the to-execute code has \n's in it, indent each subsequent line.
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StringRef Code = Matches[0]->second;
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std::pair<StringRef, StringRef> Split = Code.split('\n');
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OS << Indent << Split.first << "\t // \"" << Matches[0]->first << "\"\n";
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Code = Split.second;
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while (!Code.empty()) {
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Split = Code.split('\n');
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OS << Indent << Split.first << "\n";
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Code = Split.second;
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}
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return false;
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}
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// Bucket the matches by the character we are comparing.
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std::map<char, std::vector<const StringPair*> > MatchesByLetter;
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for (unsigned i = 0, e = Matches.size(); i != e; ++i)
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MatchesByLetter[Matches[i]->first[CharNo]].push_back(Matches[i]);
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// If we have exactly one bucket to match, see how many characters are common
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// across the whole set and match all of them at once.
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if (MatchesByLetter.size() == 1) {
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unsigned FirstNonCommonLetter = FindFirstNonCommonLetter(Matches);
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unsigned NumChars = FirstNonCommonLetter-CharNo;
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// Emit code to break out if the prefix doesn't match.
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if (NumChars == 1) {
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// Do the comparison with if (Str[1] != 'f')
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// FIXME: Need to escape general characters.
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OS << Indent << "if (" << StrVariableName << "[" << CharNo << "] != '"
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<< Matches[0]->first[CharNo] << "')\n";
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OS << Indent << " break;\n";
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} else {
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// Do the comparison with if (Str.substr(1, 3) != "foo").
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// FIXME: Need to escape general strings.
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OS << Indent << "if (" << StrVariableName << ".substr(" << CharNo << ", "
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<< NumChars << ") != \"";
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OS << Matches[0]->first.substr(CharNo, NumChars) << "\")\n";
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OS << Indent << " break;\n";
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}
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return EmitStringMatcherForChar(Matches, FirstNonCommonLetter, IndentCount);
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}
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// Otherwise, we have multiple possible things, emit a switch on the
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// character.
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OS << Indent << "switch (" << StrVariableName << "[" << CharNo << "]) {\n";
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OS << Indent << "default: break;\n";
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for (std::map<char, std::vector<const StringPair*> >::iterator LI =
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MatchesByLetter.begin(), E = MatchesByLetter.end(); LI != E; ++LI) {
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// TODO: escape hard stuff (like \n) if we ever care about it.
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OS << Indent << "case '" << LI->first << "':\t // "
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<< LI->second.size() << " string";
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if (LI->second.size() != 1) OS << 's';
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OS << " to match.\n";
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if (EmitStringMatcherForChar(LI->second, CharNo+1, IndentCount+1))
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OS << Indent << " break;\n";
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}
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OS << Indent << "}\n";
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return true;
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}
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/// Emit - Top level entry point.
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///
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void StringMatcher::Emit(unsigned Indent) const {
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// If nothing to match, just fall through.
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if (Matches.empty()) return;
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// First level categorization: group strings by length.
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std::map<unsigned, std::vector<const StringPair*> > MatchesByLength;
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for (unsigned i = 0, e = Matches.size(); i != e; ++i)
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MatchesByLength[Matches[i].first.size()].push_back(&Matches[i]);
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// Output a switch statement on length and categorize the elements within each
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// bin.
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OS.indent(Indent*2+2) << "switch (" << StrVariableName << ".size()) {\n";
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OS.indent(Indent*2+2) << "default: break;\n";
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for (std::map<unsigned, std::vector<const StringPair*> >::iterator LI =
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MatchesByLength.begin(), E = MatchesByLength.end(); LI != E; ++LI) {
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OS.indent(Indent*2+2) << "case " << LI->first << ":\t // "
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<< LI->second.size()
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<< " string" << (LI->second.size() == 1 ? "" : "s") << " to match.\n";
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if (EmitStringMatcherForChar(LI->second, 0, Indent))
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OS.indent(Indent*2+4) << "break;\n";
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}
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OS.indent(Indent*2+2) << "}\n";
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}
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