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//===- 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 "llvm/TableGen/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");
// If the to-execute code has \n's in it, indent each subsequent line.
StringRef Code = Matches[0]->second;
std::pair<StringRef, StringRef> Split = Code.split('\n');
OS << Indent << Split.first << "\t // \"" << Matches[0]->first << "\"\n";
Code = Split.second;
while (!Code.empty()) {
Split = Code.split('\n');
OS << Indent << Split.first << "\n";
Code = Split.second;
}
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 memcmp(Str.data()+1, "foo", 3).
// FIXME: Need to escape general strings.
OS << Indent << "if (memcmp(" << StrVariableName << ".data()+" << CharNo
<< ", \"" << Matches[0]->first.substr(CharNo, NumChars) << "\", "
<< 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() << " string";
if (LI->second.size() != 1) OS << 's';
OS << " 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(unsigned Indent) const {
// If nothing to match, just fall through.
if (Matches.empty()) return;
// 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.indent(Indent*2+2) << "switch (" << StrVariableName << ".size()) {\n";
OS.indent(Indent*2+2) << "default: break;\n";
for (std::map<unsigned, std::vector<const StringPair*> >::iterator LI =
MatchesByLength.begin(), E = MatchesByLength.end(); LI != E; ++LI) {
OS.indent(Indent*2+2) << "case " << LI->first << ":\t // "
<< LI->second.size()
<< " string" << (LI->second.size() == 1 ? "" : "s") << " to match.\n";
if (EmitStringMatcherForChar(LI->second, 0, Indent))
OS.indent(Indent*2+4) << "break;\n";
}
OS.indent(Indent*2+2) << "}\n";
}
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