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//===- StringMatcher.cpp - Generate a matcher for input strings -----------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file implements the StringMatcher class.
//
//===----------------------------------------------------------------------===//
#include "llvm/TableGen/StringMatcher.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/Support/raw_ostream.h"
#include <cassert>
#include <map>
#include <string>
#include <utility>
#include <vector>
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 (const StringMatcher::StringPair *Match : Matches)
if (Match->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, bool IgnoreDuplicates) 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()) {
if (Matches.size() > 1 && !IgnoreDuplicates)
report_fatal_error("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 (const StringPair *Match : Matches)
MatchesByLetter[Match->first[CharNo]].push_back(Match);
// 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 << ") != 0)\n";
OS << Indent << " break;\n";
}
return EmitStringMatcherForChar(Matches, FirstNonCommonLetter, IndentCount,
IgnoreDuplicates);
}
// Otherwise, we have multiple possible things, emit a switch on the
// character.
OS << Indent << "switch (" << StrVariableName << "[" << CharNo << "]) {\n";
OS << Indent << "default: break;\n";
for (const auto &LI : MatchesByLetter) {
// 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,
IgnoreDuplicates))
OS << Indent << " break;\n";
}
OS << Indent << "}\n";
return true;
}
/// Emit - Top level entry point.
///
void StringMatcher::Emit(unsigned Indent, bool IgnoreDuplicates) 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 (const StringPair &Match : Matches)
MatchesByLength[Match.first.size()].push_back(&Match);
// 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 (const auto &LI : MatchesByLength) {
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, IgnoreDuplicates))
OS.indent(Indent*2+4) << "break;\n";
}
OS.indent(Indent*2+2) << "}\n";
}
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