LLVM  17.0.0git
StringMatcher.cpp
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1 //===- StringMatcher.cpp - Generate a matcher for input strings -----------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file implements the StringMatcher class.
10 //
11 //===----------------------------------------------------------------------===//
12 
14 #include "llvm/ADT/StringRef.h"
17 #include <cassert>
18 #include <map>
19 #include <string>
20 #include <utility>
21 #include <vector>
22 
23 using namespace llvm;
24 
25 /// FindFirstNonCommonLetter - Find the first character in the keys of the
26 /// string pairs that is not shared across the whole set of strings. All
27 /// strings are assumed to have the same length.
28 static unsigned
29 FindFirstNonCommonLetter(const std::vector<const
30  StringMatcher::StringPair*> &Matches) {
31  assert(!Matches.empty());
32  for (unsigned i = 0, e = Matches[0]->first.size(); i != e; ++i) {
33  // Check to see if letter i is the same across the set.
34  char Letter = Matches[0]->first[i];
35 
36  for (const StringMatcher::StringPair *Match : Matches)
37  if (Match->first[i] != Letter)
38  return i;
39  }
40 
41  return Matches[0]->first.size();
42 }
43 
44 /// EmitStringMatcherForChar - Given a set of strings that are known to be the
45 /// same length and whose characters leading up to CharNo are the same, emit
46 /// code to verify that CharNo and later are the same.
47 ///
48 /// \return - True if control can leave the emitted code fragment.
49 bool StringMatcher::EmitStringMatcherForChar(
50  const std::vector<const StringPair *> &Matches, unsigned CharNo,
51  unsigned IndentCount, bool IgnoreDuplicates) const {
52  assert(!Matches.empty() && "Must have at least one string to match!");
53  std::string Indent(IndentCount * 2 + 4, ' ');
54 
55  // If we have verified that the entire string matches, we're done: output the
56  // matching code.
57  if (CharNo == Matches[0]->first.size()) {
58  if (Matches.size() > 1 && !IgnoreDuplicates)
59  report_fatal_error("Had duplicate keys to match on");
60 
61  // If the to-execute code has \n's in it, indent each subsequent line.
62  StringRef Code = Matches[0]->second;
63 
64  std::pair<StringRef, StringRef> Split = Code.split('\n');
65  OS << Indent << Split.first << "\t // \"" << Matches[0]->first << "\"\n";
66 
67  Code = Split.second;
68  while (!Code.empty()) {
69  Split = Code.split('\n');
70  OS << Indent << Split.first << "\n";
71  Code = Split.second;
72  }
73  return false;
74  }
75 
76  // Bucket the matches by the character we are comparing.
77  std::map<char, std::vector<const StringPair*>> MatchesByLetter;
78 
79  for (const StringPair *Match : Matches)
80  MatchesByLetter[Match->first[CharNo]].push_back(Match);
81 
82  // If we have exactly one bucket to match, see how many characters are common
83  // across the whole set and match all of them at once.
84  if (MatchesByLetter.size() == 1) {
85  unsigned FirstNonCommonLetter = FindFirstNonCommonLetter(Matches);
86  unsigned NumChars = FirstNonCommonLetter-CharNo;
87 
88  // Emit code to break out if the prefix doesn't match.
89  if (NumChars == 1) {
90  // Do the comparison with if (Str[1] != 'f')
91  // FIXME: Need to escape general characters.
92  OS << Indent << "if (" << StrVariableName << "[" << CharNo << "] != '"
93  << Matches[0]->first[CharNo] << "')\n";
94  OS << Indent << " break;\n";
95  } else {
96  // Do the comparison with if memcmp(Str.data()+1, "foo", 3).
97  // FIXME: Need to escape general strings.
98  OS << Indent << "if (memcmp(" << StrVariableName << ".data()+" << CharNo
99  << ", \"" << Matches[0]->first.substr(CharNo, NumChars) << "\", "
100  << NumChars << ") != 0)\n";
101  OS << Indent << " break;\n";
102  }
103 
104  return EmitStringMatcherForChar(Matches, FirstNonCommonLetter, IndentCount,
105  IgnoreDuplicates);
106  }
107 
108  // Otherwise, we have multiple possible things, emit a switch on the
109  // character.
110  OS << Indent << "switch (" << StrVariableName << "[" << CharNo << "]) {\n";
111  OS << Indent << "default: break;\n";
112 
113  for (const auto &LI : MatchesByLetter) {
114  // TODO: escape hard stuff (like \n) if we ever care about it.
115  OS << Indent << "case '" << LI.first << "':\t // " << LI.second.size()
116  << " string";
117  if (LI.second.size() != 1)
118  OS << 's';
119  OS << " to match.\n";
120  if (EmitStringMatcherForChar(LI.second, CharNo + 1, IndentCount + 1,
121  IgnoreDuplicates))
122  OS << Indent << " break;\n";
123  }
124 
125  OS << Indent << "}\n";
126  return true;
127 }
128 
129 /// Emit - Top level entry point.
130 ///
131 void StringMatcher::Emit(unsigned Indent, bool IgnoreDuplicates) const {
132  // If nothing to match, just fall through.
133  if (Matches.empty()) return;
134 
135  // First level categorization: group strings by length.
136  std::map<unsigned, std::vector<const StringPair*>> MatchesByLength;
137 
138  for (const StringPair &Match : Matches)
139  MatchesByLength[Match.first.size()].push_back(&Match);
140 
141  // Output a switch statement on length and categorize the elements within each
142  // bin.
143  OS.indent(Indent*2+2) << "switch (" << StrVariableName << ".size()) {\n";
144  OS.indent(Indent*2+2) << "default: break;\n";
145 
146  for (const auto &LI : MatchesByLength) {
147  OS.indent(Indent * 2 + 2)
148  << "case " << LI.first << ":\t // " << LI.second.size() << " string"
149  << (LI.second.size() == 1 ? "" : "s") << " to match.\n";
150  if (EmitStringMatcherForChar(LI.second, 0, Indent, IgnoreDuplicates))
151  OS.indent(Indent*2+4) << "break;\n";
152  }
153 
154  OS.indent(Indent*2+2) << "}\n";
155 }
i
i
Definition: README.txt:29
llvm::StringMatcher::StringPair
std::pair< std::string, std::string > StringPair
Definition: StringMatcher.h:32
llvm
This is an optimization pass for GlobalISel generic memory operations.
Definition: AddressRanges.h:18
StringRef.h
llvm::tgtok::Code
@ Code
Definition: TGLexer.h:50
ErrorHandling.h
llvm::StringMatcher::Emit
void Emit(unsigned Indent=0, bool IgnoreDuplicates=false) const
Emit - Top level entry point.
Definition: StringMatcher.cpp:131
llvm::DiagnosticPredicateTy::Match
@ Match
FindFirstNonCommonLetter
static unsigned FindFirstNonCommonLetter(const std::vector< const StringMatcher::StringPair * > &Matches)
FindFirstNonCommonLetter - Find the first character in the keys of the string pairs that is not share...
Definition: StringMatcher.cpp:29
llvm::logicalview::LVOutputKind::Split
@ Split
llvm::StringRef::substr
constexpr StringRef substr(size_t Start, size_t N=npos) const
Return a reference to the substring from [Start, Start + N).
Definition: StringRef.h:559
llvm::report_fatal_error
void report_fatal_error(Error Err, bool gen_crash_diag=true)
Report a serious error, calling any installed error handler.
Definition: Error.cpp:145
StringMatcher.h
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constexpr double e
Definition: MathExtras.h:31
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Definition: StringTableBuilder.cpp:68
assert
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llvm::StringRef
StringRef - Represent a constant reference to a string, i.e.
Definition: StringRef.h:50
llvm::raw_ostream::indent
raw_ostream & indent(unsigned NumSpaces)
indent - Insert 'NumSpaces' spaces.
Definition: raw_ostream.cpp:494
raw_ostream.h