LLVM  15.0.0git
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"
16 #include <cassert>
17 #include <map>
18 #include <string>
19 #include <utility>
20 #include <vector>
21 
22 using namespace llvm;
23 
24 /// FindFirstNonCommonLetter - Find the first character in the keys of the
25 /// string pairs that is not shared across the whole set of strings. All
26 /// strings are assumed to have the same length.
27 static unsigned
28 FindFirstNonCommonLetter(const std::vector<const
29  StringMatcher::StringPair*> &Matches) {
30  assert(!Matches.empty());
31  for (unsigned i = 0, e = Matches[0]->first.size(); i != e; ++i) {
32  // Check to see if letter i is the same across the set.
33  char Letter = Matches[0]->first[i];
34 
35  for (const StringMatcher::StringPair *Match : Matches)
36  if (Match->first[i] != Letter)
37  return i;
38  }
39 
40  return Matches[0]->first.size();
41 }
42 
43 /// EmitStringMatcherForChar - Given a set of strings that are known to be the
44 /// same length and whose characters leading up to CharNo are the same, emit
45 /// code to verify that CharNo and later are the same.
46 ///
47 /// \return - True if control can leave the emitted code fragment.
48 bool StringMatcher::EmitStringMatcherForChar(
49  const std::vector<const StringPair *> &Matches, unsigned CharNo,
50  unsigned IndentCount, bool IgnoreDuplicates) const {
51  assert(!Matches.empty() && "Must have at least one string to match!");
52  std::string Indent(IndentCount * 2 + 4, ' ');
53 
54  // If we have verified that the entire string matches, we're done: output the
55  // matching code.
56  if (CharNo == Matches[0]->first.size()) {
57  if (Matches.size() > 1 && !IgnoreDuplicates)
58  report_fatal_error("Had duplicate keys to match on");
59 
60  // If the to-execute code has \n's in it, indent each subsequent line.
61  StringRef Code = Matches[0]->second;
62 
63  std::pair<StringRef, StringRef> Split = Code.split('\n');
64  OS << Indent << Split.first << "\t // \"" << Matches[0]->first << "\"\n";
65 
66  Code = Split.second;
67  while (!Code.empty()) {
68  Split = Code.split('\n');
69  OS << Indent << Split.first << "\n";
70  Code = Split.second;
71  }
72  return false;
73  }
74 
75  // Bucket the matches by the character we are comparing.
76  std::map<char, std::vector<const StringPair*>> MatchesByLetter;
77 
78  for (const StringPair *Match : Matches)
79  MatchesByLetter[Match->first[CharNo]].push_back(Match);
80 
81  // If we have exactly one bucket to match, see how many characters are common
82  // across the whole set and match all of them at once.
83  if (MatchesByLetter.size() == 1) {
84  unsigned FirstNonCommonLetter = FindFirstNonCommonLetter(Matches);
85  unsigned NumChars = FirstNonCommonLetter-CharNo;
86 
87  // Emit code to break out if the prefix doesn't match.
88  if (NumChars == 1) {
89  // Do the comparison with if (Str[1] != 'f')
90  // FIXME: Need to escape general characters.
91  OS << Indent << "if (" << StrVariableName << "[" << CharNo << "] != '"
92  << Matches[0]->first[CharNo] << "')\n";
93  OS << Indent << " break;\n";
94  } else {
95  // Do the comparison with if memcmp(Str.data()+1, "foo", 3).
96  // FIXME: Need to escape general strings.
97  OS << Indent << "if (memcmp(" << StrVariableName << ".data()+" << CharNo
98  << ", \"" << Matches[0]->first.substr(CharNo, NumChars) << "\", "
99  << NumChars << ") != 0)\n";
100  OS << Indent << " break;\n";
101  }
102 
103  return EmitStringMatcherForChar(Matches, FirstNonCommonLetter, IndentCount,
104  IgnoreDuplicates);
105  }
106 
107  // Otherwise, we have multiple possible things, emit a switch on the
108  // character.
109  OS << Indent << "switch (" << StrVariableName << "[" << CharNo << "]) {\n";
110  OS << Indent << "default: break;\n";
111 
112  for (const auto &LI : MatchesByLetter) {
113  // TODO: escape hard stuff (like \n) if we ever care about it.
114  OS << Indent << "case '" << LI.first << "':\t // " << LI.second.size()
115  << " string";
116  if (LI.second.size() != 1)
117  OS << 's';
118  OS << " to match.\n";
119  if (EmitStringMatcherForChar(LI.second, CharNo + 1, IndentCount + 1,
120  IgnoreDuplicates))
121  OS << Indent << " break;\n";
122  }
123 
124  OS << Indent << "}\n";
125  return true;
126 }
127 
128 /// Emit - Top level entry point.
129 ///
130 void StringMatcher::Emit(unsigned Indent, bool IgnoreDuplicates) const {
131  // If nothing to match, just fall through.
132  if (Matches.empty()) return;
133 
134  // First level categorization: group strings by length.
135  std::map<unsigned, std::vector<const StringPair*>> MatchesByLength;
136 
137  for (const StringPair &Match : Matches)
138  MatchesByLength[Match.first.size()].push_back(&Match);
139 
140  // Output a switch statement on length and categorize the elements within each
141  // bin.
142  OS.indent(Indent*2+2) << "switch (" << StrVariableName << ".size()) {\n";
143  OS.indent(Indent*2+2) << "default: break;\n";
144 
145  for (const auto &LI : MatchesByLength) {
146  OS.indent(Indent * 2 + 2)
147  << "case " << LI.first << ":\t // " << LI.second.size() << " string"
148  << (LI.second.size() == 1 ? "" : "s") << " to match.\n";
149  if (EmitStringMatcherForChar(LI.second, 0, Indent, IgnoreDuplicates))
150  OS.indent(Indent*2+4) << "break;\n";
151  }
152 
153  OS.indent(Indent*2+2) << "}\n";
154 }
i
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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:17
StringRef.h
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@ Code
Definition: TGLexer.h:50
llvm::StringMatcher::Emit
void Emit(unsigned Indent=0, bool IgnoreDuplicates=false) const
Emit - Top level entry point.
Definition: StringMatcher.cpp:130
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:28
llvm::StringRef::substr
LLVM_NODISCARD StringRef substr(size_t Start, size_t N=npos) const
Return a reference to the substring from [Start, Start + N).
Definition: StringRef.h:615
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:57
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Definition: StringTableBuilder.cpp:68
assert
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llvm::StringRef
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Definition: StringRef.h:58
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raw_ostream & indent(unsigned NumSpaces)
indent - Insert 'NumSpaces' spaces.
Definition: raw_ostream.cpp:496
raw_ostream.h