[FileCheck] Don't use regex to find prefixes

llvm/include/llvm/FileCheck/FileCheck.h

@@ -187,24 +187,14 @@ class FileCheck {
   explicit FileCheck(FileCheckRequest Req);
   ~FileCheck();
 
-  // Combines the check prefixes into a single regex so that we can efficiently
-  // scan for any of the set.
-  //
-  // The semantics are that the longest-match wins which matches our regex
-  // library.
-  Regex buildCheckPrefixRegex();
-
   /// Reads the check file from \p Buffer and records the expected strings it
   /// contains. Errors are reported against \p SM.
   ///
-  /// Only expected strings whose prefix is one of those listed in \p PrefixRE
-  /// are recorded. \returns true in case of an error, false otherwise.
-  ///
   /// If \p ImpPatBufferIDRange, then the range (inclusive start, exclusive end)
   /// of IDs for source buffers added to \p SM for implicit patterns are
   /// recorded in it.  The range is empty if there are none.
   bool
-  readCheckFile(SourceMgr &SM, StringRef Buffer, Regex &PrefixRE,
+  readCheckFile(SourceMgr &SM, StringRef Buffer,
                 std::pair<unsigned, unsigned> *ImpPatBufferIDRange = nullptr);
 
   bool ValidateCheckPrefixes();

llvm/lib/FileCheck/FileCheck.cpp

@@ -1634,6 +1634,60 @@ static size_t SkipWord(StringRef Str, size_t Loc) {
   return Loc;
 }
 
+static const char *DefaultCheckPrefixes[] = {"CHECK"};
+static const char *DefaultCommentPrefixes[] = {"COM", "RUN"};
+
+static void addDefaultPrefixes(FileCheckRequest &Req) {
+  if (Req.CheckPrefixes.empty()) {
+    for (const char *Prefix : DefaultCheckPrefixes)
+      Req.CheckPrefixes.push_back(Prefix);
+    Req.IsDefaultCheckPrefix = true;
+  }
+  if (Req.CommentPrefixes.empty())
+    for (const char *Prefix : DefaultCommentPrefixes)
+      Req.CommentPrefixes.push_back(Prefix);
+}
+
+struct PrefixMatcher {
+  /// Prefixes and their first occurrence past the current position.
+  SmallVector<std::pair<StringRef, size_t>> Prefixes;
+  StringRef Input;
+
+  PrefixMatcher(ArrayRef<StringRef> CheckPrefixes,
+                ArrayRef<StringRef> CommentPrefixes, StringRef Input)
+      : Input(Input) {
+    for (StringRef Prefix : CheckPrefixes)
+      Prefixes.push_back({Prefix, Input.find(Prefix)});
+    for (StringRef Prefix : CommentPrefixes)
+      Prefixes.push_back({Prefix, Input.find(Prefix)});
+
+    // Sort by descending length.
+    llvm::sort(Prefixes,
+               [](auto A, auto B) { return A.first.size() > B.first.size(); });
+  }
+
+  /// Find the next match of a prefix in Buffer.
+  /// Returns empty StringRef if not found.
+  StringRef match(StringRef Buffer) {
+    assert(Buffer.data() >= Input.data() &&
+           Buffer.data() + Buffer.size() == Input.data() + Input.size() &&
+           "Buffer must be suffix of Input");
+
+    size_t From = Buffer.data() - Input.data();
+    StringRef Match;
+    for (auto &[Prefix, Pos] : Prefixes) {
+      // If the last occurrence was before From, find the next one after From.
+      if (Pos < From)
+        Pos = Input.find(Prefix, From);
+      // Find the first prefix with the lowest position.
+      if (Pos != StringRef::npos &&
+          (Match.empty() || size_t(Match.data() - Input.data()) > Pos))
+        Match = StringRef(Input.substr(Pos, Prefix.size()));
+    }
+    return Match;
+  }
+};
+
 /// Searches the buffer for the first prefix in the prefix regular expression.
 ///
 /// This searches the buffer using the provided regular expression, however it
@@ -1658,20 +1712,16 @@ static size_t SkipWord(StringRef Str, size_t Loc) {
 /// If no valid prefix is found, the state of Buffer, LineNumber, and CheckTy
 /// is unspecified.
 static std::pair<StringRef, StringRef>
-FindFirstMatchingPrefix(const FileCheckRequest &Req, Regex &PrefixRE,
+FindFirstMatchingPrefix(const FileCheckRequest &Req, PrefixMatcher &Matcher,
                         StringRef &Buffer, unsigned &LineNumber,
                         Check::FileCheckType &CheckTy) {
-  SmallVector<StringRef, 2> Matches;
-
   while (!Buffer.empty()) {
-    // Find the first (longest) match using the RE.
-    if (!PrefixRE.match(Buffer, &Matches))
+    // Find the first (longest) prefix match.
+    StringRef Prefix = Matcher.match(Buffer);
+    if (Prefix.empty())
       // No match at all, bail.
       return {StringRef(), StringRef()};
 
-    StringRef Prefix = Matches[0];
-    Matches.clear();
-
     assert(Prefix.data() >= Buffer.data() &&
            Prefix.data() < Buffer.data() + Buffer.size() &&
            "Prefix doesn't start inside of buffer!");
@@ -1720,7 +1770,7 @@ FileCheck::FileCheck(FileCheckRequest Req)
 FileCheck::~FileCheck() = default;
 
 bool FileCheck::readCheckFile(
-    SourceMgr &SM, StringRef Buffer, Regex &PrefixRE,
+    SourceMgr &SM, StringRef Buffer,
     std::pair<unsigned, unsigned> *ImpPatBufferIDRange) {
   if (ImpPatBufferIDRange)
     ImpPatBufferIDRange->first = ImpPatBufferIDRange->second = 0;
@@ -1769,6 +1819,8 @@ bool FileCheck::readCheckFile(
   // found.
   unsigned LineNumber = 1;
 
+  addDefaultPrefixes(Req);
+  PrefixMatcher Matcher(Req.CheckPrefixes, Req.CommentPrefixes, Buffer);
   std::set<StringRef> PrefixesNotFound(Req.CheckPrefixes.begin(),
                                        Req.CheckPrefixes.end());
   const size_t DistinctPrefixes = PrefixesNotFound.size();
@@ -1779,7 +1831,7 @@ bool FileCheck::readCheckFile(
     StringRef UsedPrefix;
     StringRef AfterSuffix;
     std::tie(UsedPrefix, AfterSuffix) =
-        FindFirstMatchingPrefix(Req, PrefixRE, Buffer, LineNumber, CheckTy);
+        FindFirstMatchingPrefix(Req, Matcher, Buffer, LineNumber, CheckTy);
     if (UsedPrefix.empty())
       break;
     if (CheckTy != Check::CheckComment)
@@ -2431,9 +2483,6 @@ static bool ValidatePrefixes(StringRef Kind, StringSet<> &UniquePrefixes,
   return true;
 }
 
-static const char *DefaultCheckPrefixes[] = {"CHECK"};
-static const char *DefaultCommentPrefixes[] = {"COM", "RUN"};
-
 bool FileCheck::ValidateCheckPrefixes() {
   StringSet<> UniquePrefixes;
   // Add default prefixes to catch user-supplied duplicates of them below.
@@ -2454,33 +2503,6 @@ bool FileCheck::ValidateCheckPrefixes() {
   return true;
 }
 
-Regex FileCheck::buildCheckPrefixRegex() {
-  if (Req.CheckPrefixes.empty()) {
-    for (const char *Prefix : DefaultCheckPrefixes)
-      Req.CheckPrefixes.push_back(Prefix);
-    Req.IsDefaultCheckPrefix = true;
-  }
-  if (Req.CommentPrefixes.empty()) {
-    for (const char *Prefix : DefaultCommentPrefixes)
-      Req.CommentPrefixes.push_back(Prefix);
-  }
-
-  // We already validated the contents of CheckPrefixes and CommentPrefixes so
-  // just concatenate them as alternatives.
-  SmallString<32> PrefixRegexStr;
-  for (size_t I = 0, E = Req.CheckPrefixes.size(); I != E; ++I) {
-    if (I != 0)
-      PrefixRegexStr.push_back('|');
-    PrefixRegexStr.append(Req.CheckPrefixes[I]);
-  }
-  for (StringRef Prefix : Req.CommentPrefixes) {
-    PrefixRegexStr.push_back('|');
-    PrefixRegexStr.append(Prefix);
-  }
-
-  return Regex(PrefixRegexStr);
-}
-
 Error FileCheckPatternContext::defineCmdlineVariables(
     ArrayRef<StringRef> CmdlineDefines, SourceMgr &SM) {
   assert(GlobalVariableTable.empty() && GlobalNumericVariableTable.empty() &&

llvm/unittests/CodeGen/GlobalISel/GISelMITest.h

@@ -189,8 +189,7 @@ static inline bool CheckMachineFunction(const MachineFunction &MF,
   SourceMgr SM;
   SM.AddNewSourceBuffer(MemoryBuffer::getMemBuffer(CheckFileText, "CheckFile"),
                         SMLoc());
-  Regex PrefixRE = FC.buildCheckPrefixRegex();
-  if (FC.readCheckFile(SM, CheckFileText, PrefixRE))
+  if (FC.readCheckFile(SM, CheckFileText))
     return false;
 
   auto OutBuffer = OutputBuf->getBuffer();

llvm/unittests/MIR/MachineMetadata.cpp

@@ -193,8 +193,7 @@ static bool checkOutput(std::string CheckString, std::string Output) {
   SourceMgr SM;
   SM.AddNewSourceBuffer(MemoryBuffer::getMemBuffer(CheckFileText, "CheckFile"),
                         SMLoc());
-  Regex PrefixRE = FC.buildCheckPrefixRegex();
-  if (FC.readCheckFile(SM, CheckFileText, PrefixRE))
+  if (FC.readCheckFile(SM, CheckFileText))
     return false;
 
   auto OutBuffer = OutputBuffer->getBuffer();

llvm/utils/FileCheck/FileCheck.cpp

@@ -810,17 +810,6 @@ int main(int argc, char **argv) {
   if (!FC.ValidateCheckPrefixes())
     return 2;
 
-  Regex PrefixRE = FC.buildCheckPrefixRegex();
-  std::string REError;
-  if (!PrefixRE.isValid(REError)) {
-    errs() << "Unable to combine check-prefix strings into a prefix regular "
-              "expression! This is likely a bug in FileCheck's verification of "
-              "the check-prefix strings. Regular expression parsing failed "
-              "with the following error: "
-           << REError << "\n";
-    return 2;
-  }
-
   SourceMgr SM;
 
   // Read the expected strings from the check file.
@@ -842,7 +831,7 @@ int main(int argc, char **argv) {
                             SMLoc());
 
   std::pair<unsigned, unsigned> ImpPatBufferIDRange;
-  if (FC.readCheckFile(SM, CheckFileText, PrefixRE, &ImpPatBufferIDRange))
+  if (FC.readCheckFile(SM, CheckFileText, &ImpPatBufferIDRange))
     return 2;
 
   // Open the file to check and add it to SourceMgr.