Refactor FileCheck to make it usable as an API

https://reviews.llvm.org/D50283
reviewed by bogner

This patch refactors FileCheck's implementation into support so it can
be used from C++ in other places (Unit tests).

llvm-svn: 339192

1 files changed, 1340 insertions, 0 deletions

diff --git a/llvm/lib/Support/FileCheck.cpp b/llvm/lib/Support/FileCheck.cpp
new file mode 100644
index 0000000..386fa80
--- /dev/null
+++ b/llvm/lib/Support/FileCheck.cpp
@@ -0,0 +1,1340 @@
+//===- FileCheck.cpp - Check that File's Contents match what is expected --===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// FileCheck does a line-by line check of a file that validates whether it
+// contains the expected content.  This is useful for regression tests etc.
+//
+// This file implements most of the API that will be used by the FileCheck utility
+// as well as various unittests.
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Support/FileCheck.h"
+#include "llvm/ADT/StringSet.h"
+#include <list>
+#include <map>
+
+using namespace llvm;
+
+/// Parses the given string into the Pattern.
+///
+/// \p Prefix provides which prefix is being matched, \p SM provides the
+/// SourceMgr used for error reports, and \p LineNumber is the line number in
+/// the input file from which the pattern string was read. Returns true in
+/// case of an error, false otherwise.
+bool FileCheckPattern::ParsePattern(StringRef PatternStr, StringRef Prefix,
+                           SourceMgr &SM, unsigned LineNumber,
+                           const FileCheckRequest &Req) {
+  bool MatchFullLinesHere = Req.MatchFullLines && CheckTy != Check::CheckNot;
+
+  this->LineNumber = LineNumber;
+  PatternLoc = SMLoc::getFromPointer(PatternStr.data());
+
+  if (!(Req.NoCanonicalizeWhiteSpace && Req.MatchFullLines))
+    // Ignore trailing whitespace.
+    while (!PatternStr.empty() &&
+           (PatternStr.back() == ' ' || PatternStr.back() == '\t'))
+      PatternStr = PatternStr.substr(0, PatternStr.size() - 1);
+
+  // Check that there is something on the line.
+  if (PatternStr.empty() && CheckTy != Check::CheckEmpty) {
+    SM.PrintMessage(PatternLoc, SourceMgr::DK_Error,
+                    "found empty check string with prefix '" + Prefix + ":'");
+    return true;
+  }
+
+  if (!PatternStr.empty() && CheckTy == Check::CheckEmpty) {
+    SM.PrintMessage(
+        PatternLoc, SourceMgr::DK_Error,
+        "found non-empty check string for empty check with prefix '" + Prefix +
+            ":'");
+    return true;
+  }
+
+  if (CheckTy == Check::CheckEmpty) {
+    RegExStr = "(\n$)";
+    return false;
+  }
+
+  // Check to see if this is a fixed string, or if it has regex pieces.
+  if (!MatchFullLinesHere &&
+      (PatternStr.size() < 2 || (PatternStr.find("{{") == StringRef::npos &&
+                                 PatternStr.find("[[") == StringRef::npos))) {
+    FixedStr = PatternStr;
+    return false;
+  }
+
+  if (MatchFullLinesHere) {
+    RegExStr += '^';
+    if (!Req.NoCanonicalizeWhiteSpace)
+      RegExStr += " *";
+  }
+
+  // Paren value #0 is for the fully matched string.  Any new parenthesized
+  // values add from there.
+  unsigned CurParen = 1;
+
+  // Otherwise, there is at least one regex piece.  Build up the regex pattern
+  // by escaping scary characters in fixed strings, building up one big regex.
+  while (!PatternStr.empty()) {
+    // RegEx matches.
+    if (PatternStr.startswith("{{")) {
+      // This is the start of a regex match.  Scan for the }}.
+      size_t End = PatternStr.find("}}");
+      if (End == StringRef::npos) {
+        SM.PrintMessage(SMLoc::getFromPointer(PatternStr.data()),
+                        SourceMgr::DK_Error,
+                        "found start of regex string with no end '}}'");
+        return true;
+      }
+
+      // Enclose {{}} patterns in parens just like [[]] even though we're not
+      // capturing the result for any purpose.  This is required in case the
+      // expression contains an alternation like: CHECK:  abc{{x|z}}def.  We
+      // want this to turn into: "abc(x|z)def" not "abcx|zdef".
+      RegExStr += '(';
+      ++CurParen;
+
+      if (AddRegExToRegEx(PatternStr.substr(2, End - 2), CurParen, SM))
+        return true;
+      RegExStr += ')';
+
+      PatternStr = PatternStr.substr(End + 2);
+      continue;
+    }
+
+    // Named RegEx matches.  These are of two forms: [[foo:.*]] which matches .*
+    // (or some other regex) and assigns it to the FileCheck variable 'foo'. The
+    // second form is [[foo]] which is a reference to foo.  The variable name
+    // itself must be of the form "[a-zA-Z_][0-9a-zA-Z_]*", otherwise we reject
+    // it.  This is to catch some common errors.
+    if (PatternStr.startswith("[[")) {
+      // Find the closing bracket pair ending the match.  End is going to be an
+      // offset relative to the beginning of the match string.
+      size_t End = FindRegexVarEnd(PatternStr.substr(2), SM);
+
+      if (End == StringRef::npos) {
+        SM.PrintMessage(SMLoc::getFromPointer(PatternStr.data()),
+                        SourceMgr::DK_Error,
+                        "invalid named regex reference, no ]] found");
+        return true;
+      }
+
+      StringRef MatchStr = PatternStr.substr(2, End);
+      PatternStr = PatternStr.substr(End + 4);
+
+      // Get the regex name (e.g. "foo").
+      size_t NameEnd = MatchStr.find(':');
+      StringRef Name = MatchStr.substr(0, NameEnd);
+
+      if (Name.empty()) {
+        SM.PrintMessage(SMLoc::getFromPointer(Name.data()), SourceMgr::DK_Error,
+                        "invalid name in named regex: empty name");
+        return true;
+      }
+
+      // Verify that the name/expression is well formed. FileCheck currently
+      // supports @LINE, @LINE+number, @LINE-number expressions. The check here
+      // is relaxed, more strict check is performed in \c EvaluateExpression.
+      bool IsExpression = false;
+      for (unsigned i = 0, e = Name.size(); i != e; ++i) {
+        if (i == 0) {
+          if (Name[i] == '$')  // Global vars start with '$'
+            continue;
+          if (Name[i] == '@') {
+            if (NameEnd != StringRef::npos) {
+              SM.PrintMessage(SMLoc::getFromPointer(Name.data()),
+                              SourceMgr::DK_Error,
+                              "invalid name in named regex definition");
+              return true;
+            }
+            IsExpression = true;
+            continue;
+          }
+        }
+        if (Name[i] != '_' && !isalnum(Name[i]) &&
+            (!IsExpression || (Name[i] != '+' && Name[i] != '-'))) {
+          SM.PrintMessage(SMLoc::getFromPointer(Name.data() + i),
+                          SourceMgr::DK_Error, "invalid name in named regex");
+          return true;
+        }
+      }
+
+      // Name can't start with a digit.
+      if (isdigit(static_cast<unsigned char>(Name[0]))) {
+        SM.PrintMessage(SMLoc::getFromPointer(Name.data()), SourceMgr::DK_Error,
+                        "invalid name in named regex");
+        return true;
+      }
+
+      // Handle [[foo]].
+      if (NameEnd == StringRef::npos) {
+        // Handle variables that were defined earlier on the same line by
+        // emitting a backreference.
+        if (VariableDefs.find(Name) != VariableDefs.end()) {
+          unsigned VarParenNum = VariableDefs[Name];
+          if (VarParenNum < 1 || VarParenNum > 9) {
+            SM.PrintMessage(SMLoc::getFromPointer(Name.data()),
+                            SourceMgr::DK_Error,
+                            "Can't back-reference more than 9 variables");
+            return true;
+          }
+          AddBackrefToRegEx(VarParenNum);
+        } else {
+          VariableUses.push_back(std::make_pair(Name, RegExStr.size()));
+        }
+        continue;
+      }
+
+      // Handle [[foo:.*]].
+      VariableDefs[Name] = CurParen;
+      RegExStr += '(';
+      ++CurParen;
+
+      if (AddRegExToRegEx(MatchStr.substr(NameEnd + 1), CurParen, SM))
+        return true;
+
+      RegExStr += ')';
+    }
+
+    // Handle fixed string matches.
+    // Find the end, which is the start of the next regex.
+    size_t FixedMatchEnd = PatternStr.find("{{");
+    FixedMatchEnd = std::min(FixedMatchEnd, PatternStr.find("[["));
+    RegExStr += Regex::escape(PatternStr.substr(0, FixedMatchEnd));
+    PatternStr = PatternStr.substr(FixedMatchEnd);
+  }
+
+  if (MatchFullLinesHere) {
+    if (!Req.NoCanonicalizeWhiteSpace)
+      RegExStr += " *";
+    RegExStr += '$';
+  }
+
+  return false;
+}
+
+bool FileCheckPattern::AddRegExToRegEx(StringRef RS, unsigned &CurParen, SourceMgr &SM) {
+  Regex R(RS);
+  std::string Error;
+  if (!R.isValid(Error)) {
+    SM.PrintMessage(SMLoc::getFromPointer(RS.data()), SourceMgr::DK_Error,
+                    "invalid regex: " + Error);
+    return true;
+  }
+
+  RegExStr += RS.str();
+  CurParen += R.getNumMatches();
+  return false;
+}
+
+void FileCheckPattern::AddBackrefToRegEx(unsigned BackrefNum) {
+  assert(BackrefNum >= 1 && BackrefNum <= 9 && "Invalid backref number");
+  std::string Backref = std::string("\\") + std::string(1, '0' + BackrefNum);
+  RegExStr += Backref;
+}
+
+/// Evaluates expression and stores the result to \p Value.
+///
+/// Returns true on success and false when the expression has invalid syntax.
+bool FileCheckPattern::EvaluateExpression(StringRef Expr, std::string &Value) const {
+  // The only supported expression is @LINE([\+-]\d+)?
+  if (!Expr.startswith("@LINE"))
+    return false;
+  Expr = Expr.substr(StringRef("@LINE").size());
+  int Offset = 0;
+  if (!Expr.empty()) {
+    if (Expr[0] == '+')
+      Expr = Expr.substr(1);
+    else if (Expr[0] != '-')
+      return false;
+    if (Expr.getAsInteger(10, Offset))
+      return false;
+  }
+  Value = llvm::itostr(LineNumber + Offset);
+  return true;
+}
+
+/// Matches the pattern string against the input buffer \p Buffer
+///
+/// This returns the position that is matched or npos if there is no match. If
+/// there is a match, the size of the matched string is returned in \p
+/// MatchLen.
+///
+/// The \p VariableTable StringMap provides the current values of filecheck
+/// variables and is updated if this match defines new values.
+size_t FileCheckPattern::Match(StringRef Buffer, size_t &MatchLen,
+                      StringMap<StringRef> &VariableTable) const {
+  // If this is the EOF pattern, match it immediately.
+  if (CheckTy == Check::CheckEOF) {
+    MatchLen = 0;
+    return Buffer.size();
+  }
+
+  // If this is a fixed string pattern, just match it now.
+  if (!FixedStr.empty()) {
+    MatchLen = FixedStr.size();
+    return Buffer.find(FixedStr);
+  }
+
+  // Regex match.
+
+  // If there are variable uses, we need to create a temporary string with the
+  // actual value.
+  StringRef RegExToMatch = RegExStr;
+  std::string TmpStr;
+  if (!VariableUses.empty()) {
+    TmpStr = RegExStr;
+
+    unsigned InsertOffset = 0;
+    for (const auto &VariableUse : VariableUses) {
+      std::string Value;
+
+      if (VariableUse.first[0] == '@') {
+        if (!EvaluateExpression(VariableUse.first, Value))
+          return StringRef::npos;
+      } else {
+        StringMap<StringRef>::iterator it =
+            VariableTable.find(VariableUse.first);
+        // If the variable is undefined, return an error.
+        if (it == VariableTable.end())
+          return StringRef::npos;
+
+        // Look up the value and escape it so that we can put it into the regex.
+        Value += Regex::escape(it->second);
+      }
+
+      // Plop it into the regex at the adjusted offset.
+      TmpStr.insert(TmpStr.begin() + VariableUse.second + InsertOffset,
+                    Value.begin(), Value.end());
+      InsertOffset += Value.size();
+    }
+
+    // Match the newly constructed regex.
+    RegExToMatch = TmpStr;
+  }
+
+  SmallVector<StringRef, 4> MatchInfo;
+  if (!Regex(RegExToMatch, Regex::Newline).match(Buffer, &MatchInfo))
+    return StringRef::npos;
+
+  // Successful regex match.
+  assert(!MatchInfo.empty() && "Didn't get any match");
+  StringRef FullMatch = MatchInfo[0];
+
+  // If this defines any variables, remember their values.
+  for (const auto &VariableDef : VariableDefs) {
+    assert(VariableDef.second < MatchInfo.size() && "Internal paren error");
+    VariableTable[VariableDef.first] = MatchInfo[VariableDef.second];
+  }
+
+  // Like CHECK-NEXT, CHECK-EMPTY's match range is considered to start after
+  // the required preceding newline, which is consumed by the pattern in the
+  // case of CHECK-EMPTY but not CHECK-NEXT.
+  size_t MatchStartSkip = CheckTy == Check::CheckEmpty;
+  MatchLen = FullMatch.size() - MatchStartSkip;
+  return FullMatch.data() - Buffer.data() + MatchStartSkip;
+}
+
+
+/// Computes an arbitrary estimate for the quality of matching this pattern at
+/// the start of \p Buffer; a distance of zero should correspond to a perfect
+/// match.
+unsigned
+FileCheckPattern::ComputeMatchDistance(StringRef Buffer,
+                              const StringMap<StringRef> &VariableTable) const {
+  // Just compute the number of matching characters. For regular expressions, we
+  // just compare against the regex itself and hope for the best.
+  //
+  // FIXME: One easy improvement here is have the regex lib generate a single
+  // example regular expression which matches, and use that as the example
+  // string.
+  StringRef ExampleString(FixedStr);
+  if (ExampleString.empty())
+    ExampleString = RegExStr;
+
+  // Only compare up to the first line in the buffer, or the string size.
+  StringRef BufferPrefix = Buffer.substr(0, ExampleString.size());
+  BufferPrefix = BufferPrefix.split('\n').first;
+  return BufferPrefix.edit_distance(ExampleString);
+}
+
+void FileCheckPattern::PrintVariableUses(const SourceMgr &SM, StringRef Buffer,
+                                const StringMap<StringRef> &VariableTable,
+                                SMRange MatchRange) const {
+  // If this was a regular expression using variables, print the current
+  // variable values.
+  if (!VariableUses.empty()) {
+    for (const auto &VariableUse : VariableUses) {
+      SmallString<256> Msg;
+      raw_svector_ostream OS(Msg);
+      StringRef Var = VariableUse.first;
+      if (Var[0] == '@') {
+        std::string Value;
+        if (EvaluateExpression(Var, Value)) {
+          OS << "with expression \"";
+          OS.write_escaped(Var) << "\" equal to \"";
+          OS.write_escaped(Value) << "\"";
+        } else {
+          OS << "uses incorrect expression \"";
+          OS.write_escaped(Var) << "\"";
+        }
+      } else {
+        StringMap<StringRef>::const_iterator it = VariableTable.find(Var);
+
+        // Check for undefined variable references.
+        if (it == VariableTable.end()) {
+          OS << "uses undefined variable \"";
+          OS.write_escaped(Var) << "\"";
+        } else {
+          OS << "with variable \"";
+          OS.write_escaped(Var) << "\" equal to \"";
+          OS.write_escaped(it->second) << "\"";
+        }
+      }
+
+      if (MatchRange.isValid())
+        SM.PrintMessage(MatchRange.Start, SourceMgr::DK_Note, OS.str(),
+                        {MatchRange});
+      else
+        SM.PrintMessage(SMLoc::getFromPointer(Buffer.data()),
+                        SourceMgr::DK_Note, OS.str());
+    }
+  }
+}
+
+void FileCheckPattern::PrintFuzzyMatch(
+    const SourceMgr &SM, StringRef Buffer,
+    const StringMap<StringRef> &VariableTable) const {
+  // Attempt to find the closest/best fuzzy match.  Usually an error happens
+  // because some string in the output didn't exactly match. In these cases, we
+  // would like to show the user a best guess at what "should have" matched, to
+  // save them having to actually check the input manually.
+  size_t NumLinesForward = 0;
+  size_t Best = StringRef::npos;
+  double BestQuality = 0;
+
+  // Use an arbitrary 4k limit on how far we will search.
+  for (size_t i = 0, e = std::min(size_t(4096), Buffer.size()); i != e; ++i) {
+    if (Buffer[i] == '\n')
+      ++NumLinesForward;
+
+    // Patterns have leading whitespace stripped, so skip whitespace when
+    // looking for something which looks like a pattern.
+    if (Buffer[i] == ' ' || Buffer[i] == '\t')
+      continue;
+
+    // Compute the "quality" of this match as an arbitrary combination of the
+    // match distance and the number of lines skipped to get to this match.
+    unsigned Distance = ComputeMatchDistance(Buffer.substr(i), VariableTable);
+    double Quality = Distance + (NumLinesForward / 100.);
+
+    if (Quality < BestQuality || Best == StringRef::npos) {
+      Best = i;
+      BestQuality = Quality;
+    }
+  }
+
+  // Print the "possible intended match here" line if we found something
+  // reasonable and not equal to what we showed in the "scanning from here"
+  // line.
+  if (Best && Best != StringRef::npos && BestQuality < 50) {
+    SM.PrintMessage(SMLoc::getFromPointer(Buffer.data() + Best),
+                    SourceMgr::DK_Note, "possible intended match here");
+
+    // FIXME: If we wanted to be really friendly we would show why the match
+    // failed, as it can be hard to spot simple one character differences.
+  }
+}
+
+/// Finds the closing sequence of a regex variable usage or definition.
+///
+/// \p Str has to point in the beginning of the definition (right after the
+/// opening sequence). Returns the offset of the closing sequence within Str,
+/// or npos if it was not found.
+size_t FileCheckPattern::FindRegexVarEnd(StringRef Str, SourceMgr &SM) {
+  // Offset keeps track of the current offset within the input Str
+  size_t Offset = 0;
+  // [...] Nesting depth
+  size_t BracketDepth = 0;
+
+  while (!Str.empty()) {
+    if (Str.startswith("]]") && BracketDepth == 0)
+      return Offset;
+    if (Str[0] == '\\') {
+      // Backslash escapes the next char within regexes, so skip them both.
+      Str = Str.substr(2);
+      Offset += 2;
+    } else {
+      switch (Str[0]) {
+      default:
+        break;
+      case '[':
+        BracketDepth++;
+        break;
+      case ']':
+        if (BracketDepth == 0) {
+          SM.PrintMessage(SMLoc::getFromPointer(Str.data()),
+                          SourceMgr::DK_Error,
+                          "missing closing \"]\" for regex variable");
+          exit(1);
+        }
+        BracketDepth--;
+        break;
+      }
+      Str = Str.substr(1);
+      Offset++;
+    }
+  }
+
+  return StringRef::npos;
+}
+
+/// Canonicalize whitespaces in the file. Line endings are replaced with
+/// UNIX-style '\n'.
+StringRef
+llvm::FileCheck::CanonicalizeFile(MemoryBuffer &MB,
+                                  SmallVectorImpl<char> &OutputBuffer) {
+  OutputBuffer.reserve(MB.getBufferSize());
+
+  for (const char *Ptr = MB.getBufferStart(), *End = MB.getBufferEnd();
+       Ptr != End; ++Ptr) {
+    // Eliminate trailing dosish \r.
+    if (Ptr <= End - 2 && Ptr[0] == '\r' && Ptr[1] == '\n') {
+      continue;
+    }
+
+    // If current char is not a horizontal whitespace or if horizontal
+    // whitespace canonicalization is disabled, dump it to output as is.
+    if (Req.NoCanonicalizeWhiteSpace || (*Ptr != ' ' && *Ptr != '\t')) {
+      OutputBuffer.push_back(*Ptr);
+      continue;
+    }
+
+    // Otherwise, add one space and advance over neighboring space.
+    OutputBuffer.push_back(' ');
+    while (Ptr + 1 != End && (Ptr[1] == ' ' || Ptr[1] == '\t'))
+      ++Ptr;
+  }
+
+  // Add a null byte and then return all but that byte.
+  OutputBuffer.push_back('\0');
+  return StringRef(OutputBuffer.data(), OutputBuffer.size() - 1);
+}
+
+static bool IsPartOfWord(char c) {
+  return (isalnum(c) || c == '-' || c == '_');
+}
+
+// Get the size of the prefix extension.
+static size_t CheckTypeSize(Check::FileCheckType Ty) {
+  switch (Ty) {
+  case Check::CheckNone:
+  case Check::CheckBadNot:
+    return 0;
+
+  case Check::CheckPlain:
+    return sizeof(":") - 1;
+
+  case Check::CheckNext:
+    return sizeof("-NEXT:") - 1;
+
+  case Check::CheckSame:
+    return sizeof("-SAME:") - 1;
+
+  case Check::CheckNot:
+    return sizeof("-NOT:") - 1;
+
+  case Check::CheckDAG:
+    return sizeof("-DAG:") - 1;
+
+  case Check::CheckLabel:
+    return sizeof("-LABEL:") - 1;
+
+  case Check::CheckEmpty:
+    return sizeof("-EMPTY:") - 1;
+
+  case Check::CheckEOF:
+    llvm_unreachable("Should not be using EOF size");
+  }
+
+  llvm_unreachable("Bad check type");
+}
+
+// Get a description of the type.
+static std::string CheckTypeName(StringRef Prefix, Check::FileCheckType Ty) {
+  switch (Ty) {
+  case Check::CheckNone:
+    return "invalid";
+  case Check::CheckPlain:
+    return Prefix;
+  case Check::CheckNext:
+    return Prefix.str() + "-NEXT";
+  case Check::CheckSame:
+    return Prefix.str() + "-SAME";
+  case Check::CheckNot:
+    return Prefix.str() + "-NOT";
+  case Check::CheckDAG:
+    return Prefix.str() + "-DAG";
+  case Check::CheckLabel:
+    return Prefix.str() + "-LABEL";
+  case Check::CheckEmpty:
+    return Prefix.str() + "-EMPTY";
+  case Check::CheckEOF:
+    return "implicit EOF";
+  case Check::CheckBadNot:
+    return "bad NOT";
+  }
+  llvm_unreachable("unknown FileCheckType");
+}
+
+static Check::FileCheckType FindCheckType(StringRef Buffer, StringRef Prefix) {
+  if (Buffer.size() <= Prefix.size())
+    return Check::CheckNone;
+
+  char NextChar = Buffer[Prefix.size()];
+
+  // Verify that the : is present after the prefix.
+  if (NextChar == ':')
+    return Check::CheckPlain;
+
+  if (NextChar != '-')
+    return Check::CheckNone;
+
+  StringRef Rest = Buffer.drop_front(Prefix.size() + 1);
+  if (Rest.startswith("NEXT:"))
+    return Check::CheckNext;
+
+  if (Rest.startswith("SAME:"))
+    return Check::CheckSame;
+
+  if (Rest.startswith("NOT:"))
+    return Check::CheckNot;
+
+  if (Rest.startswith("DAG:"))
+    return Check::CheckDAG;
+
+  if (Rest.startswith("LABEL:"))
+    return Check::CheckLabel;
+
+  if (Rest.startswith("EMPTY:"))
+    return Check::CheckEmpty;
+
+  // You can't combine -NOT with another suffix.
+  if (Rest.startswith("DAG-NOT:") || Rest.startswith("NOT-DAG:") ||
+      Rest.startswith("NEXT-NOT:") || Rest.startswith("NOT-NEXT:") ||
+      Rest.startswith("SAME-NOT:") || Rest.startswith("NOT-SAME:") ||
+      Rest.startswith("EMPTY-NOT:") || Rest.startswith("NOT-EMPTY:"))
+    return Check::CheckBadNot;
+
+  return Check::CheckNone;
+}
+
+// From the given position, find the next character after the word.
+static size_t SkipWord(StringRef Str, size_t Loc) {
+  while (Loc < Str.size() && IsPartOfWord(Str[Loc]))
+    ++Loc;
+  return Loc;
+}
+
+/// Search the buffer for the first prefix in the prefix regular expression.
+///
+/// This searches the buffer using the provided regular expression, however it
+/// enforces constraints beyond that:
+/// 1) The found prefix must not be a suffix of something that looks like
+///    a valid prefix.
+/// 2) The found prefix must be followed by a valid check type suffix using \c
+///    FindCheckType above.
+///
+/// The first match of the regular expression to satisfy these two is returned,
+/// otherwise an empty StringRef is returned to indicate failure.
+///
+/// If this routine returns a valid prefix, it will also shrink \p Buffer to
+/// start at the beginning of the returned prefix, increment \p LineNumber for
+/// each new line consumed from \p Buffer, and set \p CheckTy to the type of
+/// check found by examining the suffix.
+///
+/// If no valid prefix is found, the state of Buffer, LineNumber, and CheckTy
+/// is unspecified.
+static StringRef FindFirstMatchingPrefix(Regex &PrefixRE, 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))
+      // No match at all, bail.
+      return 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!");
+    size_t Loc = Prefix.data() - Buffer.data();
+    StringRef Skipped = Buffer.substr(0, Loc);
+    Buffer = Buffer.drop_front(Loc);
+    LineNumber += Skipped.count('\n');
+
+    // Check that the matched prefix isn't a suffix of some other check-like
+    // word.
+    // FIXME: This is a very ad-hoc check. it would be better handled in some
+    // other way. Among other things it seems hard to distinguish between
+    // intentional and unintentional uses of this feature.
+    if (Skipped.empty() || !IsPartOfWord(Skipped.back())) {
+      // Now extract the type.
+      CheckTy = FindCheckType(Buffer, Prefix);
+
+      // If we've found a valid check type for this prefix, we're done.
+      if (CheckTy != Check::CheckNone)
+        return Prefix;
+    }
+
+    // If we didn't successfully find a prefix, we need to skip this invalid
+    // prefix and continue scanning. We directly skip the prefix that was
+    // matched and any additional parts of that check-like word.
+    Buffer = Buffer.drop_front(SkipWord(Buffer, Prefix.size()));
+  }
+
+  // We ran out of buffer while skipping partial matches so give up.
+  return StringRef();
+}
+
+/// Read the check file, which specifies the sequence of expected strings.
+///
+/// The strings are added to the CheckStrings vector. Returns true in case of
+/// an error, false otherwise.
+bool llvm::FileCheck::ReadCheckFile(SourceMgr &SM, StringRef Buffer,
+                                    Regex &PrefixRE,
+                                    std::vector<FileCheckString> &CheckStrings) {
+  std::vector<FileCheckPattern> ImplicitNegativeChecks;
+  for (const auto &PatternString : Req.ImplicitCheckNot) {
+    // Create a buffer with fake command line content in order to display the
+    // command line option responsible for the specific implicit CHECK-NOT.
+    std::string Prefix = "-implicit-check-not='";
+    std::string Suffix = "'";
+    std::unique_ptr<MemoryBuffer> CmdLine = MemoryBuffer::getMemBufferCopy(
+        Prefix + PatternString + Suffix, "command line");
+
+    StringRef PatternInBuffer =
+        CmdLine->getBuffer().substr(Prefix.size(), PatternString.size());
+    SM.AddNewSourceBuffer(std::move(CmdLine), SMLoc());
+
+    ImplicitNegativeChecks.push_back(FileCheckPattern(Check::CheckNot));
+    ImplicitNegativeChecks.back().ParsePattern(PatternInBuffer,
+                                               "IMPLICIT-CHECK", SM, 0, Req);
+  }
+
+  std::vector<FileCheckPattern> DagNotMatches = ImplicitNegativeChecks;
+
+  // LineNumber keeps track of the line on which CheckPrefix instances are
+  // found.
+  unsigned LineNumber = 1;
+
+  while (1) {
+    Check::FileCheckType CheckTy;
+
+    // See if a prefix occurs in the memory buffer.
+    StringRef UsedPrefix = FindFirstMatchingPrefix(PrefixRE, Buffer, LineNumber,
+                                                   CheckTy);
+    if (UsedPrefix.empty())
+      break;
+    assert(UsedPrefix.data() == Buffer.data() &&
+           "Failed to move Buffer's start forward, or pointed prefix outside "
+           "of the buffer!");
+
+    // Location to use for error messages.
+    const char *UsedPrefixStart = UsedPrefix.data();
+
+    // Skip the buffer to the end.
+    Buffer = Buffer.drop_front(UsedPrefix.size() + CheckTypeSize(CheckTy));
+
+    // Complain about useful-looking but unsupported suffixes.
+    if (CheckTy == Check::CheckBadNot) {
+      SM.PrintMessage(SMLoc::getFromPointer(Buffer.data()), SourceMgr::DK_Error,
+                      "unsupported -NOT combo on prefix '" + UsedPrefix + "'");
+      return true;
+    }
+
+    // Okay, we found the prefix, yay. Remember the rest of the line, but ignore
+    // leading whitespace.
+    if (!(Req.NoCanonicalizeWhiteSpace && Req.MatchFullLines))
+      Buffer = Buffer.substr(Buffer.find_first_not_of(" \t"));
+
+    // Scan ahead to the end of line.
+    size_t EOL = Buffer.find_first_of("\n\r");
+
+    // Remember the location of the start of the pattern, for diagnostics.
+    SMLoc PatternLoc = SMLoc::getFromPointer(Buffer.data());
+
+    // Parse the pattern.
+    FileCheckPattern P(CheckTy);
+    if (P.ParsePattern(Buffer.substr(0, EOL), UsedPrefix, SM, LineNumber, Req))
+      return true;
+
+    // Verify that CHECK-LABEL lines do not define or use variables
+    if ((CheckTy == Check::CheckLabel) && P.hasVariable()) {
+      SM.PrintMessage(
+          SMLoc::getFromPointer(UsedPrefixStart), SourceMgr::DK_Error,
+          "found '" + UsedPrefix + "-LABEL:'"
+                                   " with variable definition or use");
+      return true;
+    }
+
+    Buffer = Buffer.substr(EOL);
+
+    // Verify that CHECK-NEXT/SAME/EMPTY lines have at least one CHECK line before them.
+    if ((CheckTy == Check::CheckNext || CheckTy == Check::CheckSame ||
+         CheckTy == Check::CheckEmpty) &&
+        CheckStrings.empty()) {
+      StringRef Type = CheckTy == Check::CheckNext
+                           ? "NEXT"
+                           : CheckTy == Check::CheckEmpty ? "EMPTY" : "SAME";
+      SM.PrintMessage(SMLoc::getFromPointer(UsedPrefixStart),
+                      SourceMgr::DK_Error,
+                      "found '" + UsedPrefix + "-" + Type +
+                          "' without previous '" + UsedPrefix + ": line");
+      return true;
+    }
+
+    // Handle CHECK-DAG/-NOT.
+    if (CheckTy == Check::CheckDAG || CheckTy == Check::CheckNot) {
+      DagNotMatches.push_back(P);
+      continue;
+    }
+
+    // Okay, add the string we captured to the output vector and move on.
+    CheckStrings.emplace_back(P, UsedPrefix, PatternLoc);
+    std::swap(DagNotMatches, CheckStrings.back().DagNotStrings);
+    DagNotMatches = ImplicitNegativeChecks;
+  }
+
+  // Add an EOF pattern for any trailing CHECK-DAG/-NOTs, and use the first
+  // prefix as a filler for the error message.
+  if (!DagNotMatches.empty()) {
+    CheckStrings.emplace_back(FileCheckPattern(Check::CheckEOF), *Req.CheckPrefixes.begin(),
+                              SMLoc::getFromPointer(Buffer.data()));
+    std::swap(DagNotMatches, CheckStrings.back().DagNotStrings);
+  }
+
+  if (CheckStrings.empty()) {
+    errs() << "error: no check strings found with prefix"
+           << (Req.CheckPrefixes.size() > 1 ? "es " : " ");
+    auto I = Req.CheckPrefixes.begin();
+    auto E = Req.CheckPrefixes.end();
+    if (I != E) {
+      errs() << "\'" << *I << ":'";
+      ++I;
+    }
+    for (; I != E; ++I)
+      errs() << ", \'" << *I << ":'";
+
+    errs() << '\n';
+    return true;
+  }
+
+  return false;
+}
+
+static void PrintMatch(bool ExpectedMatch, const SourceMgr &SM,
+                       StringRef Prefix, SMLoc Loc, const FileCheckPattern &Pat,
+                       StringRef Buffer, StringMap<StringRef> &VariableTable,
+                       size_t MatchPos, size_t MatchLen,
+                       const FileCheckRequest &Req) {
+  if (ExpectedMatch) {
+    if (!Req.Verbose)
+      return;
+    if (!Req.VerboseVerbose && Pat.getCheckTy() == Check::CheckEOF)
+      return;
+  }
+  SMLoc MatchStart = SMLoc::getFromPointer(Buffer.data() + MatchPos);
+  SMLoc MatchEnd = SMLoc::getFromPointer(Buffer.data() + MatchPos + MatchLen);
+  SMRange MatchRange(MatchStart, MatchEnd);
+  SM.PrintMessage(
+      Loc, ExpectedMatch ? SourceMgr::DK_Remark : SourceMgr::DK_Error,
+      CheckTypeName(Prefix, Pat.getCheckTy()) + ": " +
+          (ExpectedMatch ? "expected" : "excluded") +
+          " string found in input");
+  SM.PrintMessage(MatchStart, SourceMgr::DK_Note, "found here", {MatchRange});
+  Pat.PrintVariableUses(SM, Buffer, VariableTable, MatchRange);
+}
+
+static void PrintMatch(bool ExpectedMatch, const SourceMgr &SM,
+                       const FileCheckString &CheckStr, StringRef Buffer,
+                       StringMap<StringRef> &VariableTable, size_t MatchPos,
+                       size_t MatchLen, FileCheckRequest &Req) {
+  PrintMatch(ExpectedMatch, SM, CheckStr.Prefix, CheckStr.Loc, CheckStr.Pat,
+             Buffer, VariableTable, MatchPos, MatchLen, Req);
+}
+
+static void PrintNoMatch(bool ExpectedMatch, const SourceMgr &SM,
+                         StringRef Prefix, SMLoc Loc, const FileCheckPattern &Pat,
+                         StringRef Buffer,
+                         StringMap<StringRef> &VariableTable,
+                         bool VerboseVerbose) {
+  if (!ExpectedMatch && !VerboseVerbose)
+    return;
+
+  // Otherwise, we have an error, emit an error message.
+  SM.PrintMessage(Loc,
+                  ExpectedMatch ? SourceMgr::DK_Error : SourceMgr::DK_Remark,
+                  CheckTypeName(Prefix, Pat.getCheckTy()) + ": " +
+                      (ExpectedMatch ? "expected" : "excluded") +
+                      " string not found in input");
+
+  // Print the "scanning from here" line.  If the current position is at the
+  // end of a line, advance to the start of the next line.
+  Buffer = Buffer.substr(Buffer.find_first_not_of(" \t\n\r"));
+
+  SM.PrintMessage(SMLoc::getFromPointer(Buffer.data()), SourceMgr::DK_Note,
+                  "scanning from here");
+
+  // Allow the pattern to print additional information if desired.
+  Pat.PrintVariableUses(SM, Buffer, VariableTable);
+  if (ExpectedMatch)
+    Pat.PrintFuzzyMatch(SM, Buffer, VariableTable);
+}
+
+static void PrintNoMatch(bool ExpectedMatch, const SourceMgr &SM,
+                         const FileCheckString &CheckStr, StringRef Buffer,
+                         StringMap<StringRef> &VariableTable,
+                         bool VerboseVerbose) {
+  PrintNoMatch(ExpectedMatch, SM, CheckStr.Prefix, CheckStr.Loc, CheckStr.Pat,
+               Buffer, VariableTable, VerboseVerbose);
+}
+
+/// Count the number of newlines in the specified range.
+static unsigned CountNumNewlinesBetween(StringRef Range,
+                                        const char *&FirstNewLine) {
+  unsigned NumNewLines = 0;
+  while (1) {
+    // Scan for newline.
+    Range = Range.substr(Range.find_first_of("\n\r"));
+    if (Range.empty())
+      return NumNewLines;
+
+    ++NumNewLines;
+
+    // Handle \n\r and \r\n as a single newline.
+    if (Range.size() > 1 && (Range[1] == '\n' || Range[1] == '\r') &&
+        (Range[0] != Range[1]))
+      Range = Range.substr(1);
+    Range = Range.substr(1);
+
+    if (NumNewLines == 1)
+      FirstNewLine = Range.begin();
+  }
+}
+
+/// Match check string and its "not strings" and/or "dag strings".
+size_t FileCheckString::Check(const SourceMgr &SM, StringRef Buffer,
+                          bool IsLabelScanMode, size_t &MatchLen,
+                          StringMap<StringRef> &VariableTable,
+                          FileCheckRequest &Req) const {
+  size_t LastPos = 0;
+  std::vector<const FileCheckPattern *> NotStrings;
+
+  // IsLabelScanMode is true when we are scanning forward to find CHECK-LABEL
+  // bounds; we have not processed variable definitions within the bounded block
+  // yet so cannot handle any final CHECK-DAG yet; this is handled when going
+  // over the block again (including the last CHECK-LABEL) in normal mode.
+  if (!IsLabelScanMode) {
+    // Match "dag strings" (with mixed "not strings" if any).
+    LastPos = CheckDag(SM, Buffer, NotStrings, VariableTable, Req);
+    if (LastPos == StringRef::npos)
+      return StringRef::npos;
+  }
+
+  // Match itself from the last position after matching CHECK-DAG.
+  StringRef MatchBuffer = Buffer.substr(LastPos);
+  size_t MatchPos = Pat.Match(MatchBuffer, MatchLen, VariableTable);
+  if (MatchPos == StringRef::npos) {
+    PrintNoMatch(true, SM, *this, MatchBuffer, VariableTable, Req.VerboseVerbose);
+    return StringRef::npos;
+  }
+  PrintMatch(true, SM, *this, MatchBuffer, VariableTable, MatchPos, MatchLen, Req);
+
+  // Similar to the above, in "label-scan mode" we can't yet handle CHECK-NEXT
+  // or CHECK-NOT
+  if (!IsLabelScanMode) {
+    StringRef SkippedRegion = Buffer.substr(LastPos, MatchPos);
+
+    // If this check is a "CHECK-NEXT", verify that the previous match was on
+    // the previous line (i.e. that there is one newline between them).
+    if (CheckNext(SM, SkippedRegion))
+      return StringRef::npos;
+
+    // If this check is a "CHECK-SAME", verify that the previous match was on
+    // the same line (i.e. that there is no newline between them).
+    if (CheckSame(SM, SkippedRegion))
+      return StringRef::npos;
+
+    // If this match had "not strings", verify that they don't exist in the
+    // skipped region.
+    if (CheckNot(SM, SkippedRegion, NotStrings, VariableTable, Req))
+      return StringRef::npos;
+  }
+
+  return LastPos + MatchPos;
+}
+
+/// Verify there is a single line in the given buffer.
+bool FileCheckString::CheckNext(const SourceMgr &SM, StringRef Buffer) const {
+  if (Pat.getCheckTy() != Check::CheckNext &&
+      Pat.getCheckTy() != Check::CheckEmpty)
+    return false;
+
+  Twine CheckName =
+      Prefix +
+      Twine(Pat.getCheckTy() == Check::CheckEmpty ? "-EMPTY" : "-NEXT");
+
+  // Count the number of newlines between the previous match and this one.
+  assert(Buffer.data() !=
+             SM.getMemoryBuffer(SM.FindBufferContainingLoc(
+                                    SMLoc::getFromPointer(Buffer.data())))
+                 ->getBufferStart() &&
+         "CHECK-NEXT and CHECK-EMPTY can't be the first check in a file");
+
+  const char *FirstNewLine = nullptr;
+  unsigned NumNewLines = CountNumNewlinesBetween(Buffer, FirstNewLine);
+
+  if (NumNewLines == 0) {
+    SM.PrintMessage(Loc, SourceMgr::DK_Error,
+                    CheckName + ": is on the same line as previous match");
+    SM.PrintMessage(SMLoc::getFromPointer(Buffer.end()), SourceMgr::DK_Note,
+                    "'next' match was here");
+    SM.PrintMessage(SMLoc::getFromPointer(Buffer.data()), SourceMgr::DK_Note,
+                    "previous match ended here");
+    return true;
+  }
+
+  if (NumNewLines != 1) {
+    SM.PrintMessage(Loc, SourceMgr::DK_Error,
+                    CheckName +
+                        ": is not on the line after the previous match");
+    SM.PrintMessage(SMLoc::getFromPointer(Buffer.end()), SourceMgr::DK_Note,
+                    "'next' match was here");
+    SM.PrintMessage(SMLoc::getFromPointer(Buffer.data()), SourceMgr::DK_Note,
+                    "previous match ended here");
+    SM.PrintMessage(SMLoc::getFromPointer(FirstNewLine), SourceMgr::DK_Note,
+                    "non-matching line after previous match is here");
+    return true;
+  }
+
+  return false;
+}
+
+/// Verify there is no newline in the given buffer.
+bool FileCheckString::CheckSame(const SourceMgr &SM, StringRef Buffer) const {
+  if (Pat.getCheckTy() != Check::CheckSame)
+    return false;
+
+  // Count the number of newlines between the previous match and this one.
+  assert(Buffer.data() !=
+             SM.getMemoryBuffer(SM.FindBufferContainingLoc(
+                                    SMLoc::getFromPointer(Buffer.data())))
+                 ->getBufferStart() &&
+         "CHECK-SAME can't be the first check in a file");
+
+  const char *FirstNewLine = nullptr;
+  unsigned NumNewLines = CountNumNewlinesBetween(Buffer, FirstNewLine);
+
+  if (NumNewLines != 0) {
+    SM.PrintMessage(Loc, SourceMgr::DK_Error,
+                    Prefix +
+                        "-SAME: is not on the same line as the previous match");
+    SM.PrintMessage(SMLoc::getFromPointer(Buffer.end()), SourceMgr::DK_Note,
+                    "'next' match was here");
+    SM.PrintMessage(SMLoc::getFromPointer(Buffer.data()), SourceMgr::DK_Note,
+                    "previous match ended here");
+    return true;
+  }
+
+  return false;
+}
+
+/// Verify there's no "not strings" in the given buffer.
+bool FileCheckString::CheckNot(const SourceMgr &SM, StringRef Buffer,
+                           const std::vector<const FileCheckPattern *> &NotStrings,
+                           StringMap<StringRef> &VariableTable,
+                           const FileCheckRequest &Req) const {
+  for (const FileCheckPattern *Pat : NotStrings) {
+    assert((Pat->getCheckTy() == Check::CheckNot) && "Expect CHECK-NOT!");
+
+    size_t MatchLen = 0;
+    size_t Pos = Pat->Match(Buffer, MatchLen, VariableTable);
+
+    if (Pos == StringRef::npos) {
+      PrintNoMatch(false, SM, Prefix, Pat->getLoc(), *Pat, Buffer,
+                   VariableTable, Req.VerboseVerbose);
+      continue;
+    }
+
+    PrintMatch(false, SM, Prefix, Pat->getLoc(), *Pat, Buffer, VariableTable,
+               Pos, MatchLen, Req);
+
+    return true;
+  }
+
+  return false;
+}
+
+/// Match "dag strings" and their mixed "not strings".
+size_t FileCheckString::CheckDag(const SourceMgr &SM, StringRef Buffer,
+                             std::vector<const FileCheckPattern *> &NotStrings,
+                             StringMap<StringRef> &VariableTable,
+                             const FileCheckRequest &Req) const {
+  if (DagNotStrings.empty())
+    return 0;
+
+  // The start of the search range.
+  size_t StartPos = 0;
+
+  struct MatchRange {
+    size_t Pos;
+    size_t End;
+  };
+  // A sorted list of ranges for non-overlapping CHECK-DAG matches.  Match
+  // ranges are erased from this list once they are no longer in the search
+  // range.
+  std::list<MatchRange> MatchRanges;
+
+  // We need PatItr and PatEnd later for detecting the end of a CHECK-DAG
+  // group, so we don't use a range-based for loop here.
+  for (auto PatItr = DagNotStrings.begin(), PatEnd = DagNotStrings.end();
+       PatItr != PatEnd; ++PatItr) {
+    const FileCheckPattern &Pat = *PatItr;
+    assert((Pat.getCheckTy() == Check::CheckDAG ||
+            Pat.getCheckTy() == Check::CheckNot) &&
+           "Invalid CHECK-DAG or CHECK-NOT!");
+
+    if (Pat.getCheckTy() == Check::CheckNot) {
+      NotStrings.push_back(&Pat);
+      continue;
+    }
+
+    assert((Pat.getCheckTy() == Check::CheckDAG) && "Expect CHECK-DAG!");
+
+    // CHECK-DAG always matches from the start.
+    size_t MatchLen = 0, MatchPos = StartPos;
+
+    // Search for a match that doesn't overlap a previous match in this
+    // CHECK-DAG group.
+    for (auto MI = MatchRanges.begin(), ME = MatchRanges.end(); true; ++MI) {
+      StringRef MatchBuffer = Buffer.substr(MatchPos);
+      size_t MatchPosBuf = Pat.Match(MatchBuffer, MatchLen, VariableTable);
+      // With a group of CHECK-DAGs, a single mismatching means the match on
+      // that group of CHECK-DAGs fails immediately.
+      if (MatchPosBuf == StringRef::npos) {
+        PrintNoMatch(true, SM, Prefix, Pat.getLoc(), Pat, MatchBuffer,
+                     VariableTable, Req.VerboseVerbose);
+        return StringRef::npos;
+      }
+      // Re-calc it as the offset relative to the start of the original string.
+      MatchPos += MatchPosBuf;
+      if (Req.VerboseVerbose)
+        PrintMatch(true, SM, Prefix, Pat.getLoc(), Pat, Buffer, VariableTable,
+                   MatchPos, MatchLen, Req);
+      MatchRange M{MatchPos, MatchPos + MatchLen};
+      if (Req.AllowDeprecatedDagOverlap) {
+        // We don't need to track all matches in this mode, so we just maintain
+        // one match range that encompasses the current CHECK-DAG group's
+        // matches.
+        if (MatchRanges.empty())
+          MatchRanges.insert(MatchRanges.end(), M);
+        else {
+          auto Block = MatchRanges.begin();
+          Block->Pos = std::min(Block->Pos, M.Pos);
+          Block->End = std::max(Block->End, M.End);
+        }
+        break;
+      }
+      // Iterate previous matches until overlapping match or insertion point.
+      bool Overlap = false;
+      for (; MI != ME; ++MI) {
+        if (M.Pos < MI->End) {
+          // !Overlap => New match has no overlap and is before this old match.
+          // Overlap => New match overlaps this old match.
+          Overlap = MI->Pos < M.End;
+          break;
+        }
+      }
+      if (!Overlap) {
+        // Insert non-overlapping match into list.
+        MatchRanges.insert(MI, M);
+        break;
+      }
+      if (Req.VerboseVerbose) {
+        SMLoc OldStart = SMLoc::getFromPointer(Buffer.data() + MI->Pos);
+        SMLoc OldEnd = SMLoc::getFromPointer(Buffer.data() + MI->End);
+        SMRange OldRange(OldStart, OldEnd);
+        SM.PrintMessage(OldStart, SourceMgr::DK_Note,
+                        "match discarded, overlaps earlier DAG match here",
+                        {OldRange});
+      }
+      MatchPos = MI->End;
+    }
+    if (!Req.VerboseVerbose)
+      PrintMatch(true, SM, Prefix, Pat.getLoc(), Pat, Buffer, VariableTable,
+                 MatchPos, MatchLen, Req);
+
+    // Handle the end of a CHECK-DAG group.
+    if (std::next(PatItr) == PatEnd ||
+        std::next(PatItr)->getCheckTy() == Check::CheckNot) {
+      if (!NotStrings.empty()) {
+        // If there are CHECK-NOTs between two CHECK-DAGs or from CHECK to
+        // CHECK-DAG, verify that there are no 'not' strings occurred in that
+        // region.
+        StringRef SkippedRegion =
+            Buffer.slice(StartPos, MatchRanges.begin()->Pos);
+        if (CheckNot(SM, SkippedRegion, NotStrings, VariableTable, Req))
+          return StringRef::npos;
+        // Clear "not strings".
+        NotStrings.clear();
+      }
+      // All subsequent CHECK-DAGs and CHECK-NOTs should be matched from the
+      // end of this CHECK-DAG group's match range.
+      StartPos = MatchRanges.rbegin()->End;
+      // Don't waste time checking for (impossible) overlaps before that.
+      MatchRanges.clear();
+    }
+  }
+
+  return StartPos;
+}
+
+// A check prefix must contain only alphanumeric, hyphens and underscores.
+static bool ValidateCheckPrefix(StringRef CheckPrefix) {
+  Regex Validator("^[a-zA-Z0-9_-]*$");
+  return Validator.match(CheckPrefix);
+}
+
+bool llvm::FileCheck::ValidateCheckPrefixes() {
+  StringSet<> PrefixSet;
+
+  for (StringRef Prefix : Req.CheckPrefixes) {
+    // Reject empty prefixes.
+    if (Prefix == "")
+      return false;
+
+    if (!PrefixSet.insert(Prefix).second)
+      return false;
+
+    if (!ValidateCheckPrefix(Prefix))
+      return false;
+  }
+
+  return true;
+}
+
+// Combines the check prefixes into a single regex so that we can efficiently
+// scan for any of the set.
+//
+// The semantics are that the longest-match wins which matches our regex
+// library.
+Regex llvm::FileCheck::buildCheckPrefixRegex() {
+  // I don't think there's a way to specify an initial value for cl::list,
+  // so if nothing was specified, add the default
+  if (Req.CheckPrefixes.empty())
+    Req.CheckPrefixes.push_back("CHECK");
+
+  // We already validated the contents of CheckPrefixes so just concatenate
+  // them as alternatives.
+  SmallString<32> PrefixRegexStr;
+  for (StringRef Prefix : Req.CheckPrefixes) {
+    if (Prefix != Req.CheckPrefixes.front())
+      PrefixRegexStr.push_back('|');
+
+    PrefixRegexStr.append(Prefix);
+  }
+
+  return Regex(PrefixRegexStr);
+}
+
+// Remove local variables from \p VariableTable. Global variables
+// (start with '$') are preserved.
+static void ClearLocalVars(StringMap<StringRef> &VariableTable) {
+  SmallVector<StringRef, 16> LocalVars;
+  for (const auto &Var : VariableTable)
+    if (Var.first()[0] != '$')
+      LocalVars.push_back(Var.first());
+
+  for (const auto &Var : LocalVars)
+    VariableTable.erase(Var);
+}
+
+/// Check the input to FileCheck provided in the \p Buffer against the \p
+/// CheckStrings read from the check file.
+///
+/// Returns false if the input fails to satisfy the checks.
+bool llvm::FileCheck::CheckInput(SourceMgr &SM, StringRef Buffer,
+                ArrayRef<FileCheckString> CheckStrings) {
+  bool ChecksFailed = false;
+
+  /// VariableTable - This holds all the current filecheck variables.
+  StringMap<StringRef> VariableTable;
+
+  for (const auto& Def : Req.GlobalDefines)
+    VariableTable.insert(StringRef(Def).split('='));
+
+  unsigned i = 0, j = 0, e = CheckStrings.size();
+  while (true) {
+    StringRef CheckRegion;
+    if (j == e) {
+      CheckRegion = Buffer;
+    } else {
+      const FileCheckString &CheckLabelStr = CheckStrings[j];
+      if (CheckLabelStr.Pat.getCheckTy() != Check::CheckLabel) {
+        ++j;
+        continue;
+      }
+
+      // Scan to next CHECK-LABEL match, ignoring CHECK-NOT and CHECK-DAG
+      size_t MatchLabelLen = 0;
+      size_t MatchLabelPos =
+          CheckLabelStr.Check(SM, Buffer, true, MatchLabelLen, VariableTable,
+                              Req);
+      if (MatchLabelPos == StringRef::npos)
+        // Immediately bail of CHECK-LABEL fails, nothing else we can do.
+        return false;
+
+      CheckRegion = Buffer.substr(0, MatchLabelPos + MatchLabelLen);
+      Buffer = Buffer.substr(MatchLabelPos + MatchLabelLen);
+      ++j;
+    }
+
+    if (Req.EnableVarScope)
+      ClearLocalVars(VariableTable);
+
+    for (; i != j; ++i) {
+      const FileCheckString &CheckStr = CheckStrings[i];
+
+      // Check each string within the scanned region, including a second check
+      // of any final CHECK-LABEL (to verify CHECK-NOT and CHECK-DAG)
+      size_t MatchLen = 0;
+      size_t MatchPos =
+          CheckStr.Check(SM, CheckRegion, false, MatchLen, VariableTable, Req);
+
+      if (MatchPos == StringRef::npos) {
+        ChecksFailed = true;
+        i = j;
+        break;
+      }
+
+      CheckRegion = CheckRegion.substr(MatchPos + MatchLen);
+    }
+
+    if (j == e)
+      break;
+  }
+
+  // Success if no checks failed.
+  return !ChecksFailed;
+}