--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/flang/lib/Parser/instrumented-parser.cpp	Mon May 25 11:55:54 2020 +0900
@@ -0,0 +1,77 @@
+//===-- lib/Parser/instrumented-parser.cpp --------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "flang/Parser/instrumented-parser.h"
+#include "flang/Parser/message.h"
+#include "flang/Parser/provenance.h"
+#include "llvm/Support/raw_ostream.h"
+#include <map>
+
+namespace Fortran::parser {
+
+void ParsingLog::clear() { perPos_.clear(); }
+
+// In the logs, just use the addresses of the message texts to sort the
+// map keys.
+bool operator<(const MessageFixedText &x, const MessageFixedText &y) {
+  return x.text().begin() < y.text().begin();
+}
+
+bool ParsingLog::Fails(
+    const char *at, const MessageFixedText &tag, ParseState &state) {
+  std::size_t offset{reinterpret_cast<std::size_t>(at)};
+  auto posIter{perPos_.find(offset)};
+  if (posIter == perPos_.end()) {
+    return false;
+  }
+  auto tagIter{posIter->second.perTag.find(tag)};
+  if (tagIter == posIter->second.perTag.end()) {
+    return false;
+  }
+  auto &entry{tagIter->second};
+  if (entry.deferred && !state.deferMessages()) {
+    return false; // don't fail fast, we want to generate messages
+  }
+  ++entry.count;
+  if (!state.deferMessages()) {
+    state.messages().Copy(entry.messages);
+  }
+  return !entry.pass;
+}
+
+void ParsingLog::Note(const char *at, const MessageFixedText &tag, bool pass,
+    const ParseState &state) {
+  std::size_t offset{reinterpret_cast<std::size_t>(at)};
+  auto &entry{perPos_[offset].perTag[tag]};
+  if (++entry.count == 1) {
+    entry.pass = pass;
+    entry.deferred = state.deferMessages();
+    if (!entry.deferred) {
+      entry.messages.Copy(state.messages());
+    }
+  } else {
+    CHECK(entry.pass == pass);
+    if (entry.deferred && !state.deferMessages()) {
+      entry.deferred = false;
+      entry.messages.Copy(state.messages());
+    }
+  }
+}
+
+void ParsingLog::Dump(llvm::raw_ostream &o, const CookedSource &cooked) const {
+  for (const auto &posLog : perPos_) {
+    const char *at{reinterpret_cast<const char *>(posLog.first)};
+    for (const auto &tagLog : posLog.second.perTag) {
+      Message{at, tagLog.first}.Emit(o, cooked, true);
+      auto &entry{tagLog.second};
+      o << "  " << (entry.pass ? "pass" : "fail") << " " << entry.count << '\n';
+      entry.messages.Emit(o, cooked);
+    }
+  }
+}
+} // namespace Fortran::parser