diff --git a/clang/runtime/CMakeLists.txt b/clang/runtime/CMakeLists.txt
--- a/clang/runtime/CMakeLists.txt
+++ b/clang/runtime/CMakeLists.txt
@@ -132,7 +132,7 @@
     # Add top-level targets for various compiler-rt test suites.
     set(COMPILER_RT_TEST_SUITES check-fuzzer check-asan check-hwasan check-asan-dynamic check-dfsan
       check-lsan check-msan check-sanitizer check-tsan check-ubsan check-ubsan-minimal
-      check-profile check-cfi check-cfi-and-supported check-safestack)
+      check-profile check-cfi check-cfi-and-supported check-safestack check-gwp_asan)
     foreach(test_suite ${COMPILER_RT_TEST_SUITES})
       get_ext_project_build_command(run_test_suite ${test_suite})
       add_custom_target(${test_suite}
diff --git a/compiler-rt/lib/gwp_asan/CMakeLists.txt b/compiler-rt/lib/gwp_asan/CMakeLists.txt
--- a/compiler-rt/lib/gwp_asan/CMakeLists.txt
+++ b/compiler-rt/lib/gwp_asan/CMakeLists.txt
@@ -7,6 +7,8 @@
 )
 
 set(GWP_ASAN_HEADERS
+  definitions.h
+  mutex.h
   random.h
 )
 
@@ -37,3 +39,7 @@
       ADDITIONAL_HEADERS ${GWP_ASAN_HEADERS}
       CFLAGS ${GWP_ASAN_CFLAGS})
 endif()
+
+if(COMPILER_RT_INCLUDE_TESTS)
+  add_subdirectory(tests)
+endif()
diff --git a/compiler-rt/lib/gwp_asan/definitions.h b/compiler-rt/lib/gwp_asan/definitions.h
new file mode 100644
--- /dev/null
+++ b/compiler-rt/lib/gwp_asan/definitions.h
@@ -0,0 +1,14 @@
+//===-- gwp_asan_definitions.h ----------------------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef GWP_ASAN_DEFINITIONS_H_
+#define GWP_ASAN_DEFINITIONS_H_
+
+#define ALWAYS_INLINE inline __attribute__((always_inline))
+
+#endif // GWP_ASAN_DEFINITIONS_H_
diff --git a/compiler-rt/lib/gwp_asan/mutex.h b/compiler-rt/lib/gwp_asan/mutex.h
new file mode 100644
--- /dev/null
+++ b/compiler-rt/lib/gwp_asan/mutex.h
@@ -0,0 +1,103 @@
+//===-- mutex.h -------------------------------------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// TODO(hctim): Move this implementation and Scudo's implementation into a
+// unified base implementation. We shouldn't need to have separate
+// implementations for this.
+
+#ifndef GWP_ASAN_MUTEX_H_
+#define GWP_ASAN_MUTEX_H_
+
+#include "gwp_asan/definitions.h"
+
+#include <stdint.h>
+
+#ifdef __unix__
+#include <sched.h>
+#endif // defined(__unix__)
+
+namespace gwp_asan {
+class Mutex {
+public:
+  void lock();
+  bool tryLock();
+  void unlock();
+
+private:
+  // How many cycles do we yield on the processor per call to yieldProcessor().
+  static constexpr unsigned kProcessorYieldCount = 10;
+  void yieldProcessor();
+  void yieldPlatform();
+
+  void lockSlow();
+
+  bool Locked = false;
+  static_assert(
+      __atomic_always_lock_free(sizeof(Locked), /*Typical Alignment*/ 0),
+      "gwp_asan::Mutex::Locked is not lock-free on this architecture.");
+};
+
+class ScopedLock {
+public:
+  explicit ScopedLock(Mutex &Mx) : Mu(Mx) { Mu.lock(); }
+  ~ScopedLock() { Mu.unlock(); }
+  ScopedLock(const ScopedLock &) = delete;
+
+private:
+  Mutex &Mu;
+};
+
+ALWAYS_INLINE void Mutex::lock() {
+  if (tryLock())
+    return;
+  lockSlow();
+}
+
+ALWAYS_INLINE bool Mutex::tryLock() {
+  return !__atomic_exchange_n(&Locked, true, __ATOMIC_ACQUIRE);
+}
+
+ALWAYS_INLINE void Mutex::unlock() {
+  __atomic_store_n(&Locked, false, __ATOMIC_RELEASE);
+}
+
+ALWAYS_INLINE void Mutex::yieldProcessor() {
+  __atomic_signal_fence(__ATOMIC_SEQ_CST);
+#if defined(__i386__) || defined(__x86_64__)
+  for (unsigned i = 0; i < kProcessorYieldCount; ++i)
+    asm volatile("pause");
+#elif defined(__aarch64__) || defined(__arm__)
+  for (unsigned i = 0; i < kProcessorYieldCount; ++i)
+    asm volatile("yield");
+#else
+#error "GWP-ASan on this architecture is not supported."
+#endif
+  __atomic_signal_fence(__ATOMIC_SEQ_CST);
+}
+
+ALWAYS_INLINE void Mutex::lockSlow() {
+  for (uint32_t i = 0;; ++i) {
+    if (i < 10)
+      yieldProcessor();
+    else
+      yieldPlatform();
+
+    if (!__atomic_load_n(&Locked, __ATOMIC_RELAXED) && tryLock())
+      return;
+  }
+}
+
+#ifdef __unix__
+ALWAYS_INLINE void Mutex::yieldPlatform() { sched_yield(); }
+#else
+#error "GWP-ASan on this platform is not supported."
+#endif
+
+} // namespace gwp_asan
+
+#endif // GWP_ASAN_MUTEX_H_
diff --git a/compiler-rt/lib/gwp_asan/tests/CMakeLists.txt b/compiler-rt/lib/gwp_asan/tests/CMakeLists.txt
new file mode 100644
--- /dev/null
+++ b/compiler-rt/lib/gwp_asan/tests/CMakeLists.txt
@@ -0,0 +1,49 @@
+include(CompilerRTCompile)
+
+set(GWP_ASAN_UNITTEST_CFLAGS
+  ${COMPILER_RT_UNITTEST_CFLAGS}
+  ${COMPILER_RT_GTEST_CFLAGS}
+  -I${COMPILER_RT_SOURCE_DIR}/lib/
+  -O2)
+
+file(GLOB GWP_ASAN_HEADERS ../*.h)
+file(GLOB GWP_ASAN_UNITTESTS *.cpp)
+set(GWP_ASAN_UNIT_TEST_HEADERS
+  ${GWP_ASAN_HEADERS})
+
+add_custom_target(GwpAsanUnitTests)
+set_target_properties(GwpAsanUnitTests PROPERTIES FOLDER "Compiler-RT Tests")
+
+set(GWP_ASAN_UNITTEST_LINK_FLAGS ${COMPILER_RT_UNITTEST_LINK_FLAGS})
+list(APPEND GWP_ASAN_UNITTEST_LINK_FLAGS --driver-mode=g++)
+if(NOT WIN32)
+  list(APPEND GWP_ASAN_UNITTEST_LINK_FLAGS -lpthread)
+endif()
+
+if(COMPILER_RT_DEFAULT_TARGET_ARCH IN_LIST GWP_ASAN_SUPPORTED_ARCH)
+  # GWP-ASan unit tests are only run on the host machine.
+  set(arch ${COMPILER_RT_DEFAULT_TARGET_ARCH})
+
+  set(GWP_ASAN_TEST_RUNTIME RTGwpAsanTest.${arch})
+
+  set(GWP_ASAN_TEST_RUNTIME_OBJECTS
+    $<TARGET_OBJECTS:RTGwpAsan.${arch}>)
+
+  add_library(${GWP_ASAN_TEST_RUNTIME} STATIC
+    ${GWP_ASAN_TEST_RUNTIME_OBJECTS})
+
+  set_target_properties(${GWP_ASAN_TEST_RUNTIME} PROPERTIES
+    ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
+    FOLDER "Compiler-RT Runtime tests")
+
+  set(GwpAsanTestObjects)
+  generate_compiler_rt_tests(GwpAsanTestObjects
+    GwpAsanUnitTests "GwpAsan-${arch}-Test" ${arch}
+    SOURCES ${GWP_ASAN_UNITTESTS} ${COMPILER_RT_GTEST_SOURCE}
+    RUNTIME ${GWP_ASAN_TEST_RUNTIME}
+    DEPS gtest ${GWP_ASAN_UNIT_TEST_HEADERS}
+    CFLAGS ${GWP_ASAN_UNITTEST_CFLAGS}
+    LINK_FLAGS ${GWP_ASAN_UNITTEST_LINK_FLAGS})
+  set_target_properties(GwpAsanUnitTests PROPERTIES
+    RUNTIME_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR})
+endif()
diff --git a/compiler-rt/lib/gwp_asan/tests/driver.cpp b/compiler-rt/lib/gwp_asan/tests/driver.cpp
new file mode 100644
--- /dev/null
+++ b/compiler-rt/lib/gwp_asan/tests/driver.cpp
@@ -0,0 +1,14 @@
+//===-- driver.cc -----------------------------------------------*- C++ -*-===//
+//
+// 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 "gtest/gtest.h"
+
+int main(int argc, char **argv) {
+  testing::InitGoogleTest(&argc, argv);
+  return RUN_ALL_TESTS();
+}
diff --git a/compiler-rt/lib/gwp_asan/tests/mutex_test.cpp b/compiler-rt/lib/gwp_asan/tests/mutex_test.cpp
new file mode 100644
--- /dev/null
+++ b/compiler-rt/lib/gwp_asan/tests/mutex_test.cpp
@@ -0,0 +1,105 @@
+//===-- mutex_test.cpp ------------------------------------------*- C++ -*-===//
+//
+// 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 "gwp_asan/mutex.h"
+#include "gtest/gtest.h"
+
+#include <atomic>
+#include <mutex>
+#include <thread>
+#include <vector>
+
+using gwp_asan::Mutex;
+using gwp_asan::ScopedLock;
+
+TEST(GwpAsanMutexTest, ConstructionTest) {
+  Mutex Mu;
+
+  ASSERT_TRUE(Mu.tryLock());
+  ASSERT_FALSE(Mu.tryLock());
+  Mu.unlock();
+
+  Mu.lock();
+  Mu.unlock();
+
+  // Ensure that the mutex actually unlocked.
+  ASSERT_TRUE(Mu.tryLock());
+  Mu.unlock();
+}
+
+TEST(GwpAsanMutexTest, ScopedConstructionTest) {
+  Mutex Mu;
+  { ScopedLock L(Mu); }
+  // Locking will fail here if the scoped lock failed to unlock.
+  EXPECT_TRUE(Mu.tryLock());
+  Mu.unlock();
+}
+
+static constexpr unsigned kNumLocksInARow = 1000;
+void lockTask(std::atomic<bool> *StartingGun, Mutex *Mu) {
+  while (!StartingGun->load())
+    ;
+  for (unsigned i = 0; i < kNumLocksInARow; ++i) {
+    ScopedLock L(*Mu);
+  }
+}
+
+TEST(GwpAsanMutexTest, ThreadedConstructionTest) {
+  Mutex Mu;
+  std::atomic<bool> StartingGun{false};
+
+  std::thread T1(lockTask, &StartingGun, &Mu);
+  std::thread T2(lockTask, &StartingGun, &Mu);
+
+  StartingGun.store(true);
+  T1.join();
+  T2.join();
+
+  // Locking will fail here if the scoped lock failed to unlock.
+  EXPECT_TRUE(Mu.tryLock());
+  Mu.unlock();
+}
+
+void thrashTask(std::atomic<bool> *StartingGun, Mutex *Mu, unsigned *Counter,
+                unsigned NumIterations) {
+  while (!StartingGun->load())
+    ;
+  for (unsigned i = 0; i < NumIterations; ++i) {
+    ScopedLock L(*Mu);
+    (*Counter)++;
+  }
+}
+
+void runThrashTest(unsigned NumThreads, unsigned CounterMax) {
+  std::vector<std::thread> Threads;
+  if (std::thread::hardware_concurrency() < NumThreads) {
+    NumThreads = std::thread::hardware_concurrency();
+  }
+
+  ASSERT_TRUE(CounterMax % NumThreads == 0);
+
+  std::atomic<bool> StartingGun{false};
+  Mutex Mu;
+  unsigned Counter = 0;
+
+  for (unsigned i = 0; i < NumThreads; ++i)
+    Threads.emplace_back(thrashTask, &StartingGun, &Mu, &Counter,
+                         CounterMax / NumThreads);
+
+  StartingGun.store(true);
+  for (auto &T : Threads)
+    T.join();
+
+  EXPECT_EQ(CounterMax, Counter);
+}
+
+TEST(GwpAsanMutexTest, ThrashTests) {
+  runThrashTest(2, 10000);
+  runThrashTest(4, 10000);
+  runThrashTest(4, 100000);
+}
diff --git a/compiler-rt/test/gwp_asan/CMakeLists.txt b/compiler-rt/test/gwp_asan/CMakeLists.txt
--- a/compiler-rt/test/gwp_asan/CMakeLists.txt
+++ b/compiler-rt/test/gwp_asan/CMakeLists.txt
@@ -0,0 +1,45 @@
+set(GWP_ASAN_LIT_SOURCE_DIR ${CMAKE_CURRENT_SOURCE_DIR})
+set(GWP_ASAN_LIT_BINARY_DIR ${CMAKE_CURRENT_BINARY_DIR})
+
+set(GWP_ASAN_TESTSUITES)
+
+set(GWP_ASAN_UNITTEST_DEPS)
+set(GWP_ASAN_TEST_DEPS
+  ${SANITIZER_COMMON_LIT_TEST_DEPS}
+  gwp_asan)
+
+if (COMPILER_RT_INCLUDE_TESTS)
+  list(APPEND GWP_ASAN_TEST_DEPS GwpAsanUnitTests)
+  configure_lit_site_cfg(
+    ${CMAKE_CURRENT_SOURCE_DIR}/unit/lit.site.cfg.in
+    ${CMAKE_CURRENT_BINARY_DIR}/unit/lit.site.cfg)
+  add_lit_testsuite(check-gwp_asan-unit "Running GWP-ASan unit tests"
+    ${CMAKE_CURRENT_BINARY_DIR}/unit
+    DEPENDS ${GWP_ASAN_TEST_DEPS})
+  set_target_properties(check-gwp_asan-unit PROPERTIES FOLDER
+    "Compiler-RT Tests")
+    list(APPEND GWP_ASAN_TEST_DEPS check-gwp_asan-unit)
+endif()
+
+configure_lit_site_cfg(
+  ${CMAKE_CURRENT_SOURCE_DIR}/lit.site.cfg.in
+  ${CMAKE_CURRENT_BINARY_DIR}/lit.site.cfg
+  )
+
+foreach(arch ${GWP_ASAN_SUPPORTED_ARCH})
+  set(GWP_ASAN_TEST_TARGET_ARCH ${arch})
+  string(TOLOWER "-${arch}" GWP_ASAN_TEST_CONFIG_SUFFIX)
+  get_test_cc_for_arch(${arch} GWP_ASAN_TEST_TARGET_CC GWP_ASAN_TEST_TARGET_CFLAGS)
+  string(TOUPPER ${arch} ARCH_UPPER_CASE)
+  set(CONFIG_NAME ${ARCH_UPPER_CASE}${OS_NAME}Config)
+
+  configure_lit_site_cfg(
+    ${CMAKE_CURRENT_SOURCE_DIR}/lit.site.cfg.in
+    ${CMAKE_CURRENT_BINARY_DIR}/${CONFIG_NAME}/lit.site.cfg)
+  list(APPEND GWP_ASAN_TESTSUITES ${CMAKE_CURRENT_BINARY_DIR}/${CONFIG_NAME})
+endforeach()
+
+add_lit_testsuite(check-gwp_asan "Running the GWP-ASan tests"
+  ${GWP_ASAN_TESTSUITES}
+  DEPENDS ${GWP_ASAN_TEST_DEPS})
+set_target_properties(check-gwp_asan PROPERTIES FOLDER "Compiler-RT Misc")
diff --git a/compiler-rt/test/gwp_asan/dummy_test.cc b/compiler-rt/test/gwp_asan/dummy_test.cc
new file mode 100644
--- /dev/null
+++ b/compiler-rt/test/gwp_asan/dummy_test.cc
@@ -0,0 +1,4 @@
+// Exists to simply stop warnings about lit not discovering any tests here.
+// RUN: %clang %s
+
+int main() { return 0; }
diff --git a/compiler-rt/test/gwp_asan/lit.cfg b/compiler-rt/test/gwp_asan/lit.cfg
new file mode 100644
--- /dev/null
+++ b/compiler-rt/test/gwp_asan/lit.cfg
@@ -0,0 +1,31 @@
+# -*- Python -*-
+
+import os
+
+# Setup config name.
+config.name = 'GWP-ASan' + config.name_suffix
+
+# Setup source root.
+config.test_source_root = os.path.dirname(__file__)
+
+# Test suffixes.
+config.suffixes = ['.c', '.cc', '.cpp', '.test']
+
+# C & CXX flags.
+c_flags = ([config.target_cflags])
+
+# Android doesn't want -lrt.
+if not config.android:
+  c_flags += ["-lrt"]
+
+cxx_flags = (c_flags + config.cxx_mode_flags + ["-std=c++11"])
+
+def build_invocation(compile_flags):
+  return " " + " ".join([config.clang] + compile_flags) + " "
+
+# Add substitutions.
+config.substitutions.append(("%clang ", build_invocation(c_flags)))
+
+# GWP-ASan tests are currently supported on Linux only.
+if config.host_os not in ['Linux']:
+   config.unsupported = True
diff --git a/compiler-rt/test/gwp_asan/lit.site.cfg.in b/compiler-rt/test/gwp_asan/lit.site.cfg.in
new file mode 100644
--- /dev/null
+++ b/compiler-rt/test/gwp_asan/lit.site.cfg.in
@@ -0,0 +1,11 @@
+@LIT_SITE_CFG_IN_HEADER@
+
+config.name_suffix = "@GWP_ASAN_TEST_CONFIG_SUFFIX@"
+config.target_arch = "@GWP_ASAN_TEST_TARGET_ARCH@"
+config.target_cflags = "@GWP_ASAN_TEST_TARGET_CFLAGS@"
+
+# Load common config for all compiler-rt lit tests.
+lit_config.load_config(config, "@COMPILER_RT_BINARY_DIR@/test/lit.common.configured")
+
+# Load tool-specific config that would do the real work.
+lit_config.load_config(config, "@GWP_ASAN_LIT_SOURCE_DIR@/lit.cfg")
diff --git a/compiler-rt/test/gwp_asan/unit/lit.site.cfg.in b/compiler-rt/test/gwp_asan/unit/lit.site.cfg.in
new file mode 100644
--- /dev/null
+++ b/compiler-rt/test/gwp_asan/unit/lit.site.cfg.in
@@ -0,0 +1,9 @@
+@LIT_SITE_CFG_IN_HEADER@
+
+config.name = "GwpAsan-Unittest"
+# Load common config for all compiler-rt unit tests.
+lit_config.load_config(config, "@COMPILER_RT_BINARY_DIR@/unittests/lit.common.unit.configured")
+
+config.test_exec_root = os.path.join("@COMPILER_RT_BINARY_DIR@",
+                                     "lib", "gwp_asan", "tests")
+config.test_source_root = config.test_exec_root