diff --git a/libcxx/test/libcxx/algorithms/debug_less.pass.cpp b/libcxx/test/libcxx/algorithms/debug_less.pass.cpp
index 5d1b575b5129b6..6a05b8db67a8b1 100644
--- a/libcxx/test/libcxx/algorithms/debug_less.pass.cpp
+++ b/libcxx/test/libcxx/algorithms/debug_less.pass.cpp
@@ -183,6 +183,7 @@ inline bool operator<(FooImp<T> const& x, Tag<0> y) {
 template <class T>
 inline bool operator<(Tag<0>, FooImp<T> const&) {
     static_assert(sizeof(FooImp<T>) != sizeof(FooImp<T>), "should not be instantiated");
+    return false;
 }
 
 template <class T>
@@ -193,6 +194,7 @@ inline bool operator<(Tag<1> x, FooImp<T> const& y) {
 template <class T>
 inline bool operator<(FooImp<T> const&, Tag<1>) {
     static_assert(sizeof(FooImp<T>) != sizeof(FooImp<T>), "should not be instantiated");
+    return false;
 }
 
 typedef FooImp<> Foo;
diff --git a/libcxx/test/libcxx/atomics/libcpp-has-no-threads.pass.cpp b/libcxx/test/libcxx/atomics/libcpp-has-no-threads.pass.cpp
index af2d55e1a4a3d7..b52ba642522310 100644
--- a/libcxx/test/libcxx/atomics/libcpp-has-no-threads.pass.cpp
+++ b/libcxx/test/libcxx/atomics/libcpp-has-no-threads.pass.cpp
@@ -8,7 +8,7 @@
 // XFAIL: libcpp-has-no-threads
 
 #ifdef _LIBCPP_HAS_NO_THREADS
-#error This should be XFAIL'd for the purpose of detecting that the LIT feature\
+#error This should be XFAILed for the purpose of detecting that the LIT feature\
    'libcpp-has-no-threads' is available iff _LIBCPP_HAS_NO_THREADS is defined
 #endif
 
diff --git a/libcxx/test/libcxx/containers/associative/undef_min_max.pass.cpp b/libcxx/test/libcxx/containers/associative/undef_min_max.pass.cpp
index 1408da97402957..ff15f355f82550 100644
--- a/libcxx/test/libcxx/containers/associative/undef_min_max.pass.cpp
+++ b/libcxx/test/libcxx/containers/associative/undef_min_max.pass.cpp
@@ -6,8 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#if defined(__GNUC__) || defined(__clang__)
-#pragma GCC diagnostic ignored "-W#warnings"
+#if defined(__clang__)
+#pragma clang diagnostic ignored "-W#warnings"
 #endif
 
 #define min THIS IS A NASTY MACRO!
diff --git a/libcxx/test/libcxx/containers/gnu_cxx/hash_map.pass.cpp b/libcxx/test/libcxx/containers/gnu_cxx/hash_map.pass.cpp
index df413186959de0..ff268cd0c53c70 100644
--- a/libcxx/test/libcxx/containers/gnu_cxx/hash_map.pass.cpp
+++ b/libcxx/test/libcxx/containers/gnu_cxx/hash_map.pass.cpp
@@ -6,11 +6,13 @@
 //
 //===----------------------------------------------------------------------===//
 
-
 // Prevent emission of the deprecated warning.
 #ifdef __clang__
 #pragma clang diagnostic ignored "-W#warnings"
 #endif
+#ifdef __GNUC__
+#pragma GCC diagnostic ignored "-Wcpp"
+#endif
 
 #include <ext/hash_map>
 #include <cassert>
diff --git a/libcxx/test/libcxx/containers/gnu_cxx/hash_map_name_lookup.pass.cpp b/libcxx/test/libcxx/containers/gnu_cxx/hash_map_name_lookup.pass.cpp
index bfcb8aeda3f93a..31e877eda82267 100644
--- a/libcxx/test/libcxx/containers/gnu_cxx/hash_map_name_lookup.pass.cpp
+++ b/libcxx/test/libcxx/containers/gnu_cxx/hash_map_name_lookup.pass.cpp
@@ -10,6 +10,9 @@
 #ifdef __clang__
 #pragma clang diagnostic ignored "-W#warnings"
 #endif
+#ifdef __GNUC__
+#pragma GCC diagnostic push "-Wcpp"
+#endif
 
 // Poison the std:: names we might use inside __gnu_cxx to ensure they're
 // properly qualified.
diff --git a/libcxx/test/libcxx/containers/gnu_cxx/hash_set.pass.cpp b/libcxx/test/libcxx/containers/gnu_cxx/hash_set.pass.cpp
index 307ba7368d162d..bfdbb38b2a891d 100644
--- a/libcxx/test/libcxx/containers/gnu_cxx/hash_set.pass.cpp
+++ b/libcxx/test/libcxx/containers/gnu_cxx/hash_set.pass.cpp
@@ -6,11 +6,13 @@
 //
 //===----------------------------------------------------------------------===//
 
-
 // Prevent emission of the deprecated warning.
 #ifdef __clang__
 #pragma clang diagnostic ignored "-W#warnings"
 #endif
+#ifdef __GNUC__
+#pragma GCC diagnostic ignored "-Wcpp"
+#endif
 
 #include <ext/hash_set>
 #include <cassert>
diff --git a/libcxx/test/libcxx/containers/gnu_cxx/hash_set_name_lookup.pass.cpp b/libcxx/test/libcxx/containers/gnu_cxx/hash_set_name_lookup.pass.cpp
index b3e1e19566329c..6e50137ceb7163 100644
--- a/libcxx/test/libcxx/containers/gnu_cxx/hash_set_name_lookup.pass.cpp
+++ b/libcxx/test/libcxx/containers/gnu_cxx/hash_set_name_lookup.pass.cpp
@@ -10,6 +10,10 @@
 #ifdef __clang__
 #pragma clang diagnostic ignored "-W#warnings"
 #endif
+#ifdef __GNUC__
+#pragma GCC diagnostic ignored "-Wcpp"
+#endif
+
 // Poison the std:: names we might use inside __gnu_cxx to ensure they're
 // properly qualified.
 struct allocator;
diff --git a/libcxx/test/libcxx/numerics/c.math/undef_min_max.pass.cpp b/libcxx/test/libcxx/numerics/c.math/undef_min_max.pass.cpp
index ba1696eb2405c9..a9f50171543b9d 100644
--- a/libcxx/test/libcxx/numerics/c.math/undef_min_max.pass.cpp
+++ b/libcxx/test/libcxx/numerics/c.math/undef_min_max.pass.cpp
@@ -5,8 +5,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#if defined(__GNUC__) || defined(__clang__)
-#pragma GCC diagnostic ignored "-W#warnings"
+#if defined(__clang__)
+#pragma clang diagnostic ignored "-W#warnings"
 #endif
 
 #define min THIS IS A NASTY MACRO!
diff --git a/libcxx/test/support/container_debug_tests.h b/libcxx/test/support/container_debug_tests.h
index 36496c24e2bc34..e0b0df3b3b60ed 100644
--- a/libcxx/test/support/container_debug_tests.h
+++ b/libcxx/test/support/container_debug_tests.h
@@ -11,7 +11,7 @@
 
 #include <ciso646>
 #ifndef _LIBCPP_VERSION
-#error This header may only be used for libc++ tests"
+#error This header may only be used for libc++ tests
 #endif
 
 #ifndef _LIBCPP_DEBUG
diff --git a/libcxx/test/support/debug_mode_helper.h b/libcxx/test/support/debug_mode_helper.h
index ed111ab127ce79..8256f3eb382830 100644
--- a/libcxx/test/support/debug_mode_helper.h
+++ b/libcxx/test/support/debug_mode_helper.h
@@ -287,6 +287,7 @@ inline bool ExpectDeath(const char* stmt, Func&& func, DebugInfoMatcher Matcher)
   case DeathTest::RK_MatchFailure:
       return OnFailure("matcher failed");
   }
+  assert(false && "unreachable");
 }
 
 template <class Func>