diff --git a/libcxx/include/__atomic/is_always_lock_free.h b/libcxx/include/__atomic/is_always_lock_free.h
--- a/libcxx/include/__atomic/is_always_lock_free.h
+++ b/libcxx/include/__atomic/is_always_lock_free.h
@@ -20,7 +20,7 @@
 template <class _Tp>
 struct __libcpp_is_always_lock_free {
   // __atomic_always_lock_free is available in all Standard modes
-  static const bool __value = __atomic_always_lock_free(sizeof(_Tp), 0);
+  static const bool __value = __atomic_always_lock_free(sizeof(_Tp), nullptr);
 };
 
 _LIBCPP_END_NAMESPACE_STD
diff --git a/libcxx/include/cmath b/libcxx/include/cmath
--- a/libcxx/include/cmath
+++ b/libcxx/include/cmath
@@ -547,8 +547,8 @@
 
 #if _LIBCPP_STD_VER >= 17
 inline _LIBCPP_INLINE_VISIBILITY float       hypot(       float __x,       float __y,       float __z ) { return sqrt(__x*__x + __y*__y + __z*__z); }
-inline _LIBCPP_INLINE_VISIBILITY double      hypot(      double __x,      double __y,      double __z ) { return sqrt(__x*__x + __y*__y + __z*__z); }
-inline _LIBCPP_INLINE_VISIBILITY long double hypot( long double __x, long double __y, long double __z ) { return sqrt(__x*__x + __y*__y + __z*__z); }
+inline _LIBCPP_INLINE_VISIBILITY double      hypot(      double __x,      double __y,      double __z ) { return sqrtf(__x*__x + __y*__y + __z*__z); }
+inline _LIBCPP_INLINE_VISIBILITY long double hypot( long double __x, long double __y, long double __z ) { return sqrtl(__x*__x + __y*__y + __z*__z); }
 
 template <class _A1, class _A2, class _A3>
 inline _LIBCPP_INLINE_VISIBILITY
diff --git a/libcxx/include/string b/libcxx/include/string
--- a/libcxx/include/string
+++ b/libcxx/include/string
@@ -874,7 +874,7 @@
     }
 
 public:
-  _LIBCPP_TEMPLATE_DATA_VIS static const size_type npos = -1;
+  _LIBCPP_TEMPLATE_DATA_VIS static const size_type npos = numeric_limits<size_type>::max();
 
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string()
       _NOEXCEPT_(is_nothrow_default_constructible<allocator_type>::value)
diff --git a/libcxx/include/string_view b/libcxx/include/string_view
--- a/libcxx/include/string_view
+++ b/libcxx/include/string_view
@@ -286,7 +286,7 @@
     using reverse_iterator       = const_reverse_iterator;
     using size_type              = size_t;
     using difference_type        = ptrdiff_t;
-    static _LIBCPP_CONSTEXPR const size_type npos = -1; // size_type(-1);
+    static _LIBCPP_CONSTEXPR const size_type npos = numeric_limits<size_type>::max() ; // size_type(-1);
 
     static_assert((!is_array<value_type>::value), "Character type of basic_string_view must not be an array");
     static_assert(( is_standard_layout<value_type>::value), "Character type of basic_string_view must be standard-layout");
diff --git a/libcxx/include/variant b/libcxx/include/variant
--- a/libcxx/include/variant
+++ b/libcxx/include/variant
@@ -342,7 +342,7 @@
   using type = __type_pack_element<_Ip, _Types...>;
 };
 
-inline constexpr size_t variant_npos = static_cast<size_t>(-1);
+inline constexpr size_t variant_npos = numeric_limits<size_t>::max();
 
 _LIBCPP_HIDE_FROM_ABI constexpr int __choose_index_type(unsigned int __num_elem) {
   if (__num_elem < numeric_limits<unsigned char>::max())
diff --git a/libcxx/utils/libcxx/test/params.py b/libcxx/utils/libcxx/test/params.py
--- a/libcxx/utils/libcxx/test/params.py
+++ b/libcxx/utils/libcxx/test/params.py
@@ -21,6 +21,10 @@
     "-Wextra",
     "-Wshadow",
     "-Wundef",
+    "-Wimplicit-float-conversion",
+    "-Wmacro-redefined",
+    "-Wsign-conversion",
+    "-Wzero-as-null-pointer-constant",
     "-Wunused-template",
     "-Wno-unused-command-line-argument",
     "-Wno-attributes",