diff --git a/CMakeLists.txt b/CMakeLists.txt
index 0cc7e575..7c0f67af 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -84,6 +84,17 @@ endif()
 # Process options
 # -----------------------------------------------------------------------------
 
+# put -Wall early so other warnings can be disabled selectively
+if(CMAKE_C_COMPILER_ID MATCHES "AppleClang|Clang")
+  list(APPEND mi_cflags -Wall -Wextra -Wpedantic)
+endif()
+if(CMAKE_C_COMPILER_ID MATCHES "GNU")
+    list(APPEND mi_cflags -Wall -Wextra)
+endif()
+if(CMAKE_C_COMPILER_ID MATCHES "Intel")
+    list(APPEND mi_cflags -Wall)
+endif()
+
 if(CMAKE_C_COMPILER_ID MATCHES "MSVC|Intel")
   set(MI_USE_CXX "ON")
 endif()
@@ -186,6 +197,10 @@ endif()
 if(MI_SEE_ASM)
   message(STATUS "Generate assembly listings (MI_SEE_ASM=ON)")
   list(APPEND mi_cflags -save-temps)
+  if(CMAKE_C_COMPILER_ID MATCHES "AppleClang|Clang")
+    message(STATUS "No GNU Line marker")
+    list(APPEND mi_cflags -Wno-gnu-line-marker)
+  endif()
 endif()
 
 if(MI_CHECK_FULL)
@@ -279,17 +294,17 @@ endif()
 
 # Compiler flags
 if(CMAKE_C_COMPILER_ID MATCHES "AppleClang|Clang|GNU")
-  list(APPEND mi_cflags -Wall -Wextra -Wno-unknown-pragmas -fvisibility=hidden)
+  list(APPEND mi_cflags -Wno-unknown-pragmas -fvisibility=hidden)
   if(NOT MI_USE_CXX)
     list(APPEND mi_cflags -Wstrict-prototypes)
   endif()
   if(CMAKE_C_COMPILER_ID MATCHES "AppleClang|Clang")
-    list(APPEND mi_cflags -Wpedantic -Wno-static-in-inline)
+    list(APPEND mi_cflags -Wno-static-in-inline)
   endif()
 endif()
 
 if(CMAKE_C_COMPILER_ID MATCHES "Intel")
-  list(APPEND mi_cflags -Wall -fvisibility=hidden)
+  list(APPEND mi_cflags -fvisibility=hidden)
 endif()
 
 if(CMAKE_C_COMPILER_ID MATCHES "AppleClang|Clang|GNU|Intel" AND NOT CMAKE_SYSTEM_NAME MATCHES "Haiku")
diff --git a/include/mimalloc/internal.h b/include/mimalloc/internal.h
index 99acbe6a..f939f9d4 100644
--- a/include/mimalloc/internal.h
+++ b/include/mimalloc/internal.h
@@ -437,9 +437,14 @@ static inline mi_page_t* _mi_heap_get_free_small_page(mi_heap_t* heap, size_t si
 // Large aligned blocks may be aligned at N*MI_SEGMENT_SIZE (inside a huge segment > MI_SEGMENT_SIZE),
 // and we need align "down" to the segment info which is `MI_SEGMENT_SIZE` bytes before it;
 // therefore we align one byte before `p`.
+// We check for NULL afterwards on 64-bit systems to improve codegen for `mi_free`.
 static inline mi_segment_t* _mi_ptr_segment(const void* p) {
-  mi_assert_internal(p != NULL);
-  return (mi_segment_t*)(((uintptr_t)p - 1) & ~MI_SEGMENT_MASK);
+  mi_segment_t* const segment = (mi_segment_t*)(((uintptr_t)p - 1) & ~MI_SEGMENT_MASK);
+  #if MI_INTPTR_SIZE <= 4
+  return (p==NULL ? NULL : segment);
+  #else
+  return ((intptr_t)segment <= 0 ? NULL : segment);
+  #endif
 }
 
 static inline mi_page_t* mi_slice_to_page(mi_slice_t* s) {
@@ -454,6 +459,7 @@ static inline mi_slice_t* mi_page_to_slice(mi_page_t* p) {
 
 // Segment belonging to a page
 static inline mi_segment_t* _mi_page_segment(const mi_page_t* page) {
+  mi_assert_internal(page!=NULL);
   mi_segment_t* segment = _mi_ptr_segment(page);
   mi_assert_internal(segment == NULL || ((mi_slice_t*)page >= segment->slices && (mi_slice_t*)page < segment->slices + segment->slice_entries));
   return segment;
@@ -488,6 +494,7 @@ static inline uint8_t* _mi_page_start(const mi_segment_t* segment, const mi_page
 
 // Get the page containing the pointer
 static inline mi_page_t* _mi_ptr_page(void* p) {
+  mi_assert_internal(p!=NULL);
   return _mi_segment_page_of(_mi_ptr_segment(p), p);
 }
 
diff --git a/src/free.c b/src/free.c
index 7c5a5cc9..32d5c460 100644
--- a/src/free.c
+++ b/src/free.c
@@ -100,7 +100,6 @@ void mi_decl_noinline _mi_free_generic(mi_segment_t* segment, mi_page_t* page, b
 static inline mi_segment_t* mi_checked_ptr_segment(const void* p, const char* msg)
 {
   MI_UNUSED(msg);
-  mi_assert(p != NULL);
 
 #if (MI_DEBUG>0)
   if mi_unlikely(((uintptr_t)p & (MI_INTPTR_SIZE - 1)) != 0) {
@@ -110,7 +109,7 @@ static inline mi_segment_t* mi_checked_ptr_segment(const void* p, const char* ms
 #endif
 
   mi_segment_t* const segment = _mi_ptr_segment(p);
-  mi_assert_internal(segment != NULL);
+  if mi_unlikely(segment==NULL) return segment;
 
 #if (MI_DEBUG>0)
   if mi_unlikely(!mi_is_in_heap_region(p)) {
@@ -141,10 +140,11 @@ static inline mi_segment_t* mi_checked_ptr_segment(const void* p, const char* ms
 // Fast path written carefully to prevent register spilling on the stack
 void mi_free(void* p) mi_attr_noexcept
 {
-  if mi_unlikely(p == NULL) return;
   mi_segment_t* const segment = mi_checked_ptr_segment(p,"mi_free");
-  const bool          is_local= (_mi_prim_thread_id() == mi_atomic_load_relaxed(&segment->thread_id));
-  mi_page_t* const    page    = _mi_segment_page_of(segment, p);
+  if mi_unlikely(segment==NULL) return;
+
+  const bool is_local = (_mi_prim_thread_id() == mi_atomic_load_relaxed(&segment->thread_id));
+  mi_page_t* const page = _mi_segment_page_of(segment, p);
 
   if mi_likely(is_local) {                        // thread-local free?
     if mi_likely(page->flags.full_aligned == 0) { // and it is not a full page (full pages need to move from the full bin), nor has aligned blocks (aligned blocks need to be unaligned)
@@ -166,6 +166,7 @@ void mi_free(void* p) mi_attr_noexcept
 // return true if successful
 bool _mi_free_delayed_block(mi_block_t* block) {
   // get segment and page
+  mi_assert_internal(block!=NULL);
   const mi_segment_t* const segment = _mi_ptr_segment(block);
   mi_assert_internal(_mi_ptr_cookie(segment) == segment->cookie);
   mi_assert_internal(_mi_thread_id() == segment->thread_id);
@@ -310,8 +311,8 @@ static size_t mi_decl_noinline mi_page_usable_aligned_size_of(const mi_segment_t
 }
 
 static inline size_t _mi_usable_size(const void* p, const char* msg) mi_attr_noexcept {
-  if (p == NULL) return 0;
   const mi_segment_t* const segment = mi_checked_ptr_segment(p, msg);
+  if mi_unlikely(segment==NULL) return 0;
   const mi_page_t* const page = _mi_segment_page_of(segment, p);
   if mi_likely(!mi_page_has_aligned(page)) {
     const mi_block_t* block = (const mi_block_t*)p;