rearrange STL allocator code: remove pragma, ifdef for C++11

ide/vs2019/mimalloc.vcxproj

@@ -111,7 +111,7 @@
   </ItemDefinitionGroup>
   <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Debug|x64'">
     <ClCompile>
-      <WarningLevel>Level2</WarningLevel>
+      <WarningLevel>Level4</WarningLevel>
       <Optimization>Disabled</Optimization>
       <SDLCheck>true</SDLCheck>
       <ConformanceMode>true</ConformanceMode>

include/mimalloc-internal.h

@@ -167,6 +167,11 @@ bool        _mi_page_is_valid(mi_page_t* page);
 
 // Overflow detecting multiply
 static inline bool mi_mul_overflow(size_t count, size_t size, size_t* total) {
+  // quick check for the case where count is one (common for C++ allocators)
+  if (count==1) {
+    *total = size;
+    return false;
+  }
 #if __has_builtin(__builtin_umul_overflow) || __GNUC__ >= 5
 #include <limits.h>   // UINT_MAX, ULONG_MAX
 #if (SIZE_MAX == UINT_MAX)

include/mimalloc.h

@@ -73,8 +73,6 @@ terms of the MIT license. A copy of the license can be found in the file
 #include <stdbool.h>    // bool
 
 #ifdef __cplusplus
-#include <type_traits> // true_type
-
 extern "C" {
 #endif
 
@@ -337,41 +335,33 @@ mi_decl_export void* mi_new_aligned_nothrow(size_t n, size_t alignment) mi_attr_
 }
 #endif
 
+// ---------------------------------------------------------------------------------------------
+// Implement the C++ std::allocator interface for use in STL containers.
+// (note: see `mimalloc-new-delete.h` for overriding the new/delete operators globally)
+// ---------------------------------------------------------------------------------------------
 #ifdef __cplusplus
 
-// ------------------------------------------------------
-// STL allocator - an extension to hook mimalloc into STL 
-// containers in place of std::allocator.
-// ------------------------------------------------------
+#if (__cplusplus >= 201103L) || (_MSC_VER > 1900)  // C++11
+#include <type_traits> // true_type
+#endif
 
-#pragma warning(disable: 4100)
-template <class T>
-struct mi_stl_allocator {
+template<class T> struct mi_stl_allocator {
   typedef T value_type;
-  
+#if (__cplusplus >= 201103L) || (_MSC_VER > 1900)  // C++11
   using propagate_on_container_copy_assignment = std::true_type;
   using propagate_on_container_move_assignment = std::true_type;
   using propagate_on_container_swap = std::true_type;
   using is_always_equal = std::true_type;
-
-  mi_stl_allocator() noexcept {}
-  mi_stl_allocator(const mi_stl_allocator& other) noexcept {}
-  template <class U>
-  mi_stl_allocator(const mi_stl_allocator<U>& other) noexcept {}
-
-  T* allocate(size_t n, const void* hint = 0) {
-    return (T*)mi_mallocn(n, sizeof(T));
-  }
-
-  void deallocate(T* p, size_t n) {
-    mi_free(p);
-  }
+#endif
+  mi_stl_allocator() mi_attr_noexcept {}
+  mi_stl_allocator(const mi_stl_allocator& other) mi_attr_noexcept { (void)other; }
+  template<class U> mi_stl_allocator(const mi_stl_allocator<U>& other) mi_attr_noexcept { (void)other; }
+  T* allocate(size_t n, const void* hint = 0) { (void)hint; return (T*)mi_mallocn(n, sizeof(T)); }
+  void deallocate(T* p, size_t n)             { mi_free_size(p,n); }
 };
 
-template <class T1, class T2>
-bool operator==(const mi_stl_allocator<T1>& lhs, const mi_stl_allocator<T2>& rhs) noexcept { return true; }
-template <class T1, class T2>
-bool operator!=(const mi_stl_allocator<T1>& lhs, const mi_stl_allocator<T2>& rhs) noexcept { return false; }
-#endif
+template<class T1,class T2> bool operator==(const mi_stl_allocator<T1>& lhs, const mi_stl_allocator<T2>& rhs) mi_attr_noexcept { (void)lhs; (void)rhs; return true; }
+template<class T1,class T2> bool operator!=(const mi_stl_allocator<T1>& lhs, const mi_stl_allocator<T2>& rhs) mi_attr_noexcept { (void)lhs; (void)rhs; return false; }
+#endif // __cplusplus
 
 #endif

src/alloc.c

@@ -443,12 +443,7 @@ mi_decl_allocator void* mi_calloc(size_t count, size_t size) mi_attr_noexcept {
 // Uninitialized `calloc`
 extern mi_decl_allocator void* mi_heap_mallocn(mi_heap_t* heap, size_t count, size_t size) mi_attr_noexcept {
   size_t total;
-  if (count==1) {
-    total = size;
-  }
-  else if (mi_mul_overflow(count, size, &total)) {
-    return NULL;
-  }
+  if (mi_mul_overflow(count, size, &total)) return NULL;
   return mi_heap_malloc(heap, total);
 }