[libc++][NFC] Refactor the core logic of operator new into helper functions

This will make it easier to implement new(nothrow) without calling
the throwing version of new when exceptions are disabled. See
https://llvm.org/D150610 for the full discussion.

Author: ldionne

libcxx/src/new.cpp

@@ -20,7 +20,7 @@
 // in this shared library, so that they can be overridden by programs
 // that define non-weak copies of the functions.
 
-_LIBCPP_WEAK void* operator new(std::size_t size) _THROW_BAD_ALLOC {
+static void* operator_new_impl(std::size_t size) noexcept {
   if (size == 0)
     size = 1;
   void* p;
@@ -31,15 +31,20 @@ _LIBCPP_WEAK void* operator new(std::size_t size) _THROW_BAD_ALLOC {
     if (nh)
       nh();
     else
-#  ifndef _LIBCPP_HAS_NO_EXCEPTIONS
-      throw std::bad_alloc();
-#  else
       break;
-#  endif
   }
   return p;
 }
 
+_LIBCPP_WEAK void* operator new(std::size_t size) _THROW_BAD_ALLOC {
+  void* p = operator_new_impl(size);
+#  ifndef _LIBCPP_HAS_NO_EXCEPTIONS
+  if (p == nullptr)
+    throw std::bad_alloc();
+#  endif
+  return p;
+}
+
 _LIBCPP_WEAK void* operator new(size_t size, const std::nothrow_t&) noexcept {
   void* p = nullptr;
 #  ifndef _LIBCPP_HAS_NO_EXCEPTIONS
@@ -82,7 +87,7 @@ _LIBCPP_WEAK void operator delete[](void* ptr, size_t) noexcept { ::operator del
 
 #  if !defined(_LIBCPP_HAS_NO_LIBRARY_ALIGNED_ALLOCATION)
 
-_LIBCPP_WEAK void* operator new(std::size_t size, std::align_val_t alignment) _THROW_BAD_ALLOC {
+static void* operator_new_aligned_impl(std::size_t size, std::align_val_t alignment) noexcept {
   if (size == 0)
     size = 1;
   if (static_cast<size_t>(alignment) < sizeof(void*))
@@ -91,25 +96,26 @@ _LIBCPP_WEAK void* operator new(std::size_t size, std::align_val_t alignment) _T
   // Try allocating memory. If allocation fails and there is a new_handler,
   // call it to try free up memory, and try again until it succeeds, or until
   // the new_handler decides to terminate.
-  //
-  // If allocation fails and there is no new_handler, we throw bad_alloc
-  // (or return nullptr if exceptions are disabled).
   void* p;
   while ((p = std::__libcpp_aligned_alloc(static_cast<std::size_t>(alignment), size)) == nullptr) {
     std::new_handler nh = std::get_new_handler();
     if (nh)
       nh();
-    else {
-#    ifndef _LIBCPP_HAS_NO_EXCEPTIONS
-      throw std::bad_alloc();
-#    else
+    else
       break;
-#    endif
-    }
   }
   return p;
 }
 
+_LIBCPP_WEAK void* operator new(std::size_t size, std::align_val_t alignment) _THROW_BAD_ALLOC {
+  void* p = operator_new_aligned_impl(size, alignment);
+#    ifndef _LIBCPP_HAS_NO_EXCEPTIONS
+  if (p == nullptr)
+    throw std::bad_alloc();
+#    endif
+  return p;
+}
+
 _LIBCPP_WEAK void* operator new(size_t size, std::align_val_t alignment, const std::nothrow_t&) noexcept {
   void* p = nullptr;
 #    ifndef _LIBCPP_HAS_NO_EXCEPTIONS

libcxxabi/src/stdlib_new_delete.cpp

@@ -30,8 +30,7 @@
 // in this shared library, so that they can be overridden by programs
 // that define non-weak copies of the functions.
 
-_LIBCPP_WEAK
-void* operator new(std::size_t size) _THROW_BAD_ALLOC {
+static void* operator_new_impl(std::size_t size) noexcept {
   if (size == 0)
     size = 1;
   void* p;
@@ -42,15 +41,21 @@ void* operator new(std::size_t size) _THROW_BAD_ALLOC {
     if (nh)
       nh();
     else
-#ifndef _LIBCPP_HAS_NO_EXCEPTIONS
-      throw std::bad_alloc();
-#else
       break;
-#endif
   }
   return p;
 }
 
+_LIBCPP_WEAK
+void* operator new(std::size_t size) _THROW_BAD_ALLOC {
+  void* p = operator_new_impl(size);
+#ifndef _LIBCPP_HAS_NO_EXCEPTIONS
+  if (p == nullptr)
+    throw std::bad_alloc();
+#endif
+  return p;
+}
+
 _LIBCPP_WEAK
 void* operator new(size_t size, const std::nothrow_t&) noexcept {
   void* p = nullptr;
@@ -102,8 +107,7 @@ void operator delete[](void* ptr, size_t) noexcept { ::operator delete[](ptr); }
 
 #if !defined(_LIBCPP_HAS_NO_LIBRARY_ALIGNED_ALLOCATION)
 
-_LIBCPP_WEAK
-void* operator new(std::size_t size, std::align_val_t alignment) _THROW_BAD_ALLOC {
+static void* operator_new_aligned_impl(std::size_t size, std::align_val_t alignment) noexcept {
   if (size == 0)
     size = 1;
   if (static_cast<size_t>(alignment) < sizeof(void*))
@@ -112,25 +116,27 @@ void* operator new(std::size_t size, std::align_val_t alignment) _THROW_BAD_ALLO
   // Try allocating memory. If allocation fails and there is a new_handler,
   // call it to try free up memory, and try again until it succeeds, or until
   // the new_handler decides to terminate.
-  //
-  // If allocation fails and there is no new_handler, we throw bad_alloc
-  // (or return nullptr if exceptions are disabled).
   void* p;
   while ((p = std::__libcpp_aligned_alloc(static_cast<std::size_t>(alignment), size)) == nullptr) {
     std::new_handler nh = std::get_new_handler();
     if (nh)
       nh();
-    else {
-#  ifndef _LIBCPP_HAS_NO_EXCEPTIONS
-      throw std::bad_alloc();
-#  else
+    else
       break;
-#  endif
-    }
   }
   return p;
 }
 
+_LIBCPP_WEAK
+void* operator new(std::size_t size, std::align_val_t alignment) _THROW_BAD_ALLOC {
+  void* p = operator_new_aligned_impl(size, alignment);
+#  ifndef _LIBCPP_HAS_NO_EXCEPTIONS
+  if (p == nullptr)
+    throw std::bad_alloc();
+#  endif
+  return p;
+}
+
 _LIBCPP_WEAK
 void* operator new(size_t size, std::align_val_t alignment, const std::nothrow_t&) noexcept {
   void* p = nullptr;