PR libstdc++/77691 increase allocation size to at least alignment

It's not safe to assume that malloc(n) returns memory aligned to more
than n, so when relying on the guaranteed alignment of malloc ensure
that the number of bytes allocated is at least as large as the
alignment.

	PR libstdc++/77691
	* include/experimental/memory_resource (__resource_adaptor_imp): Do
	not allocate sizes smaller than alignment when relying on guaranteed
	alignment.
	* testsuite/experimental/memory_resource/new_delete_resource.cc:
	Adjust expected number of bytes allocated for alignof(max_align_t).

From-SVN: r265068

libstdc++-v3/ChangeLog

+2018-10-12  Jonathan Wakely  <jwakely@redhat.com>
+
+	PR libstdc++/77691
+	* include/experimental/memory_resource (__resource_adaptor_imp): Do
+	not allocate sizes smaller than alignment when relying on guaranteed
+	alignment.
+	* testsuite/experimental/memory_resource/new_delete_resource.cc:
+	Adjust expected number of bytes allocated for alignof(max_align_t).
+
 2018-10-11  François Dumont  <fdumont@gcc.gnu.org>
 
 	* include/debug/forward_list

libstdc++-v3/include/experimental/memory_resource

@@ -421,7 +421,12 @@ namespace pmr {
       do_allocate(size_t __bytes, size_t __alignment) override
       {
 	if (__alignment <= __guaranteed_alignment<_Alloc>::value)
-	  return _M_alloc.allocate(__bytes);
+	  {
+	    if (__bytes < __alignment)
+	      __bytes = __alignment;
+	    return _M_alloc.allocate(__bytes);
+	  }
+
 
 	const _AlignMgr __mgr(__bytes, __alignment);
 	// Assume _M_alloc returns 1-byte aligned memory, so allocate enough
@@ -437,6 +442,8 @@ namespace pmr {
 	auto __ptr = static_cast<char*>(__p);
 	if (__alignment <= __guaranteed_alignment<_Alloc>::value)
 	  {
+	    if (__bytes < __alignment)
+	      __bytes = __alignment;
 	    _M_alloc.deallocate(__ptr, __bytes);
 	    return;
 	  }

libstdc++-v3/testsuite/experimental/memory_resource/new_delete_resource.cc

@@ -109,11 +109,13 @@ test03()
   using std::size_t;
   void* p = nullptr;
 
+  auto max = [](int n, int a) { return n > a ? n : a; };
+
   bytes_allocated = 0;
 
   memory_resource* r1 = new_delete_resource();
-  p = r1->allocate(1);
-  VERIFY( bytes_allocated == 1 );
+  p = r1->allocate(1); // uses alignment = alignof(max_align_t)
+  VERIFY( bytes_allocated <= alignof(max_align_t) );
   VERIFY( aligned<max_align_t>(p) );
   r1->deallocate(p, 1);
   VERIFY( bytes_allocated == 0 );
@@ -125,13 +127,13 @@ test03()
   VERIFY( bytes_allocated == 0 );
 
   p = r1->allocate(3, alignof(short));
-  VERIFY( bytes_allocated == 3 );
+  VERIFY( bytes_allocated == max(3, alignof(short)) );
   VERIFY( aligned<short>(p) );
   r1->deallocate(p, 3, alignof(short));
   VERIFY( bytes_allocated == 0 );
 
   p = r1->allocate(4, alignof(long));
-  VERIFY( bytes_allocated == 4 );
+  VERIFY( bytes_allocated == max(4, alignof(long)) );
   VERIFY( aligned<long>(p) );
   r1->deallocate(p, 4, alignof(long));
   VERIFY( bytes_allocated == 0 );