re PR c++/65945 (C++ alignment of nullptr_t is 1 and might cause unaligned stores to the frame)

	PR c++/65945
	* decl.c (cxx_init_decl_processing): Set TYPE_ALIGN of nullptr_t.
	* class.c (layout_nonempty_base_or_field): Warn if that affects
	the offset of a field.

From-SVN: r225270

5 files changed, 53 insertions, 0 deletions

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 33fe38e..2ade465 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,10 @@
+2015-07-01  Jason Merrill  <jason@redhat.com>
+
+	PR c++/65945
+	* decl.c (cxx_init_decl_processing): Set TYPE_ALIGN of nullptr_t.
+	* class.c (layout_nonempty_base_or_field): Warn if that affects
+	the offset of a field.
+
 2015-07-01  Paolo Carlini  <paolo.carlini@oracle.com>
 
 	PR c++/60365
diff --git a/gcc/cp/class.c b/gcc/cp/class.c
index 2547b91..b5f2c34 100644
--- a/gcc/cp/class.c
+++ b/gcc/cp/class.c
@@ -4281,6 +4281,25 @@ layout_nonempty_base_or_field (record_layout_info rli,
 				       : TYPE_ALIGN (type)));
 	  normalize_rli (rli);
 	}
+      else if (TREE_CODE (type) == NULLPTR_TYPE
+	       && warn_abi && abi_version_crosses (9))
+	{
+	  /* Before ABI v9, we were giving nullptr_t alignment of 1; if
+	     the offset wasn't aligned like a pointer when we started to
+	     layout this field, that affects its position.  */
+	  tree pos = rli_size_unit_so_far (&old_rli);
+	  if (int_cst_value (pos) % TYPE_ALIGN_UNIT (ptr_type_node) != 0)
+	    {
+	      if (abi_version_at_least (9))
+		warning_at (DECL_SOURCE_LOCATION (decl), OPT_Wabi,
+			    "alignment of %qD increased in -fabi-version=9 "
+			    "(GCC 5.2)", decl);
+	      else
+		warning_at (DECL_SOURCE_LOCATION (decl), OPT_Wabi, "alignment "
+			    "of %qD will increase in -fabi-version=9", decl);
+	    }
+	  break;
+	}
       else
 	/* There was no conflict.  We're done laying out this field.  */
 	break;
diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index 9fabde7..8bea2e3 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -4007,6 +4007,8 @@ cxx_init_decl_processing (void)
     TYPE_SIZE_UNIT (nullptr_type_node) = size_int (GET_MODE_SIZE (ptr_mode));
     TYPE_UNSIGNED (nullptr_type_node) = 1;
     TYPE_PRECISION (nullptr_type_node) = GET_MODE_BITSIZE (ptr_mode);
+    if (abi_version_at_least (9))
+      TYPE_ALIGN (nullptr_type_node) = GET_MODE_ALIGNMENT (ptr_mode);
     SET_TYPE_MODE (nullptr_type_node, ptr_mode);
     record_builtin_type (RID_MAX, "decltype(nullptr)", nullptr_type_node);
     nullptr_node = build_int_cst (nullptr_type_node, 0);
diff --git a/gcc/testsuite/g++.dg/abi/nullptr-align.C b/gcc/testsuite/g++.dg/abi/nullptr-align.C
new file mode 100644
index 0000000..7de365a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/abi/nullptr-align.C
@@ -0,0 +1,5 @@
+// PR c++/65945
+// { dg-do compile { target c++11 } }
+// { dg-options "-fabi-version=9" }
+
+static_assert(alignof (decltype (nullptr)) == alignof (void *), "");
diff --git a/gcc/testsuite/g++.dg/abi/nullptr-align2.C b/gcc/testsuite/g++.dg/abi/nullptr-align2.C
new file mode 100644
index 0000000..66a9011
--- /dev/null
+++ b/gcc/testsuite/g++.dg/abi/nullptr-align2.C
@@ -0,0 +1,20 @@
+// { dg-do compile { target c++11 } }
+// { dg-options "-fabi-version=0 -Wabi=8" }
+
+struct A
+{
+  decltype(nullptr) n;
+  decltype(nullptr) n2;
+};
+
+struct B
+{
+  void *p;
+  decltype(nullptr) n;
+};
+
+struct C
+{
+  char c;
+  decltype(nullptr) n;		// { dg-warning "alignment" }
+};