c-family: attribute ((aligned, mode)) [PR100545]

The problem here was that handle_mode_attribute clobbered the changes of any
previous attribute, only copying type qualifiers to the new type.  And
common_handle_aligned_attribute had previously set up the typedef, so when
we later called set_underlying_type it saw DECL_ORIGINAL_TYPE set and just
returned, even though handle_mode_attribute had messed up the TREE_TYPE.
So, let's fix handle_mode_attribute to copy attributes, alignment, and
typedefness to the new type.

	PR c/100545

gcc/c-family/ChangeLog:

	* c-attribs.cc (handle_mode_attribute): Copy attributes, aligned,
	and typedef.
	* c-common.cc (set_underlying_type): Add assert.

gcc/testsuite/ChangeLog:

	* c-c++-common/attr-mode-1.c: New test.
	* c-c++-common/attr-mode-2.c: New test.

1 files changed, 15 insertions, 1 deletions

diff --git a/gcc/c-family/c-attribs.cc b/gcc/c-family/c-attribs.cc
index 111a33f..b1953a4 100644
--- a/gcc/c-family/c-attribs.cc
+++ b/gcc/c-family/c-attribs.cc
@@ -2199,7 +2199,21 @@ handle_mode_attribute (tree *node, tree name, tree args,
 	  return NULL_TREE;
 	}
 
-      *node = build_qualified_type (typefm, TYPE_QUALS (type));
+      /* Copy any quals and attributes to the new type.  */
+      *node = build_type_attribute_qual_variant (typefm, TYPE_ATTRIBUTES (type),
+						 TYPE_QUALS (type));
+      if (TYPE_USER_ALIGN (type))
+	*node = build_aligned_type (*node, TYPE_ALIGN (type));
+
+      tree decl = node[2];
+      if (decl && TYPE_NAME (type) == decl)
+	{
+	  /* Set up the typedef all over again.  */
+	  DECL_ORIGINAL_TYPE (decl) = NULL_TREE;
+	  TREE_TYPE (decl) = *node;
+	  set_underlying_type (decl);
+	  *node = TREE_TYPE (decl);
+	}
     }
 
   return NULL_TREE;