Re: [C++ PATCH] Fix a regression from build_cplus_array_type recent change (PR c++/54038)

[Jason Merrill]

On 07/20/2012 09:26 AM, Jakub Jelinek wrote:
As detailed in the PR, I believe we should only add c into m's variant chain
if m's element type is the main variant of c's element type.

We want c to get onto the appropriate variant chain even if it isn't 
m's, so I'm applying this patch instead.

Tested x86_64-pc-linux-gnu, applying to trunk and 4.7.
commit 3e16b98aa7e47f321974b5623cd68d2671a87f1e
Author: Jason Merrill <ja...@redhat.com>
Date:   Fri Jul 20 11:19:07 2012 -0400

    	PR c++/54038
    	* tree.c (build_cplus_array_type): Use build_cplus_array_type to build
    	canonical array type rather than mess with its TYPE_*_VARIANT.

diff --git a/gcc/cp/tree.c b/gcc/cp/tree.c
index 1e98f85..de9e0f6 100644
--- a/gcc/cp/tree.c
+++ b/gcc/cp/tree.c
@@ -786,7 +786,18 @@ build_cplus_array_type (tree elt_type, tree index_type)
 	}
     }
   else
-    t = build_array_type (elt_type, index_type);
+    {
+      if (!TYPE_STRUCTURAL_EQUALITY_P (elt_type)
+	  && !(index_type && TYPE_STRUCTURAL_EQUALITY_P (index_type))
+	  && (TYPE_CANONICAL (elt_type) != elt_type
+	      || (index_type && TYPE_CANONICAL (index_type) != index_type)))
+	/* Make sure that the canonical type is on the appropriate
+	   variants list.  */
+	build_cplus_array_type
+	  (TYPE_CANONICAL (elt_type),
+	   index_type ? TYPE_CANONICAL (index_type) : index_type);
+      t = build_array_type (elt_type, index_type);
+    }
 
   /* We want TYPE_MAIN_VARIANT of an array to strip cv-quals from the
      element type as well, so fix it up if needed.  */
@@ -794,7 +805,6 @@ build_cplus_array_type (tree elt_type, tree index_type)
     {
       tree m = build_cplus_array_type (TYPE_MAIN_VARIANT (elt_type),
 				       index_type);
-      tree c = TYPE_CANONICAL (t);
 
       if (TYPE_MAIN_VARIANT (t) != m)
 	{
@@ -802,15 +812,6 @@ build_cplus_array_type (tree elt_type, tree index_type)
 	  TYPE_NEXT_VARIANT (t) = TYPE_NEXT_VARIANT (m);
 	  TYPE_NEXT_VARIANT (m) = t;
 	}
-
-      /* If we built a new array type for TYPE_CANONICAL, add
-	 that to the list of variants as well.  */
-      if (c && c != t && TYPE_MAIN_VARIANT (c) != m)
-	{
-	  TYPE_MAIN_VARIANT (c) = m;
-	  TYPE_NEXT_VARIANT (c) = t;
-	  TYPE_NEXT_VARIANT (m) = c;
-	}
     }
 
   /* Push these needs up so that initialization takes place
diff --git a/gcc/testsuite/g++.dg/other/array7.C b/gcc/testsuite/g++.dg/other/array7.C
new file mode 100644
index 0000000..72322f0
--- /dev/null
+++ b/gcc/testsuite/g++.dg/other/array7.C
@@ -0,0 +1,9 @@
+// PR c++/54038
+
+extern const char *const v[];
+typedef char T;
+void foo (const T *const[]);
+struct A
+{
+  static const char *const a[];
+};