PR c/27184: bad alias sets for incomplete array types

[Alexandre Oliva <aoliva at redhat dot com>]

The testcase included in the patch below fails at -O2 because the
pointers to arrays with unknown bounds are regarded as unrelated
types.  That's because incomplete array types were not unified by
build_array_type, presumably to avoid modifying shared types if/when
such incomplete array types get completed, even though there was only
one case that set TYPE_DOMAIN without avoiding modifying shared array
types.  Other languages didn't seem to be affected, and the testsuite
results supported this impression.

Bootstrapped and tested on amd64-linux-gnu.  Ok to install?

for  gcc/ChangeLog
from  Alexandre Oliva  <aoliva@redhat.com>

	PR c/27184
	* tree.c (build_array_type): Unify array types with
	unspecified index_type.
	* c-decl.c (grokdeclarator): Make sure we do not modify a
	unified incomplete array type.
	* c-typeck.c (store_init_value): Create distinct type before
	filling in the index type in an initializer from a compound
	literal.

for  gcc/testsuite/ChangeLog
from  Alexandre Oliva  <aoliva@redhat.com>

	PR c/27184
	* gcc.dg/torture/pr27184.c: New test.

Index: gcc/c-decl.c
===================================================================
--- gcc/c-decl.c.orig	2006-05-29 05:57:01.000000000 -0300
+++ gcc/c-decl.c	2006-05-29 15:48:19.000000000 -0300
@@ -4291,6 +4291,18 @@ grokdeclarator (const struct c_declarato
 		    size_varies = 1;
 		  }
 	      }
+	    else if (decl_context == TYPENAME)
+	      {
+		if (array_parm_vla_unspec_p)
+		  {
+		    /* The error is printed elsewhere.  We use this to
+		       avoid messing up with incomplete array types of
+		       the same type, that would otherwise be modified
+		       below.  */
+		    itype = build_range_type (sizetype, size_zero_node,
+					      NULL_TREE);
+		  }
+	      }
 
 	     /* Complain about arrays of incomplete types.  */
 	    if (!COMPLETE_TYPE_P (type))
@@ -4299,11 +4311,22 @@ grokdeclarator (const struct c_declarato
 		type = error_mark_node;
 	      }
 	    else
+	      /* When itype is NULL, a shared incomplete array type is
+		 returned for all array of a given type.  Elsewhere we
+		 make sure we don't complete that type before copying
+		 it, but here we want to make sure we don't ever
+		 modify the shared type, so we gcc_assert (itype)
+		 below.  */
 	      type = build_array_type (type, itype);
 
 	    if (type != error_mark_node)
 	      {
 		if (size_varies)
+		  /* It is ok to modify type here even if itype is
+		     NULL: if size_varies, we're in a
+		     multi-dimentional array and the inner type has
+		     variable size, so the enclosing shared array type
+		     must too.  */
 		  C_TYPE_VARIABLE_SIZE (type) = 1;
 
 		/* The GCC extension for zero-length arrays differs from
@@ -4311,11 +4334,13 @@ grokdeclarator (const struct c_declarato
 		   zero.  */
 		if (size && integer_zerop (size))
 		  {
+		    gcc_assert (itype);
 		    TYPE_SIZE (type) = bitsize_zero_node;
 		    TYPE_SIZE_UNIT (type) = size_zero_node;
 		  }
 		if (array_parm_vla_unspec_p)
 		  {
+		    gcc_assert (itype);
 		    /* The type is complete.  C99 6.7.5.2p4  */
 		    TYPE_SIZE (type) = bitsize_zero_node;
 		    TYPE_SIZE_UNIT (type) = size_zero_node;
Index: gcc/c-typeck.c
===================================================================
--- gcc/c-typeck.c.orig	2006-05-29 05:57:01.000000000 -0300
+++ gcc/c-typeck.c	2006-05-29 06:03:46.000000000 -0300
@@ -4301,16 +4301,18 @@ store_init_value (tree decl, tree init)
 
       if (TREE_CODE (inside_init) == COMPOUND_LITERAL_EXPR)
 	{
-	  tree decl = COMPOUND_LITERAL_EXPR_DECL (inside_init);
+	  tree cldecl = COMPOUND_LITERAL_EXPR_DECL (inside_init);
 
-	  if (TYPE_DOMAIN (TREE_TYPE (decl)))
+	  if (TYPE_DOMAIN (TREE_TYPE (cldecl)))
 	    {
 	      /* For int foo[] = (int [3]){1}; we need to set array size
 		 now since later on array initializer will be just the
 		 brace enclosed list of the compound literal.  */
-	      TYPE_DOMAIN (type) = TYPE_DOMAIN (TREE_TYPE (decl));
+	      type = build_distinct_type_copy (TYPE_MAIN_VARIANT (type));
+	      TREE_TYPE (decl) = type;
+	      TYPE_DOMAIN (type) = TYPE_DOMAIN (TREE_TYPE (cldecl));
 	      layout_type (type);
-	      layout_decl (decl, 0);
+	      layout_decl (cldecl, 0);
 	    }
 	}
     }
Index: gcc/tree.c
===================================================================
--- gcc/tree.c.orig	2006-05-29 05:57:01.000000000 -0300
+++ gcc/tree.c	2006-05-29 06:03:46.000000000 -0300
@@ -5060,7 +5060,11 @@ build_array_type (tree elt_type, tree in
   
   if (index_type == 0)
     {
-      layout_type (t);
+      tree save = t;
+      hashcode = iterative_hash_object (TYPE_HASH (elt_type), hashcode);
+      t = type_hash_canon (hashcode, t);
+      if (save == t)
+	layout_type (t);
       return t;
     }
 
Index: gcc/testsuite/gcc.dg/torture/pr27184.c
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ gcc/testsuite/gcc.dg/torture/pr27184.c	2006-05-29 06:03:36.000000000 -0300
@@ -0,0 +1,22 @@
+/* Copyright 2006 Free Software Foundation */
+
+/* Make sure a and a1 alias each other.
+   Incomplete array types used to not be unified, which broke aliasing.  */
+
+/* { dg-do run } */
+
+typedef long atype[];
+typedef long atype1[];
+int NumSift (atype *a, atype1 *a1)
+{
+  (*a)[0] = 0;
+  (*a1)[0] = 1;
+  return (*a)[0];
+}
+int main(void)
+{
+  long a[2];
+  if (!NumSift(&a, &a))
+    __builtin_abort ();
+  return 0;
+}

-- 
Alexandre Oliva         http://www.lsd.ic.unicamp.br/~oliva/
Secretary for FSF Latin America        http://www.fsfla.org/
Red Hat Compiler Engineer   aoliva@{redhat.com, gcc.gnu.org}
Free Software Evangelist  oliva@{lsd.ic.unicamp.br, gnu.org}