fix middle-end/19687

[Richard Henderson <rth at redhat dot com>]

After seeing Alan Modra post an incorrect patch for this problem,
I was spurred to make this an execute test to validate correctness.

Tested on i386-linux.


r~



Index: expr.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/expr.c,v
retrieving revision 1.776
diff -u -p -r1.776 expr.c
--- expr.c	27 Jan 2005 00:07:41 -0000	1.776
+++ expr.c	30 Jan 2005 02:13:20 -0000
@@ -4364,29 +4364,33 @@ categorize_ctor_elements_1 (tree ctor, H
 	  || TREE_CODE (TREE_TYPE (ctor)) == QUAL_UNION_TYPE))
     {
       tree init_sub_type;
+      bool clear_this = true;
 
-      /* We don't expect more than one element of the union to be
-	 initialized.  Not sure what we should do otherwise... */
       list = CONSTRUCTOR_ELTS (ctor);
-      gcc_assert (TREE_CHAIN (list) == NULL);
-
-      init_sub_type = TREE_TYPE (TREE_VALUE (list));
-
-      /* ??? We could look at each element of the union, and find the
-	 largest element.  Which would avoid comparing the size of the
-	 initialized element against any tail padding in the union.
-	 Doesn't seem worth the effort...  */
-      if (simple_cst_equal (TYPE_SIZE (TREE_TYPE (ctor)), 
-			    TYPE_SIZE (init_sub_type)) == 1)
-	{
-	  /* And now we have to find out if the element itself is fully
-	     constructed.  E.g. for union { struct { int a, b; } s; } u
-	     = { .s = { .a = 1 } }.  */
-	  if (elt_count != count_type_elements (init_sub_type))
-	    *p_must_clear = true;
+      if (list)
+	{
+	  /* We don't expect more than one element of the union to be
+	     initialized.  Not sure what we should do otherwise... */
+          gcc_assert (TREE_CHAIN (list) == NULL);
+
+          init_sub_type = TREE_TYPE (TREE_VALUE (list));
+
+	  /* ??? We could look at each element of the union, and find the
+	     largest element.  Which would avoid comparing the size of the
+	     initialized element against any tail padding in the union.
+	     Doesn't seem worth the effort...  */
+	  if (simple_cst_equal (TYPE_SIZE (TREE_TYPE (ctor)), 
+				TYPE_SIZE (init_sub_type)) == 1)
+	    {
+	      /* And now we have to find out if the element itself is fully
+		 constructed.  E.g. for union { struct { int a, b; } s; } u
+		 = { .s = { .a = 1 } }.  */
+	      if (elt_count == count_type_elements (init_sub_type))
+		clear_this = false;
+	    }
 	}
-      else
-	*p_must_clear = true;
+
+      *p_must_clear = clear_this;
     }
 
   *p_nz_elts += nz_elts;
Index: testsuite/gcc.c-torture/execute/pr19687.c
===================================================================
RCS file: testsuite/gcc.c-torture/execute/pr19687.c
diff -N testsuite/gcc.c-torture/execute/pr19687.c
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ testsuite/gcc.c-torture/execute/pr19687.c	30 Jan 2005 02:13:20 -0000
@@ -0,0 +1,18 @@
+extern void abort (void);
+
+union U
+{
+  int i, j[4];
+};
+
+int main ()
+{
+  union U t = {};
+  int i;
+
+  for (i = 0; i < 4; ++i)
+    if (t.j[i] != 0)
+      abort ();
+
+  return 0;
+}