Index: gcc/emit-rtl.c
===================================================================
--- gcc/emit-rtl.c	2012-11-10 22:17:24.797602770 +0000
+++ gcc/emit-rtl.c	2012-11-10 22:19:17.779228832 +0000
@@ -1679,11 +1679,7 @@ set_mem_attributes_minus_bitpos (rtx ref
     attrs.align = MAX (attrs.align, TYPE_ALIGN (type));
 
   /* If the size is known, we can set that.  */
-  if (TYPE_SIZE_UNIT (type) && host_integerp (TYPE_SIZE_UNIT (type), 1))
-    {
-      attrs.size_known_p = true;
-      attrs.size = tree_low_cst (TYPE_SIZE_UNIT (type), 1);
-    }
+  tree new_size = TYPE_SIZE_UNIT (type);
 
   /* If T is not a type, we may be able to deduce some more information about
      the expression.  */
@@ -1742,13 +1738,7 @@ set_mem_attributes_minus_bitpos (rtx ref
 	  attrs.offset_known_p = true;
 	  attrs.offset = 0;
 	  apply_bitpos = bitpos;
-	  if (DECL_SIZE_UNIT (t) && host_integerp (DECL_SIZE_UNIT (t), 1))
-	    {
-	      attrs.size_known_p = true;
-	      attrs.size = tree_low_cst (DECL_SIZE_UNIT (t), 1);
-	    }
-	  else
-	    attrs.size_known_p = false;
+	  new_size = DECL_SIZE_UNIT (t);
 	  attrs.align = DECL_ALIGN (t);
 	  align_computed = true;
 	}
@@ -1763,19 +1753,15 @@ set_mem_attributes_minus_bitpos (rtx ref
 	  align_computed = true;
 	}
 
-      /* If this is a field reference and not a bit-field, record it.  */
-      /* ??? There is some information that can be gleaned from bit-fields,
-	 such as the word offset in the structure that might be modified.
-	 But skip it for now.  */
-      else if (TREE_CODE (t) == COMPONENT_REF
-	       && ! DECL_BIT_FIELD (TREE_OPERAND (t, 1)))
+      /* If this is a field reference, record it.  */
+      else if (TREE_CODE (t) == COMPONENT_REF)
 	{
 	  attrs.expr = t;
 	  attrs.offset_known_p = true;
 	  attrs.offset = 0;
 	  apply_bitpos = bitpos;
-	  /* ??? Any reason the field size would be different than
-	     the size we got from the type?  */
+	  if (DECL_BIT_FIELD (TREE_OPERAND (t, 1)))
+	    new_size = DECL_SIZE_UNIT (TREE_OPERAND (t, 1));
 	}
 
       /* If this is an array reference, look for an outer field reference.  */
@@ -1861,6 +1847,12 @@ set_mem_attributes_minus_bitpos (rtx ref
   else
     as = TYPE_ADDR_SPACE (type);
 
+  if (host_integerp (new_size, 1))
+    {
+      attrs.size_known_p = true;
+      attrs.size = tree_low_cst (new_size, 1);
+    }
+
   /* If we modified OFFSET based on T, then subtract the outstanding
      bit position offset.  Similarly, increase the size of the accessed
      object to contain the negative offset.  */
Index: gcc/expr.c
===================================================================
--- gcc/expr.c	2012-11-10 22:19:14.000000000 +0000
+++ gcc/expr.c	2012-11-10 22:21:17.615919793 +0000
@@ -4821,8 +4821,6 @@ expand_assignment (tree to, tree from, b
 		 done for MEM.  Also set MEM_KEEP_ALIAS_SET_P if needed.  */
 	      if (volatilep)
 		MEM_VOLATILE_P (to_rtx) = 1;
-	      if (component_uses_parent_alias_set (to))
-		MEM_KEEP_ALIAS_SET_P (to_rtx) = 1;
 	    }
 
 	  if (optimize_bitfield_assignment_op (bitsize, bitpos,