diff --git a/gcc/c/c-parser.cc b/gcc/c/c-parser.cc
index c31349dae2ff..a6ed5ac43bb1 100644
--- a/gcc/c/c-parser.cc
+++ b/gcc/c/c-parser.cc
@@ -10850,9 +10850,12 @@ c_parser_postfix_expression (c_parser *parser)
 	    if (c_parser_next_token_is (parser, CPP_NAME))
 	      {
 		c_token *comp_tok = c_parser_peek_token (parser);
+		/* Ignore the counted_by attribute for reference inside
+		   offsetof since the information is not useful at all.  */
 		offsetof_ref
 		  = build_component_ref (loc, offsetof_ref, comp_tok->value,
-					 comp_tok->location, UNKNOWN_LOCATION);
+					 comp_tok->location, UNKNOWN_LOCATION,
+					 false);
 		c_parser_consume_token (parser);
 		while (c_parser_next_token_is (parser, CPP_DOT)
 		       || c_parser_next_token_is (parser,
@@ -10879,11 +10882,14 @@ c_parser_postfix_expression (c_parser *parser)
 			    break;
 			  }
 			c_token *comp_tok = c_parser_peek_token (parser);
+			/* Ignore the counted_by attribute for reference inside
+			   offsetof since the information is not useful.  */
 			offsetof_ref
 			  = build_component_ref (loc, offsetof_ref,
 						 comp_tok->value,
 						 comp_tok->location,
-						 UNKNOWN_LOCATION);
+						 UNKNOWN_LOCATION,
+						 false);
 			c_parser_consume_token (parser);
 		      }
 		    else
diff --git a/gcc/c/c-tree.h b/gcc/c/c-tree.h
index c7c23edc4840..59b69ca54f0f 100644
--- a/gcc/c/c-tree.h
+++ b/gcc/c/c-tree.h
@@ -778,7 +778,7 @@ extern void mark_exp_read (tree);
 extern tree composite_type (tree, tree);
 extern tree lookup_field (tree, tree);
 extern tree build_component_ref (location_t, tree, tree, location_t,
-				 location_t);
+				 location_t, bool = true);
 extern tree build_array_ref (location_t, tree, tree);
 extern tree build_omp_array_section (location_t, tree, tree, tree);
 extern tree build_external_ref (location_t, tree, bool, tree *);
diff --git a/gcc/c/c-typeck.cc b/gcc/c/c-typeck.cc
index cead0a055068..f7b0e08459b0 100644
--- a/gcc/c/c-typeck.cc
+++ b/gcc/c/c-typeck.cc
@@ -2546,15 +2546,116 @@ should_suggest_deref_p (tree datum_type)
     return false;
 }
 
+/* For a SUBDATUM field of a structure or union DATUM, generate a REF to
+   the object that represents its counted_by per the attribute counted_by
+   attached to this field if it's a flexible array member field, otherwise
+   return NULL_TREE.
+   set COUNTED_BY_TYPE to the TYPE of the counted_by field.
+   For example, if:
+
+    struct P {
+      int k;
+      int x[] __attribute__ ((counted_by (k)));
+    } *p;
+
+    for:
+    p->x
+
+    the ref to the object that represents its element count will be:
+
+    &(p->k)
+
+*/
+static tree
+build_counted_by_ref (tree datum, tree subdatum, tree *counted_by_type)
+{
+  tree type = TREE_TYPE (datum);
+  if (!(c_flexible_array_member_type_p (TREE_TYPE (subdatum))))
+    return NULL_TREE;
+
+  tree attr_counted_by = lookup_attribute ("counted_by",
+					   DECL_ATTRIBUTES (subdatum));
+  tree counted_by_ref = NULL_TREE;
+  *counted_by_type = NULL_TREE;
+  if (attr_counted_by)
+    {
+      tree field_id = TREE_VALUE (TREE_VALUE (attr_counted_by));
+      counted_by_ref
+	= build_component_ref (UNKNOWN_LOCATION,
+			       datum, field_id,
+			       UNKNOWN_LOCATION, UNKNOWN_LOCATION);
+      counted_by_ref = build_fold_addr_expr (counted_by_ref);
+
+      /* Get the TYPE of the counted_by field.  */
+      tree counted_by_field = lookup_field (type, field_id);
+      gcc_assert (counted_by_field);
+
+      do
+	{
+	  *counted_by_type = TREE_TYPE (TREE_VALUE (counted_by_field));
+	  counted_by_field = TREE_CHAIN (counted_by_field);
+	}
+      while (counted_by_field);
+    }
+  return counted_by_ref;
+}
+
+/* Given a COMPONENT_REF REF with the location LOC, the corresponding
+   COUNTED_BY_REF, and the COUNTED_BY_TYPE, generate an INDIRECT_REF
+   to a call to the internal function .ACCESS_WITH_SIZE.
+
+   REF
+
+   to:
+
+   (*.ACCESS_WITH_SIZE (REF, COUNTED_BY_REF, 1, (TYPE_OF_SIZE)0, -1))
+
+   NOTE: The return type of this function is the POINTER type pointing
+   to the original flexible array type.
+   Then the type of the INDIRECT_REF is the original flexible array type.
+
+   The type of the first argument of this function is a POINTER type
+   to the original flexible array type.
+
+   The 4th argument of the call is a constant 0 with the TYPE of the
+   object pointed by COUNTED_BY_REF.
+
+  */
+static tree
+build_access_with_size_for_counted_by (location_t loc, tree ref,
+				       tree counted_by_ref,
+				       tree counted_by_type)
+{
+  gcc_assert (c_flexible_array_member_type_p (TREE_TYPE (ref)));
+  /* The result type of the call is a pointer to the flexible array type.  */
+  tree result_type = build_pointer_type (TREE_TYPE (ref));
+
+  tree call
+    = build_call_expr_internal_loc (loc, IFN_ACCESS_WITH_SIZE,
+				    result_type, 5,
+				    array_to_pointer_conversion (loc, ref),
+				    counted_by_ref,
+				    build_int_cst (integer_type_node, 1),
+				    build_int_cst (counted_by_type, 0),
+				    build_int_cst (integer_type_node, -1));
+  /* Wrap the call with an INDIRECT_REF with the flexible array type.  */
+  call = build1 (INDIRECT_REF, TREE_TYPE (ref), call);
+  SET_EXPR_LOCATION (call, loc);
+  return call;
+}
+
 /* Make an expression to refer to the COMPONENT field of structure or
    union value DATUM.  COMPONENT is an IDENTIFIER_NODE.  LOC is the
    location of the COMPONENT_REF.  COMPONENT_LOC is the location
    of COMPONENT.  ARROW_LOC is the location of the first -> operand if
-   it is from -> operator.  */
+   it is from -> operator.
+   If HANDLE_COUNTED_BY is true, check the counted_by attribute and generate
+   a call to .ACCESS_WITH_SIZE.  Otherwise, ignore the attribute.  */
 
 tree
 build_component_ref (location_t loc, tree datum, tree component,
-		     location_t component_loc, location_t arrow_loc)
+		     location_t component_loc, location_t arrow_loc,
+		     bool handle_counted_by)
 {
   tree type = TREE_TYPE (datum);
   enum tree_code code = TREE_CODE (type);
@@ -2626,7 +2727,13 @@ build_component_ref (location_t loc, tree datum, tree component,
 	  int quals;
 	  tree subtype;
 	  bool use_datum_quals;
-
+	  tree counted_by_type = NULL_TREE;
+	  /* Do not handle counted_by when in typeof and alignof operator.  */
+	  handle_counted_by = handle_counted_by && !in_typeof && !in_alignof;
+	  tree counted_by_ref = handle_counted_by
+				? build_counted_by_ref (datum, subdatum,
+							&counted_by_type)
+				: NULL_TREE;
 	  if (TREE_TYPE (subdatum) == error_mark_node)
 	    return error_mark_node;
 
@@ -2645,6 +2752,12 @@ build_component_ref (location_t loc, tree datum, tree component,
 	  ref = build3 (COMPONENT_REF, subtype, datum, subdatum,
 			NULL_TREE);
 	  SET_EXPR_LOCATION (ref, loc);
+
+	  if (counted_by_ref)
+	    ref = build_access_with_size_for_counted_by (loc, ref,
+							 counted_by_ref,
+							 counted_by_type);
+
 	  if (TREE_READONLY (subdatum)
 	      || (use_datum_quals && TREE_READONLY (datum)))
 	    TREE_READONLY (ref) = 1;
@@ -5048,7 +5161,11 @@ build_unary_op (location_t location, enum tree_code code, tree xarg,
 	  goto return_build_unary_op;
 	}
 
-      /* Ordinary case; arg is a COMPONENT_REF or a decl.  */
+      /* Ordinary case; arg is a COMPONENT_REF or a decl, or a call to
+	 .ACCESS_WITH_SIZE.  */
+      if (is_access_with_size_p (arg))
+	arg = TREE_OPERAND (TREE_OPERAND (CALL_EXPR_ARG (arg, 0), 0), 0);
+
       argtype = TREE_TYPE (arg);
 
       /* If the lvalue is const or volatile, merge that into the type
@@ -5195,6 +5312,9 @@ lvalue_p (const_tree ref)
     case BIND_EXPR:
       return TREE_CODE (TREE_TYPE (ref)) == ARRAY_TYPE;
 
+    case CALL_EXPR:
+      return is_access_with_size_p (ref);
+
     default:
       return false;
     }
diff --git a/gcc/internal-fn.cc b/gcc/internal-fn.cc
index a07f25f3aee3..e744080ee670 100644
--- a/gcc/internal-fn.cc
+++ b/gcc/internal-fn.cc
@@ -3393,6 +3393,41 @@ expand_DEFERRED_INIT (internal_fn, gcall *stmt)
     }
 }
 
+/* Expand the IFN_ACCESS_WITH_SIZE function:
+   ACCESS_WITH_SIZE (REF_TO_OBJ, REF_TO_SIZE, CLASS_OF_SIZE,
+		     TYPE_OF_SIZE, ACCESS_MODE)
+   which returns the REF_TO_OBJ same as the 1st argument;
+
+   1st argument REF_TO_OBJ: The reference to the object;
+   2nd argument REF_TO_SIZE: The reference to the size of the object,
+   3rd argument CLASS_OF_SIZE: The size referenced by the REF_TO_SIZE represents
+     0: the number of bytes.
+     1: the number of the elements of the object type;
+   4th argument TYPE_OF_SIZE: A constant 0 with its TYPE being the same as the TYPE
+    of the object referenced by REF_TO_SIZE
+   5th argument ACCESS_MODE:
+    -1: Unknown access semantics
+     0: none
+     1: read_only
+     2: write_only
+     3: read_write
+
+   Both the return type and the type of the first argument of this
+   function have been converted from the incomplete array type to
+   the corresponding pointer type.
+
+   For each call to a .ACCESS_WITH_SIZE, replace it with its 1st argument.  */
+static void
+expand_ACCESS_WITH_SIZE (internal_fn, gcall *stmt)
+{
+  tree lhs = gimple_call_lhs (stmt);
+  tree ref_to_obj = gimple_call_arg (stmt, 0);
+  if (lhs)
+    expand_assignment (lhs, ref_to_obj, false);
+  else
+    emit_insn (expand_normal (ref_to_obj));
+}
+
 /* The size of an OpenACC compute dimension.  */
 
 static void
diff --git a/gcc/internal-fn.def b/gcc/internal-fn.def
index c14d30365c14..0801c8bfe61d 100644
--- a/gcc/internal-fn.def
+++ b/gcc/internal-fn.def
@@ -510,6 +510,10 @@ DEF_INTERNAL_FN (PHI, 0, NULL)
    automatic variable.  */
 DEF_INTERNAL_FN (DEFERRED_INIT, ECF_CONST | ECF_LEAF | ECF_NOTHROW, NULL)
 
+/* A function to associate the access size and access mode information
+   with the corresponding reference to an object.  */
+DEF_INTERNAL_FN (ACCESS_WITH_SIZE, ECF_LEAF | ECF_NOTHROW, NULL)
+
 /* DIM_SIZE and DIM_POS return the size of a particular compute
    dimension and the executing thread's position within that
    dimension.  DIM_POS is pure (and not const) so that it isn't
diff --git a/gcc/testsuite/gcc.dg/flex-array-counted-by-2.c b/gcc/testsuite/gcc.dg/flex-array-counted-by-2.c
new file mode 100644
index 000000000000..d4899a63af3c
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/flex-array-counted-by-2.c
@@ -0,0 +1,112 @@
+/* Test the code generation for the new attribute counted_by.
+   And also the offsetof operator on such array.  */
+/* { dg-do run } */
+/* { dg-options "-O2 -fdump-tree-original" } */
+
+#include <stdlib.h>
+
+struct annotated {
+  int b;
+  char c[] __attribute__ ((counted_by (b)));
+} *array_annotated;
+
+static struct annotated static_annotated = { sizeof "hello", "hello" };
+static char *y = static_annotated.c;
+
+struct flex {
+  int b;
+  char c[]; 
+}; 
+
+struct nested_annotated {
+  struct {
+    union {
+      int b;
+      float f;	
+    };
+    int n;
+  };
+  char c[] __attribute__ ((counted_by (b)));
+} *array_nested_annotated;
+
+static struct nested_annotated nested_static_annotated
+				 = { sizeof "hello1", 0, "hello1" };
+static char *nested_y = nested_static_annotated.c;
+
+struct nested_flex {
+  struct {
+    union {
+      int b;
+      float f;	
+    };
+    int n;
+  };
+  char c[];
+};
+
+void __attribute__((__noinline__)) setup (int normal_count, int attr_count)
+{
+  array_annotated
+    = (struct annotated *)malloc (sizeof (struct annotated)
+				  + attr_count *  sizeof (char));
+  array_annotated->b = attr_count;
+
+  array_nested_annotated
+    = (struct nested_annotated *)malloc (sizeof (struct nested_annotated)
+					 + attr_count *  sizeof (char));
+  array_nested_annotated->b = attr_count;
+
+  return;
+}
+
+void __attribute__((__noinline__)) test (char a, char b)
+{
+  if (__builtin_offsetof (struct annotated, c[0])
+      != __builtin_offsetof (struct flex, c[0]))
+    abort ();
+  if (__builtin_offsetof (struct annotated, c[1])
+      != __builtin_offsetof (struct flex, c[1]))
+    abort ();
+  if (__builtin_offsetof (struct nested_annotated, c[0]) 
+      != __builtin_offsetof (struct nested_flex, c[0])) 
+    abort ();
+  if (__builtin_offsetof (struct nested_annotated, c[1]) 
+      != __builtin_offsetof (struct nested_flex, c[1])) 
+    abort ();
+
+  if (__builtin_types_compatible_p (typeof (array_annotated->c),
+				    typeof (&(array_annotated->c)[0])))
+    abort ();
+  if (__builtin_types_compatible_p (typeof (array_nested_annotated->c),
+				    typeof (&(array_nested_annotated->c)[0])))
+    abort ();
+
+  if (__alignof (array_annotated->c) != __alignof (char))
+    abort ();
+  if (__alignof (array_nested_annotated->c) != __alignof (char))
+    abort ();
+
+  if ((unsigned long) array_annotated->c != (unsigned long) &array_annotated->c)
+    abort ();
+  if ((unsigned long) array_nested_annotated->c
+       != (unsigned long) &array_nested_annotated->c)
+    abort ();
+
+  array_annotated->c[2] = a;
+  array_nested_annotated->c[3] = b;
+
+  if (y[2] != 'l') abort ();
+  if (nested_y[4] !='o') abort ();
+
+}
+
+int main(int argc, char *argv[])
+{
+  setup (10,10);   
+  test ('A', 'B');
+  if (array_annotated->c[2] != 'A') abort ();
+  if (array_nested_annotated->c[3] != 'B') abort ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump-times "ACCESS_WITH_SIZE" 8 "original" } } */
diff --git a/gcc/tree-ssa-alias.cc b/gcc/tree-ssa-alias.cc
index e7c1c1aa6243..8c070e173bdd 100644
--- a/gcc/tree-ssa-alias.cc
+++ b/gcc/tree-ssa-alias.cc
@@ -2823,6 +2823,7 @@ ref_maybe_used_by_call_p_1 (gcall *call, ao_ref *ref, bool tbaa_p)
 	return false;
       case IFN_MASK_STORE_LANES:
       case IFN_MASK_LEN_STORE_LANES:
+      case IFN_ACCESS_WITH_SIZE:
 	goto process_args;
       case IFN_MASK_LOAD:
       case IFN_LEN_LOAD:
@@ -3073,6 +3074,7 @@ call_may_clobber_ref_p_1 (gcall *call, ao_ref *ref, bool tbaa_p)
       case IFN_UBSAN_OBJECT_SIZE:
       case IFN_UBSAN_PTR:
       case IFN_ASAN_CHECK:
+      case IFN_ACCESS_WITH_SIZE:
 	return false;
       case IFN_MASK_STORE:
       case IFN_LEN_STORE:
diff --git a/gcc/tree-ssa-dce.cc b/gcc/tree-ssa-dce.cc
index 636c471d4c89..a54fb1b754dd 100644
--- a/gcc/tree-ssa-dce.cc
+++ b/gcc/tree-ssa-dce.cc
@@ -1459,8 +1459,8 @@ eliminate_unnecessary_stmts (bool aggressive)
 		  update_stmt (stmt);
 		  release_ssa_name (name);
 
-		  /* GOMP_SIMD_LANE (unless three argument) or ASAN_POISON
-		     without lhs is not needed.  */
+		  /* GOMP_SIMD_LANE (unless three argument), ASAN_POISON
+		     or .ACCESS_WITH_SIZE without lhs is not needed.  */
 		  if (gimple_call_internal_p (stmt))
 		    switch (gimple_call_internal_fn (stmt))
 		      {
@@ -1470,6 +1470,7 @@ eliminate_unnecessary_stmts (bool aggressive)
 			  break;
 			/* FALLTHRU */
 		      case IFN_ASAN_POISON:
+		      case IFN_ACCESS_WITH_SIZE:
 			remove_dead_stmt (&gsi, bb, to_remove_edges);
 			break;
 		      default:
diff --git a/gcc/tree.cc b/gcc/tree.cc
index 3dff8c510832..5fdb425f612a 100644
--- a/gcc/tree.cc
+++ b/gcc/tree.cc
@@ -4068,7 +4068,8 @@ process_call_operands (tree t)
   int i = call_expr_flags (t);
 
   /* Calls have side-effects, except those to const or pure functions.  */
-  if ((i & ECF_LOOPING_CONST_OR_PURE) || !(i & (ECF_CONST | ECF_PURE)))
+  if ((i & ECF_LOOPING_CONST_OR_PURE)
+      || (!(i & (ECF_CONST | ECF_PURE)) && !is_access_with_size_p (t)))
     side_effects = true;
   /* Propagate TREE_READONLY of arguments for const functions.  */
   if (i & ECF_CONST)
@@ -13362,6 +13363,28 @@ component_ref_size (tree ref, special_array_member *sam /* = NULL */)
 	  ? NULL_TREE : size_zero_node);
 }
 
+/* Return true if the given node CALL is a call to a .ACCESS_WITH_SIZE
+   function.  */
+bool
+is_access_with_size_p (const_tree call)
+{
+  if (TREE_CODE (call) != CALL_EXPR)
+    return false;
+  if (CALL_EXPR_IFN (call) == IFN_ACCESS_WITH_SIZE)
+    return true;
+  return false;
+}
+
+/* Get the corresponding reference from the call to a .ACCESS_WITH_SIZE.
+ * i.e the first argument of this call.  Return NULL_TREE otherwise.  */
+tree
+get_ref_from_access_with_size (tree call)
+{
+  if (is_access_with_size_p (call))
+    return  CALL_EXPR_ARG (call, 0);
+  return NULL_TREE;
+}
+
 /* Return the machine mode of T.  For vectors, returns the mode of the
    inner type.  The main use case is to feed the result to HONOR_NANS,
    avoiding the BLKmode that a direct TYPE_MODE (T) might return.  */
diff --git a/gcc/tree.h b/gcc/tree.h
index 972a067a1f7a..fbaef3e5fb5c 100644
--- a/gcc/tree.h
+++ b/gcc/tree.h
@@ -5760,6 +5760,14 @@ extern special_array_member component_ref_sam_type (tree);
    cannot be determined.  */
 extern tree component_ref_size (tree, special_array_member * = NULL);
 
+/* Return true if the given node is a call to a .ACCESS_WITH_SIZE
+   function.  */
+extern bool is_access_with_size_p (const_tree);
+
+/* Get the corresponding reference from the call to a .ACCESS_WITH_SIZE,
+ * i.e. the first argument of this call.  Return NULL_TREE otherwise.  */
+extern tree get_ref_from_access_with_size (tree);
+
 extern int tree_map_base_eq (const void *, const void *);
 extern unsigned int tree_map_base_hash (const void *);
 extern bool tree_map_base_marked_p (const void *);
diff --git a/gcc/varasm.cc b/gcc/varasm.cc
index fa17eff551e8..d75b23668925 100644
--- a/gcc/varasm.cc
+++ b/gcc/varasm.cc
@@ -5082,6 +5082,11 @@ initializer_constant_valid_p_1 (tree value, tree endtype, tree *cache)
 	}
       return ret;
 
+    case CALL_EXPR:
+      /* For a call to .ACCESS_WITH_SIZE, check the first argument.  */
+      if (tree ref = get_ref_from_access_with_size (value))
+	return initializer_constant_valid_p_1 (ref, endtype, cache);
+      /* FALLTHROUGH.  */
     default:
       break;
     }
@@ -5276,6 +5281,11 @@ output_constant (tree exp, unsigned HOST_WIDE_INT size, unsigned int align,
 	exp = TREE_OPERAND (exp, 0);
     }
 
+  /* For a call to .ACCESS_WITH_SIZE, check the first argument.  */
+  if (TREE_CODE (exp) == CALL_EXPR)
+    if (tree ref = get_ref_from_access_with_size (exp))
+      exp = ref;
+
   code = TREE_CODE (TREE_TYPE (exp));
   thissize = int_size_in_bytes (TREE_TYPE (exp));
 
