diff --git a/gcc/Makefile.in b/gcc/Makefile.in
index 375d5f5..f3bb168 100644
--- a/gcc/Makefile.in
+++ b/gcc/Makefile.in
@@ -2226,7 +2226,8 @@ stor-layout.o : stor-layout.c $(CONFIG_H) $(SYSTEM_H) coretypes.h $(TM_H) \
 asan.o : asan.c asan.h $(CONFIG_H) $(SYSTEM_H) $(GIMPLE_H) \
    output.h coretypes.h $(GIMPLE_PRETTY_PRINT_H) \
    tree-iterator.h $(TREE_FLOW_H) $(TREE_PASS_H) \
-   $(TARGET_H) $(EXPR_H) $(OPTABS_H) $(TM_P_H) langhooks.h
+   $(TARGET_H) $(EXPR_H) $(OPTABS_H) $(TM_P_H) langhooks.h \
+   $(HASH_TABLE_H) alloc-pool.h
 tsan.o : $(CONFIG_H) $(SYSTEM_H) $(TREE_H) $(TREE_INLINE_H) \
    $(GIMPLE_H) $(DIAGNOSTIC_H) langhooks.h \
    $(TM_H) coretypes.h $(TREE_DUMP_H) $(TREE_PASS_H) $(CGRAPH_H) $(GGC_H) \
diff --git a/gcc/asan.c b/gcc/asan.c
index f05e36c..3cb9511 100644
--- a/gcc/asan.c
+++ b/gcc/asan.c
@@ -34,6 +34,8 @@ along with GCC; see the file COPYING3.  If not see
 #include "output.h"
 #include "tm_p.h"
 #include "langhooks.h"
+#include "hash-table.h"
+#include "alloc-pool.h"
 
 /* AddressSanitizer finds out-of-bounds and use-after-free bugs
    with <2x slowdown on average.
@@ -212,6 +214,620 @@ alias_set_type asan_shadow_set = -1;
    alias set is used for all shadow memory accesses.  */
 static GTY(()) tree shadow_ptr_types[2];
 
+/* Hashtable support for memory references used by gimple
+   statements.  */
+
+/* This type represents a reference to a memory region.  */
+struct asan_mem_ref
+{
+  /* The expression of the begining of the memory region.  */
+  tree start;
+
+  /* The size of the access (can be 1, 2, 4, 8, 16 for now).  */
+  char access_size;
+};
+
+static alloc_pool asan_mem_ref_alloc_pool;
+
+/* This creates the alloc pool used to store the instances of
+   asan_mem_ref that are stored in the hash table asan_mem_ref_ht.  */
+
+static alloc_pool
+asan_mem_ref_get_alloc_pool ()
+{
+  if (asan_mem_ref_alloc_pool == NULL)
+    asan_mem_ref_alloc_pool = create_alloc_pool ("asan_mem_ref",
+						 sizeof (asan_mem_ref),
+						 10);
+  return asan_mem_ref_alloc_pool;
+    
+}
+
+/* Initializes an instance of asan_mem_ref.  */
+
+static void
+asan_mem_ref_init (asan_mem_ref *ref, tree start, char access_size)
+{
+  ref->start = start;
+  ref->access_size = access_size;
+}
+
+/* Allocates memory for an instance of asan_mem_ref into the memory
+   pool returned by asan_mem_ref_get_alloc_pool and initialize it.
+   START is the address of (or the expression pointing to) the
+   beginning of memory reference.  ACCESS_SIZE is the size of the
+   access to the referenced memory.  */
+
+static asan_mem_ref*
+asan_mem_ref_new (tree start, char access_size)
+{
+  asan_mem_ref *ref =
+    (asan_mem_ref *) pool_alloc (asan_mem_ref_get_alloc_pool ());
+
+  asan_mem_ref_init (ref, start, access_size);
+  return ref;
+}
+
+/* This builds and returns a pointer to the end of the memory region
+   that starts at START and of length LEN.  */
+
+tree
+asan_mem_ref_get_end (tree start, tree len)
+{
+  if (len == NULL_TREE || integer_zerop (len))
+    return start;
+
+  return fold_build2 (POINTER_PLUS_EXPR, TREE_TYPE (start), start, len);
+}
+
+/*  Return a tree expression that represents the end of the referenced
+    memory region.  Beware that this function can actually build a new
+    tree expression.  */
+
+tree
+asan_mem_ref_get_end (const asan_mem_ref *ref, tree len)
+{
+  return asan_mem_ref_get_end (ref->start, len);
+}
+
+struct asan_mem_ref_hasher
+  : typed_noop_remove <asan_mem_ref>
+{
+  typedef asan_mem_ref value_type;
+  typedef asan_mem_ref compare_type;
+
+  static inline hashval_t hash (const value_type *);
+  static inline bool equal (const value_type *, const compare_type *);
+};
+
+/* Hash a memory reference.  */
+
+inline hashval_t
+asan_mem_ref_hasher::hash (const asan_mem_ref *mem_ref)
+{
+  hashval_t h = iterative_hash_expr (mem_ref->start, 0);
+  h = iterative_hash_hashval_t (h, mem_ref->access_size);
+  return h;
+}
+
+/* Compare two memory references.  We accept the length of either
+   memory references to be NULL_TREE.  */
+
+inline bool
+asan_mem_ref_hasher::equal (const asan_mem_ref *m1,
+			    const asan_mem_ref *m2)
+{
+  return (m1->access_size == m2->access_size
+	  && operand_equal_p (m1->start, m2->start, 0));
+}
+
+static hash_table <asan_mem_ref_hasher> asan_mem_ref_ht;
+
+/* Returns a reference to the hash table containing memory references.
+   This function ensures that the hash table is created.  Note that
+   this hash table is updated by the function
+   update_mem_ref_hash_table.  */
+
+static hash_table <asan_mem_ref_hasher> &
+get_mem_ref_hash_table ()
+{
+  if (!asan_mem_ref_ht.is_created ())
+    asan_mem_ref_ht.create (10);
+
+  return asan_mem_ref_ht;
+}
+
+/* Clear all entries from the memory references hash table.  */
+
+static void
+empty_mem_ref_hash_table ()
+{
+  if (asan_mem_ref_ht.is_created ())
+    asan_mem_ref_ht.empty ();
+}
+
+/* Free the memory references hash table.  */
+
+static void
+free_mem_ref_resources ()
+{
+  if (asan_mem_ref_ht.is_created ())
+    asan_mem_ref_ht.dispose ();
+
+  if (asan_mem_ref_alloc_pool)
+    {
+      free_alloc_pool (asan_mem_ref_alloc_pool);
+      asan_mem_ref_alloc_pool = NULL;
+    }
+}
+
+/* Return true iff the memory reference REF has been instrumented.  */
+
+static bool
+has_mem_ref_been_instrumented (tree ref, char access_size)
+{
+  asan_mem_ref r;
+  asan_mem_ref_init (&r, ref, access_size);
+
+  return (get_mem_ref_hash_table ().find (&r) != NULL);
+}
+
+/* Return true iff the memory reference REF has been instrumented.  */
+
+static bool
+has_mem_ref_been_instrumented (const asan_mem_ref *ref)
+{
+  return has_mem_ref_been_instrumented (ref->start, ref->access_size);
+}
+
+/* Return true iff access to memory region starting at REF and of
+   length LEN has been instrumented.  */
+
+static bool
+has_mem_ref_been_instrumented (const asan_mem_ref *ref, tree len)
+{
+  /* First let's see if the address of the beginning of REF has been
+     instrumented.  */
+  if (!has_mem_ref_been_instrumented (ref))
+    return false;
+
+  if (len != 0)
+    {
+      /* Let's see if the end of the region has been instrumented.  */
+      if (!has_mem_ref_been_instrumented (asan_mem_ref_get_end (ref, len),
+					  ref->access_size))
+	return false;
+    }
+  return true;
+}
+
+/* Set REF to the memory reference present in a gimple assignment
+   ASSIGNMENT.  Return true upon successful completion, false
+   otherwise.  */
+
+static bool
+get_mem_ref_of_assignment (const gimple assignment,
+			   asan_mem_ref *ref,
+			   bool *ref_is_store)
+{
+  gcc_assert (gimple_assign_single_p (assignment));
+
+  if (gimple_store_p (assignment))
+    {
+      ref->start = gimple_assign_lhs (assignment);
+      *ref_is_store = true;
+    }
+  else if (gimple_assign_load_p (assignment))
+    {
+      ref->start = gimple_assign_rhs1 (assignment);
+      *ref_is_store = false;
+    }
+  else
+    return false;
+
+  ref->access_size = int_size_in_bytes (TREE_TYPE (ref->start));
+  return true;
+}
+
+/* Return the memory references contained in a gimple statement
+   representing a builtin call that has to do with memory access.  */
+
+static bool
+get_mem_refs_of_builtin_call (const gimple call,
+			      asan_mem_ref *src0,
+			      tree *src0_len,
+			      bool *src0_is_store,
+			      asan_mem_ref *src1,
+			      tree *src1_len,
+			      bool *src1_is_store,
+			      asan_mem_ref *dst,
+			      tree *dst_len,
+			      bool *dst_is_store,
+			      bool *dest_is_deref)
+{
+  gcc_checking_assert (gimple_call_builtin_p (call, BUILT_IN_NORMAL));
+
+  tree callee = gimple_call_fndecl (call);
+  tree source0 = NULL_TREE, source1 = NULL_TREE,
+    dest = NULL_TREE, len = NULL_TREE;
+  bool is_store = true, got_reference_p = false;
+  char access_size = 1;
+
+  switch (DECL_FUNCTION_CODE (callee))
+    {
+      /* (s, s, n) style memops.  */
+    case BUILT_IN_BCMP:
+    case BUILT_IN_MEMCMP:
+      source0 = gimple_call_arg (call, 0);
+      source1 = gimple_call_arg (call, 1);
+      len = gimple_call_arg (call, 2);
+      break;
+
+      /* (src, dest, n) style memops.  */
+    case BUILT_IN_BCOPY:
+      source0 = gimple_call_arg (call, 0);
+      dest = gimple_call_arg (call, 1);
+      len = gimple_call_arg (call, 2);
+      break;
+
+      /* (dest, src, n) style memops.  */
+    case BUILT_IN_MEMCPY:
+    case BUILT_IN_MEMCPY_CHK:
+    case BUILT_IN_MEMMOVE:
+    case BUILT_IN_MEMMOVE_CHK:
+    case BUILT_IN_MEMPCPY:
+    case BUILT_IN_MEMPCPY_CHK:
+      dest = gimple_call_arg (call, 0);
+      source0 = gimple_call_arg (call, 1);
+      len = gimple_call_arg (call, 2);
+      break;
+
+      /* (dest, n) style memops.  */
+    case BUILT_IN_BZERO:
+      dest = gimple_call_arg (call, 0);
+      len = gimple_call_arg (call, 1);
+      break;
+
+      /* (dest, x, n) style memops*/
+    case BUILT_IN_MEMSET:
+    case BUILT_IN_MEMSET_CHK:
+      dest = gimple_call_arg (call, 0);
+      len = gimple_call_arg (call, 2);
+      break;
+
+    case BUILT_IN_STRLEN:
+      source0 = gimple_call_arg (call, 0);
+      len = gimple_call_lhs (call);
+      break ;
+
+    /* And now the __atomic* and __sync builtins.
+       These are handled differently from the classical memory memory
+       access builtins above.  */
+
+    case BUILT_IN_ATOMIC_LOAD_1:
+    case BUILT_IN_ATOMIC_LOAD_2:
+    case BUILT_IN_ATOMIC_LOAD_4:
+    case BUILT_IN_ATOMIC_LOAD_8:
+    case BUILT_IN_ATOMIC_LOAD_16:
+      is_store = false;
+      /* fall through.  */
+
+    case BUILT_IN_SYNC_FETCH_AND_ADD_1:
+    case BUILT_IN_SYNC_FETCH_AND_ADD_2:
+    case BUILT_IN_SYNC_FETCH_AND_ADD_4:
+    case BUILT_IN_SYNC_FETCH_AND_ADD_8:
+    case BUILT_IN_SYNC_FETCH_AND_ADD_16:
+
+    case BUILT_IN_SYNC_FETCH_AND_SUB_1:
+    case BUILT_IN_SYNC_FETCH_AND_SUB_2:
+    case BUILT_IN_SYNC_FETCH_AND_SUB_4:
+    case BUILT_IN_SYNC_FETCH_AND_SUB_8:
+    case BUILT_IN_SYNC_FETCH_AND_SUB_16:
+
+    case BUILT_IN_SYNC_FETCH_AND_OR_1:
+    case BUILT_IN_SYNC_FETCH_AND_OR_2:
+    case BUILT_IN_SYNC_FETCH_AND_OR_4:
+    case BUILT_IN_SYNC_FETCH_AND_OR_8:
+    case BUILT_IN_SYNC_FETCH_AND_OR_16:
+
+    case BUILT_IN_SYNC_FETCH_AND_AND_1:
+    case BUILT_IN_SYNC_FETCH_AND_AND_2:
+    case BUILT_IN_SYNC_FETCH_AND_AND_4:
+    case BUILT_IN_SYNC_FETCH_AND_AND_8:
+    case BUILT_IN_SYNC_FETCH_AND_AND_16:
+
+    case BUILT_IN_SYNC_FETCH_AND_XOR_1:
+    case BUILT_IN_SYNC_FETCH_AND_XOR_2:
+    case BUILT_IN_SYNC_FETCH_AND_XOR_4:
+    case BUILT_IN_SYNC_FETCH_AND_XOR_8:
+    case BUILT_IN_SYNC_FETCH_AND_XOR_16:
+
+    case BUILT_IN_SYNC_FETCH_AND_NAND_1:
+    case BUILT_IN_SYNC_FETCH_AND_NAND_2:
+    case BUILT_IN_SYNC_FETCH_AND_NAND_4:
+    case BUILT_IN_SYNC_FETCH_AND_NAND_8:
+
+    case BUILT_IN_SYNC_ADD_AND_FETCH_1:
+    case BUILT_IN_SYNC_ADD_AND_FETCH_2:
+    case BUILT_IN_SYNC_ADD_AND_FETCH_4:
+    case BUILT_IN_SYNC_ADD_AND_FETCH_8:
+    case BUILT_IN_SYNC_ADD_AND_FETCH_16:
+
+    case BUILT_IN_SYNC_SUB_AND_FETCH_1:
+    case BUILT_IN_SYNC_SUB_AND_FETCH_2:
+    case BUILT_IN_SYNC_SUB_AND_FETCH_4:
+    case BUILT_IN_SYNC_SUB_AND_FETCH_8:
+    case BUILT_IN_SYNC_SUB_AND_FETCH_16:
+
+    case BUILT_IN_SYNC_OR_AND_FETCH_1:
+    case BUILT_IN_SYNC_OR_AND_FETCH_2:
+    case BUILT_IN_SYNC_OR_AND_FETCH_4:
+    case BUILT_IN_SYNC_OR_AND_FETCH_8:
+    case BUILT_IN_SYNC_OR_AND_FETCH_16:
+
+    case BUILT_IN_SYNC_AND_AND_FETCH_1:
+    case BUILT_IN_SYNC_AND_AND_FETCH_2:
+    case BUILT_IN_SYNC_AND_AND_FETCH_4:
+    case BUILT_IN_SYNC_AND_AND_FETCH_8:
+    case BUILT_IN_SYNC_AND_AND_FETCH_16:
+
+    case BUILT_IN_SYNC_XOR_AND_FETCH_1:
+    case BUILT_IN_SYNC_XOR_AND_FETCH_2:
+    case BUILT_IN_SYNC_XOR_AND_FETCH_4:
+    case BUILT_IN_SYNC_XOR_AND_FETCH_8:
+    case BUILT_IN_SYNC_XOR_AND_FETCH_16:
+
+    case BUILT_IN_SYNC_NAND_AND_FETCH_1:
+    case BUILT_IN_SYNC_NAND_AND_FETCH_2:
+    case BUILT_IN_SYNC_NAND_AND_FETCH_4:
+    case BUILT_IN_SYNC_NAND_AND_FETCH_8:
+
+    case BUILT_IN_SYNC_BOOL_COMPARE_AND_SWAP_1:
+    case BUILT_IN_SYNC_BOOL_COMPARE_AND_SWAP_2:
+    case BUILT_IN_SYNC_BOOL_COMPARE_AND_SWAP_4:
+    case BUILT_IN_SYNC_BOOL_COMPARE_AND_SWAP_8:
+    case BUILT_IN_SYNC_BOOL_COMPARE_AND_SWAP_16:
+
+    case BUILT_IN_SYNC_VAL_COMPARE_AND_SWAP_1:
+    case BUILT_IN_SYNC_VAL_COMPARE_AND_SWAP_2:
+    case BUILT_IN_SYNC_VAL_COMPARE_AND_SWAP_4:
+    case BUILT_IN_SYNC_VAL_COMPARE_AND_SWAP_8:
+    case BUILT_IN_SYNC_VAL_COMPARE_AND_SWAP_16:
+
+    case BUILT_IN_SYNC_LOCK_TEST_AND_SET_1:
+    case BUILT_IN_SYNC_LOCK_TEST_AND_SET_2:
+    case BUILT_IN_SYNC_LOCK_TEST_AND_SET_4:
+    case BUILT_IN_SYNC_LOCK_TEST_AND_SET_8:
+    case BUILT_IN_SYNC_LOCK_TEST_AND_SET_16:
+
+    case BUILT_IN_SYNC_LOCK_RELEASE_1:
+    case BUILT_IN_SYNC_LOCK_RELEASE_2:
+    case BUILT_IN_SYNC_LOCK_RELEASE_4:
+    case BUILT_IN_SYNC_LOCK_RELEASE_8:
+    case BUILT_IN_SYNC_LOCK_RELEASE_16:
+
+    case BUILT_IN_ATOMIC_EXCHANGE_1:
+    case BUILT_IN_ATOMIC_EXCHANGE_2:
+    case BUILT_IN_ATOMIC_EXCHANGE_4:
+    case BUILT_IN_ATOMIC_EXCHANGE_8:
+    case BUILT_IN_ATOMIC_EXCHANGE_16:
+
+    case BUILT_IN_ATOMIC_COMPARE_EXCHANGE_1:
+    case BUILT_IN_ATOMIC_COMPARE_EXCHANGE_2:
+    case BUILT_IN_ATOMIC_COMPARE_EXCHANGE_4:
+    case BUILT_IN_ATOMIC_COMPARE_EXCHANGE_8:
+    case BUILT_IN_ATOMIC_COMPARE_EXCHANGE_16:
+
+    case BUILT_IN_ATOMIC_STORE_1:
+    case BUILT_IN_ATOMIC_STORE_2:
+    case BUILT_IN_ATOMIC_STORE_4:
+    case BUILT_IN_ATOMIC_STORE_8:
+    case BUILT_IN_ATOMIC_STORE_16:
+
+    case BUILT_IN_ATOMIC_ADD_FETCH_1:
+    case BUILT_IN_ATOMIC_ADD_FETCH_2:
+    case BUILT_IN_ATOMIC_ADD_FETCH_4:
+    case BUILT_IN_ATOMIC_ADD_FETCH_8:
+    case BUILT_IN_ATOMIC_ADD_FETCH_16:
+
+    case BUILT_IN_ATOMIC_SUB_FETCH_1:
+    case BUILT_IN_ATOMIC_SUB_FETCH_2:
+    case BUILT_IN_ATOMIC_SUB_FETCH_4:
+    case BUILT_IN_ATOMIC_SUB_FETCH_8:
+    case BUILT_IN_ATOMIC_SUB_FETCH_16:
+
+    case BUILT_IN_ATOMIC_AND_FETCH_1:
+    case BUILT_IN_ATOMIC_AND_FETCH_2:
+    case BUILT_IN_ATOMIC_AND_FETCH_4:
+    case BUILT_IN_ATOMIC_AND_FETCH_8:
+    case BUILT_IN_ATOMIC_AND_FETCH_16:
+
+    case BUILT_IN_ATOMIC_NAND_FETCH_1:
+    case BUILT_IN_ATOMIC_NAND_FETCH_2:
+    case BUILT_IN_ATOMIC_NAND_FETCH_4:
+    case BUILT_IN_ATOMIC_NAND_FETCH_8:
+    case BUILT_IN_ATOMIC_NAND_FETCH_16:
+
+    case BUILT_IN_ATOMIC_XOR_FETCH_1:
+    case BUILT_IN_ATOMIC_XOR_FETCH_2:
+    case BUILT_IN_ATOMIC_XOR_FETCH_4:
+    case BUILT_IN_ATOMIC_XOR_FETCH_8:
+    case BUILT_IN_ATOMIC_XOR_FETCH_16:
+
+    case BUILT_IN_ATOMIC_OR_FETCH_1:
+    case BUILT_IN_ATOMIC_OR_FETCH_2:
+    case BUILT_IN_ATOMIC_OR_FETCH_4:
+    case BUILT_IN_ATOMIC_OR_FETCH_8:
+    case BUILT_IN_ATOMIC_OR_FETCH_16:
+
+    case BUILT_IN_ATOMIC_FETCH_ADD_1:
+    case BUILT_IN_ATOMIC_FETCH_ADD_2:
+    case BUILT_IN_ATOMIC_FETCH_ADD_4:
+    case BUILT_IN_ATOMIC_FETCH_ADD_8:
+    case BUILT_IN_ATOMIC_FETCH_ADD_16:
+
+    case BUILT_IN_ATOMIC_FETCH_SUB_1:
+    case BUILT_IN_ATOMIC_FETCH_SUB_2:
+    case BUILT_IN_ATOMIC_FETCH_SUB_4:
+    case BUILT_IN_ATOMIC_FETCH_SUB_8:
+    case BUILT_IN_ATOMIC_FETCH_SUB_16:
+
+    case BUILT_IN_ATOMIC_FETCH_AND_1:
+    case BUILT_IN_ATOMIC_FETCH_AND_2:
+    case BUILT_IN_ATOMIC_FETCH_AND_4:
+    case BUILT_IN_ATOMIC_FETCH_AND_8:
+    case BUILT_IN_ATOMIC_FETCH_AND_16:
+
+    case BUILT_IN_ATOMIC_FETCH_NAND_1:
+    case BUILT_IN_ATOMIC_FETCH_NAND_2:
+    case BUILT_IN_ATOMIC_FETCH_NAND_4:
+    case BUILT_IN_ATOMIC_FETCH_NAND_8:
+    case BUILT_IN_ATOMIC_FETCH_NAND_16:
+
+    case BUILT_IN_ATOMIC_FETCH_XOR_1:
+    case BUILT_IN_ATOMIC_FETCH_XOR_2:
+    case BUILT_IN_ATOMIC_FETCH_XOR_4:
+    case BUILT_IN_ATOMIC_FETCH_XOR_8:
+    case BUILT_IN_ATOMIC_FETCH_XOR_16:
+
+    case BUILT_IN_ATOMIC_FETCH_OR_1:
+    case BUILT_IN_ATOMIC_FETCH_OR_2:
+    case BUILT_IN_ATOMIC_FETCH_OR_4:
+    case BUILT_IN_ATOMIC_FETCH_OR_8:
+    case BUILT_IN_ATOMIC_FETCH_OR_16:
+      {
+	dest = gimple_call_arg (call, 0);
+	/* DEST represents the address of a memory location.
+	   instrument_derefs wants the memory location, so lets
+	   dereference the address DEST before handing it to
+	   instrument_derefs.  */
+	if (TREE_CODE (dest) == ADDR_EXPR)
+	  dest = TREE_OPERAND (dest, 0);
+	else if (TREE_CODE (dest) == SSA_NAME)
+	  dest = build2 (MEM_REF, TREE_TYPE (TREE_TYPE (dest)),
+			 dest, build_int_cst (TREE_TYPE (dest), 0));
+	else
+	  gcc_unreachable ();
+
+	access_size = int_size_in_bytes (TREE_TYPE (dest));
+      }
+
+    default:
+      /* The other builtins memory access are not instrumented in this
+	 function because they either don't have any length parameter,
+	 or their length parameter is just a limit.  */
+      break;
+    }
+
+  if (len != NULL_TREE)
+    {
+      if (source0 != NULL_TREE)
+	{
+	  src0->start = source0;
+	  src0->access_size = access_size;
+	  *src0_len = len;
+	  *src0_is_store = false;
+	}
+
+      if (source1 != NULL_TREE)
+	{
+	  src1->start = source1;
+	  src1->access_size = access_size;
+	  *src1_len = len;
+	  *src1_is_store = false;
+	}
+
+      if (dest != NULL_TREE)
+	{
+	  dst->start = dest;
+	  dst->access_size = access_size;
+	  *dst_len = len;
+	  *dst_is_store = true;
+	}
+
+      got_reference_p = true;
+    }
+    else
+      {
+	if (dest)
+	  {
+	    dst->start = dest;
+	    dst->access_size = access_size;
+	    *dst_len = NULL_TREE;
+	    *dst_is_store = is_store;
+	    *dest_is_deref = true;
+	    got_reference_p = true;
+	  }
+      }
+
+    return got_reference_p;
+}
+
+/* Return true iff a given gimple statement has been instrumented.
+   Note that the statement is "defined" by the memory references it
+   contains.  */
+
+static bool
+has_stmt_been_instrumented_p (gimple stmt)
+{
+  if (gimple_assign_single_p (stmt))
+    {
+      bool r_is_store;
+      asan_mem_ref r;
+      asan_mem_ref_init (&r, NULL, 1);
+
+      if (get_mem_ref_of_assignment (stmt, &r, &r_is_store))
+	return has_mem_ref_been_instrumented (&r);
+    }
+  else if (gimple_call_builtin_p (stmt, BUILT_IN_NORMAL))
+    {
+      asan_mem_ref src0, src1, dest;
+      asan_mem_ref_init (&src0, NULL, 1);
+      asan_mem_ref_init (&src1, NULL, 1);
+      asan_mem_ref_init (&dest, NULL, 1);
+
+      tree src0_len = NULL_TREE, src1_len = NULL_TREE, dest_len = NULL_TREE;
+      bool src0_is_store = false, src1_is_store = false,
+	dest_is_store = false, dest_is_deref = false;
+      if (get_mem_refs_of_builtin_call (stmt,
+					&src0, &src0_len, &src0_is_store,
+					&src1, &src1_len, &src1_is_store,
+					&dest, &dest_len, &dest_is_store,
+					&dest_is_deref))
+	{
+	  if (src0.start != NULL_TREE
+	      && !has_mem_ref_been_instrumented (&src0, src0_len))
+	    return false;
+
+	  if (src1.start != NULL_TREE
+	      && !has_mem_ref_been_instrumented (&src1, src1_len))
+	    return false;
+
+	  if (dest.start != NULL_TREE
+	      && !has_mem_ref_been_instrumented (&dest, dest_len))
+	    return false;
+
+	  return true;
+	}
+    }
+  return false;
+}
+
+/*  Insert a memory reference into the hash table.  */
+
+static void
+update_mem_ref_hash_table (tree ref, char access_size)
+{
+  hash_table <asan_mem_ref_hasher> ht = get_mem_ref_hash_table ();
+
+  asan_mem_ref r;
+  asan_mem_ref_init (&r, ref, access_size);
+
+  asan_mem_ref **slot = ht.find_slot (&r, INSERT);
+  if (*slot == NULL)
+    *slot = asan_mem_ref_new (ref, access_size);
+}
+
 /* Initialize shadow_ptr_types array.  */
 
 static void
@@ -835,7 +1451,7 @@ build_check_stmt (location_t location, tree base, gimple_stmt_iterator *iter,
 
 static void
 instrument_derefs (gimple_stmt_iterator *iter, tree t,
-		  location_t location, bool is_store)
+		   location_t location, bool is_store)
 {
   tree type, base;
   HOST_WIDE_INT size_in_bytes;
@@ -878,8 +1494,14 @@ instrument_derefs (gimple_stmt_iterator *iter, tree t,
     }
 
   base = build_fold_addr_expr (t);
-  build_check_stmt (location, base, iter, /*before_p=*/true,
-		    is_store, size_in_bytes);
+  if (!has_mem_ref_been_instrumented (base, size_in_bytes))
+    {
+      build_check_stmt (location, base, iter, /*before_p=*/true,
+			is_store, size_in_bytes);
+      update_mem_ref_hash_table (base, size_in_bytes);
+      update_mem_ref_hash_table (t, size_in_bytes);
+    }
+
 }
 
 /* Instrument an access to a contiguous memory region that starts at
@@ -903,6 +1525,12 @@ instrument_mem_region_access (tree base, tree len,
   gimple_stmt_iterator gsi = *iter;
 
   basic_block fallthrough_bb = NULL, then_bb = NULL;
+
+  /* If the beginning of the memory region has already been
+     instrumented, do not instrument it.  */
+  if (has_mem_ref_been_instrumented (base, 1))
+    goto after_first_instrumentation;
+
   if (!is_gimple_constant (len))
     {
       /* So, the length of the memory area to asan-protect is
@@ -945,9 +1573,19 @@ instrument_mem_region_access (tree base, tree len,
   else
     *iter = gsi;
 
+  update_mem_ref_hash_table (base, 1);
+
+ after_first_instrumentation:
+
   /* We want to instrument the access at the end of the memory region,
      which is at (base + len - 1).  */
 
+  /* If the end of the memory region has already been instrumented, do
+     not instrument it. */
+  tree end = asan_mem_ref_get_end (base, len);
+  if (has_mem_ref_been_instrumented (end, 1))
+    return;
+
   /* offset = len - 1;  */
   len = unshare_expr (len);
   tree offset;
@@ -982,434 +1620,221 @@ instrument_mem_region_access (tree base, tree len,
       g = gimple_build_assign_with_ops (MINUS_EXPR, t, len,
 					build_int_cst (size_type_node, 1));
       gimple_set_location (g, location);
-      gimple_seq_add_stmt_without_update (&seq, g);
-      offset = gimple_assign_lhs (g);
-    }
-
-  /* _1 = base;  */
-  base = unshare_expr (base);
-  gimple region_end =
-    gimple_build_assign_with_ops (TREE_CODE (base),
-				  make_ssa_name (TREE_TYPE (base), NULL),
-				  base, NULL);
-  gimple_set_location (region_end, location);
-  gimple_seq_add_stmt_without_update (&seq, region_end);
-  gsi_insert_seq_before (&gsi, seq, GSI_SAME_STMT);
-  gsi_prev (&gsi);
-
-  /* _2 = _1 + offset;  */
-  region_end =
-    gimple_build_assign_with_ops (POINTER_PLUS_EXPR,
-				  make_ssa_name (TREE_TYPE (base), NULL),
-				  gimple_assign_lhs (region_end),
-				  offset);
-  gimple_set_location (region_end, location);
-  gsi_insert_after (&gsi, region_end, GSI_NEW_STMT);
-
-  /* instrument access at _2;  */
-  build_check_stmt (location, gimple_assign_lhs (region_end),
-		    &gsi, /*before_p=*/false, is_store, 1);
-}
-
-/* Instrument the call (to the builtin strlen function) pointed to by
-   ITER.
-
-   This function instruments the access to the first byte of the
-   argument, right before the call.  After the call it instruments the
-   access to the last byte of the argument; it uses the result of the
-   call to deduce the offset of that last byte.
-
-   Upon completion, iff the call has actullay been instrumented, this
-   function returns TRUE and *ITER points to the statement logically
-   following the built-in strlen function call *ITER was initially
-   pointing to.  Otherwise, the function returns FALSE and *ITER
-   remains unchanged.  */
-
-static bool
-instrument_strlen_call (gimple_stmt_iterator *iter)
-{
-  gimple call = gsi_stmt (*iter);
-  gcc_assert (is_gimple_call (call));
-
-  tree callee = gimple_call_fndecl (call);
-  gcc_assert (is_builtin_fn (callee)
-	      && DECL_BUILT_IN_CLASS (callee) == BUILT_IN_NORMAL
-	      && DECL_FUNCTION_CODE (callee) == BUILT_IN_STRLEN);
-
-  tree len = gimple_call_lhs (call);
-  if (len == NULL)
-    /* Some passes might clear the return value of the strlen call;
-       bail out in that case.  Return FALSE as we are not advancing
-       *ITER.  */
-    return false;
-  gcc_assert (INTEGRAL_TYPE_P (TREE_TYPE (len)));
-
-  location_t loc = gimple_location (call);
-  tree str_arg = gimple_call_arg (call, 0);
-
-  /* Instrument the access to the first byte of str_arg.  i.e:
-
-     _1 = str_arg; instrument (_1); */
-  gimple str_arg_ssa =
-    gimple_build_assign_with_ops (NOP_EXPR,
-				  make_ssa_name (build_pointer_type
-						 (char_type_node), NULL),
-				  str_arg, NULL);
-  gimple_set_location (str_arg_ssa, loc);
-  gimple_stmt_iterator gsi = *iter;
-  gsi_insert_before (&gsi, str_arg_ssa, GSI_NEW_STMT);
-  build_check_stmt (loc, gimple_assign_lhs (str_arg_ssa), &gsi,
-		    /*before_p=*/false, /*is_store=*/false, 1);
-
-  /* If we initially had an instruction like:
-
-	 int n = strlen (str)
-
-     we now want to instrument the access to str[n], after the
-     instruction above.*/
-
-  /* So let's build the access to str[n] that is, access through the
-     pointer_plus expr: (_1 + len).  */
-  gimple stmt =
-    gimple_build_assign_with_ops (POINTER_PLUS_EXPR,
-				  make_ssa_name (TREE_TYPE (str_arg),
-						 NULL),
-				  gimple_assign_lhs (str_arg_ssa),
-				  len);
-  gimple_set_location (stmt, loc);
-  gsi_insert_after (&gsi, stmt, GSI_NEW_STMT);
-
-  build_check_stmt (loc, gimple_assign_lhs (stmt), &gsi,
-		    /*before_p=*/false, /*is_store=*/false, 1);
-
-  /* Ensure that iter points to the statement logically following the
-     one it was initially pointing to.  */
-  *iter = gsi;
-  /* As *ITER has been advanced to point to the next statement, let's
-     return true to inform transform_statements that it shouldn't
-     advance *ITER anymore; otherwises it will skip that next
-     statement, which wouldn't be instrumented.  */
-  return true;
-}
-
-/* Instrument the call to a built-in memory access function that is
-   pointed to by the iterator ITER.
-
-   Upon completion, return TRUE iff *ITER has been advanced to the
-   statement following the one it was originally pointing to.  */
-
-static bool
-instrument_builtin_call (gimple_stmt_iterator *iter)
-{
-  gimple call = gsi_stmt (*iter);
-
-  gcc_checking_assert (is_gimple_builtin_call (call));
-
-  tree callee = gimple_call_fndecl (call);
-  location_t loc = gimple_location (call);
-  tree source0 = NULL_TREE, source1 = NULL_TREE,
-    dest = NULL_TREE, len = NULL_TREE;
-  bool is_store = true;
-
-  switch (DECL_FUNCTION_CODE (callee))
-    {
-      /* (s, s, n) style memops.  */
-    case BUILT_IN_BCMP:
-    case BUILT_IN_MEMCMP:
-      source0 = gimple_call_arg (call, 0);
-      source1 = gimple_call_arg (call, 1);
-      len = gimple_call_arg (call, 2);
-      break;
-
-      /* (src, dest, n) style memops.  */
-    case BUILT_IN_BCOPY:
-      source0 = gimple_call_arg (call, 0);
-      dest = gimple_call_arg (call, 1);
-      len = gimple_call_arg (call, 2);
-      break;
-
-      /* (dest, src, n) style memops.  */
-    case BUILT_IN_MEMCPY:
-    case BUILT_IN_MEMCPY_CHK:
-    case BUILT_IN_MEMMOVE:
-    case BUILT_IN_MEMMOVE_CHK:
-    case BUILT_IN_MEMPCPY:
-    case BUILT_IN_MEMPCPY_CHK:
-      dest = gimple_call_arg (call, 0);
-      source0 = gimple_call_arg (call, 1);
-      len = gimple_call_arg (call, 2);
-      break;
-
-      /* (dest, n) style memops.  */
-    case BUILT_IN_BZERO:
-      dest = gimple_call_arg (call, 0);
-      len = gimple_call_arg (call, 1);
-      break;
-
-      /* (dest, x, n) style memops*/
-    case BUILT_IN_MEMSET:
-    case BUILT_IN_MEMSET_CHK:
-      dest = gimple_call_arg (call, 0);
-      len = gimple_call_arg (call, 2);
-      break;
-
-    case BUILT_IN_STRLEN:
-      return instrument_strlen_call (iter);
-
-    /* And now the __atomic* and __sync builtins.
-       These are handled differently from the classical memory memory
-       access builtins above.  */
-
-    case BUILT_IN_ATOMIC_LOAD_1:
-    case BUILT_IN_ATOMIC_LOAD_2:
-    case BUILT_IN_ATOMIC_LOAD_4:
-    case BUILT_IN_ATOMIC_LOAD_8:
-    case BUILT_IN_ATOMIC_LOAD_16:
-      is_store = false;
-      /* fall through.  */
-
-    case BUILT_IN_SYNC_FETCH_AND_ADD_1:
-    case BUILT_IN_SYNC_FETCH_AND_ADD_2:
-    case BUILT_IN_SYNC_FETCH_AND_ADD_4:
-    case BUILT_IN_SYNC_FETCH_AND_ADD_8:
-    case BUILT_IN_SYNC_FETCH_AND_ADD_16:
-
-    case BUILT_IN_SYNC_FETCH_AND_SUB_1:
-    case BUILT_IN_SYNC_FETCH_AND_SUB_2:
-    case BUILT_IN_SYNC_FETCH_AND_SUB_4:
-    case BUILT_IN_SYNC_FETCH_AND_SUB_8:
-    case BUILT_IN_SYNC_FETCH_AND_SUB_16:
-
-    case BUILT_IN_SYNC_FETCH_AND_OR_1:
-    case BUILT_IN_SYNC_FETCH_AND_OR_2:
-    case BUILT_IN_SYNC_FETCH_AND_OR_4:
-    case BUILT_IN_SYNC_FETCH_AND_OR_8:
-    case BUILT_IN_SYNC_FETCH_AND_OR_16:
-
-    case BUILT_IN_SYNC_FETCH_AND_AND_1:
-    case BUILT_IN_SYNC_FETCH_AND_AND_2:
-    case BUILT_IN_SYNC_FETCH_AND_AND_4:
-    case BUILT_IN_SYNC_FETCH_AND_AND_8:
-    case BUILT_IN_SYNC_FETCH_AND_AND_16:
-
-    case BUILT_IN_SYNC_FETCH_AND_XOR_1:
-    case BUILT_IN_SYNC_FETCH_AND_XOR_2:
-    case BUILT_IN_SYNC_FETCH_AND_XOR_4:
-    case BUILT_IN_SYNC_FETCH_AND_XOR_8:
-    case BUILT_IN_SYNC_FETCH_AND_XOR_16:
-
-    case BUILT_IN_SYNC_FETCH_AND_NAND_1:
-    case BUILT_IN_SYNC_FETCH_AND_NAND_2:
-    case BUILT_IN_SYNC_FETCH_AND_NAND_4:
-    case BUILT_IN_SYNC_FETCH_AND_NAND_8:
-
-    case BUILT_IN_SYNC_ADD_AND_FETCH_1:
-    case BUILT_IN_SYNC_ADD_AND_FETCH_2:
-    case BUILT_IN_SYNC_ADD_AND_FETCH_4:
-    case BUILT_IN_SYNC_ADD_AND_FETCH_8:
-    case BUILT_IN_SYNC_ADD_AND_FETCH_16:
-
-    case BUILT_IN_SYNC_SUB_AND_FETCH_1:
-    case BUILT_IN_SYNC_SUB_AND_FETCH_2:
-    case BUILT_IN_SYNC_SUB_AND_FETCH_4:
-    case BUILT_IN_SYNC_SUB_AND_FETCH_8:
-    case BUILT_IN_SYNC_SUB_AND_FETCH_16:
-
-    case BUILT_IN_SYNC_OR_AND_FETCH_1:
-    case BUILT_IN_SYNC_OR_AND_FETCH_2:
-    case BUILT_IN_SYNC_OR_AND_FETCH_4:
-    case BUILT_IN_SYNC_OR_AND_FETCH_8:
-    case BUILT_IN_SYNC_OR_AND_FETCH_16:
+      gimple_seq_add_stmt_without_update (&seq, g);
+      offset = gimple_assign_lhs (g);
+    }
 
-    case BUILT_IN_SYNC_AND_AND_FETCH_1:
-    case BUILT_IN_SYNC_AND_AND_FETCH_2:
-    case BUILT_IN_SYNC_AND_AND_FETCH_4:
-    case BUILT_IN_SYNC_AND_AND_FETCH_8:
-    case BUILT_IN_SYNC_AND_AND_FETCH_16:
+  /* _1 = base;  */
+  base = unshare_expr (base);
+  gimple region_end =
+    gimple_build_assign_with_ops (TREE_CODE (base),
+				  make_ssa_name (TREE_TYPE (base), NULL),
+				  base, NULL);
+  gimple_set_location (region_end, location);
+  gimple_seq_add_stmt_without_update (&seq, region_end);
+  gsi_insert_seq_before (&gsi, seq, GSI_SAME_STMT);
+  gsi_prev (&gsi);
 
-    case BUILT_IN_SYNC_XOR_AND_FETCH_1:
-    case BUILT_IN_SYNC_XOR_AND_FETCH_2:
-    case BUILT_IN_SYNC_XOR_AND_FETCH_4:
-    case BUILT_IN_SYNC_XOR_AND_FETCH_8:
-    case BUILT_IN_SYNC_XOR_AND_FETCH_16:
+  /* _2 = _1 + offset;  */
+  region_end =
+    gimple_build_assign_with_ops (POINTER_PLUS_EXPR,
+				  make_ssa_name (TREE_TYPE (base), NULL),
+				  gimple_assign_lhs (region_end),
+				  offset);
+  gimple_set_location (region_end, location);
+  gsi_insert_after (&gsi, region_end, GSI_NEW_STMT);
 
-    case BUILT_IN_SYNC_NAND_AND_FETCH_1:
-    case BUILT_IN_SYNC_NAND_AND_FETCH_2:
-    case BUILT_IN_SYNC_NAND_AND_FETCH_4:
-    case BUILT_IN_SYNC_NAND_AND_FETCH_8:
+  /* instrument access at _2;  */
+  build_check_stmt (location, gimple_assign_lhs (region_end),
+		    &gsi, /*before_p=*/false, is_store, 1);
 
-    case BUILT_IN_SYNC_BOOL_COMPARE_AND_SWAP_1:
-    case BUILT_IN_SYNC_BOOL_COMPARE_AND_SWAP_2:
-    case BUILT_IN_SYNC_BOOL_COMPARE_AND_SWAP_4:
-    case BUILT_IN_SYNC_BOOL_COMPARE_AND_SWAP_8:
-    case BUILT_IN_SYNC_BOOL_COMPARE_AND_SWAP_16:
+  update_mem_ref_hash_table (end, 1);
+}
 
-    case BUILT_IN_SYNC_VAL_COMPARE_AND_SWAP_1:
-    case BUILT_IN_SYNC_VAL_COMPARE_AND_SWAP_2:
-    case BUILT_IN_SYNC_VAL_COMPARE_AND_SWAP_4:
-    case BUILT_IN_SYNC_VAL_COMPARE_AND_SWAP_8:
-    case BUILT_IN_SYNC_VAL_COMPARE_AND_SWAP_16:
+/* Instrument the call (to the builtin strlen function) pointed to by
+   ITER.
 
-    case BUILT_IN_SYNC_LOCK_TEST_AND_SET_1:
-    case BUILT_IN_SYNC_LOCK_TEST_AND_SET_2:
-    case BUILT_IN_SYNC_LOCK_TEST_AND_SET_4:
-    case BUILT_IN_SYNC_LOCK_TEST_AND_SET_8:
-    case BUILT_IN_SYNC_LOCK_TEST_AND_SET_16:
+   This function instruments the access to the first byte of the
+   argument, right before the call.  After the call it instruments the
+   access to the last byte of the argument; it uses the result of the
+   call to deduce the offset of that last byte.
 
-    case BUILT_IN_SYNC_LOCK_RELEASE_1:
-    case BUILT_IN_SYNC_LOCK_RELEASE_2:
-    case BUILT_IN_SYNC_LOCK_RELEASE_4:
-    case BUILT_IN_SYNC_LOCK_RELEASE_8:
-    case BUILT_IN_SYNC_LOCK_RELEASE_16:
+   Upon completion, iff the call has actullay been instrumented, this
+   function returns TRUE and *ITER points to the statement logically
+   following the built-in strlen function call *ITER was initially
+   pointing to.  Otherwise, the function returns FALSE and *ITER
+   remains unchanged.  */
 
-    case BUILT_IN_ATOMIC_EXCHANGE_1:
-    case BUILT_IN_ATOMIC_EXCHANGE_2:
-    case BUILT_IN_ATOMIC_EXCHANGE_4:
-    case BUILT_IN_ATOMIC_EXCHANGE_8:
-    case BUILT_IN_ATOMIC_EXCHANGE_16:
+static bool
+instrument_strlen_call (gimple_stmt_iterator *iter)
+{
+  gimple call = gsi_stmt (*iter);
+  gcc_assert (is_gimple_call (call));
 
-    case BUILT_IN_ATOMIC_COMPARE_EXCHANGE_1:
-    case BUILT_IN_ATOMIC_COMPARE_EXCHANGE_2:
-    case BUILT_IN_ATOMIC_COMPARE_EXCHANGE_4:
-    case BUILT_IN_ATOMIC_COMPARE_EXCHANGE_8:
-    case BUILT_IN_ATOMIC_COMPARE_EXCHANGE_16:
+  tree callee = gimple_call_fndecl (call);
+  gcc_assert (is_builtin_fn (callee)
+	      && DECL_BUILT_IN_CLASS (callee) == BUILT_IN_NORMAL
+	      && DECL_FUNCTION_CODE (callee) == BUILT_IN_STRLEN);
 
-    case BUILT_IN_ATOMIC_STORE_1:
-    case BUILT_IN_ATOMIC_STORE_2:
-    case BUILT_IN_ATOMIC_STORE_4:
-    case BUILT_IN_ATOMIC_STORE_8:
-    case BUILT_IN_ATOMIC_STORE_16:
+  tree len = gimple_call_lhs (call);
+  if (len == NULL)
+    /* Some passes might clear the return value of the strlen call;
+       bail out in that case.  Return FALSE as we are not advancing
+       *ITER.  */
+    return false;
+  gcc_assert (INTEGRAL_TYPE_P (TREE_TYPE (len)));
 
-    case BUILT_IN_ATOMIC_ADD_FETCH_1:
-    case BUILT_IN_ATOMIC_ADD_FETCH_2:
-    case BUILT_IN_ATOMIC_ADD_FETCH_4:
-    case BUILT_IN_ATOMIC_ADD_FETCH_8:
-    case BUILT_IN_ATOMIC_ADD_FETCH_16:
+  location_t loc = gimple_location (call);
+  tree str_arg = gimple_call_arg (call, 0);
 
-    case BUILT_IN_ATOMIC_SUB_FETCH_1:
-    case BUILT_IN_ATOMIC_SUB_FETCH_2:
-    case BUILT_IN_ATOMIC_SUB_FETCH_4:
-    case BUILT_IN_ATOMIC_SUB_FETCH_8:
-    case BUILT_IN_ATOMIC_SUB_FETCH_16:
+  /* Instrument the access to the first byte of str_arg.  i.e:
 
-    case BUILT_IN_ATOMIC_AND_FETCH_1:
-    case BUILT_IN_ATOMIC_AND_FETCH_2:
-    case BUILT_IN_ATOMIC_AND_FETCH_4:
-    case BUILT_IN_ATOMIC_AND_FETCH_8:
-    case BUILT_IN_ATOMIC_AND_FETCH_16:
+     _1 = str_arg; instrument (_1); */
+  gimple str_arg_ssa =
+    gimple_build_assign_with_ops (NOP_EXPR,
+				  make_ssa_name (build_pointer_type
+						 (char_type_node), NULL),
+				  str_arg, NULL);
+  gimple_set_location (str_arg_ssa, loc);
+  gimple_stmt_iterator gsi = *iter;
+  gsi_insert_before (&gsi, str_arg_ssa, GSI_NEW_STMT);
+  build_check_stmt (loc, gimple_assign_lhs (str_arg_ssa), &gsi,
+		    /*before_p=*/false, /*is_store=*/false, 1);
 
-    case BUILT_IN_ATOMIC_NAND_FETCH_1:
-    case BUILT_IN_ATOMIC_NAND_FETCH_2:
-    case BUILT_IN_ATOMIC_NAND_FETCH_4:
-    case BUILT_IN_ATOMIC_NAND_FETCH_8:
-    case BUILT_IN_ATOMIC_NAND_FETCH_16:
+  /* If we initially had an instruction like:
 
-    case BUILT_IN_ATOMIC_XOR_FETCH_1:
-    case BUILT_IN_ATOMIC_XOR_FETCH_2:
-    case BUILT_IN_ATOMIC_XOR_FETCH_4:
-    case BUILT_IN_ATOMIC_XOR_FETCH_8:
-    case BUILT_IN_ATOMIC_XOR_FETCH_16:
+	 int n = strlen (str)
 
-    case BUILT_IN_ATOMIC_OR_FETCH_1:
-    case BUILT_IN_ATOMIC_OR_FETCH_2:
-    case BUILT_IN_ATOMIC_OR_FETCH_4:
-    case BUILT_IN_ATOMIC_OR_FETCH_8:
-    case BUILT_IN_ATOMIC_OR_FETCH_16:
+     we now want to instrument the access to str[n], after the
+     instruction above.*/
 
-    case BUILT_IN_ATOMIC_FETCH_ADD_1:
-    case BUILT_IN_ATOMIC_FETCH_ADD_2:
-    case BUILT_IN_ATOMIC_FETCH_ADD_4:
-    case BUILT_IN_ATOMIC_FETCH_ADD_8:
-    case BUILT_IN_ATOMIC_FETCH_ADD_16:
+  /* So let's build the access to str[n] that is, access through the
+     pointer_plus expr: (_1 + len).  */
+  gimple stmt =
+    gimple_build_assign_with_ops (POINTER_PLUS_EXPR,
+				  make_ssa_name (TREE_TYPE (str_arg),
+						 NULL),
+				  gimple_assign_lhs (str_arg_ssa),
+				  len);
+  gimple_set_location (stmt, loc);
+  gsi_insert_after (&gsi, stmt, GSI_NEW_STMT);
 
-    case BUILT_IN_ATOMIC_FETCH_SUB_1:
-    case BUILT_IN_ATOMIC_FETCH_SUB_2:
-    case BUILT_IN_ATOMIC_FETCH_SUB_4:
-    case BUILT_IN_ATOMIC_FETCH_SUB_8:
-    case BUILT_IN_ATOMIC_FETCH_SUB_16:
+  build_check_stmt (loc, gimple_assign_lhs (stmt), &gsi,
+		    /*before_p=*/false, /*is_store=*/false, 1);
 
-    case BUILT_IN_ATOMIC_FETCH_AND_1:
-    case BUILT_IN_ATOMIC_FETCH_AND_2:
-    case BUILT_IN_ATOMIC_FETCH_AND_4:
-    case BUILT_IN_ATOMIC_FETCH_AND_8:
-    case BUILT_IN_ATOMIC_FETCH_AND_16:
+  /* Ensure that iter points to the statement logically following the
+     one it was initially pointing to.  */
+  *iter = gsi;
+  /* As *ITER has been advanced to point to the next statement, let's
+     return true to inform transform_statements that it shouldn't
+     advance *ITER anymore; otherwises it will skip that next
+     statement, which wouldn't be instrumented.  */
+  return true;
+}
 
-    case BUILT_IN_ATOMIC_FETCH_NAND_1:
-    case BUILT_IN_ATOMIC_FETCH_NAND_2:
-    case BUILT_IN_ATOMIC_FETCH_NAND_4:
-    case BUILT_IN_ATOMIC_FETCH_NAND_8:
-    case BUILT_IN_ATOMIC_FETCH_NAND_16:
+/* Instrument the call to a built-in memory access function that is
+   pointed to by the iterator ITER.
 
-    case BUILT_IN_ATOMIC_FETCH_XOR_1:
-    case BUILT_IN_ATOMIC_FETCH_XOR_2:
-    case BUILT_IN_ATOMIC_FETCH_XOR_4:
-    case BUILT_IN_ATOMIC_FETCH_XOR_8:
-    case BUILT_IN_ATOMIC_FETCH_XOR_16:
+   Upon completion, return TRUE iff *ITER has been advanced to the
+   statement following the one it was originally pointing to.  */
 
-    case BUILT_IN_ATOMIC_FETCH_OR_1:
-    case BUILT_IN_ATOMIC_FETCH_OR_2:
-    case BUILT_IN_ATOMIC_FETCH_OR_4:
-    case BUILT_IN_ATOMIC_FETCH_OR_8:
-    case BUILT_IN_ATOMIC_FETCH_OR_16:
-      {
-	dest = gimple_call_arg (call, 0);
-	/* So DEST represents the address of a memory location.
-	   instrument_derefs wants the memory location, so lets
-	   dereference the address DEST before handing it to
-	   instrument_derefs.  */
-	if (TREE_CODE (dest) == ADDR_EXPR)
-	  dest = TREE_OPERAND (dest, 0);
-	else if (TREE_CODE (dest) == SSA_NAME)
-	  dest = build2 (MEM_REF, TREE_TYPE (TREE_TYPE (dest)),
-			 dest, build_int_cst (TREE_TYPE (dest), 0));
-	else
-	  gcc_unreachable ();
+static bool
+instrument_builtin_call (gimple_stmt_iterator *iter)
+{
+  bool iter_advanced_p = false;
+  gimple call = gsi_stmt (*iter);
 
-	instrument_derefs (iter, dest, loc, is_store);
-	return false;
-      }
+  gcc_checking_assert (gimple_call_builtin_p (call, BUILT_IN_NORMAL));
 
-    default:
-      /* The other builtins memory access are not instrumented in this
-	 function because they either don't have any length parameter,
-	 or their length parameter is just a limit.  */
-      break;
-    }
+  tree callee = gimple_call_fndecl (call);
+  location_t loc = gimple_location (call);
 
-  if (len != NULL_TREE)
+  if (DECL_FUNCTION_CODE (callee) == BUILT_IN_STRLEN)
+    iter_advanced_p = instrument_strlen_call (iter);
+  else
     {
-      if (source0 != NULL_TREE)
-	instrument_mem_region_access (source0, len, iter,
-				      loc, /*is_store=*/false);
-      if (source1 != NULL_TREE)
-	instrument_mem_region_access (source1, len, iter,
-				      loc, /*is_store=*/false);
-      else if (dest != NULL_TREE)
-	instrument_mem_region_access (dest, len, iter,
-				      loc, /*is_store=*/true);
-
-      *iter = gsi_for_stmt (call);
-      return false;
+      asan_mem_ref src0, src1, dest;
+      asan_mem_ref_init (&src0, NULL, 1);
+      asan_mem_ref_init (&src1, NULL, 1);
+      asan_mem_ref_init (&dest, NULL, 1);
+
+      tree src0_len = NULL_TREE, src1_len = NULL_TREE, dest_len = NULL_TREE;
+      bool src0_is_store = false, src1_is_store = false,
+	dest_is_store = false, dest_is_deref = false;
+
+      if (get_mem_refs_of_builtin_call (call,
+					&src0, &src0_len, &src0_is_store,
+					&src1, &src0_len, &src1_is_store,
+					&dest, &dest_len, &dest_is_store,
+					&dest_is_deref))
+	{
+	  if (dest_is_deref)
+	    {
+	      instrument_derefs (iter, dest.start, loc, dest_is_store);
+	      gsi_next (iter);
+	      iter_advanced_p = true;
+	    }
+	  else if (src0_len || src1_len || dest_len)
+	    {
+	      if (src0.start)
+		instrument_mem_region_access (src0.start, src0_len,
+					      iter, loc, /*is_store=*/false);
+	      if (src1.start != NULL_TREE)
+		instrument_mem_region_access (src1.start, src1_len,
+					      iter, loc, /*is_store=*/false);
+	      if (dest.start != NULL_TREE)
+		instrument_mem_region_access (dest.start, dest_len,
+					      iter, loc, /*is_store=*/true);
+	      *iter = gsi_for_stmt (call);
+	      gsi_next (iter);
+	      iter_advanced_p = true;
+	    }
+	}
     }
-  return false;
+  return iter_advanced_p;
 }
 
 /*  Instrument the assignment statement ITER if it is subject to
-    instrumentation.  */
+    instrumentation.  Return TRUE iff instrumentation actually
+    happened.  In that case, the iterator ITER is advanced to the next
+    logical expression following the one initially pointed to by ITER,
+    and the relevant memory reference that which access has been
+    instrumented is added to the memory references hash table.  */
 
-static void
-instrument_assignment (gimple_stmt_iterator *iter)
+static bool
+maybe_instrument_assignment (gimple_stmt_iterator *iter)
 {
   gimple s = gsi_stmt (*iter);
 
   gcc_assert (gimple_assign_single_p (s));
 
+  tree ref_expr = NULL_TREE;
+  bool is_store, is_instrumented = false;
+
   if (gimple_store_p (s))
-    instrument_derefs (iter, gimple_assign_lhs (s),
-		       gimple_location (s), true);
+    {
+      ref_expr = gimple_assign_lhs (s);
+      is_store = true;
+      instrument_derefs (iter, ref_expr,
+			 gimple_location (s),
+			 is_store);
+      is_instrumented = true;
+    }
+ 
   if (gimple_assign_load_p (s))
-    instrument_derefs (iter, gimple_assign_rhs1 (s),
-		       gimple_location (s), false);
+    {
+      ref_expr = gimple_assign_rhs1 (s);
+      is_store = false;
+      instrument_derefs (iter, ref_expr,
+			 gimple_location (s),
+			 is_store);
+      is_instrumented = true;
+    }
+
+  if (is_instrumented)
+    gsi_next (iter);
+
+  return is_instrumented;
 }
 
 /* Instrument the function call pointed to by the iterator ITER, if it
@@ -1424,10 +1849,11 @@ static bool
 maybe_instrument_call (gimple_stmt_iterator *iter)
 {
   gimple stmt = gsi_stmt (*iter);
-  bool is_builtin = is_gimple_builtin_call (stmt);
-  if (is_builtin
-      && instrument_builtin_call (iter))
+  bool is_builtin = gimple_call_builtin_p (stmt, BUILT_IN_NORMAL);
+
+  if (is_builtin && instrument_builtin_call (iter))
     return true;
+
   if (gimple_call_noreturn_p (stmt))
     {
       if (is_builtin)
@@ -1449,11 +1875,10 @@ maybe_instrument_call (gimple_stmt_iterator *iter)
   return false;
 }
 
-/* asan: this looks too complex. Can this be done simpler? */
-/* Transform
-   1) Memory references.
-   2) BUILTIN_ALLOCA calls.
-*/
+/* Walk each instruction of all basic block and instrument those that
+   represent memory references: loads, stores, or function calls.
+   In a given basic block, this function avoids instrumenting memory
+   references that have already been instrumented.  */
 
 static void
 transform_statements (void)
@@ -1464,23 +1889,38 @@ transform_statements (void)
 
   FOR_EACH_BB (bb)
     {
+      empty_mem_ref_hash_table ();
+
       if (bb->index >= saved_last_basic_block) continue;
       for (i = gsi_start_bb (bb); !gsi_end_p (i);)
 	{
 	  gimple s = gsi_stmt (i);
 
-	  if (gimple_assign_single_p (s))
-	    instrument_assignment (&i);
-	  else if (is_gimple_call (s))
+	  if (has_stmt_been_instrumented_p (s))
+	    gsi_next (&i);
+	  else if (gimple_assign_single_p (s)
+		   && maybe_instrument_assignment (&i))
+	    /*  Nothing to do as maybe_instrument_assignment advanced
+		the iterator I.  */;
+	  else if (is_gimple_call (s) && maybe_instrument_call (&i))
+	    /*  Nothing to do as maybe_instrument_call
+		advanced the iterator I.  */;
+	  else
 	    {
-	      if (maybe_instrument_call (&i))
-		/* Avoid gsi_next (&i), because maybe_instrument_call
-		   advanced the I iterator already.  */
-		continue;
+	      /* No instrumentation happened.
+
+		 If the current instruction is a function call, let's
+		 forget about the memory references that got
+		 instrumented.  Otherwise we might miss some
+		 instrumentation opportunities.  */
+	      if (is_gimple_call (s))
+		empty_mem_ref_hash_table ();
+
+	      gsi_next (&i);
 	    }
-	  gsi_next (&i);
 	}
     }
+  free_mem_ref_resources ();
 }
 
 /* Build
diff --git a/gcc/testsuite/c-c++-common/asan/inc.c b/gcc/testsuite/c-c++-common/asan/inc.c
new file mode 100644
index 0000000..b7a8902
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/asan/inc.c
@@ -0,0 +1,19 @@
+/* { dg-options "-fdump-tree-asan0" } */
+/* { dg-do compile } */
+
+void
+foo(int *a)
+{
+  (*a)++;
+}
+
+int
+main ()
+{
+  int a = 0;
+  foo (&a);
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump-times "__builtin___asan_report" 1 "asan0" } }  */
+/* { dg-final { scan-tree-dump "__builtin___asan_report_load4" "asan0" } }  */
diff --git a/gcc/testsuite/c-c++-common/asan/no-redundant-instrumentation-1.c b/gcc/testsuite/c-c++-common/asan/no-redundant-instrumentation-1.c
new file mode 100644
index 0000000..f87b1c5
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/asan/no-redundant-instrumentation-1.c
@@ -0,0 +1,64 @@
+/* This tests that when faced with two references to the same memory
+   location in the same basic block, the second reference should not
+   be instrumented by the Address Sanitizer.  */
+
+/* { dg-options "-fdump-tree-asan0" } */
+/* { dg-do compile } */
+
+static char tab[4] = {0};
+
+static int
+test0 ()
+{
+  /* __builtin___asan_report_store1 called 2 times for the two stores
+     below.  */
+  tab[0] = 1;
+  tab[1] = 2;
+
+  /* __builtin___asan_report_load1 called 1 time for the store
+     below.  */
+  char t0 = tab[1];
+
+  /* This load should not be instrumented because it is to the same
+     memory location as above.  */
+  char t1 = tab[1];
+
+  return t0 + t1;
+}
+
+static int
+test1 ()
+{
+  /*__builtin___asan_report_store1 called 1 time here to instrument
+    the initialization.  */
+  char foo[4] = {1}; 
+
+  /*__builtin___asan_report_store1 called 2 times here to instrument
+    the store to the memory region of tab.  */
+  __builtin_memset (tab, 3, sizeof (tab));
+
+  /* There is no instrumentation for the two memset calls below.  */
+  __builtin_memset (tab, 4, sizeof (tab));
+  __builtin_memset (tab, 5, sizeof (tab));
+
+  /* There are 2 calls to __builtin___asan_report_store1 and 2 calls
+     to __builtin___asan_report_load1 to instrument the store to
+     (subset of) the memory region of tab.  */
+  __builtin_memcpy (&tab[1], foo, sizeof (tab) - 1);
+
+  /* This should not generate a __builtin___asan_report_load1 because
+     the reference to tab[1] has been already instrumented above.  */
+  return tab[1];
+
+  /* So for these function, there should be 7 calls to
+     __builtin___asan_report_store1.  */
+}
+
+int
+main ()
+{
+  return test0 () && test1 ();
+}
+
+/* { dg-final { scan-tree-dump-times "__builtin___asan_report_store1" 7 "asan0" } } */
+/* { dg-final { scan-tree-dump-times "__builtin___asan_report_load" 2 "asan0" }  } */
diff --git a/gcc/testsuite/c-c++-common/asan/no-redundant-instrumentation-2.c b/gcc/testsuite/c-c++-common/asan/no-redundant-instrumentation-2.c
new file mode 100644
index 0000000..2dc55eb
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/asan/no-redundant-instrumentation-2.c
@@ -0,0 +1,24 @@
+/* This tests that when faced with two references to the same memory
+   location in the same basic block, the second reference should not
+   be instrumented by the Address Sanitizer.  But in case of access to
+   overlapping regions we must be precise.  */
+
+/* { dg-options "-fdump-tree-asan0" } */
+/* { dg-do compile } */
+
+int
+main ()
+{
+  char tab[5];
+
+  /* Here, we instrument the access at offset 0 and access at offset
+     4.  */
+  __builtin_memset (tab, 1, sizeof (tab));
+  /* We instrumented access at offset 0 above already, so only access
+     at offset 3 is instrumented.  */
+  __builtin_memset (tab, 1, 3);
+}
+
+/* { dg-final { scan-tree-dump-times "__builtin___asan_report_store1" 3 "asan0" } } */
+/* { dg-final { scan-tree-dump-times "__builtin___asan_report" 3 "asan0" }  } */
+
diff --git a/gcc/testsuite/c-c++-common/asan/no-redundant-instrumentation-3.c b/gcc/testsuite/c-c++-common/asan/no-redundant-instrumentation-3.c
new file mode 100644
index 0000000..1858759
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/asan/no-redundant-instrumentation-3.c
@@ -0,0 +1,16 @@
+/* { dg-options "-fdump-tree-asan0" } */
+/* { dg-do compile } */
+
+char
+foo (__INT32_TYPE__ *p)
+{
+  /* This generates a __builtin___asan_report_load1.  */
+  __INT32_TYPE__ ret = *(char *) p;
+  /* This generates a __builtin___asan_report_store4 depending on the.  */
+  *p = 26;
+  return ret; 
+}
+
+/* { dg-final { scan-tree-dump-times "__builtin___asan_report" 2 "asan0" } } */
+/* { dg-final { scan-tree-dump-times "__builtin___asan_report_load1" 1 "asan0" } } */
+/* { dg-final { scan-tree-dump-times "__builtin___asan_report_store" 1 "asan0" } } */
