Index: gcc/emit-rtl.c
===================================================================
--- gcc/emit-rtl.c (revision 179662)
+++ gcc/emit-rtl.c (working copy)
@@ -1696,6 +1696,11 @@ set_mem_attributes_minus_bitpos (rtx ref
 	  && !TREE_THIS_VOLATILE (base))
 	MEM_READONLY_P (ref) = 1;
 
+      /* Mark static const strings readonly as well.  */
+      if (base && TREE_CODE (base) == STRING_CST && TREE_READONLY (base)
+	  && TREE_STATIC (base))
+	MEM_READONLY_P (ref) = 1;
+
       /* If this expression uses it's parent's alias set, mark it such
 	 that we won't change it.  */
       if (component_uses_parent_alias_set (t))
Index: gcc/testsuite/gcc.dg/memcpy-4.c
===================================================================
--- /dev/null (new file)
+++ gcc/testsuite/gcc.dg/memcpy-4.c (revision 0)
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-rtl-expand" } */
+
+void
+f1 (char *p)
+{
+  __builtin_memcpy (p, "123", 3);
+}
+
+/* { dg-final { scan-rtl-dump-times "mem/s/u" 3 "expand" { target mips*-*-* } } } */
+/* { dg-final { cleanup-rtl-dump "expand" } } */