* builtins.c (expand_builtin_memcpy): Optimize case when the two
	pointer arguments are the equal, non-volatile and side-effect free.
	(expand_builtin_mempcpy): Likewise.
	(expand_builtin_memmove): Likewise.
	(expand_builtin_strcpy): Likewise.
	(expand_builtin_memcmp): Likewise.
	(expand_builtin_strcmp): Likewise.
	(expand_builtin_strncmp): Likewise.

	* gcc.c-torture/execute/string-opt-18.c: New testcase.

From-SVN: r72335