PR rtl-optimization/66152
	* builtins.h (c_readstr): Declare.
	* builtins.c (c_readstr): Remove forward declaration.  Add
	null_terminated_p argument, if false, read all bytes from the
	string instead of stopping after '\0'.
	* expr.c (string_cst_read_str): New function.
	(store_expr): Use string_cst_read_str instead of
	builtin_strncpy_read_str.  Try to store by pieces the whole
	exp_len first, and only if that fails, split it up into
	store by pieces followed by clear_storage.  Formatting fix.

	* gcc.target/i386/pr66152.c: New test.

From-SVN: r268957