Remove global call sets: cselib.c

Remove global call sets: cselib.c

cselib_invalidate_regno is a no-op if REG_VALUES (i) is null,
so we can check that first.  Then, if we know what mode the register
currently has, we can check whether it's clobbered in that mode.

Using GET_MODE (values->elt->val_rtx) to get the mode of the last
set is taken from cselib_reg_set_mode.

2019-09-30  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* cselib.c (cselib_process_insn): If we know what mode a
	register was set in, check whether it is clobbered in that
	mode by a call.  Only fall back to reg_raw_mode if that fails.

From-SVN: r276318