------- Additional Comments From kazu at cs dot umass dot edu 2004-10-11 14:47 -------
The combiner does try to combine andl and testb,
but the suggested combined insn is rejected by combine_validate_cost.
The cost of "andl $1, %eax" is 4.
The cost of "testb %al, %al" is 4.
So the original total cost is 8.
The cost of the combined insn, shown below, is 12.
(set (reg:CCZ 17 flags)
(compare:CCZ (zero_extract:SI (subreg:SI (reg:QI 63) 0)
(const_int 1 [0x1])
(const_int 0 [0x0]))
(const_int 0 [0x0])))
We need to teach ix86_rtx_cost to treat
(compare (zero_extract X (const_1) ...)) the same as and.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17931
