On 05/15/12 06:00, Paulo J. Matos wrote:
> The RTL for the first two comparisons at compare-elim is:
> (insn 51 3 52 2 (set (reg:CC_NZ 13 CC)
> (compare:CC_NZ (reg:QI 0 AH [orig:27 a ] [27])
> (const_int 0 [0]))) b651.c:1 63 {*tstqi}
> (nil))
>
> (jump_insn 52 51 34 2 (set (pc)
> (if_then_else (ge (reg:CC_NZ 13 CC)
> (const_int 0 [0]))
> (label_ref 41)
> (pc))) b651.c:1 68 {*conditional_branch}
> (expr_list:REG_BR_PROB (const_int 7900 [0x1edc])
> (nil))
> -> 41)
>
> (code_label 41 43 25 4 6 "" [1 uses])
>
> (note 25 41 49 4 [bb 4] NOTE_INSN_BASIC_BLOCK)
>
> (insn 49 25 50 4 (set (reg:CC 13 CC)
> (compare:CC (reg:QI 0 AH [orig:27 a ] [27])
> (const_int 0 [0]))) b651.c:1 64 {*cmpqi}
> (nil))
>
> (jump_insn 50 49 26 4 (set (pc)
> (if_then_else (gt (reg:CC 13 CC)
> (const_int 0 [0]))
> (label_ref 13)
> (pc))) b651.c:1 68 {*conditional_branch}
> (expr_list:REG_BR_PROB (const_int 7900 [0x1edc])
> (nil))
> -> 13)
My question is, why are you generating compares in two different
modes early, before compare-elim runs? If you hadn't done that,
your redundant compare would already be eliminated.
There's some amount of support for taking a full CCmode and
using SELECT_CC_MODE to find one that fits all the uses, but
that's only used in the places we're trying to replace a clobber.
r~
