Hi David,
在 2022/11/17 21:24, David Edelsohn 写道:
> This is better, but the pattern should be near and after the existing
> cbranch<mode>4 patterns earlier in the file, not the *cbranch pattern. It
> doesn't match the comment.
Sure, I will put it after existing "cbranch<mode>4" patterns.
>
> Why are you using zero_constant predicate instead of matching (const_int 0)
> for operand 2?
The "const_int 0" is an operand other than a predicate. We need a predicate
here.
>
> Why does this need the new all_branch_comparison_operator? Can the ifcvt
> optimization correctly elide the 2 insn sequence?
Because rs6000 defines "*cbranch_2insn" insn, such insns are generated after
expand.
(jump_insn 50 47 51 11 (set (pc)
(if_then_else (ge (reg:CCFP 156)
(const_int 0 [0]))
(label_ref 53)
(pc)))
"/home/guihaoc/gcc/gcc-mainline-base/gmp/mpz/cmpabs_d.c":80:7 884
{*cbranch_2insn}
(expr_list:REG_DEAD (reg:CCFP 156)
(int_list:REG_BR_PROB 633507684 (nil)))
-> 53)
In prepare_cmp_insn, the comparison is verified by insn_operand_matches. If
extra_insn_branch_comparison_operator is not included in "cbranchcc4" predicate,
it hits ICE here.
if (GET_MODE_CLASS (mode) == MODE_CC)
{
enum insn_code icode = optab_handler (cbranch_optab, CCmode);
test = gen_rtx_fmt_ee (comparison, VOIDmode, x, y);
gcc_assert (icode != CODE_FOR_nothing
&& insn_operand_matches (icode, 0, test));
*ptest = test;
return;
}
The real conditional move is generated by emit_conditional_move_1. Commonly
"*cbranch_2insn" can't be optimized out and it returns NULL_RTX.
if (COMPARISON_P (comparison))
{
saved_pending_stack_adjust save;
save_pending_stack_adjust (&save);
last = get_last_insn ();
do_pending_stack_adjust ();
machine_mode cmpmode = comp.mode;
prepare_cmp_insn (XEXP (comparison, 0), XEXP (comparison, 1),
GET_CODE (comparison), NULL_RTX, unsignedp,
OPTAB_WIDEN, &comparison, &cmpmode);
if (comparison)
{
rtx res = emit_conditional_move_1 (target, comparison,
op2, op3, mode);
if (res != NULL_RTX)
return res;
}
delete_insns_since (last);
restore_pending_stack_adjust (&save);
I think that extra_insn_branch_comparison_operator should be included in
"cbranchcc4" predicates as such insns exist. And leave it to
emit_conditional_move which decides whether it can be optimized or not.
Thanks for your comments
Gui Haochen
