https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102239
--- Comment #6 from luoxhu at gcc dot gnu.org ---
(In reply to Segher Boessenkool from comment #5)
> (In reply to luoxhu from comment #4)
> > Simply adjust the sequence of dot instruction could produce expected code,
> > is this correct?
>
> No it isn't. Sorry.
Sorry I don't understand what is wrong...
>
> > foo:
> > .LFB0:
> > .cfi_startproc
> > rldicr. 3,3,29,1
> > beq 0,.L2
>
> This is fine, but only because it tests the EQ bit (not the LT or GT bits).
> So the generated RTL for this insn (the 2insn one) is not correct.
The generated RTL in pr102239.c.300r.split2 is:
(insn 32 8 33 2 (parallel [
(set (reg:CC 100 0 [123])
(compare:CC (and:DI (ashift:DI (reg:DI 3 3 [124])
(const_int 29 [0x1d]))
(const_int -4611686018427387904 [0xc000000000000000]))
(const_int 0 [0])))
(clobber (reg:DI 3 3 [125]))
]) "pr102239.c":4:6 238 {*rotldi3_mask_dot}
(nil))
(insn 33 32 10 2 (set (reg:DI 3 3 [125])
(lshiftrt:DI (reg:DI 3 3 [125])
(const_int 29 [0x1d]))) "pr102239.c":4:6 278 {lshrdi3}
(nil))
(jump_insn 10 33 11 2 (set (pc)
(if_then_else (eq (reg:CC 100 0 [123])
(const_int 0 [0]))
(label_ref 15)
(pc))) "pr102239.c":4:6 868 {*cbranch}
(int_list:REG_BR_PROB 536870916 (nil))
-> 15)
rotldi3_mask_dot is what you mentioned in c#1, it is a shifted result and not
matter for comparing to 0:
> *rotl<mode>3_mask_dot cannot do this either; the base and the dot2 of that
> cannot be done, they return a shifted result, but that doesn't matter for
> comparing it to 0. So we should add a specialised version.
What specialized version to add?
