Hi Segher,
Thanks a lot for the comments.
on 2019/6/28 上午9:32, wrote:
> Hi Kewen,
>
> On Thu, Jun 27, 2019 at 10:32:18AM +0800, Kewen.Lin wrote:
>> 6: NOTE_INSN_BASIC_BLOCK 2
>> ....
>> 12: r135:CC=cmp(r122:DI,0)
>> 13: pc={(r135:CC!=0)?L52:pc}
>> REG_DEAD r135:CC
>> REG_BR_PROB 1041558836
>> 31: L31:
>> 17: NOTE_INSN_BASIC_BLOCK 3
>>
>> The above RTL seq is from pass doloop dumping with -fdump-rtl-all-slim, I
>> misunderstood that:
>> the fall through BB of BB 2 is BB 3, since BB 3 is placed just next to BB 2.
>>
>> Then I found the contradiction that BB 3 will have some uninitialized regs
>> if it's true.
>>
>> I can get the exact information with "-blocks" dumping and even detailed one
>> with "-details".
>> But I'm thinking whether it's worth to giving some information on "-slim"
>> dump (or more
>> exactly without "-blocks") to avoid some confusion especially for new comers
>> like me.
>> Or is it unnecessary? since we have "-blocks" options for that and want to
>> keep it "slim"?
>
> It's probably a good idea to spend a line on this even in slim mode, it's
> really easy to miss and get confused and waste time without it. Nice :-)
>
>> The dumping will look like:
>> 6: NOTE_INSN_BASIC_BLOCK 2
>> ...
>> 12: r135:CC=cmp(r122:DI,0)
>> 13: pc={(r135:CC!=0)?L52:pc}
>> REG_DEAD r135:CC
>> REG_BR_PROB 1041558836
>> ;; pc (fall through) -> L67
>> 31: L31:
>> 17: NOTE_INSN_BASIC_BLOCK 3
>
> I think it should say the BB number it falls through to. Is the label
> number (insn number) useful? Maybe the BB number isn't always printed
> in slim dumps?
OK, to use the label was meant to keep the same as what we print for jump
targets of jump insn. Yes, I think it's better to use BB number.
I think we can get the BB number from NOTE_INSN_BASIC_BLOCK now, it's
always printed in slim dumps.
>
> All this only happens in cfglayout mode btw, you might want to restrict
> this to that: in normal rtl mode fallthrough does fall through to the
> next insn always.
Good idea!
>
> Maybe slim dumps should always spend a line on showing basic block
> boundaries? Something visual like maybe
> ; ------------------------------
> or
> ; BB 456 ------------------------------
> or
> ; ------------ falls through to BB 123
> or
> ; ------------ falls through to BB 123
> ; BB 456 ------------------------------
>
It seems the current NOTE_INSN_BASIC_BLOCK is enough for the beginning?
> I don't use slim dumps much, they lose too much information, but maybe
> that can be fixed :-)
OK, since I haven't got used to lisp format, the slim seems more
understandable to me. If it's not used too much, maybe this confusion
and possible improvement is too trivial. :)
Thanks,
Kewen
>
>
> Segher
>
