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?
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.
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 ------------------------------
I don't use slim dumps much, they lose too much information, but maybe
that can be fixed :-)
Segher
