Re: [RFC PATCH] tree-ssa-sink: do not sink to in front of setjmp

[Alexander Monakov <amonakov@ispras.ru>]

On Mon, 13 Dec 2021, Richard Biener wrote:

> On December 13, 2021 3:25:47 PM GMT+01:00, Alexander Monakov <amonakov@ispras.ru> wrote:
> >Greetings!
> >
> >While testing our patch that reimplements -Wclobbered on GIMPLE we found
> >a case where tree-ssa-sink moves a statement to a basic block in front
> >of a setjmp call.
> >
> >I am confident that this is unintended and should be considered invalid
> >GIMPLE. 
> 
> Does CFG validation not catch this? That is, doesn't setjmp force the start of
> a new BB?

Oh, good point. There's stmt_start_bb_p which returns true for setjmp, but
gimple_verify_flow_info doesn't check it. I guess we can try adding that
and collect the fallout on bootstrap/regtest.

> I think sinking relies on dominance and post dominance here but post dominance
> may be too fragile with the abnormal cycles which are likely not backwards
> reachable from exit. 
> 
> That said, checking for abnormal preds is OK, I just want to make sure we
> detect the invalid CFG - do we? 

As above, no, otherwise it would have been caught much earlier than ICE'ing
our -Wclobbered patch :)

Thank you.
Alexander