Re: [PATCH] tree-optimization/108691 - indirect calls to setjmp

[Jakub Jelinek <jakub@redhat.com>]

On Mon, Feb 13, 2023 at 12:00:56PM +0100, Richard Biener wrote:
> DCE now chokes on indirect setjmp calls becoming direct because
> that exposes them too late to be subject to abnormal edge creation.
> The following patch honors gimple_call_ctrl_altering for those and
> _not_ treat formerly indirect calls to setjmp as calls to setjmp.
> 
> Unfortunately there's no way to have an indirect call to setjmp
> properly annotated (the returns_twice attribute is ignored on types).
> 
> RTL expansion late discovers returns-twice for the purpose of
> adding REG_SETJMP notes and also sets ->calls_setjmp
> (instead of asserting it is set).  There's no good way to
> transfer proper knowledge around here so I'm using ->calls_setjmp
> as a flag to indicate whether gimple_call_ctrl_altering was set.
> 
> Comments on what's the most sensible thing to do here?  Supporting
> returns_twice on indirect calls wouldn't be difficult, so we're
> talking about how to handle this kind of "legacy" situation?

One thing is supporting returns_twice on function types, but another one
is that initially none of the calls will be marked that way and even later,
it is up to the user if they mark it or not.

Could we e.g. prevent turning such indirect calls into direct calls?

Anyway, notice_special_calls is called in various spots, not just DCE,
wouldn't it be better to simply not set calls_setjmp flag in there if
the current function already has cfg and the call isn't ctrl altering?

	Jakub