condjump_branch_edge

[Jan Hubicka]

> 
> I don't know that it has any meaning.  What does it mean
> to have a "taken" branch when the branch *always* goes 
> somewhere else?  What's the "taken" edge for a switch?
What I am after are jumps like:
(if_then_else (cond)  (label 1) (label 2))
> 
> > Hmm, I think this will make my life quite hard.
> 
> Not at all.  You want the edge for the taken branch?  Simple:
> identify that there are exactly two outgoing edges from a
> block, and that one of them is marked FALLTHRU.  The other is
> the taken edge.
I've done this already, but then got number of misspredicts, because
of jumps like:
(if_then_else (cond) (pc) (label 2))
(these exitst on i386, see jcc_2 versus jcc_3 pattern)
I am not sure what is our notion of BR_PROB here, but my feeling
was that BR_PROB says probability of the condition to be true,
so it works in reversed for such jumps.

I see, perhaps it is cleaner to make BR_PROB mean
probability of actually taking a branch even in such reversed patterns.
I was trying to follow this patch originally, but it requires quite a lot
changes everywhere (you need to examine jump and inverse condition when
needed) and then BR_PROB is not very well defined for two way branches
mentioned above, but I see probably don't want to handle them, as wee
don't handle tablejumps.

Honza
> 
> There's no need to examine the jump insn at all.
> 
> 
> r~