[Bug tree-optimization/45522] VRP misses oppurtunity for statement folding.

["rguenther at suse dot de" <gcc-bugzilla@gcc.gnu.org>]

------- Comment #10 from rguenther at suse dot de  2010-09-04 14:11 -------
Subject: Re:  VRP misses oppurtunity for statement
 folding.

On Sat, 4 Sep 2010, hubicka at gcc dot gnu dot org wrote:

> ------- Comment #9 from hubicka at gcc dot gnu dot org  2010-09-04 13:51 -------
> Hi,
> thanks.  In meantime I made tree-ssa-pre to fold statements it produces and it
> gets me to bootstrapland with sanity check in expr.c except for Ada (with the
> patches I sent so far)

Well - that's a workaround and will cause us to miss PRE because we do
not fold during translation of expressions.  So I wouldn't go down that
route.

> So it seems that I need to basically duplicate all logic for initializer
> folding from tree-ssa-ccp.c into this function, right? I guess it makes sense,
> but it is all quite ugly.

Yes ;)

> On VN side, i wondered if we can retire more of expand this way. For example
> dojump knows that:
> a = b ror x;
> if (a != 0)
> can be folded into:
> if (b != 0)
> (ror is rotation).  I guess we should do this kind of tricks in VN instead?

Well ... it's not that easy (that's not CSE but tree-combining, so
the specific thing would fit to forwprop).

Richard.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45522