[Bug tree-optimization/15911] VRP/DOM does not like TRUTH_AND_EXPR

[law at redhat dot com]

------- Additional Comments From law at redhat dot com  2005-09-08 19:04 -------
Subject: Re:  VRP/DOM does not like
	TRUTH_AND_EXPR

On Thu, 2005-09-08 at 18:20 +0000, dnovillo at gcc dot gnu dot org
wrote:
> ------- Additional Comments From dnovillo at gcc dot gnu dot org  2005-09-08 18:20 -------
> 
> This would be fixable inside VRP.  Essentially we would need to insert chains of
> ASSERT_EXPRs to represent various predicates:
> 
>   D.1613_3 = x_2 > 5555;
>   D.1614_5 = y_4 <= 6665;
>   D.1615_6 = D.1613_3 && D.1614_5;
>   if (D.1615_6) goto <L0>; else goto <L8>;
> 
> At label L0, we know that:
> 
>   D.1615_10 = 1;
>   D.1613_11 = 1;
>   D.1614_12 = 1;
>   y_13 = ASSERT_EXPR <y_4, y_4 <= 6665>;
>   x_14 = ASSERT_EXPR <x_2, x_2 > 5555>;
> 
> which is a bit sickening.  It would be Much Better to avoid creating these
> obtuse predicates in fold(), though.
Well, we have a long standing problem with fold using BRANCH_COST to
determine how best to implement certain conditionals.  But even if that
were removed, it's fairly straightforward for a programmer (or better
yet some automated code generator) to create these "obtuse" predicates.

I think we'd be better off teaching VRP how to cope with this.


Jeff



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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15911