RFR(XS): ZGC: C2: Missing null check in LoadBarrier::bottom_type

[Erik Österlund]

Looks good.

/Erik

On 2018-05-29 16:30, Nils Eliasson wrote:
> Hi,
>
> Please review,
>
> Stefan reported a crash when using -XX:+TraceIterativeGVN. When 
> printing the types of the nodes, a loadbarrier is encountered that no 
> longer has a preceding load (in(oop) is null), and we crash when we 
> try to call bottom_type on that.
>
> We don't see this in normal runs because all useless barriers are 
> eliminated before checking types. That is not the case when debug 
> printing.
>
> Fix returns top (no possible value) if in_oop is null.
>
> http://cr.openjdk.java.net/~neliasso/zgc/fix_lb_bottom_type/webrev/
>
> Regards,
>
> Nils
>