RFR(S): 8028471: PPC64 (part 215): opto: Extend ImplicitNullCheck optimization.

[Vladimir Kozlov]

Hi, Goetz

Can you move all checks in lcm.cpp into new method and rename it to 
needs_explicit_null_check_for_read()? So the condition will be simple:

if (!was_store && needs_explicit_null_check_for_read(val)) {
   continue;
}

You should also add ShouldNotReachHere() for AIX near Unimplemented() 
for non AIX.

And, please, fix indents in new method.

Thanks,
Vladimir

On 11/20/13 2:11 AM, Lindenmaier, Goetz wrote:
> Hi,
>
> ImplicitNullChecks did not work on platforms where the zero
> page is only write protected.
>
> This change adds os property 'zero_page_read_protected' and extends
> the ImplicitNullCheck optimization to consider only stores if
> this property is not true. If a decoded compressed oop will access the
> guard page before the heap, Loads work again.
> This is needed on AIX, where the page at address '0' is only write-protected.
>
> Please review and test this change:
> http://cr.openjdk.java.net/~goetz/webrevs/8028471-0-zpage/
>
> I tagged this S, as a majority of the patches apply to the ppc platform files.
>
> Best regards,
>    Goetz.
>