RFR(M): 8220376: C2: Int >0 not recognized as !=0 for div by 0 check

[dean.long at oracle.com]

Hi Patric.  I was expecting the fix to allow the following existing 
logic in DivINode::Ideal to work:

   // Check for excluding div-zero case
   if (in(0) && (ti->_hi < 0 || ti->_lo > 0)) {
     set_req(0, NULL);           // Yank control input
     return this;
   }

by making sure the range of "ti" has been sharpened by the previous 
if-node.  I was just wondering if you looked at that solution and 
thought it was feasible.  I see Parse::sharpen_type_after_if() is almost 
doing the right thing, but only handles BoolTest::eq.

dl

On 11/12/19 6:16 AM, Patric Hedlin wrote:
> Dear all,
>
> I would like to ask for help to review the following change/update:
>
> Issue:  https://bugs.openjdk.java.net/browse/JDK-8220376
> Webrev: http://cr.openjdk.java.net/~phedlin/tr8220376/
>
> 8220376: C2: Int >0 not recognized as !=0 for div by 0 check
>
>     Adding a simple subsumption test to IfNode::Ideal to enable a local
>     short-circuit for (obviously) redundant if-nodes.
>
> Testing: hs-tier1-4, hs-precheckin-comp
>
>
> Best regards,
> Patric
>