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

[Vladimir Ivanov]

>>
>> +  if (is_If() && (cmp = in(1)->in(1))->Opcode() == Op_CmpP) {
>> +    if (cmp->in(2) != NULL && // make sure cmp is not already dead
>> +        cmp->in(2)->bottom_type() == TypePtr::NULL_PTR) {
>>
>> Merge nested ifs?
>>
> I to have problems with this part but for other reasons. What about: (?)
> 
> -  Node* cmp;
>     int dist = 4;               // Cutoff limit for search
> -  if (is_If() && (cmp = in(1)->in(1))->Opcode() == Op_CmpP) {
> -    if (cmp->in(2) != NULL && // make sure cmp is not already dead
> +  if (is_If() && in(1)->is_Bool()) {
> +    Node* cmp = in(1)->in(1);
> +    if (cmp->Opcode() == Op_CmpP &&
> +        cmp->in(2) != NULL && // make sure cmp is not already dead

Looks even better.

Best regards,
Vladimir Ivanov

>> Looks like extracting the following code into a helper function (along 
>> with the enum and the table) can improve readability.
>>
>> +  int drel = subsuming_bool_test_encode(dom->in(1));
>> +  int trel = subsuming_bool_test_encode(bol);
>> +  int bout = pre->is_IfFalse() ? 1 : 0;
>> +
>> +  if (drel < 0 || trel < 0) {
>> +    return NULL;
>> +  }
>> +  int br = s_subsume_map[trel][2*drel+bout];
>> +  if (br == na) {
>> +    return NULL;
>> +  }
>>
>> New function can return intcon(0/1) or bol(or NULL?) and the caller 
>> decides whether the update is needed.
>>
>>> On 12/11/2019 15:16, 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
>