RFR(S): 8149745: C2 should optimize long accumulations in a counted loop

[Vladimir Kozlov]

That is why we need 2 reviews! :)

Vladimir K

On 2/15/16 9:38 AM, Vladimir Ivanov wrote:
> Roland,
>
> +       Node* ratio_idx = MulINode::make(bt, conv_phi, ratio);
>
> A typo? Shouldn't MulNode::make be used?
>
> Best regards,
> Vladimir Ivanov
>
> On 2/15/16 12:09 PM, Roland Westrelin wrote:
>> Thanks for looking at this, Vladimir. Here is a new webrev:
>>
>> http://cr.openjdk.java.net/~roland/8149745/webrev.01/
>>
>>> incr2->Opcode() is called several time now but it is virtual method. Can you put it in local variable?
>>
>> Done.
>>
>>> Add assert before next line assert(opc == Op_AddI || opc == Op_AddL
>>> +     BasicType bt = incr2->Opcode() == Op_AddI ? T_INT : T_LONG;
>>
>> Done.
>>
>>> May need to add cast (jlong)stride2->get_int() to make all CC happy:
>>> jlong stride_con2 = (bt == T_INT) ? stride2->get_int() : stride2->get_long();
>>
>> Done.
>>
>>> You need to add new ConvI2LNode(init2) in case bt == T_LONG:
>>>
>>> Node* diff = SubNode::make(bt, init2, ratio_init);
>>
>> I don’t think it’s required. init2 is an input to the Phi of type long when bt == T_LONG.
>>
>> Roland.
>>
>>>
>>> Otherwise this looks good.
>>>
>>> Thanks,
>>> Vlaidmir
>>>
>>> On 2/12/16 7:53 AM, Roland Westrelin wrote:
>>>> http://cr.openjdk.java.net/~roland/8149745/webrev.00/
>>>>
>>>> This extends the code that looks for a parallel induction variable to long accumulations so in the following code:
>>>>
>>>> public static long testLongAcc() {
>>>>     long acc = 0;
>>>>
>>>>     for (int i = 0; i < 1000; i++) {
>>>>         acc += 8;
>>>>     }
>>>>
>>>>     return acc;
>>>> }
>>>>
>>>> the loop is optimized out.
>>>>
>>>> What I find puzzling is that code for integer accumulations doesn’t try to estimate the benefit of turning one AddI
>>>> into a more expensive MulI + AddI. Maybe it’s too unpredictable but in the case of the long accumulations would we
>>>> want to check that, for instance, the long Phi has no use in the loop?
>>>>
>>>> Roland.
>>>>
>>>>
>>