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

[Vladimir Kozlov]

incr2->Opcode() is called several time now but it is virtual method. Can you put it in local variable?

Add assert before next line assert(opc == Op_AddI || opc == Op_AddL
+     BasicType bt = incr2->Opcode() == Op_AddI ? T_INT : T_LONG;

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();

You need to add new ConvI2LNode(init2) in case bt == T_LONG:

Node* diff = SubNode::make(bt, init2, ratio_init);

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.
>
>