[15] RFR (M): 8237581: Improve allocation expansion

[Vladimir Ivanov]

Thanks for separating the fix from the refactoring.

> Refactoring:
> 
> http://cr.openjdk.java.net/~neliasso/8237581/webrev.refactor/

Looks good.

> The actual change (on top of the refactoring)
> 
> http://cr.openjdk.java.net/~neliasso/8237581/webrev.change/

Overall, looks good.

I'd prefer to see yank_alloc_node(alloc) case separated.

What do you think about the following?

  if (!allocation_has_use) {
    InitializeNode* init = alloc->initialization();
    if (init != NULL) {
      yank_initalize_node(init);
      assert(init->outcnt() == 0, "all uses must be deleted");
      _igvn.remove_dead_node(init);
    }
    if (!always_slow) {
       // Remove allocation node and return.
       // Size is a non-negative constant -> no initial check needed -> 
directly to fast path.
       // Also, no usages -> empty fast path -> no fall out to slow path 
-> nothing left.
      yank_alloc_node(alloc);
      return;
    }
  }

Best regards,
Vladimir Ivanov

> 
> 
> Best regards,
> Nils Eliasson
> 
> On 2020-01-24 09:36, Nils Eliasson wrote:
>> Hi,
>>
>> This patch improves expand_allocate_common when there is no use of the 
>> allocation.
>>
>> Three cases are improved:
>>
>> - With unknown allocation length - don't expand the fast path. No 
>> allocation is needed when it isn't used. NegativeArraySizeException 
>> will still be caught by the slowpath.
>> - With known length inside the legal range - No fast path or slow path 
>> is needed. The allocation node is removed.
>> - With known length outside the legal range - only a slow path is needed.
>>
>> I also refactored the code a bit, keeping the general structure for 
>> easy diff, but extracting some routines too make it more readable.
>>
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8237581
>> Webrev: http://cr.openjdk.java.net/~neliasso/8237581/webrev.03/
>>
>> Please review!
>>
>> Best regards,
>> Nils Eliasson
>>
>>
>