[15] RFR(S): 8237950: C2 compilation fails with "Live Node limit exceeded limit" during ConvI2L::Ideal optimization

[Tobias Hartmann]

Thanks Nils!

Best regards,
Tobias

On 19.06.20 11:32, Nils Eliasson wrote:
> +1
> 
> Best regards,
> Nils
> 
> On 2020-06-18 17:43, Vladimir Kozlov wrote:
>> Good.
>>
>> Thanks,
>> Vladimir
>>
>> On 6/17/20 11:17 PM, Tobias Hartmann wrote:
>>> Hi,
>>>
>>> performance testing revealed a slight regression with microbenchmarks due to ConvI2L nodes not
>>> always being processed by IGVN and therefore not being optimized.
>>>
>>> Here's a new version that makes sure that such ConvI2L are always recorded for IGVN. Performance
>>> numbers look good now.
>>> http://cr.openjdk.java.net/~thartmann/8237950/webrev.01/
>>>
>>> Thanks,
>>> Tobias
>>>
>>>
>>> On 16.06.20 08:34, Tobias Hartmann wrote:
>>>> Thanks Vladimir! I'll run our regular performance testing.
>>>>
>>>> Best regards,
>>>> Tobias
>>>>
>>>> On 15.06.20 20:02, Vladimir Kozlov wrote:
>>>>> +1
>>>>>
>>>>> I would suggest to do our regular performance testing to make sure there is no regression.
>>>>>
>>>>> Thanks,
>>>>> Vladimir
>>>>>
>>>>> On 6/15/20 6:31 AM, Nils Eliasson wrote:
>>>>>> Hi Tobias,
>>>>>>
>>>>>> The change looks reasonable.
>>>>>>
>>>>>> Reviewed.
>>>>>>
>>>>>> Best regards,
>>>>>> Nils
>>>>>>
>>>>>> On 2020-06-15 13:22, Tobias Hartmann wrote:
>>>>>>> Hi,
>>>>>>>
>>>>>>> please review the following patch:
>>>>>>> https://bugs.openjdk.java.net/browse/JDK-8237950
>>>>>>> http://cr.openjdk.java.net/~thartmann/8237950/webrev.00/
>>>>>>>
>>>>>>> A long chain of StringBuffer.append calls is optimized by C2's string concatenation optimization
>>>>>>> which emits direct stores into the String internal byte array.
>>>>>>> GraphKit::array_element_address emits
>>>>>>> ConvI2L nodes for the array index (see Compile::conv_I2X_index) without any range check
>>>>>>> dependent
>>>>>>> CastII nodes because the bounds are known. As a result, the ConvI2L ideal optimization jumps
>>>>>>> in and
>>>>>>> creates over 34000 new ConvI2L nodes while pushing them through the long chain of AddNodes.
>>>>>>> We hit
>>>>>>> the node limit because during GVN, dead nodes are not removed.
>>>>>>>
>>>>>>> I propose to simply postpone that optimization to IGVN. This only affects array accesses
>>>>>>> emitted for
>>>>>>> the string concat optimizations because "normal" array accesses have a range check dependent
>>>>>>> CastII
>>>>>>> which blocks that ConvI2L optimization during parsing.
>>>>>>>
>>>>>>> Thanks,
>>>>>>> Tobias
>>>>>>
>