review request: 7147464: Java crashed while executing method with over 8k of dneg operations

[Vladimir Kozlov]

This looks good.

Thanks,
Vladimir

Dean Long wrote:
> Thanks.  Updated:
> 
>     http://cr.openjdk.java.net/~dlong/7147464/webrev.2/
> 
> dl
> 
> On 07/13/2012 12:05 PM, Vladimir Kozlov wrote:
>> I would call states PROCESS_INPUTS, PROCESS_OUTPUTS instead.
>>
>> Next lines could be moved just after progress_state check
>>
>> +    if (progress_state == PROCESS_INPUTS) {
>> +      // After following inputs, continue to outputs
>> +      _stack.set_index(PROCESS_OUTPUTS);
>>
>> that allow you to remove setting index in output processing code.
>>
>> Vladimir
>>
>> Dean Long wrote:
>>> OK.  The new webrev is here:
>>>
>>> http://cr.openjdk.java.net/~dlong/7147464/webrev.1/
>>>
>>> dl
>>>
>>> On 07/12/2012 12:57 PM, Vladimir Kozlov wrote:
>>>> Dean,
>>>>
>>>> Use enum values with meaningful names instead of 0/1 for 
>>>> progress_state.
>>>> You don't need to pop/push dead node to change progress state - use 
>>>> set_index(i) method. Also there is is_nonempty() method to use 
>>>> instead of !is_empty().
>>>>
>>>> Vladimir
>>>>
>>>> Dean Long wrote:
>>>>> http://cr.openjdk.java.net/~dlong/7147464/
>>>>> Summary of changes: 77 lines changed: 38 ins; 7 del; 32 mod; 2264 
>>>>> unchg
>>>>>
>>>>> Deep recursion in PhaseIterGVN::remove_globally_dead_node() can 
>>>>> cause a stack overflow crash.  The test in the bug report causes 
>>>>> recursion that is 10000 levels deep.  The solution is to make the 
>>>>> method iterative with an explicit stack.
>>>>>
>>>>> The new version does not follow the recursive version exactly. It 
>>>>> does the recursive step of following a dead input only after all 
>>>>> the inputs have been looked at and some may have been pushed to the 
>>>>> worklist.  This could potentially cause a little more work if those 
>>>>> inputs are later found to be dead and have to be removed from the 
>>>>> worklist.  But in practice this almost never happens.  Out of 
>>>>> 93319791 calls to remove_globally_dead_node, it found a dead node 
>>>>> that was pushed to the worklist only 1181 times, so I don't think 
>>>>> following the original algorithm is worth the added complexity.  By 
>>>>> the way the original algorithm has the same flaw but to a lesser 
>>>>> degree, because it follows dead inputs in the order they are seen. 
>>>>> If this was truly a performance problem, then dead inputs should be 
>>>>> followed first.
>>>>>
>>>>> Tested with CTW and the CVM dneg test from bug report.  In CTW 
>>>>> testing the average depth of the explicit stack was 1.53939 and the 
>>>>> maximum depth was 541.  99.957% of the time the depth was 16 or less.
>>>>>
>>>>> Thanks to Vladimir Kozlov for implementation and testing 
>>>>> suggestions (but any bugs are mine).
>>>>>
>>>>> dl
>>>
>>>
> 
>