review request: 7147464: Java crashed while executing method with over 8k of dneg operations
Vladimir Kozlov
vladimir.kozlov at oracle.com
Fri Jul 13 12:05:13 PDT 2012
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
>
>
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