RFR(XS) 8032894: Remove dead code in Pressure::lower

[Niclas Adlertz]

Hi Vladimir,

Here is an attempt at making it clearer by making all _*_pressure fields private.

http://cr.openjdk.java.net/~adlertz/JDK-8032894/webrev01/

Kind Regards,
Niclas Adlertz

On 2014-01-30 00:22, Vladimir Kozlov wrote:
>  > Do you still want me to add the assert even though we only find a new
>  > _final_pressure when raising?
>
> No, but I want you to look on my suggestion:
>
>  > May be all _*_pressure fields should be private and code which updates
>  > them is located in one place. Then it would be more obvious that code
>  > you are removing is useless.
>
> Thanks,
> Vladimir
>
> On 1/29/14 3:05 PM, Niclas Adlertz wrote:
>> Hi Vladimir,
>>
>> On 2014-01-29 23:31, Vladimir Kozlov wrote:> Hi Niclas
>>>
>>> On 1/29/14 2:02 PM, Niclas Adlertz wrote:
>>>> Hi Vladimir,
>>>>
>>>> The initial states of _current_pressure and _final_pressure are computed
>>>> in PhaseChaitin::compute_initial_block_pressure().
>>>> We loop through all live ranges that are in the LIVE_OUT of the block,
>>>> and raise the _current_pressure (for either int or float) for each live
>>>> range. If the _current_pressure is bigger than the _final_pressure
>>>> (which is initially 0), we set the _final_pressure to be
>>>> _current_pressure. We check this each time we increase the
>>>> _current_pressure. This is done in Pressure::raise(). (I.e. the
>>>> _final_pressure is the highest value of _current_pressure that we ever
>>>> encounter in the block)
>>>
>>> It is not accurate, it could be higher. You overwrite it in
>>> check_for_high_pressure_transition_at_fatproj().
>> In a way it is accurate, because at a fat_proj the _current_pressure
>> will be raised and then lowered right after (stepping backwards) since
>> the fat_proj is only "live" at its definition.
>> (That's why we never change the _current_pressure at a fat_proj but
>> still look for a _final_pressure change).
>>
>>>
>>> May be all _*_pressure fields should be private and code which updates
>>> them is located in one place. Then it would be more obvious that code
>>> you are removing is useless.
>>>
>>>>
>>>> The _high_pressure_limit is passed into the constructor of the Pressure
>>>> class. This is done in the beginning of the build_ifg_physical():
>>>>
>>>> Pressure int_pressure(last_inst + 1, INTPRESSURE);
>>>> Pressure float_pressure(last_inst + 1, FLOATPRESSURE);
>>>>
>>>>> How we can get case (_current_pressure == _high_pressure_limit)?
>>>> When we lower the pressure, it is assumed that we lower each time by 1
>>>> (this happens every time we remove a definition from the LIVE_OUT when
>>>> stepping backwards in the block). So if _current_pressure is greater
>>>> than _high_pressure_limit, and we lower the _current_pressure, we might
>>>> hit the case when _current_pressure == _high_pressure_limit. If so, we
>>>> have found a Low to High pressure transition in the block. (Low to High
>>>> when starting from the top of the block)
>>>> However, there is one problem with this case, since the pressure could
>>>> be lowered by more than 1. (Long or Double will lower it by 2). So we
>>>> might miss a transition when lowering. There is already a bug
>>>> (JDK-8032886) filed for this which will be out soon. I didn't fix this
>>>> bug in the clean up since I wanted them to be separate commits.
>>>
>>> Okay, sounds good.
>>>
>>> Thanks,
>>> Vladimir
>>>
>>
>> Do you still want me to add the assert even though we only find a new
>> _final_pressure when raising?
>>
>> Kind Regards,
>> Niclas Adlertz
>>
>>>>
>>>> Kind Regards,
>>>> Niclas Adlertz
>>>>
>>>>
>>>> On 2014-01-29 19:53, Vladimir Kozlov wrote:
>>>>> What is initial state of _current_pressure, _high_pressure_limit,
>>>>> _final_pressure? How we can get case (_current_pressure ==
>>>>> _high_pressure_limit)? May be we should replace the code with assert:
>>>>>
>>>>> assert(_current_pressure <= _final_pressure
>>>>>
>>>>> Thanks,
>>>>> Vladimir
>>>>>
>>>>> On 1/29/14 4:09 AM, Niclas Adlertz wrote:
>>>>>> Hi all,
>>>>>>
>>>>>> When building the physical IFG, we step backwards in each block, and
>>>>>> remove things that are defined from the LIVE_OUT, (and lower the
>>>>>> current
>>>>>> pressure) and add input to the LIVE_OUT (and raising the current
>>>>>> pressure). Each time we lower or raise the current pressure, we
>>>>>> check if
>>>>>> it's bigger than the current maximum pressure, known as
>>>>>> final_pressure.
>>>>>> However the final_pressure can never increase when removing
>>>>>> definitions
>>>>>> (i.e. lower the current pressure) so the check for a new
>>>>>> final_pressure
>>>>>> in Pressure::lower is useless.
>>>>>>
>>>>>> webrev: http://cr.openjdk.java.net/~adlertz/JDK-8032894/webrev00/
>>>>>> bug: https://bugs.openjdk.java.net/browse/JDK-8032894
>>>>>>
>>>>>> Kind Regards,
>>>>>> Niclas Adlertz