RFR(M): 8038297 Avoid placing CTI immediately following cbcond instruction on T4

[Christian Thalinger]

Looks good.

On Apr 10, 2014, at 3:48 PM, Igor Veresov <igor.veresov at oracle.com> wrote:

> Vladimir, thanks for the review!
> 
> Here is the corrected webrev:  http://cr.openjdk.java.net/~iveresov/8038297/webrev.01/
> 
> Thanks!
> igor
> 
> On Apr 10, 2014, at 2:29 PM, Vladimir Kozlov <vladimir.kozlov at oracle.com> wrote:
> 
>> Igor,
>> 
>> Please, clean up code style of if() in  MachEpilogNode methods you touched in sparc.ad. The same in output_h.cpp.
>> 
>> I think you should separate into 2 flags Flag_avoid_before and Flag_avoid_after:
>> 
>> Flag_avoid_back_to_back  = Flag_may_be_short_branch << 1, // Flag has two bits
>> 
>> And use them instead of new MachNode::AvoidBackToBackFlag. I don't like next expression:
>> 
>> ins_avoid_back_to_back() * Flag_avoid_back_to_back
>> 
>> thanks,
>> Vladimir
>> 
>> On 4/10/14 11:54 AM, Igor Veresov wrote:
>>> We need to put nops between cbcond instructions and CTI instructions,
>>> because otherwise it causes a pipeline flush.
>>> This change extends the notion of the avoid_back_to_back instruction
>>> attribute to hold a 2 bits flag, with bits being AVOID_BEFORE and
>>> AVOID_AFTER.  The meaning of the bits is that an instruction with the
>>> AVOID_BEFORE flag cannot immediately follow one with AVOID_AFTER flag.
>>> The assembler has been modified accordingly to ensure that we don’t have
>>> a CTI instruction immediately following a cbcond instruction.
>>> 
>>> Webrev: http://cr.openjdk.java.net/~iveresov/8038297/webrev.00/
>>> 
>>> Testing: CTW, hotspot regression tests, JPRT
>>> 
>>> There is a significant performance gain on the microbenchmark that
>>> exposed the problem.
>>> Before with -XX:+UseCBCond: 106.985ns
>>> Before with -XX:-UseCBCond: 94.8967ns
>>> After with -XX:+UseCBCond: 94.5262ns
>>> 
>>> 
>>> Other performance results (some gains with jetstream and volano):
>>> ==============================================================================
>>> vanilla.logs:
>>>  Benchmark           Samples        Mean     Stdev             Geomean
>>> Weight
>>>  reference_server         20    16136.35    107.24
>>>    jetstream              20      153.30      1.63             0.10
>>>    scimark                20      353.47      5.78             0.15
>>>    specjbb2000            20   220984.11    638.71             0.15
>>>    specjbb2005            20   287778.70   3987.52             0.25
>>>    specjvm98              20      295.09      1.41             0.15
>>>    volano25               20   224179.95   5213.65             0.20
>>> ==============================================================================
>>> hack1.logs:
>>>  Benchmark           Samples        Mean     Stdev   %Diff     P
>>> Significant
>>>  reference_server         20    16357.48    111.46    1.37 0.000
>>>   Yes
>>>    jetstream              20      160.82      2.07    4.90 0.000
>>>   Yes
>>>    scimark                20      351.65      5.53   -0.51 0.316
>>>     *
>>>    specjbb2000            20   221142.43   1247.38    0.07 0.617
>>>     *
>>>    specjbb2005            20   288196.75   4598.83    0.15 0.760
>>>     *
>>>    specjvm98              20      298.11      0.89    1.02 0.000
>>>   Yes
>>>    volano25               20   232848.15   3952.61    3.87 0.000
>>>   Yes
>>> ==============================================================================
>