Request for reviews (S): 6973329: C2 with Zero based COOP produces code with broken anti-dependency on x86

[Vladimir Kozlov]

Thank you, Tom

Vladimir

Tom Rodriguez wrote:
> I think that looks good.  Not using must_clone nodes in implicit null checks is a good fix.
> 
> tom
> 
> On Aug 10, 2010, at 11:17 AM, Vladimir Kozlov wrote:
> 
>> http://cr.openjdk.java.net/~kvn/6973329/webrev
>>
>> Fixed 6973329: C2 with Zero based COOP produces code with broken anti-dependency on x86
>>
>> Main problem: RA ignores anti-dependence when placing a clone of
>> a node which produces flags (or any rematerializable nodes).
>> The code generating implicit_null_check may move such nodes
>> above nodes modifying flags which will force RA to clone it.
>>
>> Solution:
>> Recompile without subsuming loads if RA try to clone a node with anti_dependence.
>> Do not use nodes which produce flags in implicit null checks.
>>
>> Added regression test based on failure I saw in SPECjEnterprise2010.
>>
>> JPRT, SPECjEnterprise2010
>>
>> Notes:
>> I collected statistic about how many dependences are found per
>> each call to insert_anti_dependences(). And how many recompilation
>> without subsuming loads and total bailout happened in new RA code.
>>
>> CTW rt.jar:
>> 1431559 made anti_dependence checks, 5497392 found anti_dependences (384%),
>> 128477 did not find anti_dependences ( 8%)
>>
>> jvm2008:
>> 200020 made anti_dependence checks, 724530 found anti_dependences (362%),
>> 10339 did not find anti_dependences ( 5%)
>>
>> Originally I thought about adding new Node flag has_anti_dependence which I
>> would set in insert_anti_dependences() and check it in the clone_node() in RA.
>> But looking on this statistic I decided to use existing flag
>> needs_anti_dependence_check. After that number of recompilation without
>> subsuming loads changed from 115 to 127 (in CTW rt.jar). I think it is acceptable.
>>
>> Next I found that this recompilation number could be significantly reduced
>> if I exclude nodes which produce flags from implicit null checks.
>>
>> Before:
>> CTW rt.jar:
>> RA: 127 recompile without subsume_loads, 0 bailout compilation
>> jvm2008:
>> RA: 140 recompile without subsume_loads, 0 bailout compilation
>>
>> After:
>> CTW rt.jar:
>> RA: 39 recompile without subsume_loads, 0 bailout compilation
>> jvm2008:
>> RA: 3 recompile without subsume_loads, 0 bailout compilation
>>
>>
>