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List:       openjdk-hotspot-runtime-dev
Subject:    8240245: Avoid calling is_shared_class_visible() in SystemDictionary::load_shared_class()
From:       Yumin Qi <yumin.qi () oracle ! com>
Date:       2020-05-22 15:45:42
Message-ID: 76909ea0-2aca-61e7-cea6-d4bfa3c866ef () oracle ! com
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Hi, Please review

   bug: 8240245: https://bugs.openjdk.java.net/browse/JDK-8240245
   Webrev: http://cr.openjdk.java.net/~minqi/2020/8240245/webrev-00/

Summary: When -Xbootclasspath/a: and --module-path are not specified, 
for bultin loaders, is_shared_class_visible will always return true so 
we can skip such check. Another optimization is guarding the call to 
load_shared_class with UseSharedSpaces, save unnecessary calls for 
non-shared run.

For java -version, the performance data:

Results of " perf stat -r 40 bin/java -Xshare:on 
-XX:SharedArchiveFile=jdk2.jsa -Xint -version "
    1:     59008853    59008564 (  -289)                41.100 40.342 ( 
-0.758)      --
    2:     58983285    59026645 ( 43360)  ++++          39.841 40.708 (  
0.867)    ++
    3:     59008801    59005425 ( -3376)                39.903 40.881 (  
0.978)   +++
    4:     59032045    58990500 (-41545)      ----      39.809 40.443 (  
0.634)    ++
    5:     59029813    58976124 (-53689)      -----     40.121 39.238 ( 
-0.883)      --
    6:     59036617    58998279 (-38338)      ----      40.644 39.875 ( 
-0.769)      --
    7:     59003768    59005109 (  1341)                39.416 38.991 ( 
-0.425)      -
    8:     58972545    58985824 ( 13279)     +          40.811 40.001 ( 
-0.810)      --
    9:     59007110    58981883 (-25227)      --        40.969 39.090 ( 
-1.879)      -----
   10:     58992934    58987333 ( -5601)      -         40.521 40.371 ( 
-0.150)
============================================================
           59007573    58996566 (-11006)      -         40.310 39.989 ( 
-0.321)      -
instr delta =       -11006    -0.0187%
time  delta =       -0.321 ms -0.7966%

Tests:  tier1,tier2

Thanks
Yumin
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