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  1. JDK
  2. JDK-8156207

Resource allocated BitMaps are often cleared unnecessarily

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    • Resolved In Build:
      b08

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        Description

        This bug relates to JDK-8155638 where bitmaps where cleared twice.

        There are places where we don't clear the bitmaps twice, but the initial clearing is unnecessary, since the following code will set all bits.

        See, for example:
        http://cr.openjdk.java.net/~stefank/8155638/webrev.01/src/share/vm/c1/c1_IR.cpp.udiff.html

        where _requires_phi_function is cleared even when all bits are going to be set to 1.

        and:
        http://cr.openjdk.java.net/~stefank/8155638/webrev.01/src/share/vm/compiler/methodLiveness.cpp.frames.html

        in MethodLiveness::BasicBlock::get_liveness_at

        1010 ResourceBitMap g(_gen.size()); g.set_from(_gen);
        1011 ResourceBitMap k(_kill.size()); k.set_from(_kill);

        where we first clear the bitmap, then copy all bits with set_from. Before G1 was introduced, the unnecessary clearing was not done.

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                • Assignee:
                  chagedorn Christian Hagedorn
                  Reporter:
                  stefank Stefan Karlsson
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