RFR (XS) JDK-8006280 - structure packing for 64-bit (resend)

[Ioi Lam]

(re-sending with public-accessible bug URL).

WebRev:
http://cr.openjdk.java.net/~iklam/8006280/reorder_metadata_001/

Bug: Need to reorder metadata structures to reduce size (64-bit)
      http://bugs.sun.com/view_bug.do?bug_id=8006280

Sponsor: Jiangli

Summary:

On x64:

   + Klass: 8 byte reduction
   + InstanceKlass: 8 byte reduction (in addition to reduction in Klass)
   + Method: 8 byte reduction

   This is verified by using the "pahole" script (as described in bug report)

On ARM-EABI:

   I also manually verify that this change for ARM-EABI (which requires
   8-byte alignment for jlong but not pointers):

   + Klass: 8 byte reduction
   + InstanceKlass: no change (apart from Klass reduction) -- no jlong fields
   + Method: no change -- no jlong fields

   Before: (linux_armvfp_2.6-productEmb/jre/lib/arm/minimal/libjvm.diz

     (gdb) p &((Klass*)0)->_alloc_count
     $1 = (juint *) 0x58
     (gdb) p &((Klass*)0)->_last_biased_lock_bulk_revocation_time
     $2 = (jlong *) 0x60
     (gdb) p sizeof(Klass)
     $3 = 120

     The "hole" was at address 0x5c

   After:

     (gdb) p &((Klass*)0)->_access_flags
     $7 = (AccessFlags *) 0x54
     (gdb) p &((Klass*)0)->_last_biased_lock_bulk_revocation_time
     $8 = (jlong *) 0x58
     (gdb) p sizeof(Klass)
     $6 = 112

Tests run:

+ JPRT -- (hotspot only, on hotspotwest queue, including embedded builds)

+ UTE/vm.quick.testlist, 100% passed


Thanks
Ioi







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