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From "Mikhail Fursov" <mike.fur...@gmail.com>
Subject Re: [DRLVM][Helper inlining] GC write barrier inline?
Date Tue, 12 Dec 2006 12:48:29 GMT
Xiao Feng,
I missed one very important line in gc_heap_slot_write_ref:
  *p_slot = p_target;

and now I understand why replacing the old call with WB helper you sent in
the initial message does not work.
I'm going to add store operation into the helper now and retest it.

+ I'm ok to discuss and clean up GC interface as you proposed after the most
simple version of WB is working.


On 12/12/06, Xiao-Feng Li <xiaofeng.li@gmail.com> wrote:
>
> Mikhail, the gc_heap_slot_write_ref  is an old GC interface in ORP.
> The original idea for this interface is, any Java heap slot reference
> store should go through this GC function, including VM and Java
> application. So this function does the real reference store, the
> original store in JITted code will not be emitted. Hence the OPT write
> barrier has no problem.
>
> The problem with this interface is, it has no clear definition about
> whether a write barrier is needed or not. That's why I suggested to
> use a new interface gc_heap_slot_write_barrier for the helper inlining
> work. The code for it is the same as gc_heap_slot_write_ref for
> generational GC (without the check for needing barrier or not). Since
> the WB inlined helper is only invoked when generational GC is run, the
> check is redundant completely.
>
> I am not sure if I make it clear.
>
> Thanks,
> xiaofeng
>
> On 12/11/06, Mikhail Fursov <mike.fursov@gmail.com> wrote:
> > Xiao-Feng,
> > I'm slightly confused about current WB support in Jitrino.OPT, so I need
> an
> > advice.
> >
> > The problem: I think that write barriers in Jitrino OPT do not work.
> >
> > Example (see for lines marked with =>):
> >
> >
> > HIR with WB disabled:
> >
> >   I1:defarg.ths -) t1:cls:java/net/URLClassLoader$4
> >   I2:tauisnonnull      t1 -) t2:tau
> >   I3:tauhastype      t1,cls:java/net/URLClassLoader$4 -) t3:tau
> >   I4:defarg -) t4:cls:java/net/URLClassLoader
> >   I5:tauhastype      t4,cls:java/net/URLClassLoader -) t5:tau
> >   I6:defarg -) t6:cls:java/lang/String
> >   I7:tauhastype      t6,cls:java/lang/String -) t7:tau
> >   I8:ldflda    [t1.java/net/URLClassLoader$4::this$0] -)
> > t8:ref:cls:java/net/URLClassLoader
> > =>  I9:stind.unc:o   t4 ((t2,t3,t5)) -) [t8]
> >   I10:ldflda    [t1.java/net/URLClassLoader$4::val$clsName] -)
> > t9:ref:cls:java/lang/String
> > =>  I11:stind.unc:str t6 ((t2,t3,t7)) -) [t9]
> >   I12:tauunsafe() -) t10:tau
> >   I13:call      java/lang/Object::_init_(t1) ((t2,t10)) -)
> >
> >
> > The same HIR with WB enabled:
> >
> >   Successors: L5 UNWIND
> >   I1:defarg.ths -) t1:cls:java/net/URLClassLoader$4
> >   I2:tauisnonnull      t1 -) t2:tau
> >   I3:tauhastype      t1,cls:java/net/URLClassLoader$4 -) t3:tau
> >   I4:defarg -) t4:cls:java/net/URLClassLoader
> >   I5:tauhastype      t4,cls:java/net/URLClassLoader -) t5:tau
> >   I6:defarg -) t6:cls:java/lang/String
> >   I7:tauhastype      t6,cls:java/lang/String -) t7:tau
> >   I8:ldflda    [t1.java/net/URLClassLoader$4::this$0] -)
> > t8:ref:cls:java/net/URLClassLoader
> > =>  I9:stref.wb.unc   t4 ((t2,t3,t5)) -) [t8 t1]
> >   I10:ldflda    [t1.java/net/URLClassLoader$4::val$clsName] -)
> > t9:ref:cls:java/lang/String
> > =>  I11:stref.wb.unc   t6 ((t2,t3,t7)) -) [t9 t1]
> >   I12:tauunsafe() -) t10:tau
> >   I13:call      java/lang/Object::_init_(t1) ((t2,t10)) -)
> >
> >
> >
> > The LIR with WB disabled
> >
> >     I1: t4:ref:cls:java/net/URLClassLoader (ID:s5(EFLGS):uint32) =ADD
> >
> t0:cls:java/net/URLClassLoader$4,t3(0:fo:java/net/URLClassLoader$4.this$0):intptr
> >
> > =>    I2: (AD:t6[t4]:object) =CopyPseudoInst/MOV
> > (AU:t1:cls:java/net/URLClassLoader)
> >     I3: t8:ref:cls:java/lang/String (ID:s5(EFLGS):uint32) =ADD
> >
> t0:cls:java/net/URLClassLoader$4,t7(0:fo:java/net/URLClassLoader$4.val$clsName):intptr
> >
> > =>    I4: (AD:t9[t8]:string) =CopyPseudoInst/MOV
> > (AU:t2:cls:java/lang/String)
> >
> >
> >
> >
> > The same LIR with WB enabled
> >
> >     I1: t4:ref:cls:java/net/URLClassLoader (ID:s5(EFLGS):uint32) =ADD
> >
> t0:cls:java/net/URLClassLoader$4,t3(0:fo:java/net/URLClassLoader$4.this$0):intptr
> >
> > =>    I2: CALL t6(0:h:WriteBarrier):ptr:intptr
> >
> (AU:t0:cls:java/net/URLClassLoader$4,t4:ref:cls:java/net/URLClassLoader,t1:cls:java/net/URLClassLoader)
> >
> >     I3: t8:ref:cls:java/lang/String (ID:s5(EFLGS):uint32) =ADD
> >
> t0:cls:java/net/URLClassLoader$4,t7(0:fo:java/net/URLClassLoader$4.val$clsName):intptr
> >
> > =>    I4: CALL t9(0:h:WriteBarrier):ptr:intptr
> >
> (AU:t0:cls:java/net/URLClassLoader$4,t8:ref:cls:java/lang/String,t2:cls:java/lang/String)
> >
> >
> >
> > The question is what is in the CALL? I see only the method:
> > gc_heap_slot_write_ref and this method does not save anything into
> fields.
> > Does it mean that WB support in Jitrino.OPT is incomplete today?
> >
> > --
> > Mikhail Fursov
> >
> >
>



-- 
Mikhail Fursov

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