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From "Xiao-Feng Li" <xiaofeng...@gmail.com>
Subject Re: [drlvm][vm] New method in VM-JIT interface (was: [drlvm][jit]...)
Date Tue, 17 Apr 2007 04:08:06 GMT
On 4/14/07, Xiao-Feng Li <xiaofeng.li@gmail.com> wrote:
> On 4/13/07, Mikhail Fursov <mike.fursov@gmail.com> wrote:
> > I've attached combined JIT+VM patch to JIRA. The test failed before passes
> > now.
> > VM-guru, please check VMEXPORT Boolean
> > vm_helper_is_gc_interruptible(VM_RT_SUPPORT f) method in this patch.
>
> VM gurus, please help checking this method in H3626. Thanks, xiaofeng

Mikhail, how would you like to proceed with this patch? Thanks.

> > On 4/13/07, Alexey Varlamov <alexey.v.varlamov@gmail.com> wrote:
> > >
> > > 2007/4/13, Mikhail Fursov <mike.fursov@gmail.com>:
> > > > Rana,
> > > > thank you for the fast update.
> > > > I'll integrate this function usage into JIT and report if the problem
I
> > > have
> > > > disappeares today.
> > > >
> > > > >>BTW, how does the jit knows which helpers throw exceptions?
> > > > JIT generates stack info for every call instruction. So we can
> > > > unwind stack frame from every call.
> > > > Actually this is not enough: JIT must generate stackinfo for every push
> > > inst
> > > > also to handle SOE correctly. But this is one of the TODO list items.
> > > >
> > > >
> > > > Another problem with helper calls I know is their calling conventions.
> > > > Now the calling convention of every helper is hardcoded to JIT.
> > > > I think it worth creating another JIRA to solve the problem one day.
> > > Today I
> > > > know no bugs about it, so it's design only issue.
> > >
> > > There is one already: HARMONY-2702. Actually Jitrino provides such
> > > interface internally,
> > > CompilationInterface::getRuntimeHelperCallingConvention(), so fix
> > > should be easy enough (yet is blocked by HARMONY-3553).
> > >
> > > >
> > > >
> > > > On 4/13/07, Rana Dasgupta <rdasgupt@gmail.com> wrote:
> > > > >
> > > > > Yes, that make sense. I'll wait a bit to see if Mikhail has any more
> > > > > suggestions and change it to is_gc_interruptible.
> > > > >
> > > > > On 4/12/07, Xiao-Feng Li <xiaofeng.li@gmail.com> wrote:
> > > > > > Agree that this information better be provided by VM than JIT
> > > internals.
> > > > > >
> > > > > > Rana, Thanks for the quick work. A minor comment:
> > > > > >
> > > > > > The interface name might be better use "has_gc_safepoint" or
> > > > > > "is_gc_interruptible" than "is_suspension_point", since the
helper
> > > is
> > > > > > a function (not a point), and "suspension" is implementation
detail.
> > > > > >
> > > > > > Thanks,
> > > > > > xiaofeng
> > > > > >
> > > > > > On 4/13/07, Rana Dasgupta <rdasgupt@gmail.com> wrote:
> > > > > > > Mikhail,
> > > > > > >    I extended the vm-jit interface with a function:
> > > > > > > boolean vm_is_helper_suspension_point( VM_RT_SUPPORT f)
> > > > > > >
> > > > > > > and attached it to your JIRA.
> > > > > > >
> > > > > > >   Right now it returns true for almost every helper. But
you may
> > > want
> > > > > > > to update this instead of hardcoding in the jit. At some
point, we
> > > > > > > need some analysis to determine which helpers are interruptible.
> > > > > > >
> > > > > > >   BTW, how does the jit knows which helpers throw exceptions?
> > > > > > >
> > > > > > > Rana
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > > On 4/11/07, Mikhail Fursov <mike.fursov@gmail.com>
wrote:
> > > > > > > > On 4/12/07, Rana Dasgupta <rdasgupt@gmail.com>
wrote:
> > > > > > > > >
> > > > > > > > > On 4/11/07, Xiao-Feng Li <xiaofeng.li@gmail.com>
wrote:
> > > > > > > > > > On 4/12/07, Rana Dasgupta <rdasgupt@gmail.com>
wrote:
> > > > > > > > > > > A silly question possibly. But other
than inlined
> > > fastpaths,
> > > > > why not
> > > > > > > > > > > gcm treat all helper calls as interruptible?
> > > > > > > > > >
> > > > > > > > > > I think this needs case by case study to
decide which ones
> > > can
> > > > > be
> > > > > > > > > > interruptible. In most cases, the helper
is only an
> > > extension of
> > > > > a
> > > > > > > > > > certain bytecode operation, which can be
virtually treated
> > > as a
> > > > > > > > > > bytecode (or part of a bytecode semantics).
Normally, the
> > > > > safepoint
> > > > > > > > > > can be before or after it, but not in middle
of it. If we
> > > think
> > > > > of the
> > > > > > > > > > stack map info, the helper itself may not
stand for a formal
> > > > > method
> > > > > > > > > > frame for GC or exception handling.
> > > > > > > > >
> > > > > > > > > This is a good way to look at helper calls. My
point,
> > > > > however,  was
> > > > > > > > > not really that helper calls should be interruptible.
But that
> > > > > other
> > > > > > > > > than the fastpath for which the JIT sees the
IR, why not treat
> > > the
> > > > > > > > > calls themselves as ineligible for code motion
etc. like other
> > > > > > > > > operators with side effects? Is the cost too
high?
> > > > > > > > > Implementing the interface extension is not hard
for the VM,
> > > but
> > > > > looks
> > > > > > > > > like implementation dependant info passed from
the VM to the
> > > JIT.
> > > > > > > > >
> > > > > > > > > Here is more details:
> > > > > > > > The example of a helper that can be moved by GCM are
number
> > > > > conversion helpers.
> > > > > > > > 'i2d' never throws exceptions and this knowledge is
hardcoded in
> > > > > HLO. On the
> > > > > > > > other hand this HIR opcode is translated into LIR
vm-helper
> > > call, so
> > > > > instead
> > > > > > > > of simple Java opcode it becomes a
> > > > > > > > call. I can hardcode which vm-helper call is interruptable
and
> > > which
> > > > > is
> > > > > > > > not on the
> > > > > > > > JIT side, but think retrieving this information from
VM is a
> > > better
> > > > > solution.
> > > > > > > > Another example of uninterruptable vm-helper is
> > > > > > > > TLS accessor. This helper is placed into the middle
of the
> > > inlined
> > > > > > > > 'alloc' helper body because 'alloc' reqires TLS access.
> > > > > > > > Now  managed<->unmanaged convertion checker
in GCMap pass has
> > > > > hardcoded
> > > > > > > > knowledge that TLS access will never be suspended.
> > > > > > > >
> > > > > > > > JET compiler uses different code then OPT and maintains
special
> > > > > > > > GC-bitmasks for object operands runtime.
> > > > > > > > The per-call gc-mask maintainance is not free and
can also be
> > > > > > > > optimized if VM provides a method to describe which
call is real
> > > > > > > > suspension point and which is not.
> > > > > > > >
> > > > > > > >
> > > > > > > >
> > > > > > > > + Suspension and exception throwing are different
attributes.
> > > SOE
> > > > > can be
> > > > > > > > thrown even if method is not a suspension point. So
JIT must
> > > prepare
> > > > > stack
> > > > > > > > info for every call it generates to be able to unwind
 the
> > > frame.
> > > > > > > >
> > > > > > > > --
> > > > > > > > Mikhail Fursov
> > > > > > > >
> > > > > > >
> > > > > >
> > > > > >
> > > > > > --
> > > > > > http://xiao-feng.blogspot.com
> > > > > >
> > > > >
> > > >
> > > >
> > > >
> > > > --
> > > > Mikhail Fursov
> > > >
> > >
> >
> >
> >
> > --
> > Mikhail Fursov
> >
>
>
> --
> http://xiao-feng.blogspot.com
>


-- 
http://xiao-feng.blogspot.com

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