hg: mlvm/mlvm/jdk: cval: hang caches on classes

[Charles Oliver Nutter]

I see there's WeakReference used in there...will ClassValue have
WeakReference-like impact on GC?

I'll try to get JRuby using ClassValue for a few things soon, to help
test this out against non-ClassValue solutions.

- Charlie

On Thu, Aug 4, 2011 at 1:21 AM, John Rose <john.r.rose at oracle.com> wrote:
> Benchmarks indicate a 4x speedup from previous implementation.
> The fast path has 7 memory references.  Here's what it looks like:
>       {mov eax, (cval : ClassValue); mov edx, (type : Class)}
>   M1: mov ecx, [edx+0x60]  ;*getfield Class.classValueCache : Entry[]
>   M2: mov ebp, [ecx+0x8]   ;*arraylength
>       {mov esi, ebp; dec esi}
>   M3: and esi, [eax+0x8]   ;*iand ClassValue.hashCodeForCache
>       {cmp esi, ebp; jnc (slow)}
>   M4: mov ecx, [ecx+esi*4+0xC]  ;*aaload : Entry
>       {implicit cmp ecx, 0; jz (slow)}
>   M5: mov esi, [ecx+0x8]   ;*getfield WeakReference.referent :
> ClassValue$Version
>   M6: mov ebp, [eax+0xC]   ;*getfield ClassValue.version :
> ClassValue$Version
>       {cmp esi, ebp; jnz (slow)}
>   M7: mov eax, [ecx+0x18]  ;*getfield value
>       {mov (result : T), eax}
> That's probably good enough for most uses.
> All of the memory references are possible CSE and loop invariants.
> I saw a too-simple benchmark loop collapse completely to constant time.
> The range check (of the form a[a.length-1 & i]) could be simplified with a
> little work.
> The version check defends against ClassValue.remove.
> Maybe it could be removed by push notification, but it's probably not worth
> it.
> -- John
> On Aug 3, 2011, at 9:58 PM, john.r.rose at oracle.com wrote:
>
> Changeset: c26fceff6309
> Author:    jrose
> Date:      2011-08-03 21:57 -0700
> URL:       http://hg.openjdk.java.net/mlvm/mlvm/jdk/rev/c26fceff6309
>
> cval: hang caches on classes
>
> + cval-tune-7030453.patch
> ! series
>
>
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