RFR: 8164525: Re-examine zero form link time pre-generation

[Vladimir Ivanov]

Reviewed.

Best regards,
Vladimir Ivanov

On 8/21/16 12:59 PM, Claes Redestad wrote:
> Hi,
>
> the previous attempt to pre-generate zero LambdaForms[1] failed
> due to the current implementation surprisingly emitting placeholder
> constants to link to the associated identity function (which we can't
> properly handle when pre-generating forms) rather than simply emitting
> the corresponding bytecode directly (iconst_0, etc).
>
> It turns out the setup of Zero and Identity functions aren't being made
> intrinsic, which appears to be an oversight. Fixing this allows for more
> optimal bytecode[1].
>
> While this fix could have positive performance implications in general,
> it also makes the startup optimization from JDK-8164451 re-apply
> without issue (no test failures running RBT --test jdk/test/:tier1).
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8164525
> Webrev: http://cr.openjdk.java.net/~redestad/8164525/webrev.01/
>
> Thanks!
>
> /Claes
>
> [1] https://bugs.openjdk.java.net/browse/JDK-8164451
> [2] Before:
>
>   static java.lang.Object zero_000_L(java.lang.Object);
>     descriptor: (Ljava/lang/Object;)Ljava/lang/Object;
>     flags: ACC_STATIC
>     Code:
>       stack=2, locals=1, args_size=1
>          0: ldc           #14                 // String
> CONSTANT_PLACEHOLDER_1 <<(Object)Object :
> identity_000_L=Lambda(a0:L,a1:L)=>{a1:L}\n& Class=SimpleMethodHandle>>
>          2: checkcast     #16                 // class
> java/lang/invoke/MethodHandle
>          5: aconst_null
>          6: invokevirtual #19                 // Method
> java/lang/invoke/MethodHandle.invokeBasic:(Ljava/lang/Object;)Ljava/lang/Object;
>
>          9: areturn
>     RuntimeVisibleAnnotations:
>       0: #8()
>       1: #9()
>       2: #10()
>
> After:
>
>   static java.lang.Object zero_L(java.lang.Object);
>     descriptor: (Ljava/lang/Object;)Ljava/lang/Object;
>     flags: ACC_STATIC
>     Code:
>       stack=1, locals=1, args_size=1
>          0: aconst_null
>          1: areturn
>     RuntimeVisibleAnnotations:
>       0: #8()
>       1: #9()
>       2: #10()