[9] RFR (M): 8037209: Improvements and cleanups to bytecode assembly for lambda forms

[Vladimir Ivanov]

> Doh! crossed webrevs, thanks.
>
> Just had a quick look, this looks like a really nice improvement to the array setter/getter support, definitely simplified. IIUC the mh.viewAsType will now handle the appropriate casting. I believe it might reduce the "ceremony" for array setter/getter MHs [1].
>
> I see there is a PROFILE_LEVEL option, by default set to 0, that results in casts not being emitted:
>
> +                if (VerifyType.isNullConversion(Object.class, pclass, false)) {
> +                    if (PROFILE_LEVEL > 0)
> +                        emitReferenceCast(Object.class, arg);
> +                    return;
> +                }
> ...
> +            mv.visitLdcInsn(constantPlaceholder(cls));
> +            mv.visitTypeInsn(Opcodes.CHECKCAST, CLS);
> +            mv.visitInsn(Opcodes.SWAP);
> +            mv.visitMethodInsn(Opcodes.INVOKESTATIC, MHI, "castReference", CLL_SIG, false);
> +            if (Object[].class.isAssignableFrom(cls))
> +                mv.visitTypeInsn(Opcodes.CHECKCAST, OBJARY);
> +            else if (PROFILE_LEVEL > 0)
> +                mv.visitTypeInsn(Opcodes.CHECKCAST, OBJ);
>
> Can you explain a bit the rational for that?
These casts are redundant - they aren't required for bytecode 
correctness. The idea behind PROFILE_LEVEL is to provide more type 
information to JIT-compiler. Right now, type profiling occurs on every 
checkcast instruction. So, having these additional instructions we can 
feed C2 with more accurate information about types.

Consider this as a hack to overcome some of the limitations of current 
profiling implementation in VM.

Best regards,
Vladimir Ivanov

> Paul.
>
> [1] Below is an inlining trace for an array getter MH in the current code i obtained a few weeks ago when investigating CAS-based MHs for arrays:
>
> Inlining _isInstance on constant Class java/lang/Class
> Inlining _isInstance on constant Class [Ljava/lang/Object;
> Inlining _isInstance on constant Class [Ljava/lang/String;
> Inlining _isInstance on constant Class java/lang/String
>                              @ 12   unsafe.ArrayMHTest::get_mh_orig (19 bytes)   inline (hot)
>                                @ 12   java.lang.invoke.LambdaForm$MH/924874137::invokeExact_MT (15 bytes)   inline (hot)
>                                  @ 2   java.lang.invoke.Invokers::checkExactType (30 bytes)   inline (hot)
>                                    @ 11   java.lang.invoke.MethodHandle::type (5 bytes)   accessor
>                                  @ 11   java.lang.invoke.LambdaForm$MH/1980556943::convert (21 bytes)   inline (hot)
>                                    @ 7   java.lang.invoke.LambdaForm$MH/1892887290::getElement (20 bytes)   inline (hot)
>                                      @ 16   java.lang.invoke.LambdaForm$MH/816943783::convert (37 bytes)   inline (hot)
>                                        @ 6   java.lang.invoke.LambdaForm$BMH/1350345087::reinvoke (26 bytes)   inline (hot)
>                                          @ 12   java.lang.invoke.BoundMethodHandle$Species_LL::reinvokerTarget (8 bytes)   inline (hot)
>                                          @ 22   java.lang.invoke.LambdaForm$DMH/1162873666::invokeStatic_LL_L (15 bytes)   inline (hot)
>                                            @ 1   java.lang.invoke.DirectMethodHandle::internalMemberName (8 bytes)   inline (hot)
>                                            @ 11   sun.invoke.util.ValueConversions::castReference (20 bytes)   inline (hot)
>                                              @ 6   java.lang.Class::isInstance (0 bytes)   (intrinsic)
>                                        @ 17   java.lang.invoke.LambdaForm$BMH/1350345087::reinvoke (26 bytes)   inline (hot)
>                                          @ 12   java.lang.invoke.BoundMethodHandle$Species_LL::reinvokerTarget (8 bytes)   inline (hot)
>                                          @ 22   java.lang.invoke.LambdaForm$DMH/1162873666::invokeStatic_LL_L (15 bytes)   inline (hot)
>                                            @ 1   java.lang.invoke.DirectMethodHandle::internalMemberName (8 bytes)   inline (hot)
>                                            @ 11   sun.invoke.util.ValueConversions::castReference (20 bytes)   inline (hot)
>                                              @ 6   java.lang.Class::isInstance (0 bytes)   (intrinsic)
>                                        @ 33   java.lang.invoke.MethodHandleImpl$ArrayAccessor::getElementL (10 bytes)   inline (hot)
>                                          @ 2   java.lang.Class::cast (27 bytes)   inline (hot)
>                                            @ 6   java.lang.Class::isInstance (0 bytes)   (intrinsic)
>                                    @ 17   java.lang.invoke.LambdaForm$MH/91466391::convert (23 bytes)   inline (hot)
>                                      @ 6   java.lang.invoke.LambdaForm$BMH/1350345087::reinvoke (26 bytes)   inline (hot)
>                                        @ 12   java.lang.invoke.BoundMethodHandle$Species_LL::reinvokerTarget (8 bytes)   inline (hot)
>                                        @ 22   java.lang.invoke.LambdaForm$DMH/1162873666::invokeStatic_LL_L (15 bytes)   inline (hot)
>                                          @ 1   java.lang.invoke.DirectMethodHandle::internalMemberName (8 bytes)   inline (hot)
>                                          @ 11   sun.invoke.util.ValueConversions::castReference (20 bytes)   inline (hot)
>                                            @ 6   java.lang.Class::isInstance (0 bytes)   (intrinsic)
>                                      @ 19   java.lang.invoke.LambdaForm$MH/349834280::identity (10 bytes)   inline (hot)
>                                        @ 6   java.lang.invoke.LambdaForm$DMH/1357006072::invokeStatic_L_L (14 bytes)   inline (hot)
>                                          @ 1   java.lang.invoke.DirectMethodHandle::internalMemberName (8 bytes)   inline (hot)
>                                          @ 10   sun.invoke.util.ValueConversions::identity (2 bytes)   inline (hot)
>