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)
