ARM codegen needs to handle non-simple array copies

[JamesKingdon]

OMR::ARM::TreeEvaluator::arraycopyEvaluator in arm/codegen/OMRTreeEvaluator.cpp currently asserts when passed a non-simple array copy node. In a production build without asserts it will generate incorrect code for most non-simple array copies.

[JamesKingdon]

Running with gcpolicy optthruput should eliminate the need for write barriers, so it may be possible to quickly handle the degenerate case where complex copies can be treated as simple.

Here's the array copy that currently trips up a count=0,disableAsyncCheck -version test:

 n71n     (  1)    arraycopy  <arraycopy>[#478  helper Method] [flags 0x400 0x0 ] (Unsigned cannotOverflow forwardArrayCopy noArrayStoreCheckArrayCopy referenceArrayCopy wordElementArrayCopy )  [0x903047e8] bci=[0,1,58] rc=1 vc=145 vn=- li=3 udi=- nc=5 flg=0xd020
 n3n      (  2)      aload  sun/invoke/util/Wrapper.$VALUES [Lsun/invoke/util/Wrapper;[#616  notAccessed final Static] [flags 0xa0307 0x0 ] (X!=0 X>=0 sharedMemory )  [0x90303b28] bci=[-1,0,28] rc=2 vc=145 vn=- li=3 udi=- nc=0 flg=0x104
 n27n     (  3)      ==>anewarray (in &GPR_0x90431af0) (highWordZero Unsigned X!=0 allocationCanBeRemoved sharedMemory )
 n68n     (  1)      aiadd                                                                            [0x90304758] bci=[0,1,58] rc=1 vc=145 vn=- li=3 udi=- nc=2
 n3n      (  2)        ==>aload (X!=0 X>=0 sharedMemory )
 n67n     (  2)        iconst 8 (X!=0 X>=0 )                                                          [0x90304728] bci=[0,0,58] rc=2 vc=145 vn=- li=3 udi=- nc=0 flg=0x104
 n70n     (  1)      aiadd                                                                            [0x903047b8] bci=[0,1,58] rc=1 vc=145 vn=- li=3 udi=- nc=2
 n27n     (  3)        ==>anewarray (in &GPR_0x90431af0) (highWordZero Unsigned X!=0 allocationCanBeRemoved sharedMemory )
 n67n     (  2)        ==>iconst 8 (X!=0 X>=0 )
 n66n     (  1)      iconst 40 (X!=0 X>=0 )                                                           [0x903046f8] bci=[0,1,58] rc=1 vc=145 vn=- li=3 udi=- nc=0 flg=0x104

I'm exploring the possibility that the noArrayStoreCheckArrayCopy flag is enough to tell that this can be treated as a simple copy.
Possibly noArrayStoreCheckArrayCopy is necessary, but it's not sufficient. The key criteria is whether or not write barriers are required which can be determined from cg->comp()->getOptions()->needWriteBarriers()