[9] RFR (M): 8149741: Don't refer to stub entry points by index in external_word relocations

[Vladimir Ivanov]

http://cr.openjdk.java.net/~vlivanov/8149741/webrev.00/
https://bugs.openjdk.java.net/browse/JDK-8149741

As a followup on the discussion about using indexes instead of raw 
addresses in external relocations [1], here's the request for removal of 
the corresponding logic.

To ease reviewing I splitted the changes into 3 groups:

(1) http://cr.openjdk.java.net/~vlivanov/8149741/webrev.00.removal/

Get rid of runtime_address_to_index/index_to_runtime_address functions 
and adjust pack_data_to/unpack_data in external_word_Relocation to 
operate on raw addresses.

(2) http://cr.openjdk.java.net/~vlivanov/8149741/webrev.00.cleanup/

Different cleanups in StubCodeDesc implementation. Simplified iteration 
over the list and PrintStubCode support.

(3) http://cr.openjdk.java.net/~vlivanov/8149741/webrev.00.index/

Cleaned up some outdated usages of ExternalAddress. Its constructor 
adjusts relocation type according to address. For NULL address it 
doesn't create a relocation and there's no need in special cases then.

Also, I looked through all ExternalAddress usages, but didn't find any 
places where values which aren't external addresses are used [2]. So, I 
converted is_reloc_index check into an assert in 
external_word_Relocation::can_be_relocated(). Let me know if you see any 
problems with that.

Testing: hotspot regression tests, JPRT.

Thanks!

Best regards,
Vladimir Ivanov

[1] 
http://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/2016-February/021354.html

[2]
   static relocInfo::relocType reloc_for_target(address target) {
     // Sometimes ExternalAddress is used for values which aren't
     // exactly addresses, like the card table base.
     // external_word_type can't be used for values in the first page
     // so just skip the reloc in that case.
     return external_word_Relocation::can_be_relocated(target) ? 
relocInfo::external_word_type : relocInfo::none;
   }