RFR(S): 7194633: G1: Assertion and guarantee failures in block offset table

[John Cuthbertson]

Hi Everyone,

Can I have a couple of volunteers review the changes at: 
http://cr.openjdk.java.net/~johnc/7194633/webrev.0 ?

Background:

While I was testing the fix for 719066 I ran into several assertions and 
guarantee failures from G1's block offset table when running through 
jprt. The failures were associated with using a specific version of the 
sparc memset to initialize the offsets array (see 7192128) which was 
missing from my 7190666 workspace. The changes in this webrev are the 
instrumenation and detailed error message changes I made to verify that 
G1's block offset table was not immune to the memset issue and that the 
failures from jprt were the same issue. These detailed error messages 
were invaluable when tracking the issue down.

Testing:
GCBasher with -UseMemsetInBOT on sparc
Forcibly triggering the failures to check that the error messages made 
sense.
jprt

It is still my intent to merge G1's BOT with that of the other 
collectors and remove the large amount of duplicated code (which is a 
separate CR). When I do that, the detailed error messages will be 
included in the shared BOT code.

Thanks,

JohnC