RFR [S] 8081406: cleanup and minor extensions of the debugging facilities in CodeStrings

[Bertrand Delsart]

Hi all,

Small RFR to address minor issues in debug mode with CodeStrings

https://bugs.openjdk.java.net/browse/JDK-8081406
http://cr.openjdk.java.net/~bdelsart/8081406/webrev.00/

The change does not impact the product mode.

In non product mode, CodeStrings allows to associate a linked list of 
strings to a CodeBuffer, CodeBlob or Stub. In addition, with ASSERTS, it 
defines a boolean asserting whether the list of strings are valid.

Here are the issues addressed by this CR:

- The old code mentioned the fact that CodeStrings was not always 
correctly initialized. This is addressed by the fix, allowing 
check_valid to be added at a few locations where it could currently 
failed due to uninitialized values (like at the beginning of 
CodeStrings::free). This also makes the code more robust against future 
versions of CodeStrings.

- As a minor extension, it is now possible for platform dependent code 
to modify the comment separator used by print_block_comment, which was 
hard coded to " ;; ".

- As another minor extension, related to the validity assertions, 
freeing a code string no longer necessarily marks it (and hence its 
Stub/CodeBlob/CodeBuffer) as invalid. If CodeStrings contains only 
comment, removing them does not change the validity of the CodeStrings.
For similar reason, assignment over a non null CodeStrings is now valid 
when we can safely free the old string.

The modified code passes JPRT. It was also validated in fastdebug mode 
with the vm.compiler.testlist to check that the validity assertion were 
not triggered. One of our closed extensions also validated advanced use 
of CodeStrings::assign (included cases where the target of the 
assignment was not free).

Best regards,

Bertrand.

-- 
Bertrand Delsart,                     Grenoble Engineering Center
Oracle,         180 av. de l'Europe,          ZIRST de Montbonnot
38330 Montbonnot Saint Martin,                             FRANCE
bertrand.delsart at oracle.com             Phone : +33 4 76 18 81 23

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