RFR: JDK-8301498: Replace NULL with nullptr in cpu/x86 [v2]

[Vladimir Kozlov]

On Mon, 13 Feb 2023 09:26:07 GMT, Johan Sjölen <jsjolen at openjdk.org> wrote:

>> Hi, this PR changes all occurrences of NULL to nullptr for the subdirectory cpu/x86. Unfortunately the script that does the change isn't perfect, and so we
>> need to comb through these manually to make sure nothing has gone wrong. I also review these changes but things slip past my eyes sometimes.
>> 
>> Here are some typical things to look out for:
>> 
>> 1. No changes but copyright header changed (probably because I reverted some changes but forgot the copyright).
>> 2. Macros having their NULL changed to nullptr, these are added to the script when I find them. They should be NULL.
>> 3. nullptr in comments and logs. We try to use lower case "null" in these cases as it reads better. An exception is made when code expressions are in a comment.
>> 
>> An example of this:
>> 
>> ```c++
>> // This function returns null
>> void* ret_null();
>> // This function returns true if *x == nullptr
>> bool is_nullptr(void** x);
>> 
>> 
>> Note how `nullptr` participates in a code expression here, we really are talking about the specific value `nullptr`.
>> 
>> Thanks!
>
> Johan Sjölen has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Some more fixes

In addition to few missed placed I noticed that you keep `mov_metadata(rbx, (Metadata*)nullptr);` casting.

Is `Metadata*` something special we need to cast it?

And more general question - do we need to keep some casting for `nullptr`?
We kept them in previous PRs which are already pushed #12029 

Should we update our "spec" for `nullptr` to remove all casting or keep some? What is condition to keep?

src/hotspot/cpu/x86/interp_masm_x86.cpp line 1785:

> 1783: //       // degenerate decision tree, rooted at row[2]
> 1784: //       if (row[2].rec == rec) { row[2].incr(); goto done; }
> 1785: //       if (row[2].rec != null) { count.incr(); goto done; } // overflow

Missed change to nullptr.

-------------

Changes requested by kvn (Reviewer).

PR: https://git.openjdk.org/jdk/pull/12326