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

[David Holmes]

On Fri, 10 Feb 2023 22:43:54 GMT, Vladimir Kozlov <kvn 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!
>
> src/hotspot/cpu/x86/interp_masm_x86.cpp line 303:
> 
>> 301:     jcc(Assembler::equal, L);
>> 302:     stop("InterpreterMacroAssembler::call_VM_base:"
>> 303:          " last_sp != nullptr");
> 
> `null`

These are textual code fragments so I think `nullptr` is more appropriate - as per changes made to cpu/arm code.

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