RFR: 8313785: Fix -Wconversion warnings in prims code

[Coleen Phillimore]

On Fri, 4 Aug 2023 18:10:30 GMT, Serguei Spitsyn <sspitsyn at openjdk.org> wrote:

>> This patch fixes Wconversion in code in the src/hotspot/share/prims directory.  Most of the changes correct the types.  jfieldID's are created with the int offset returned by InstanceKlass::field_offset().
>>      int     field_offset      (int index) const { return field(index).offset(); }
>> 
>> So when we get the field offset back, it's an int.
>> 
>> Also stackwalker passes jlong, so made that consistent.
>> 
>> Tested with tier1 on Oracle supported platforms.
>
> src/hotspot/share/prims/unsafe.cpp line 111:
> 
>> 109: }
>> 110: 
>> 111: static inline int field_offset_from_byte_offset(int byte_offset) {
> 
> Nit: I wonder if the same fix is needed for the previous function at line 107 to make it consistent.
>        But I guess there is no warning related to it.

The names look almost the same, but field_offset_to_byte_offset() is called primarily passing jlong in several places so changing that would have had more fan out (and might not have been correct).
The callers of field_offset_from_byte_offset() had callers that passed int and expected int returns, so that's why I changed only that one.

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PR Review Comment: https://git.openjdk.org/jdk/pull/15160#discussion_r1284776327