RFR: 8313785: Fix -Wconversion warnings in prims code

[Dean Long]

On Fri, 4 Aug 2023 14:37:07 GMT, Coleen Phillimore <coleenp 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/methodHandles.cpp line 910:

> 908:       InstanceKlass* defc = InstanceKlass::cast(java_lang_Class::as_Klass(clazz));
> 909:       DEBUG_ONLY(clazz = nullptr);  // safety
> 910:       intptr_t vmindex  = java_lang_invoke_MemberName::vmindex(mname());

Why not do the checked_cast<int> here instead of below?
Ideally, the vmindex field would be changed to int (field offsets, itable/vtable indexes are all int), but that's more work.

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PR Review Comment: https://git.openjdk.org/jdk/pull/15160#discussion_r1284883812