RFR: 8314265: Fix -Wconversion warnings in miscellaneous runtime code [v2]

[Christian Hagedorn]

On Wed, 16 Aug 2023 12:33:47 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> When we read the 64 bit values in the code, the values are 64 bits though.  So static_cast<> to narrow the result is more correct ?
>
> This code:
> 
>       uint64_t isa;
>       if (!_reader.read_uleb128(&isa, 4)) {
>         // isa register is 4 bytes wide.
>         return false;
>       }
>       _state->_isa = isa;  // only save 4 bytes
> 
> returns 64 bit of information into isa from this read_uleb128 call, even though it passes 4.

I've quickly skimmed through the usages of `read_uleb128`. We only seem to be reading either directly into a proper `uint64_t` or we are reading 4 bytes (i.e. `check_size = 4`). In the latter case, we could either:
- add a `static_cast` for the read value when storing it into a 32 bit field, as for example for `isa` above (i.e. `_state->_isa = static_cast<uint32_t>(isa)`).
- provide a 32 bit `read_uleb128()` version that hides the casting.

I guess it's fine to just go with a `static_cast` when storing to a field for the few cases we have.

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PR Review Comment: https://git.openjdk.org/jdk/pull/15233#discussion_r1295863147