RFR: 8309685: Fix -Wconversion warnings in assembler and register code

[Coleen Phillimore]

On Fri, 9 Jun 2023 15:55:32 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

> This change widens some int arguments, narrows some int returns and adds some casts and checked_casts where the compiler was doing the implicit conversion.  I maintained existing types - ie if the parameter was short, I used a cast to short.  Also int is used in places that might be better served as unsigned int but I didn't fix that because it would be too large and risky.  The registers encode an offset in an array, so it's safe to checked_cast<> to get their encoding. This fix is limited so that the types changed and casts added are intentional.
> See CR for counts of -Wconversion warnings this resolves.
> Tested with tier1-7, also tested with tier1 on all Oracle supported platforms.

Thanks for reviewing this Kim.  I tried to limit the changes so that it's not just adding casts.  I'm glad this isn't as bad as you thought it would be.

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PR Review: https://git.openjdk.org/jdk/pull/14396#pullrequestreview-1477291447