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

[Frederic Parain]

On Wed, 21 Jun 2023 12:00:07 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

> This is essentially the same as PR https://github.com/openjdk/jdk/pull/14396 only without the asm/assembler.hpp changes for emit_int8, etc.  The casts and type changes here resolve header file -Wconversion warnings but not the 941 in assembler_x86.cpp.
> Tested with tier 1-7, and tier1 on Oracle supported platforms.

Marked as reviewed by fparain (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/14584#pullrequestreview-1493316494