RFR: 8311847: Fix -Wconversion for assembler.hpp emit_int8,16 callers

[Andrew Haley]

On Tue, 11 Jul 2023 12:45:02 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> val comes in signed, so we want to just chop off the sign.  checked_cast<unsigned>(signed val) will assert.  checked_cast<> doesn't do sign conversion.  We don't have a cast that does sign conversion.
>
> Not sure I trust this either.  I'm going to write a gtest for this.

We already have a hard guarantee that this signed value fits in the signed field. There's no need for any more asserting for that: just chop it off.

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PR Review Comment: https://git.openjdk.org/jdk/pull/14822#discussion_r1259768367