RFR: 8309685: Fix -Wconversion warnings in assembler and register code [v3]

[Dean Long]

On Wed, 14 Jun 2023 21:25:37 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> The conversion from an unsigned type to a smaller unsigned type should have just worked if you convert back, like the old checked_cast code did, but callers of emit_intxxx were sign extending so the conversion back didn't work.
>> 
>> Calls like emit_int8() are passed arguments like 0xf0, but there were multiple (~940) that are passed with something that did some bitwise calculation that was promoted up to int.
>> 
>> Maybe the emit_intxx functions should take signed int, and then I could just check range in the checked_cast() without converting the argument to signed.  That might work and still provide the range checking that we want.
>> 
>> Yes, it should be max-1.  Thank you for looking at this.
>
> Changing checked_cast<> to not convert to a signed type for T1 leads to very puzzling compiler errors.  For these emit_int8 etc functions, maybe a straight cast is the best thing, and leaving the definition checked_cast<> alone.  I'd be happy to do that as I had in my first patch.

I don't know what checked_cast<> should do for negative values when going between signed --> unsigned and for values greater than signed max for unsigned --> signed.  It seems like both should fail because the sign changes.

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PR Review Comment: https://git.openjdk.org/jdk/pull/14396#discussion_r1230338467