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

[Coleen Phillimore]

On Tue, 13 Jun 2023 14:15:00 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> The downside of this is it hides potentially real type mismatches from -Wconversion, once (if) that becomes
>> part of normal operations.
>
> Thanks for the suggested change.  The sign extension for integral promotion was a problem.  The second emit_int8 will still assert for the callers (there are still some) that pass a type that gets sign extended to int to emit_in8.  I can see how many are left once the first function is added.  Maybe it's possible to fix them all.  We'll see.

src/hotspot/cpu/x86/assembler_x86.cpp|4421 col 12| error: no matching function for call to 'Assembler::emit_int8(Assembler::ComparisonPredicate&)'                                                                                                                                          
||  4421 |   emit_int8(vcc);
||       |   ~~~~~~~~~^~~~~
|| In file included from /scratch/cphillim/hg/21more-conversion/src/hotspot/cpu/x86/assembler_x86.cpp:26:

But I made ComparisonPredicate enum a uint8_t.  Why didn't it match it?

  // Comparison predicates for integral types & FP types when using SSE
  enum ComparisonPredicate : uint8_t {

There are a bunch of these that don't like the templates.

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PR Review Comment: https://git.openjdk.org/jdk/pull/14396#discussion_r1228238911