RFR: 8371162: Compiler warns about implicit cast from long to int in shift operation [v3]

[Archie Cobbs]

> Consider code like this:
> 
> int x = 1;
> x <<= 1L;
> 
> The compiler currently emits this warning:
> 
> warning: [lossy-conversions] implicit cast from long to int in compound assignment is possibly lossy
>         x <<= 1L;
>               ^
> 
> By definition, bit shift operations only use the bottom 5 or 6 bits of the specified shift amount (in this example, `1L`), and the JLS does not require the shift amount to be any specific integral type, only that that it be some integral type. So as long all but the bottom 5 or 6 bits are zero, there is no loss of information and the warning is inappropriate.
> 
> The case where the bottom 5 or 6 bits are _not_ all zero is addressed separately in [JDK-5038439](https://bugs.openjdk.org/browse/JDK-5038439).

Archie Cobbs has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains three commits:

 - Merge branch 'master' into JDK-8371162 to fix conflict.
 - Use cleaner switch statement syntax.
 - Avoid lossy conversion warnings for 64 bit shift amounts.

-------------

Changes: https://git.openjdk.org/jdk/pull/28180/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28180&range=02
  Stats: 45 lines in 3 files changed: 39 ins; 4 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/28180.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28180/head:pull/28180

PR: https://git.openjdk.org/jdk/pull/28180