RFR: 8341581: Optimize BytecodeHelpers validate slot

[Chen Liang]

On Fri, 4 Oct 2024 23:49:42 GMT, Shaojin Wen <swen at openjdk.org> wrote:

> Use `slot & ~0xFF == 0` instead of `(slot & 0xFF) == slot` to reduce codeSize.
> 
> The following is a comparison of the bytecode before and after the modification. It can be seen that using `slot & ~0xFF == 0` will reduce one iload operation.
> 
> 
> // (slot & 0xFF) == slot
> 56: iload_0
> 57: sipush        255
> 60: iand
> 61: iload_0
> 62: if_icmpne     71
> 
> // slot & ~0xFF == 0
> 56: iload_0
> 57: sipush        -256
> 60: iand
> 61: ifne          70

Marked as reviewed by liach (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/21367#pullrequestreview-2352845364