RFR: 8288477: nmethod header size reduction

[Dean Long]

On Fri, 24 Jun 2022 09:00:26 GMT, Boris Ulasevich <bulasevich at openjdk.org> wrote:

>> src/hotspot/share/compiler/compilerDefinitions.hpp line 57:
>> 
>>> 55: 
>>> 56: // Enumeration to distinguish tiers of compilation
>>> 57: enum CompLevel : s1 {
>> 
>> Hope it won't cause gcc to generate inefficient code manupulating bytes.
>
> AARCH and AMD have load byte instructions (ldr:ldrb, mov:movzx), I believe method::comp_level() code takes the same number of instructions before/after the change.

This enum change might be hard to back-port to jdk11, which still uses an older toolchain, at least for Oracle builds.

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PR: https://git.openjdk.org/jdk/pull/9165