RFR: 8269122: The use of "extern const" for Register definitions generates poor code [v3]

[Kim Barrett]

On Tue, 22 Jun 2021 12:08:51 GMT, Andrew Haley <aph at openjdk.org> wrote:

>> Register definitions in HotSpot are declared as "extern const"
>> for ancient-historical reasons. We should stop doing that: it would
>> make the assembler significantly faster and smaller, improving both
>> bootstrap time and compilation speed.
>> 
>> This change shaves 2% off the size of the text section of libjvm.so on AArch64.
>
> Andrew Haley has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Update copyright

Changes requested by kbarrett (Reviewer).

src/hotspot/share/asm/register.hpp line 50:

> 48: #define AS_REGISTER(type,name)         ((type)name##_##type##EnumValue)
> 49: 
> 50: #ifndef USE_EXTERN_CONST_FOR_REGISTER_DEFINITIONS

I can see this conditionalization being useful for development and testing of this change, but why keep it and the old, now dead, code?

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PR: https://git.openjdk.java.net/jdk/pull/4554