RFR: JDK-8217909: Make unused r12 register (without compressed oops) available to regalloc in C2

Andrew Dinn adinn at redhat.com
Tue Feb 12 09:51:38 UTC 2019

On 12/02/2019 09:23, Nils Eliasson wrote:
> +1
> The reg classes is getting out of control. For rbp, it was acceptable,
> but with r12 as well, it has to be refactored.
> I would prefer solution that extends the ad-format. Deans suggestion is
> better than duplicating the reg classes, but modifying the reg class
> definitions without any coupling to the ad-files might cause some
> unwanted suprises in the future.
I agree that whatever mechanism is used it would be useful if it were
easy to spot. However, two points:

  Dean's magic line of code *is* in the ad file -- i.e. there is a
degree of coupling albeit not close coupling

  Adding explanatory, cross-referencing comments both to that line of
code *and* the corresponding register group definition is a much cheaper
and more manageable solution than rejigging the register declaration
grammar and associated ad file processor


Andrew Dinn
Senior Principal Software Engineer
Red Hat UK Ltd
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