Optimize `lsraRegOrder` and `buildPhysRegRecords` to skip non-AVX512 registers if AVX512 not available

[anthonycanino]

Per comment #79544 (comment) : we can optimize this section of the code to only use/initialize the AVX512 register records if AVX512 is detected at runtime. See commit 3c7acdb for a rough idea of how to structure these changes.

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Issue Details

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Per comment #79544 (comment) : we can optimize this section of the code to only use/initialize the AVX512 register records if AVX512 is detected at runtime. See commit 3c7acdb for a rough idea of how to structure these changes.

Author:	anthonycanino
Assignees:	-
Labels:	area-CodeGen-coreclr, untriaged
Milestone:	-

[anthonycanino]

@JulieLeeMSFT please assign me, we are working on this internally.

[tannergooding]

This was partially covered by #83862

[anthonycanino]

@tannergooding when I wrote this issue, this is the optimization I had in mind (#83862), i.e., fix some of the lsraRegOrder pertaining to the extra AVX512 registers.

Did you have something else in mind?

[tannergooding]

No, I had just interpreted the title as implying something additional. If everything intended to be covered was, then please feel free to close

[BruceForstall]

This is complete.