The PR to enable EVEX support by default introduced some JIT throughput regressions. The comments in that PR analyzed the cause of these regressions and identified possible follow-up investigations and improvements.

This issue tracks recovering some of the TP regressions by investigating the proposed improvements or mitigations.

For example, LSRA has a number of places with the following loop structure:

for (regNumber reg = REG_FIRST; reg < AVAILABLE_REG_COUNT; reg = REG_NEXT(reg))

and with AVX-512 available, there are an additional 16 SIMD registers and 8 opmask (k) registers, so these loops iterate more.