[NFC][X86] Reorder the registers to reduce unnecessary iterations (#70222)

* Introduce field `PositionOrder` for class `Register` and
`RegisterTuples`
* If register A's `PositionOrder` < register B's `PositionOrder`, then A
is placed before B in the enum in X86GenRegisterInfo.inc
* The new order of registers in the enum for X86 will be
      1. Registers before AVX512,
      2. AVX512 registers (X/YMM16-31, ZMM0-31, K registers)
      3. AMX registers (TMM)
      4.  APX registers (R16-R31)
* Add a new target hook `getNumSupportedRegs()` to return the number of
registers for the function (may overestimate).
* Replace `getNumRegs()` with `getNumSupportedRegs()` in LiveVariables
to eliminate iterations on unsupported registers

This patch can reduce 0.3% instruction count regression for sqlite3
during compile-stage (O3) by not iterating on APX registers
for #67702

0 files changed, 0 insertions, 0 deletions