llvm-project

01332475 - [AArch64] Enable subreg liveness tracking for streaming functions. (#174189)

[AArch64] Enable subreg liveness tracking for streaming functions. (#174189) Most use of subreg liveness tracking will be for streaming SME2 functions where it can use the strided- and contiguous form of the multi-vector LD1, see #123081 for details. Any regressions come from disabling coalescing of SUBREG_TO_REG when sub-reg liveness tracking is enabled, which may introduce some scalar `mov`s and may limit some peephole optimizations from the load-store optimizer, but the impact of disabling coalescing seems limited in practice (empirically from trying this on workloads) and we think the regressions are offset by improvements to the handling of multi-vector instructions (tuple registers) in SME2. PR #174188 addresses these issues in a separate PR.