[llvm] RegAllocGreedy: Fix use after free during last chance recoloring (PR #120697)

[Quentin Colombet via llvm-commits]

https://github.com/qcolombet approved this pull request.

LGTM.

Out of curiosity does AMDGPU rely on last chance coloring to work?

I would have expected this stage to be prohibitively expensive on this target and that you would have just disabled it (by overriding the TargetRegisterInfo::shouldUseLastChanceRecoloringForVirtReg method.)

https://github.com/llvm/llvm-project/pull/120697