[llvm] [RegisterCoalescer] Fix SUBREG_TO_REG handling in the RegisterCoalescer. (PR #96839)

[Quentin Colombet via llvm-commits]

qcolombet wrote:

> %2 [32r,112r:0) 0 at 32r  L000000000000000F [16r,112r:0) 0 at 16r  weight:0.000000e+00

What were we generating previously?

Also, shouldn't it be `L000000000000000F [16r, 32r0) 0 at 16r`, i.e., `32r` instead of `112r`?

https://github.com/llvm/llvm-project/pull/96839