[llvm] [SystemZ] Add a SystemZ specific pre-RA scheduling strategy. (PR #135076)

[Jonas Paulsson via llvm-commits]

JonPsson1 wrote:

Benchmark results of latest version ("Simplifications"):

```
                                main                experiment3 
f503.bwaves_r                    850.58s             850.06s                   -0.06%
f507.cactuBSSN_r                 341.58s             298.53s                  -12.60%
f508.namd_r                      210.27s             205.96s                   -2.05%
f510.parest_r                    511.94s             511.24s                   -0.14%
f511.povray_r                    567.91s             564.75s                   -0.56%
f519.lbm_r                       229.21s             224.75s                   -1.95%
f521.wrf_r                       413.17s             412.63s                   -0.13%
f526.blender_r                   269.10s             261.91s                   -2.67%
f527.cam4_r                      313.08s             312.95s                   -0.04%
f538.imagick_r                   369.30s             321.46s                  -12.95%
f544.nab_r                       356.19s             346.42s                   -2.74%
f549.fotonik3d_r                 359.31s             361.24s                    0.54%
f554.roms_r                      222.44s             222.47s                    0.01%
i500.perlbench_r                 309.78s             307.17s                   -0.84%
i502.gcc_r                       170.44s             169.85s                   -0.35%
i505.mcf_r                       297.10s             295.36s                   -0.59%
i520.omnetpp_r                   210.72s             210.33s                   -0.19%
i523.xalancbmk_r                 182.40s             183.41s                    0.55%
i525.x264_r                      192.64s             192.67s                    0.02%
i531.deepsjeng_r                 262.40s             262.74s                    0.13%
i541.leela_r                     478.42s             479.58s                    0.24%
i548.exchange2_r                 314.44s             311.88s                   -0.81%
i557.xz_r                        272.67s             270.14s                   -0.93%
                                                                              ------
--- total time                  7705.09s            7577.50s                 -127.59s
--- geometric mean                                                             -1.73%
```

https://github.com/llvm/llvm-project/pull/135076