[llvm] [CodeGen] Refactor DeadMIElim isDead and GISel isTriviallyDead (PR #105956)

[Tobias Stadler via llvm-commits]

tobias-stadler wrote:

AArch64 GlobalISel CTMark
O0:
```
Program                                       compile_instructions                        
                                              base-O0              patch-O0        diff   
7zip/7zip-benchmark                           142579160298.00      142443007662.00 -0.10% 
Bullet/bullet                                  61367419175.00       61242533522.00 -0.20% 
kimwitu++/kc                                   22466504799.00       22410469877.00 -0.25% 
SPASS/SPASS                                    14326291495.00       14262677945.00 -0.44% 
ClamAV/clamscan                                14145778197.00       14068220767.00 -0.55% 
tramp3d-v4/tramp3d-v4                          18327257117.00       18225535659.00 -0.56% 
mafft/pairlocalalign                            6717269770.00        6669638138.00 -0.71% 
lencod/lencod                                  12283466464.00       12179009286.00 -0.85% 
consumer-typeset/consumer-typeset              11762311006.00       11656647438.00 -0.90% 
sqlite3/sqlite3                                 4369543098.00        4314547563.00 -1.26% 
                           Geomean difference                                      -0.58% 
```

O2:
```
Program                                       compile_instructions                       
                                              base-O2              patch-O2        diff  
7zip/7zip-benchmark                           205561068160.00      205477950143.00 -0.04%
Bullet/bullet                                  99533309415.00       99444270943.00 -0.09%
SPASS/SPASS                                    42161673055.00       42091709441.00 -0.17%
ClamAV/clamscan                                52108752865.00       52020947264.00 -0.17%
tramp3d-v4/tramp3d-v4                          64953199075.00       64822894336.00 -0.20%
mafft/pairlocalalign                           31775234940.00       31708063069.00 -0.21%
lencod/lencod                                  55545156416.00       55417527751.00 -0.23%
consumer-typeset/consumer-typeset              34402637417.00       34323251919.00 -0.23%
kimwitu++/kc                                   40736268734.00       40628351259.00 -0.26%
sqlite3/sqlite3                                33818134349.00       33728194647.00 -0.27%
                           Geomean difference                                      -0.19%
```

https://github.com/llvm/llvm-project/pull/105956