[llvm] Optimize register bank and info emission. (PR #208297)

[Alexis Engelke via llvm-commits]

aengelke wrote:

```
Benchmark 1: ./llvm-tblgen-pre -gen-register-bank -I/home/engelke/llvm-project/llvm/lib/Target/AMDGPU -I/home/engelke/llvm-build2/include -I/home/engelke/llvm-project/llvm/include -I /home/engelke/llvm-project/llvm/lib/Target /home/engelke/llvm-project/llvm/lib/Target/AMDGPU/AMDGPU.td --write-if-changed -o AMDGPUGenRegisterInfo.inc
  Time (mean ± σ):     39.649 s ±  0.271 s    [User: 38.862 s, System: 0.775 s]
  Range (min … max):   39.484 s … 39.962 s    3 runs
 
  Warning: Statistical outliers were detected. Consider re-running this benchmark on a quiet system without any interferences from other programs. It might help to use the '--warmup' or '--prepare' options.
 
Benchmark 2: ./llvm-tblgen-post -gen-register-bank -I/home/engelke/llvm-project/llvm/lib/Target/AMDGPU -I/home/engelke/llvm-build2/include -I/home/engelke/llvm-project/llvm/include -I /home/engelke/llvm-project/llvm/lib/Target /home/engelke/llvm-project/llvm/lib/Target/AMDGPU/AMDGPU.td --write-if-changed -o AMDGPUGenRegisterInfo.inc
  Time (mean ± σ):     26.991 s ±  0.284 s    [User: 26.184 s, System: 0.799 s]
  Range (min … max):   26.688 s … 27.250 s    3 runs
 
Summary
  ./llvm-tblgen-post -gen-register-bank -I/home/engelke/llvm-project/llvm/lib/Target/AMDGPU -I/home/engelke/llvm-build2/include -I/home/engelke/llvm-project/llvm/include -I /home/engelke/llvm-project/llvm/lib/Target /home/engelke/llvm-project/llvm/lib/Target/AMDGPU/AMDGPU.td --write-if-changed -o AMDGPUGenRegisterInfo.inc ran
    1.47 ± 0.02 times faster than ./llvm-tblgen-pre -gen-register-bank -I/home/engelke/llvm-project/llvm/lib/Target/AMDGPU -I/home/engelke/llvm-build2/include -I/home/engelke/llvm-project/llvm/include -I /home/engelke/llvm-project/llvm/lib/Target /home/engelke/llvm-project/llvm/lib/Target/AMDGPU/AMDGPU.td --write-if-changed -o AMDGPUGenRegisterInfo.inc
```

https://github.com/llvm/llvm-project/pull/208297