[llvm] [RISCV] Refactor register list parsing and improve error messages. (PR #134938)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `flang-x86_64-windows` running on `minipc-ryzen-win` while building `llvm` at step 6 "build-unified-tree".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/166/builds/985

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 6 (build-unified-tree) failure: build (failure)
...
10.926 [116/12/17] Linking CXX executable bin\llvm-jitlink.exe
11.521 [115/12/18] Generating ../../bin/llvm-dlltool.exe
11.780 [114/12/19] Linking CXX executable bin\obj2yaml.exe
12.171 [113/12/20] Linking CXX executable bin\sanstats.exe
12.173 [112/12/21] Linking CXX executable bin\sancov.exe
12.496 [111/12/22] Linking CXX executable bin\llvm-dwarfdump.exe
12.514 [110/12/23] Linking CXX executable bin\llvm-ctxprof-util.exe
12.634 [109/12/24] Linking CXX executable bin\llvm-objcopy.exe
13.126 [108/12/25] Linking CXX executable bin\llvm-readobj.exe
14.950 [107/12/26] Linking CXX executable bin\mlir-rewrite.exe
FAILED: bin/mlir-rewrite.exe 
C:\Windows\system32\cmd.exe /C "cd . && "C:\Program Files\CMake\bin\cmake.exe" -E vs_link_exe --msvc-ver=1943 --intdir=tools\mlir\tools\mlir-rewrite\CMakeFiles\mlir-rewrite.dir --rc=C:\PROGRA~2\WI3CF2~1\10\bin\100220~1.0\x64\rc.exe --mt=C:\PROGRA~2\WI3CF2~1\10\bin\100220~1.0\x64\mt.exe --manifests  -- C:\PROGRA~1\MICROS~2\2022\COMMUN~1\VC\Tools\MSVC\1443~1.348\bin\Hostx64\x64\link.exe /nologo @CMakeFiles\mlir-rewrite.rsp  /out:bin\mlir-rewrite.exe /implib:lib\mlir-rewrite.lib /pdb:bin\mlir-rewrite.pdb /version:0.0 /machine:x64 /STACK:10000000 /INCREMENTAL:NO /subsystem:console && cd ."
LINK: command "C:\PROGRA~1\MICROS~2\2022\COMMUN~1\VC\Tools\MSVC\1443~1.348\bin\Hostx64\x64\link.exe /nologo @CMakeFiles\mlir-rewrite.rsp /out:bin\mlir-rewrite.exe /implib:lib\mlir-rewrite.lib /pdb:bin\mlir-rewrite.pdb /version:0.0 /machine:x64 /STACK:10000000 /INCREMENTAL:NO /subsystem:console /MANIFEST:EMBED,ID=1" failed (exit code 0) with the following output:

  Version 14.43.34809.0

  ExceptionCode            = C0000005
  ExceptionFlags           = 00000000
  ExceptionAddress         = 00007FF658EE36A2 (00007FF658EC0000) "C:\PROGRA~1\MICROS~2\2022\COMMUN~1\VC\Tools\MSVC\1443~1.348\bin\Hostx64\x64\link.exe"
  NumberParameters         = 00000002
  ExceptionInformation[ 0] = 0
  ExceptionInformation[ 1] = FFFFFFFFFFFFFFFF

CONTEXT:
  Rax    = 197FADA6200  R8     = 4000000000000
  Rbx    = AAAAAAAAAAAAAAAB  R9     = 0
  Rcx    = 11118  R10    = 197F96881B0
  Rdx    = 197B417B150  R11    = 29CB

  Rsp    = 487A7FC320  R12    = 0

  Rbp    = 487A7FC420  E13    = 197B3C9AB00

  Rsi    = A64E  R14    = 3A64

  Rdi    = 2000  R15    = 197B4CBC2A0

  Rip    = 7FF658EE36A2  EFlags = 10206

  SegCs  = 33  SegDs  = 2B

  SegSs  = 2B  SegEs  = 2B

  SegFs  = 53  SegGs  = 2B

  Dr0    = 0  Dr3    = 0

  Dr1    = 0  Dr6    = 0


```

</details>

https://github.com/llvm/llvm-project/pull/134938