[Bug 2099720] [NEW] [LLVM 20] Runtime fails to build on ppc64el with invalid register name

[Mateus Rodrigues de Morais]

Public bug reported:

This bug is related to the LLVM 20 transition.

The runtime component of .NET currently fails to build on ppc64el and
LLVM 20 with the error

```
[ 75%] Building ASM object pal/src/CMakeFiles/coreclrpal.dir/arch/ppc64le/debugbreak.S.o
             cd /<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/artifacts/obj/coreclr/linux.ppc64le.Release/pal/src && /usr/bin/clang -DCOMPILER_SUPPORTS_W_RESERVED_IDENTIFIER -DCORECLR -DDISABLE_CONTRACTS -DHOST_64BIT -DHOST_POWERPC64 -DHOST_UNIX -DLP64COMPATIBLE -DNDEBUG -DPIC -DTARGET_64BIT -DTARGET_LINUX -DTARGET_POWERPC64 -DTARGET_UNIX -DURTBLDENV_FRIENDLY=Retail -DUSE_STL -D_FILE_OFFSET_BITS=64 -I/<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/artifacts/obj/coreclr/linux.ppc64le.Release/pal/src -I/<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/src/coreclr/pal/src -I/<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/src/native -I/<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/src/native/inc -I/<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/src/coreclr/pal/inc -I/<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/src/coreclr/pal/../inc -I/<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/src/native/external/libunwind/include -I/<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/src/native/external/libunwind/include/tdep -I/<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/artifacts/obj/external/libunwind/include -I/<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/artifacts/obj/external/libunwind/include/tdep -I/<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/src/coreclr/pal/src/include -isystem /usr/local/include -O3 -DNDEBUG -fPIC -O3 -g -Wall -Wno-null-conversion -Wa,--noexecstack -fno-omit-frame-pointer -fms-extensions -fwrapv -fstack-protector-strong -Wno-unused-variable -Wno-unused-value -Wno-unused-function -Wno-tautological-compare -Wno-unknown-pragmas -Wimplicit-fallthrough -Wno-unused-but-set-variable -ffp-contract=off -Wno-unknown-warning-option -ferror-limit=4096 -Wno-unused-private-field -Wno-constant-logical-operand -Wno-pragma-pack -Wno-incompatible-ms-struct -Wno-reserved-identifier -Wno-unsafe-buffer-usage -Wno-single-bit-bitfield-constant-conversion -Wno-cast-function-type-strict -Wno-switch-default -fsigned-char -fvisibility=hidden -ffunction-sections -fexceptions -o CMakeFiles/coreclrpal.dir/arch/ppc64le/debugbreak.S.o -c /<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/src/coreclr/pal/src/arch/ppc64le/debugbreak.S
             /<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/src/coreclr/pal/src/arch/ppc64le/context2.S:140:15: error: invalid register name
              ld %r0, 0 +8(%R3)
                           ^
             make[5]: *** [pal/src/CMakeFiles/coreclrpal.dir/build.make:1240: pal/src/CMakeFiles/coreclrpal.dir/arch/ppc64le/context2.S.o] Error 1
```

Build examples:
- .NET 8 [https://launchpadlibrarian.net/778048663/buildlog_ubuntu-plucky-ppc64el.dotnet8_8.0.113-8.0.13-0ubuntu1_BUILDING.txt.gz]
- .NET 9 [https://launchpadlibrarian.net/778050470/buildlog_ubuntu-plucky-ppc64el.dotnet9_9.0.103-9.0.2-0ubuntu1_BUILDING.txt.gz]

** Affects: dotnet8 (Ubuntu)
     Importance: Undecided
     Assignee: Mateus Rodrigues de Morais (mateus-morais)
         Status: In Progress

** Affects: dotnet9 (Ubuntu)
     Importance: Undecided
     Assignee: Mateus Rodrigues de Morais (mateus-morais)
         Status: In Progress

** Affects: dotnet8 (Ubuntu Plucky)
     Importance: Undecided
     Assignee: Mateus Rodrigues de Morais (mateus-morais)
         Status: In Progress

** Affects: dotnet9 (Ubuntu Plucky)
     Importance: Undecided
     Assignee: Mateus Rodrigues de Morais (mateus-morais)
         Status: In Progress

** Also affects: dotnet9 (Ubuntu)
   Importance: Undecided
       Status: New

** Also affects: dotnet8 (Ubuntu Plucky)
   Importance: Undecided
       Status: New

** Also affects: dotnet9 (Ubuntu Plucky)
   Importance: Undecided
       Status: New

** Changed in: dotnet8 (Ubuntu Plucky)
     Assignee: (unassigned) => Mateus Rodrigues de Morais (mateus-morais)

** Changed in: dotnet9 (Ubuntu Plucky)
     Assignee: (unassigned) => Mateus Rodrigues de Morais (mateus-morais)

** Changed in: dotnet8 (Ubuntu Plucky)
       Status: New => In Progress

** Changed in: dotnet9 (Ubuntu Plucky)
       Status: New => In Progress

-- 
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https://bugs.launchpad.net/bugs/2099720

Title:
  [LLVM 20] Runtime fails to build on ppc64el with invalid register name

Status in dotnet8 package in Ubuntu:
  In Progress
Status in dotnet9 package in Ubuntu:
  In Progress
Status in dotnet8 source package in Plucky:
  In Progress
Status in dotnet9 source package in Plucky:
  In Progress

Bug description:
  This bug is related to the LLVM 20 transition.

  The runtime component of .NET currently fails to build on ppc64el and
  LLVM 20 with the error

  ```
  [ 75%] Building ASM object pal/src/CMakeFiles/coreclrpal.dir/arch/ppc64le/debugbreak.S.o
               cd /<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/artifacts/obj/coreclr/linux.ppc64le.Release/pal/src && /usr/bin/clang -DCOMPILER_SUPPORTS_W_RESERVED_IDENTIFIER -DCORECLR -DDISABLE_CONTRACTS -DHOST_64BIT -DHOST_POWERPC64 -DHOST_UNIX -DLP64COMPATIBLE -DNDEBUG -DPIC -DTARGET_64BIT -DTARGET_LINUX -DTARGET_POWERPC64 -DTARGET_UNIX -DURTBLDENV_FRIENDLY=Retail -DUSE_STL -D_FILE_OFFSET_BITS=64 -I/<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/artifacts/obj/coreclr/linux.ppc64le.Release/pal/src -I/<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/src/coreclr/pal/src -I/<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/src/native -I/<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/src/native/inc -I/<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/src/coreclr/pal/inc -I/<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/src/coreclr/pal/../inc -I/<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/src/native/external/libunwind/include -I/<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/src/native/external/libunwind/include/tdep -I/<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/artifacts/obj/external/libunwind/include -I/<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/artifacts/obj/external/libunwind/include/tdep -I/<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/src/coreclr/pal/src/include -isystem /usr/local/include -O3 -DNDEBUG -fPIC -O3 -g -Wall -Wno-null-conversion -Wa,--noexecstack -fno-omit-frame-pointer -fms-extensions -fwrapv -fstack-protector-strong -Wno-unused-variable -Wno-unused-value -Wno-unused-function -Wno-tautological-compare -Wno-unknown-pragmas -Wimplicit-fallthrough -Wno-unused-but-set-variable -ffp-contract=off -Wno-unknown-warning-option -ferror-limit=4096 -Wno-unused-private-field -Wno-constant-logical-operand -Wno-pragma-pack -Wno-incompatible-ms-struct -Wno-reserved-identifier -Wno-unsafe-buffer-usage -Wno-single-bit-bitfield-constant-conversion -Wno-cast-function-type-strict -Wno-switch-default -fsigned-char -fvisibility=hidden -ffunction-sections -fexceptions -o CMakeFiles/coreclrpal.dir/arch/ppc64le/debugbreak.S.o -c /<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/src/coreclr/pal/src/arch/ppc64le/debugbreak.S
               /<<PKGBUILDDIR>>/src/runtime/artifacts/source-build/self/src/src/coreclr/pal/src/arch/ppc64le/context2.S:140:15: error: invalid register name
                ld %r0, 0 +8(%R3)
                             ^
               make[5]: *** [pal/src/CMakeFiles/coreclrpal.dir/build.make:1240: pal/src/CMakeFiles/coreclrpal.dir/arch/ppc64le/context2.S.o] Error 1
  ```

  Build examples:
  - .NET 8 [https://launchpadlibrarian.net/778048663/buildlog_ubuntu-plucky-ppc64el.dotnet8_8.0.113-8.0.13-0ubuntu1_BUILDING.txt.gz]
  - .NET 9 [https://launchpadlibrarian.net/778050470/buildlog_ubuntu-plucky-ppc64el.dotnet9_9.0.103-9.0.2-0ubuntu1_BUILDING.txt.gz]

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