[clang] [llvm] [LFI][X86] Add X86 LFI target and system instruction rewrites (PR #189569)

Mon Jul 6 21:59:25 PDT 2026

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `lldb-aarch64-windows` running on `linaro-armv8-windows-msvc-05` while building `clang,llvm` at step 4 "build".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/141/builds/20326

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

```
Step 4 (build) failure: build (failure)
...
1683.602 [3466/10/3862] Building CXX object lib\Target\VE\MCTargetDesc\CMakeFiles\LLVMVEDesc.dir\VEMCCodeEmitter.cpp.obj
1684.046 [3465/10/3863] Building CXX object lib\Target\X86\MCTargetDesc\CMakeFiles\LLVMX86Desc.dir\X86ATTInstPrinter.cpp.obj
1684.133 [3464/10/3864] Building CXX object lib\Target\X86\MCTargetDesc\CMakeFiles\LLVMX86Desc.dir\X86IntelInstPrinter.cpp.obj
1684.451 [3463/10/3865] Building CXX object lib\Target\X86\MCTargetDesc\CMakeFiles\LLVMX86Desc.dir\X86InstPrinterCommon.cpp.obj
1684.771 [3462/10/3866] Building CXX object lib\Target\VE\MCTargetDesc\CMakeFiles\LLVMVEDesc.dir\VEMCTargetDesc.cpp.obj
1684.997 [3461/10/3867] Building CXX object lib\Target\X86\MCTargetDesc\CMakeFiles\LLVMX86Desc.dir\X86MnemonicTables.cpp.obj
1685.284 [3460/10/3868] Building CXX object lib\Target\X86\MCTargetDesc\CMakeFiles\LLVMX86Desc.dir\X86EncodingOptimization.cpp.obj
1686.533 [3459/10/3869] Building CXX object lib\Target\X86\MCTargetDesc\CMakeFiles\LLVMX86Desc.dir\X86MCAsmInfo.cpp.obj
1686.964 [3458/10/3870] Building CXX object lib\Target\X86\MCTargetDesc\CMakeFiles\LLVMX86Desc.dir\X86AsmBackend.cpp.obj
1687.253 [3457/10/3871] Building CXX object lib\Target\X86\MCTargetDesc\CMakeFiles\LLVMX86Desc.dir\X86MCLFIRewriter.cpp.obj
FAILED: [code=1] lib/Target/X86/MCTargetDesc/CMakeFiles/LLVMX86Desc.dir/X86MCLFIRewriter.cpp.obj 
C:\Users\tcwg\scoop\shims\ccache.exe C:\Users\tcwg\scoop\apps\llvm-arm64\current\bin\clang-cl.exe  /nologo -TP -DUNICODE -D_CRT_NONSTDC_NO_DEPRECATE -D_CRT_NONSTDC_NO_WARNINGS -D_CRT_SECURE_NO_DEPRECATE -D_CRT_SECURE_NO_WARNINGS -D_HAS_EXCEPTIONS=0 -D_SCL_SECURE_NO_DEPRECATE -D_SCL_SECURE_NO_WARNINGS -D_UNICODE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -IC:\Users\tcwg\llvm-worker\lldb-aarch64-windows\build\lib\Target\X86\MCTargetDesc -IC:\Users\tcwg\llvm-worker\lldb-aarch64-windows\llvm-project\llvm\lib\Target\X86\MCTargetDesc -IC:\Users\tcwg\llvm-worker\lldb-aarch64-windows\llvm-project\llvm\lib\Target\X86 -IC:\Users\tcwg\llvm-worker\lldb-aarch64-windows\build\lib\Target\X86 -IC:\Users\tcwg\llvm-worker\lldb-aarch64-windows\build\include -IC:\Users\tcwg\llvm-worker\lldb-aarch64-windows\llvm-project\llvm\include /DWIN32 /D_WINDOWS   /Zc:inline /Zc:__cplusplus /Oi /Brepro /bigobj /permissive- -Werror=unguarded-availability-new /W4  -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wstring-conversion -Wno-pass-failed -Wmisleading-indentation -Wctad-maybe-unsupported /Gw /O2 /Ob2 /DNDEBUG -std:c++17 -MD /EHs-c- /GR- /showIncludes /Folib\Target\X86\MCTargetDesc\CMakeFiles\LLVMX86Desc.dir\X86MCLFIRewriter.cpp.obj /Fdlib\Target\X86\MCTargetDesc\CMakeFiles\LLVMX86Desc.dir\LLVMX86Desc.pdb -c -- C:\Users\tcwg\llvm-worker\lldb-aarch64-windows\llvm-project\llvm\lib\Target\X86\MCTargetDesc\X86MCLFIRewriter.cpp
C:\Users\tcwg\llvm-worker\lldb-aarch64-windows\llvm-project\llvm\lib\Target\X86\MCTargetDesc\X86MCLFIRewriter.cpp(69,10): error: use of undeclared identifier 'X86MCRegisterClasses'; did you mean 'getX86MCRegisterClass'?
   69 |          X86MCRegisterClasses[X86::GR64RegClassID].contains(Reg);
      |          ^~~~~~~~~~~~~~~~~~~~
      |          getX86MCRegisterClass
C:\Users\tcwg\llvm-worker\lldb-aarch64-windows\build\lib\Target\X86\X86GenRegisterInfoEnums.inc(12,24): note: 'getX86MCRegisterClass' declared here
   12 | const MCRegisterClass &getX86MCRegisterClass(unsigned RC);
      |                        ^
C:\Users\tcwg\llvm-worker\lldb-aarch64-windows\llvm-project\llvm\lib\Target\X86\MCTargetDesc\X86MCLFIRewriter.cpp(69,10): error: subscript of pointer to function type 'const MCRegisterClass &(unsigned int)'
   69 |          X86MCRegisterClasses[X86::GR64RegClassID].contains(Reg);
      |          ^~~~~~~~~~~~~~~~~~~~
C:\Users\tcwg\llvm-worker\lldb-aarch64-windows\llvm-project\llvm\lib\Target\X86\MCTargetDesc\X86MCLFIRewriter.cpp(176,9): error: use of undeclared identifier 'X86MCRegisterClasses'; did you mean 'getX86MCRegisterClass'?
  176 |         X86MCRegisterClasses[X86::GR64RegClassID].contains(DestReg) &&
      |         ^~~~~~~~~~~~~~~~~~~~
      |         getX86MCRegisterClass
C:\Users\tcwg\llvm-worker\lldb-aarch64-windows\build\lib\Target\X86\X86GenRegisterInfoEnums.inc(12,24): note: 'getX86MCRegisterClass' declared here
   12 | const MCRegisterClass &getX86MCRegisterClass(unsigned RC);
      |                        ^
C:\Users\tcwg\llvm-worker\lldb-aarch64-windows\llvm-project\llvm\lib\Target\X86\MCTargetDesc\X86MCLFIRewriter.cpp(176,9): error: subscript of pointer to function type 'const MCRegisterClass &(unsigned int)'
  176 |         X86MCRegisterClasses[X86::GR64RegClassID].contains(DestReg) &&
      |         ^~~~~~~~~~~~~~~~~~~~
4 errors generated.
1687.715 [3457/9/3872] Building CXX object lib\Target\X86\MCTargetDesc\CMakeFiles\LLVMX86Desc.dir\X86MCCodeEmitter.cpp.obj
1687.782 [3457/8/3873] Building CXX object lib\Target\AMDGPU\MCTargetDesc\CMakeFiles\LLVMAMDGPUDesc.dir\AMDGPUMCTargetDesc.cpp.obj
1687.906 [3457/7/3874] Building CXX object lib\Target\X86\MCTargetDesc\CMakeFiles\LLVMX86Desc.dir\X86MachObjectWriter.cpp.obj
1688.108 [3457/6/3875] Building CXX object lib\Target\X86\MCTargetDesc\CMakeFiles\LLVMX86Desc.dir\X86ELFObjectWriter.cpp.obj
1688.140 [3457/5/3876] Building CXX object lib\Target\X86\MCTargetDesc\CMakeFiles\LLVMX86Desc.dir\X86WinCOFFObjectWriter.cpp.obj
1689.000 [3457/4/3877] Building CXX object lib\Target\RISCV\MCTargetDesc\CMakeFiles\LLVMRISCVDesc.dir\RISCVMCTargetDesc.cpp.obj
1689.106 [3457/3/3878] Building CXX object lib\Target\X86\MCTargetDesc\CMakeFiles\LLVMX86Desc.dir\X86WinCOFFStreamer.cpp.obj
1690.184 [3457/2/3879] Building CXX object lib\Target\X86\MCTargetDesc\CMakeFiles\LLVMX86Desc.dir\X86WinCOFFTargetStreamer.cpp.obj
1691.954 [3457/1/3880] Building CXX object lib\Target\X86\MCTargetDesc\CMakeFiles\LLVMX86Desc.dir\X86MCTargetDesc.cpp.obj
ninja: build stopped: subcommand failed.

```

</details>

https://github.com/llvm/llvm-project/pull/189569