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

Tue Jul 7 04:28:31 PDT 2026

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-aarch64-sve-vla` running on `linaro-g3-04` while building `clang,llvm` at step 6 "build stage 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/17/builds/16253

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

```
Step 6 (build stage 1) failure: 'ninja' (failure)
...
[4772/9869] Linking CXX static library lib/libLLVMDlltoolDriver.a
[4773/9869] Linking CXX static library lib/libLLVMLibDriver.a
[4774/9869] Linking CXX static library lib/libLLVMOrcTargetProcess.a
[4775/9869] Linking CXX static library lib/libLLVMARMDesc.a
[4776/9869] Linking CXX static library lib/libLLVMRuntimeDyld.a
[4777/9869] Linking CXX static library lib/libLLVMObjectYAML.a
[4778/9869] Linking CXX static library lib/libLLVMXRay.a
[4779/9869] Building CXX object lib/Target/X86/MCTargetDesc/CMakeFiles/LLVMX86Desc.dir/X86MCAsmInfo.cpp.o
[4780/9869] Building CXX object lib/Target/X86/CMakeFiles/LLVMX86CodeGen.dir/X86Subtarget.cpp.o
[4781/9869] Building CXX object lib/Target/X86/MCTargetDesc/CMakeFiles/LLVMX86Desc.dir/X86MCLFIRewriter.cpp.o
FAILED: lib/Target/X86/MCTargetDesc/CMakeFiles/LLVMX86Desc.dir/X86MCLFIRewriter.cpp.o 
/usr/local/bin/c++ -D_DEBUG -D_GLIBCXX_ASSERTIONS -D_GLIBCXX_USE_CXX11_ABI=1 -D_GNU_SOURCE -D_LIBCPP_HARDENING_MODE=_LIBCPP_HARDENING_MODE_EXTENSIVE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/home/tcwg-buildbot/worker/clang-aarch64-sve-vla/stage1/lib/Target/X86/MCTargetDesc -I/home/tcwg-buildbot/worker/clang-aarch64-sve-vla/llvm/llvm/lib/Target/X86/MCTargetDesc -I/home/tcwg-buildbot/worker/clang-aarch64-sve-vla/llvm/llvm/lib/Target/X86 -I/home/tcwg-buildbot/worker/clang-aarch64-sve-vla/stage1/lib/Target/X86 -I/home/tcwg-buildbot/worker/clang-aarch64-sve-vla/stage1/include -I/home/tcwg-buildbot/worker/clang-aarch64-sve-vla/llvm/llvm/include -mcpu=neoverse-512tvb -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -pedantic -Wno-long-long -Wc++98-compat-extra-semi -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 -fdiagnostics-color -ffunction-sections -fdata-sections -Xclang -fno-pch-timestamp -O3 -DNDEBUG -std=c++17 -fvisibility=hidden -UNDEBUG -fno-exceptions -funwind-tables -fno-rtti -Winvalid-pch -Xclang -include-pch -Xclang /home/tcwg-buildbot/worker/clang-aarch64-sve-vla/stage1/lib/Support/CMakeFiles/LLVMSupport.dir/cmake_pch.hxx.pch -Xclang -include -Xclang /home/tcwg-buildbot/worker/clang-aarch64-sve-vla/stage1/lib/Support/CMakeFiles/LLVMSupport.dir/cmake_pch.hxx -MD -MT lib/Target/X86/MCTargetDesc/CMakeFiles/LLVMX86Desc.dir/X86MCLFIRewriter.cpp.o -MF lib/Target/X86/MCTargetDesc/CMakeFiles/LLVMX86Desc.dir/X86MCLFIRewriter.cpp.o.d -o lib/Target/X86/MCTargetDesc/CMakeFiles/LLVMX86Desc.dir/X86MCLFIRewriter.cpp.o -c /home/tcwg-buildbot/worker/clang-aarch64-sve-vla/llvm/llvm/lib/Target/X86/MCTargetDesc/X86MCLFIRewriter.cpp
/home/tcwg-buildbot/worker/clang-aarch64-sve-vla/llvm/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
/home/tcwg-buildbot/worker/clang-aarch64-sve-vla/stage1/lib/Target/X86/X86GenRegisterInfoEnums.inc:12:24: note: 'getX86MCRegisterClass' declared here
   12 | const MCRegisterClass &getX86MCRegisterClass(unsigned RC);
      |                        ^
/home/tcwg-buildbot/worker/clang-aarch64-sve-vla/llvm/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);
      |          ^~~~~~~~~~~~~~~~~~~~
/home/tcwg-buildbot/worker/clang-aarch64-sve-vla/llvm/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
/home/tcwg-buildbot/worker/clang-aarch64-sve-vla/stage1/lib/Target/X86/X86GenRegisterInfoEnums.inc:12:24: note: 'getX86MCRegisterClass' declared here
   12 | const MCRegisterClass &getX86MCRegisterClass(unsigned RC);
      |                        ^
/home/tcwg-buildbot/worker/clang-aarch64-sve-vla/llvm/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.
[4782/9869] Building CXX object lib/Target/X86/MCTargetDesc/CMakeFiles/LLVMX86Desc.dir/X86WinCOFFObjectWriter.cpp.o
[4783/9869] Building CXX object lib/Target/X86/CMakeFiles/LLVMX86CodeGen.dir/GISel/X86LegalizerInfo.cpp.o
[4784/9869] Building CXX object lib/Target/X86/MCTargetDesc/CMakeFiles/LLVMX86Desc.dir/X86MachObjectWriter.cpp.o
[4785/9869] Building CXX object lib/Target/X86/CMakeFiles/LLVMX86CodeGen.dir/X86RegisterInfo.cpp.o
[4786/9869] Building CXX object lib/Target/X86/MCTargetDesc/CMakeFiles/LLVMX86Desc.dir/X86MCCodeEmitter.cpp.o
[4787/9869] Building CXX object lib/Target/X86/MCTargetDesc/CMakeFiles/LLVMX86Desc.dir/X86WinCOFFTargetStreamer.cpp.o
[4788/9869] Building CXX object lib/Target/X86/CMakeFiles/LLVMX86CodeGen.dir/X86SpeculativeLoadHardening.cpp.o
[4789/9869] Building CXX object tools/mlir/lib/IR/CMakeFiles/obj.MLIRIR.dir/Dominance.cpp.o
[4790/9869] Building CXX object lib/Target/X86/CMakeFiles/LLVMX86CodeGen.dir/X86FastISel.cpp.o
[4791/9869] Building CXX object lib/Target/X86/CMakeFiles/LLVMX86CodeGen.dir/X86MCInstLower.cpp.o
[4792/9869] Building CXX object lib/Passes/CMakeFiles/LLVMPasses.dir/PassBuilderPipelines.cpp.o
[4793/9869] Building CXX object tools/llvm-ar/CMakeFiles/llvm-ar.dir/llvm-ar.cpp.o
[4794/9869] Building CXX object lib/Target/X86/MCTargetDesc/CMakeFiles/LLVMX86Desc.dir/X86AsmBackend.cpp.o
[4795/9869] Building CXX object lib/Target/X86/CMakeFiles/LLVMX86CodeGen.dir/X86InstrInfo.cpp.o
[4796/9869] Building CXX object tools/llvm-profdata/CMakeFiles/llvm-profdata.dir/llvm-profdata.cpp.o
[4797/9869] Building CXX object lib/Target/X86/Disassembler/CMakeFiles/LLVMX86Disassembler.dir/X86Disassembler.cpp.o

```

</details>

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