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[Flang] Search flang_rt in clang_rt path #151954

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Merged
Meinersbur merged 4 commits into from
Aug 6, 2025
Merged

[Flang] Search flang_rt in clang_rt path #151954

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ea175cb
Do not use apple-specific scheme
Meinersbur Aug 4, 2025
4c430e7
Also use old Compiler-RT search path
Meinersbur Aug 5, 2025
3a61f79
Add ../lib unconditionally
Meinersbur Aug 5, 2025
b6d5fb1
Only add existing search paths
Meinersbur Aug 6, 2025
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10 changes: 2 additions & 8 deletions flang-rt/cmake/modules/GetToolchainDirs.cmake
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Original file line number Diff line number Diff line change
Expand Up @@ -34,14 +34,8 @@
function (get_toolchain_library_subdir outvar)
set(outval "lib")

if (APPLE)
# Required to be "darwin" for MachO toolchain.
get_toolchain_os_dirname(os_dirname)
set(outval "${outval}/${os_dirname}")
else ()
get_toolchain_arch_dirname(arch_dirname)
set(outval "${outval}/${arch_dirname}")
endif ()
get_toolchain_arch_dirname(arch_dirname)
set(outval "${outval}/${arch_dirname}")
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@luporl luporl Aug 4, 2025 •
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On my machine, both compiler-rt and flang-rt libraries are installed into <install_dir>/lib/clang/22/lib/darwin.

IIUC, this change would make flang-rt libraries be installed in a new directory, <install_dir>/lib/clang/22/lib/<target>, right?
Wouldn't it be better to make flang look for its libraries in the same path as compiler-rt?

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@Meinersbur Meinersbur Aug 5, 2025 •
edited
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On my machine, both compiler-rt and flang-rt libraries are installed into <install_dir>/lib/clang/22/lib/darwin.

That was the original intention/idea.

IIUC, this change would make flang-rt libraries be installed in a new directory, <install_dir>/lib/clang/22/lib/<target>, right? Wouldn't it be better to make flang look for its libraries in the same path as compiler-rt?

ToolChain::addFlangRTLibPath calls ToolChain::getArchSpecificLibPaths() which is overridable by the MachO ToolChain (but not actually overridden). The x86_64 is added here:

llvm-project/clang/lib/Driver/ToolChain.cpp

Line 1041 in 852cc92

AddPath({getOSLibName(), llvm::Triple::getArchTypeName(getArch())});

It felt best to avoid platform-specific exceptions making the problem more managable.

Turns out ToolChain::getArchSpecificLibPaths() is only used when using RPath. ToolChain::addFlangRTLibPath is called to fill getFilePaths. On non-MachO platforms seem that getRuntimePath() covers it, but is skipped on MachO1:

llvm-project/clang/lib/Driver/ToolChain.cpp

Lines 1010 to 1011 in 852cc92

if (Triple.isOSDarwin())
return {};

Trying another version soon

Footnotes

  1. Was this meant to return std::string(P) at some point? The bail out in the middle of the function is strange.
    EDIT: The root cause turns out to be #87866. Again. ↩


set(${outvar} "${outval}" PARENT_SCOPE)
endfunction ()
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