cmake: Windows, adjust compiler identification on compiler swap #40547
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The latest CMake on Windows doesn't add `_CRT_USE_BUILTIN_OFFSETOF` flag after we swap the compiler to clang-cl for targets like SourceKit. Also `_add_host_variant_c_compile_flags` doesn't do so, because compiler identification still points to MSVC compiler. `_CRT_USE_BUILTIN_OFFSETOF` flag is necessary for `offsetof` calls to be accepted as an integral constant expression. This patch adjusts compiler identification on compiler swap and also addresses some configuration issues related to clang-cl.
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cc @compnerd |
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@swift-ci please test |
compnerd
approved these changes
Dec 15, 2021
| # Both clang and clang-cl on Windows set CMAKE_C_SIMULATE_ID to MSVC. | ||
| # We are using CMAKE_C_COMPILER_FRONTEND_VARIANT to detect the correct | ||
| # way to pass -Xclang arguments. | ||
| if ("${CMAKE_C_COMPILER_FRONTEND_VARIANT}" STREQUAL "MSVC") |
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The critical thing to note here is the condition on L559 - we know that the compiler ID is not MSVC, so we are assuming that this is clang (the assumption is reasonable for now as even the Linux path is currently unable to be supported by gcc due to other issues).
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The latest CMake on Windows doesn't add
_CRT_USE_BUILTIN_OFFSETOFflag after we swap the compiler to clang-cl for targets like SourceKit. Also_add_host_variant_c_compile_flagsdoesn't do so, because compiler identification still points to MSVC compiler._CRT_USE_BUILTIN_OFFSETOFflag is necessary foroffsetofcalls to be accepted as an integral constant expression. Otherwise, SourceKit build fails with the following error:This patch adjusts compiler identification on compiler swap and also addresses some configuration issues related to clang-cl.
Resolves SR-NNNN.