[PATCH] D97451: [PR48898][CMake] Support MinGW Toolchain tools in llvm_ExternalProject_Add

Thu Feb 25 01:49:01 PST 2021

mstorsjo added a reviewer: rnk.
mstorsjo added a comment.

> Windows is in the unique position of having two drivers, clang-cl and normal GNU clang, depending on whether a GNU or MSVC target is used.

FWIW, the normal GNU frontend also works for the MSVC target; some finer details are omitted in that case, but it rougly does work (and if the default target of the build is an msvc target, that's what targeted when calling that frontend too).

Also FWIW, I haven't really used the runtimes build mechanism at all, because I primarily bootstrap everything from scratch in a cross compile setup, i.e. with no preexisting build tools; first building the compiler, then building the base mingw crt, the compiler-rt builtins on top of that, and then other runtimes like libunwind, libcxxabi and libcxx on top of that. In such cases, afaik the runtimes build is a bit tricky, because I'd need to build other bits (e.g. the mingw crt) between building the compiler and the rest of the llvm provided runtimes. For now I just build all of those subprojects individually afterwards.

So therefore all of this is a bit of uncharted territory for me.

There's also a separate contender for how to build runtimes (still not entirely formally supported), as a middle ground - see https://github.com/llvm/llvm-project/blob/main/libcxx/utils/ci/runtimes/CMakeLists.txt. With that one, you configure building the runtimes just like a normal standalone project (i.e. you set the cmake configuration yourself, instead of instructing the machinery to figure it out based on a target triple), but you can add a series of projects to build as e.g. `-DLLVM_ENABLE_PROJECTS="libunwind;libcxxabi;libcxx"`. That setup has worked fine for me in some initial testing.

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Comment at: llvm/cmake/modules/LLVMExternalProjectUtils.cmake:56
       string(REGEX REPLACE "^-DCMAKE_SYSTEM_NAME=(.*)$" "\\1" _cmake_system_name "${arg}")
+    elseif (arg MATCHES "^-DCMAKE_(C|ASM|CXX)_COMPILER_TARGET=(.*)-windows-(gnu|msvc).*$")
+      if (${CMAKE_MATCH_3} STREQUAL "msvc")
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Technically, you can have triples in other forms too, like `x86_64-win32`; `win32` is an alias for `windows`, and if the `-msvc` suffix is omitted it defaults to the msvc variant.

If this only deals with canonicalized triples it should be fine. And for other cases, I guess it might be fine as well (as you'd get proper results if you pass triples in the expected form at least and we can't expect to mimic all the quirks handled by the llvm internal triple parser).

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Comment at: llvm/cmake/modules/LLVMExternalProjectUtils.cmake:74
     # AIX 64-bit XCOFF and big AR format is not yet supported in some of these tools.
-    if(NOT _cmake_system_name STREQUAL AIX)
+    if(NOT _cmake_system_name STREQUAL AIX OR use_mingw_toolchain_tools)
       list(APPEND ARG_TOOLCHAIN_TOOLS lld llvm-ar llvm-ranlib llvm-nm llvm-objdump)
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I'm not quite sure I follow the logic of this condition (parentheses might help?) - is it `not (aix or mingw)` or `(not aix) or mingw`? And why doesn't the current default logic work for the mingw case? At worst it might build an unnecessary llvm-lib frontend?

Repository:
  rG LLVM Github Monorepo

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https://reviews.llvm.org/D97451