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From: Zhenghui Zhou <zhouzhenghui AT gmail DOT com>
Date: Tue, 26 Nov 2019 11:42:59 +0800
Message-ID: <CAOME8XTripBup--2v4OtrufAUS21pZySCQiK_3s+1ffvOM110g@mail.gmail.com>
Subject: CMake fails to find the LLVM package with the LLVMConfig.cmake
To: cygwin <cygwin AT cygwin DOT com>
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I'm trying to build a project in cygwin64 under windows 10 which depends the
LLVM libraries and had been built successfully under some linux
environment. The problem is that the build scripts of CMake can not find
the LLVM libraries.

I have installed LLVM-devel package of cygwin64, and cmake can located the
LLVMConfig.cmake file in /usr/lib/cmake/llvm directory which is installed
along with the LLVM packages.

An example of CMakeList.txt likes:

cmake_minimum_required(VERSION 3.1)
project(simple)
message(STATUS "Using LLVMConfig.cmake in: ${LLVM_DIR}")
find_package(LLVM REQUIRED CONFIG)
message(STATUS "Found LLVM ${LLVM_PACKAGE_VERSION}")
...

And the output reports:

-- Using LLVMConfig.cmake in: /usr/lib/cmake/llvm
CMake Error at CMakeLists.txt:10 (find_package):
  Found package configuration file:

    /usr/lib/cmake/llvm/LLVMConfig.cmake

  but it set LLVM_FOUND to FALSE so package "LLVM" is considered to be NOT
  FOUND.  Reason given by package:

  The following imported targets are referenced, but are missing:
LLVMSupport
  LLVMCore LLVMScalarOpts LLVMInstCombine LLVMTransformUtils LLVMAnalysis
  LLVMipo LLVMMC LLVMPasses LLVMLinker LLVMIRReader LLVMBitReader
  LLVMMCParser LLVMObject LLVMProfileData LLVMTarget LLVMVectorize

-- Configuring incomplete, errors occurred!

After digging for several hours, I think the problem is caused by lacking
of shared objects of LLVM. There are only static libraries of LLVM under
Cygwin/Windows.  A submit <https://reviews.llvm.org/D32668> of LLVM tells
that the shared library targets may only need on most platforms so that the
static library targets is split into theire own export file and can be
ignored, The configuration entries in LLVMConfig.cmake are:
...
  include("${LLVM_CMAKE_DIR}/LLVMExports.cmake")
  include("${LLVM_CMAKE_DIR}/LLVMStaticExports.cmake" OPTIONAL)
...
The static targets export file is set optional at the second line。However,
configuration under cygwin will fail on the first line.

So it may be figured that the second line goes in front:
...
  include("${LLVM_CMAKE_DIR}/LLVMStaticExports.cmake" OPTIONAL)
  include("${LLVM_CMAKE_DIR}/LLVMExports.cmake")
...
Everything works fine now.

Is there anything I missed or better suggestions?

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