[cmake] Use absolute paths for modules search

[rovka]

Summary

For out of tree builds, the user generally needs to specify LLVM_DIR and
MLIR_DIR on the command line so that the correct LLVM and MLIR
installations are picked up.

If the provided paths are absolute, everything works fine, however for
buildbots it is customary to work with relative paths, and that makes it
difficult for CMake to find the right modules to include.

This patch changes CMakeLists.txt to convert LLVM_DIR and MLIR_DIR to
absolute paths before adding them to CMAKE_MODULE_PATH. The inputs are
assumed to be relative to the source directory (llvm-project/flang).

[PeteSteinfeld]

Thanks for working on this!

But I couldn't get it working for me. Here's what I tried.

I started with an existing full build that includes llvm and mlir. The full path of this build is /local/home/psteinfeld/master/b4/build/. I have a script that does an out-of tree build based on this full build. Here's the script:

#!/bin/bash
cmake -G Ninja \
  -DFLANG_ENABLE_WERROR=On \
  -D LLVM_DIR=/local/home/psteinfeld/master/b4/build/lib/cmake/llvm \
  -D MLIR_DIR=/local/home/psteinfeld/master/b4/build/lib/cmake/mlir \
  -DCMAKE_BUILD_TYPE=Release ..

I then created a script that uses relative paths. Here's the contents of my new script:

#!/bin/bash
cmake -G Ninja \
  -DFLANG_ENABLE_WERROR=On \
  -D LLVM_DIR=../../../b4/build/lib/cmake/llvm \
  -D MLIR_DIR=../../../b4/build/lib/cmake/mlir \
  -DCMAKE_BUILD_TYPE=Release ..

I then downloaded the source into the directory /local/home/psteinfeld/master/diana/. I then "cd"ed to the "flang" directory and created a directory called "build" and did a "cd build". At this point, doing "pwd" yields "/local/home/psteinfeld/master/diana/flang/build". I then ran my new script. Running it produced the following errors:

...

• Performing Test C_SUPPORTS_FDATA_SECTIONS
• Performing Test C_SUPPORTS_FDATA_SECTIONS - Success
• Performing Test CXX_SUPPORTS_FDATA_SECTIONS
• Performing Test CXX_SUPPORTS_FDATA_SECTIONS - Success

CMake Error at CMakeLists.txt:81 (find_package):

Could not find a package configuration file provided by "MLIR" with any of
the following names:

  MLIRConfig.cmake
  mlir-config.cmake

Add the installation prefix of "MLIR" to CMAKE_PREFIX_PATH or set
"MLIR_DIR" to a directory containing one of the above files.  If "MLIR"
provides a separate development package or SDK, be sure it has been
installed.

• Configuring incomplete, errors occurred!

See also "/local/home/psteinfeld/master/diana/flang/build/CMakeFiles/CMakeOutput.log".
See also "/local/home/psteinfeld/master/diana/flang/build/CMakeFiles/CMakeError.log".

[rovka]

Thanks for trying this out!

That's a very surprising error, especially since the LLVM side of things seems to work just fine. I'll try to reproduce on my end.

[rovka]

Hi Pete,

I can't seem to reproduce this on my end. Could you please tell me how you obtain the build in /local/home/psteinfeld/master/b4/build/ ?

For my testing I've been using something like this:

cmake -DLLVM_TARGETS_TO_BUILD=X86 -DCMAKE_CXX_STANDARD=17 -DLLVM_ENABLE_WERROR=OFF -DLLVM_ENABLE_ASSERTIONS=ON -DCMAKE_BUILD_TYPE=Release -GNinja '-DLLVM_ENABLE_PROJECTS=llvm;mlir' -DCMAKE_INSTALL_PREFIX=../install_llvm '-DLLVM_LIT_ARGS=-v -vv' ../llvm/llvm

[tskeith]

This worked fine for me.

Pete, it might be helpful to add these lines after MLIR_DIR_ABSOLUTE is set and see if it looks correct.

message("MLIR_DIR=${MLIR_DIR}")
message("MLIR_DIR_ABSOLUTE=${MLIR_DIR_ABSOLUTE}")

[PeteSteinfeld]

I just tried again using paths relative to the location of CMakeLists.txt rather than the build directory, which for me is one level lower, and everything worked perfectly.

[rovka]

Great, thanks! :)

flang/CMakeLists.txt

if (NOT MSVC_IDE)
     set(LLVM_ENABLE_ASSERTIONS ${ENABLE_ASSERTIONS}
       CACHE BOOL "Enable assertions")
     # Assertions follow llvm's configuration.
     mark_as_advanced(LLVM_ENABLE_ASSERTIONS)
   endif()
 
   # We need a pre-built/installed version of LLVM.
   find_package(LLVM REQUIRED HINTS "${LLVM_CMAKE_PATH}")
-  list(APPEND CMAKE_MODULE_PATH ${LLVM_DIR})
+  # If the user specifies a relative path to LLVM_DIR, the calls to include
+  # LLVM modules fail. Append the absolute path to LLVM_DIR instead.
+  get_filename_component(LLVM_DIR_ABSOLUTE ${LLVM_DIR} REALPATH)
+  list(APPEND CMAKE_MODULE_PATH ${LLVM_DIR_ABSOLUTE})
 
   # If LLVM links to zlib we need the imported targets so we can too.
   if(LLVM_ENABLE_ZLIB)
     find_package(ZLIB REQUIRED)
   endif()
   option(LLVM_ENABLE_WARNINGS "Enable compiler warnings." ON)
   option(LLVM_ENABLE_PEDANTIC "Compile with pedantic enabled." ON)
   if(CMAKE_COMPILER_IS_GNUCXX)
     set(USE_NO_MAYBE_UNINITIALIZED 1)
   endif()
 
   include(CMakeParseArguments)
   include(AddLLVM)
   include(HandleLLVMOptions)
   include(VersionFromVCS)
 
   if(LINK_WITH_FIR)
     include(TableGen)
     find_package(MLIR REQUIRED CONFIG)
     # Use SYSTEM for the same reasons as for LLVM includes
     include_directories(SYSTEM ${MLIR_INCLUDE_DIRS})
-    list(APPEND CMAKE_MODULE_PATH ${MLIR_DIR})
+    # If the user specifies a relative path to MLIR_DIR, the calls to include
+    # MLIR modules fail. Append the absolute path to MLIR_DIR instead.
+    get_filename_component(MLIR_DIR_ABSOLUTE ${MLIR_DIR} REALPATH)
+    list(APPEND CMAKE_MODULE_PATH ${MLIR_DIR_ABSOLUTE})
     include(AddMLIR)
     find_program(MLIR_TABLEGEN_EXE "mlir-tblgen" ${LLVM_TOOLS_BINARY_DIR}
       NO_DEFAULT_PATH)
   endif()
 
   option(LLVM_INSTALL_TOOLCHAIN_ONLY
     "Only include toolchain files in the 'install' target." OFF)
   option(LLVM_FORCE_USE_OLD_HOST_TOOLCHAIN