[polly] Dynamic libraries are not supported on Cygwin

[carlo-bramini]

Summary

Cygwin shares the same limitations as traditional Windows executables for dynamic library loading, so disable building the dynamic library on Cygwin targets.

[efriedma]

I don't see how PIC is related to anything; can you fix the commit message to explain this is a Windows (PE/COFF) issue?

[carlo-bramini]

In D155796#4621721, @efriedma wrote:

I don't see how PIC is related to anything; can you fix the commit message to explain this is a Windows (PE/COFF) issue?

Well, I configured the sources with:

cmake ../llvm-project/llvm -G Ninja -DCMAKE_BUILD_TYPE=Release -Wno-dev -DBUILD_SHARED_LIBS=ON -DLLVM_ENABLE_PROJECTS="polly"

When linking the last file, which is lib/LLVMPolly.dll, the build process stops with thousands of error messages saying "undefined reference to xxx".
I found two solutions for this problem:

(1) I did the same change it has been done for WIN32 into those CMakeLists.txt files.
It won't emit errors, but lib/LLVMPolly.dll is not built anymore.
That's why it works.
I don't know why it has been done for WIN32, but perhaps this is the expected behaviour.

(2) first, I executed:

ninja -j1 -v

and I grabbed the command line that it is used for linking lib/LLVMPolly.dll.
It is interesting to notice that there are not additional libraries as dependecy on this command line, just object files.
Then, I copied and pasted that command line and I added these libraries at the bottom:

lib/libLLVMCore.dll.a lib/libLLVMSupport.dll.a lib/libLLVMAnalysis.dll.a lib/libLLVMTransformUtils.dll.a lib/libLLVMPasses.dll.a lib/libLLVMScalarOpts.dll.a lib/libLLVMPasses.dll.a lib/libLLVMInstCombine.dll.a lib/libLLVMipo.dll.a lib/libLLVMTarget.dll.a lib/libLLVMTargetParser.dll.a

By doing so, lib/LLVMPolly.dll is linked successfully.

Actually, I have choosen the fastest solution to be used as a patch, because, as it is written, this is done also on WIN32, although the second one would be prefered.
Perhaps, the choice to avoid the final linking had some reasons, but I don't know what they are or if there is a bug hidden somewhere into the cmake scripts or elsewhere, sorry.

[efriedma]

I attempted to fix the commit message for you; let me know if it makes sense to you.

Otherwise LGTM; how do you want to be credited in the git "author" line?

[carlo-bramini]

The title looks good to me.

Otherwise LGTM; how do you want to be credited in the git "author" line?

real name: Carlo Bramini
email address: [e-mail]

polly/cmake/CMakeLists.txt

 if (CMAKE_CONFIGURATION_TYPES)
   set(POLLY_EXPORTS_FILE_NAME "PollyExports-$<LOWER_CASE:$<CONFIG>>.cmake")
 else()
   # avoid conflicts in the build-tree when changing configuration
   set(POLLY_EXPORTS_FILE_NAME "PollyExports-all.cmake")
 endif()
 
 set(POLLY_CONFIG_EXPORTED_TARGETS Polly ${ISL_TARGET})
-if (NOT WIN32 AND LLVM_ENABLE_PIC)
+if (NOT (WIN32 OR CYGWIN) AND LLVM_ENABLE_PIC)
   # LLVMPolly is a dummy target on Win or if PIC code is disabled.
   list(APPEND POLLY_CONFIG_EXPORTED_TARGETS LLVMPolly)
 endif()
 
 # Get the target type for every exported target
 foreach(tgt IN LISTS POLLY_CONFIG_EXPORTED_TARGETS)
   get_target_property(tgt_type ${tgt} TYPE)
   string(REPLACE "_LIBRARY" "" tgt_type ${tgt_type})

polly/lib/CMakeLists.txt

 # LLVM_POLLY_LINK_INTO_TOOLS=ON, its dependencies like PollyISL are linked as
 # well.
 target_link_libraries(Polly PUBLIC
   ${ISL_TARGET}
 )
 
 # Create a loadable module Polly.so that can be loaded using
 # LLVM's/clang's "-load" option.
-if (WIN32 OR NOT LLVM_ENABLE_PIC)
+if (WIN32 OR CYGWIN OR NOT LLVM_ENABLE_PIC)
   # Add dummy target, either because loadable modules are not supported
   # as on Windows or because PIC code has been disabled
   add_custom_target(LLVMPolly)
   set_target_properties(LLVMPolly PROPERTIES FOLDER "Polly")
 else ()
   add_polly_loadable_module(LLVMPolly
     Plugin/Polly.cpp
     $<TARGET_OBJECTS:obj.Polly>