Merge pull request #21 from EnzymeAD/fix-llvm-enzyme-linkage

libLLVM.a doesn't exist, so fix how enzyme is linking LLVM

Author: ZuseZ4

enzyme/Enzyme/CMakeLists.txt

@@ -145,7 +145,20 @@ if (${ENZYME_EXTERNAL_SHARED_LIB})
     add_dependencies(Enzyme-${LLVM_VERSION_MAJOR} BlasDeclarationsIncGen)
     add_dependencies(Enzyme-${LLVM_VERSION_MAJOR} BlasTAIncGen)
     add_dependencies(Enzyme-${LLVM_VERSION_MAJOR} BlasDiffUseIncGen)
-    target_link_libraries(Enzyme-${LLVM_VERSION_MAJOR} LLVM)
+
+    # This would be the desired way to link against LLVM components,
+    # however this function is bugged and does not work with `all`, see:
+    # https://github.com/llvm/llvm-project/issues/46347
+    #llvm_map_components_to_libnames(llvm_libs all)
+    # Therefore, manually invoke llvm-config
+    execute_process(COMMAND ${LLVM_TOOLS_BINARY_DIR}/llvm-config --libs all
+                OUTPUT_VARIABLE llvm_libraries)
+    string(STRIP "${llvm_libraries}" llvm_libraries)
+    # In theory, adding --libs should also add all the -l flags,
+    # but it isn't picked up correctly by clang, so we call target_link_libraries
+    set_target_properties(Enzyme-${LLVM_VERSION_MAJOR} PROPERTIES
+        LINK_FLAGS "`${LLVM_TOOLS_BINARY_DIR}/llvm-config --ldflags`")
+    target_link_libraries(Enzyme-${LLVM_VERSION_MAJOR} ${llvm_libraries})
     install(TARGETS Enzyme-${LLVM_VERSION_MAJOR}
         EXPORT EnzymeTargets
         LIBRARY DESTINATION lib COMPONENT shlib