Avoid object libraries in the VS IDE

clang/cmake/modules/AddClang.cmake

@@ -96,8 +96,12 @@ macro(add_clang_library name)
     else()
       set(LIBTYPE STATIC)
     endif()
-    if(NOT XCODE)
+    if(NOT XCODE AND NOT MSVC_IDE)
       # The Xcode generator doesn't handle object libraries correctly.
+      # The Visual Studio CMake generator does handle object libraries
+      # correctly, but it is preferable to list the libraries with their
+      # source files (instead of the object files and the source files in
+      # a separate target in the "Object Libraries" folder)
       list(APPEND LIBTYPE OBJECT)
     endif()
     set_property(GLOBAL APPEND PROPERTY CLANG_STATIC_LIBS ${name})

clang/lib/Support/CMakeLists.txt

@@ -15,7 +15,7 @@ set(clangSupport_sources
 
 add_clang_library(clangSupport ${clangSupport_sources})
 
-if (NOT XCODE)
+if (TARGET obj.clangSupport)
   add_library(clangSupport_tablegen ALIAS obj.clangSupport)
 elseif (NOT LLVM_LINK_LLVM_DYLIB)
   add_library(clangSupport_tablegen ALIAS clangSupport)

flang/cmake/modules/AddFlang.cmake

@@ -51,19 +51,28 @@ function(add_flang_library name)
 
   endif()
 
-  if (ARG_SHARED)
+  if(ARG_SHARED AND ARG_STATIC)
+    set(LIBTYPE SHARED STATIC)
+  elseif(ARG_SHARED)
     set(LIBTYPE SHARED)
   else()
     # llvm_add_library ignores BUILD_SHARED_LIBS if STATIC is explicitly set,
     # so we need to handle it here.
-    if (BUILD_SHARED_LIBS AND NOT ARG_STATIC)
-      set(LIBTYPE SHARED OBJECT)
+    if(BUILD_SHARED_LIBS)
+      set(LIBTYPE SHARED)
     else()
-      set(LIBTYPE STATIC OBJECT)
+      set(LIBTYPE STATIC)
     endif()
-    set_property(GLOBAL APPEND PROPERTY FLANG_STATIC_LIBS ${name})
+    if(NOT XCODE AND NOT MSVC_IDE)
+      # The Xcode generator doesn't handle object libraries correctly.
+      # The Visual Studio CMake generator does handle object libraries
+      # correctly, but it is preferable to list the libraries with their
+      # source files (instead of the object files and the source files in
+      # a separate target in the "Object Libraries" folder)
+      list(APPEND LIBTYPE OBJECT)
+    endif()
+    set_property(GLOBAL APPEND PROPERTY CLANG_STATIC_LIBS ${name})
   endif()
-
   llvm_add_library(${name} ${LIBTYPE} ${ARG_UNPARSED_ARGUMENTS} ${srcs})
 
   clang_target_link_libraries(${name} PRIVATE ${ARG_CLANG_LIBS})

mlir/cmake/modules/AddMLIR.cmake

@@ -306,26 +306,23 @@ endfunction()
 #   Don't include this library in libMLIR.so.  This option should be used
 #   for test libraries, executable-specific libraries, or rarely used libraries
 #   with large dependencies.
+# OBJECT
+#   The library's object library is referenced using "obj.${name}". For this to
+#   work reliably, this flag ensures that the OBJECT library exists.
 # ENABLE_AGGREGATION
-#   Forces generation of an OBJECT library, exports additional metadata,
+#   Exports additional metadata,
 #   and installs additional object files needed to include this as part of an
 #   aggregate shared library.
 #   TODO: Make this the default for all MLIR libraries once all libraries
 #   are compatible with building an object library.
 function(add_mlir_library name)
   cmake_parse_arguments(ARG
-    "SHARED;INSTALL_WITH_TOOLCHAIN;EXCLUDE_FROM_LIBMLIR;DISABLE_INSTALL;ENABLE_AGGREGATION"
+    "SHARED;INSTALL_WITH_TOOLCHAIN;EXCLUDE_FROM_LIBMLIR;DISABLE_INSTALL;ENABLE_AGGREGATION;OBJECT"
     ""
     "ADDITIONAL_HEADERS;DEPENDS;LINK_COMPONENTS;LINK_LIBS"
     ${ARGN})
   _set_mlir_additional_headers_as_srcs(${ARG_ADDITIONAL_HEADERS})
 
-  # Is an object library needed.
-  set(NEEDS_OBJECT_LIB OFF)
-  if(ARG_ENABLE_AGGREGATION)
-    set(NEEDS_OBJECT_LIB ON)
-  endif()
-
   # Determine type of library.
   if(ARG_SHARED)
     set(LIBTYPE SHARED)
@@ -337,18 +334,39 @@ function(add_mlir_library name)
     else()
       set(LIBTYPE STATIC)
     endif()
-    # Test libraries and such shouldn't be include in libMLIR.so
-    if(NOT ARG_EXCLUDE_FROM_LIBMLIR)
-      set(NEEDS_OBJECT_LIB ON)
-      set_property(GLOBAL APPEND PROPERTY MLIR_STATIC_LIBS ${name})
-      set_property(GLOBAL APPEND PROPERTY MLIR_LLVM_LINK_COMPONENTS ${ARG_LINK_COMPONENTS})
-      set_property(GLOBAL APPEND PROPERTY MLIR_LLVM_LINK_COMPONENTS ${LLVM_LINK_COMPONENTS})
-    endif()
   endif()
 
-  if(NEEDS_OBJECT_LIB AND NOT XCODE)
-    # The Xcode generator doesn't handle object libraries correctly.
-    # We special case xcode when building aggregates.
+  # Is an object library needed...?
+  # Note that the XCode generator doesn't handle object libraries correctly and
+  # usability is degraded in the Visual Studio solution generators.
+  # llvm_add_library may also itself decide to create an object library.
+  set(NEEDS_OBJECT_LIB OFF)
+  if(ARG_OBJECT)
+    # Yes, because the target "obj.${name}" is referenced.
+    set(NEEDS_OBJECT_LIB ON)
+  endif ()
+  if(LLVM_BUILD_LLVM_DYLIB AND NOT ARG_EXCLUDE_FROM_LIBMLIR AND NOT XCODE)
+    # Yes, because in addition to the shared library, the object files are
+    # needed for linking into libMLIR.so (see mlir/tools/mlir-shlib/CMakeLists.txt).
+    # For XCode, -force_load is used instead.
+    # Windows is not supported (LLVM_BUILD_LLVM_DYLIB=ON will cause an error).
+    set(NEEDS_OBJECT_LIB ON)
+    set_property(GLOBAL APPEND PROPERTY MLIR_STATIC_LIBS ${name})
+    set_property(GLOBAL APPEND PROPERTY MLIR_LLVM_LINK_COMPONENTS ${ARG_LINK_COMPONENTS})
+    set_property(GLOBAL APPEND PROPERTY MLIR_LLVM_LINK_COMPONENTS ${LLVM_LINK_COMPONENTS})
+  endif ()
+  if(ARG_ENABLE_AGGREGATION AND NOT XCODE)
+    # Yes, because this library is added to an aggergate library such as
+    # libMLIR-C.so which is links together all the object files.
+    # For XCode, -force_load is used instead.
+    set(NEEDS_OBJECT_LIB ON)
+  endif()
+  if (NOT ARG_SHARED AND NOT ARG_EXCLUDE_FROM_LIBMLIR AND NOT XCODE AND NOT MSVC_IDE)
+    # Yes, but only for legacy reasons. Also avoid object libraries for
+    # Visual Studio solutions.
+    set(NEEDS_OBJECT_LIB ON)
+  endif()
+  if(NEEDS_OBJECT_LIB)
     list(APPEND LIBTYPE OBJECT)
   endif()
 
@@ -380,9 +398,12 @@ function(add_mlir_library name)
       # XCode has limited support for object libraries. Instead, add dep flags
       # that force the entire library to be embedded.
       list(APPEND AGGREGATE_DEPS "-force_load" "${name}")
-    else()
+    elseif(TARGET obj.${name})
+      # FIXME: *.obj can also be added via target_link_libraries since CMake 3.12.
       list(APPEND AGGREGATE_OBJECTS "$<TARGET_OBJECTS:obj.${name}>")
       list(APPEND AGGREGATE_OBJECT_LIB "obj.${name}")
+    else()
+      message(SEND_ERROR "Aggregate library not supported on this platform")
     endif()
 
     # For each declared dependency, transform it into a generator expression
@@ -402,7 +423,7 @@ function(add_mlir_library name)
 
     # In order for out-of-tree projects to build aggregates of this library,
     # we need to install the OBJECT library.
-    if(MLIR_INSTALL_AGGREGATE_OBJECTS AND NOT ARG_DISABLE_INSTALL)
+    if(TARGET "obj.${name}" AND MLIR_INSTALL_AGGREGATE_OBJECTS AND NOT ARG_DISABLE_INSTALL)
       add_mlir_library_install(obj.${name})
     endif()
   endif()
@@ -615,6 +636,7 @@ endfunction()
 function(add_mlir_public_c_api_library name)
   add_mlir_library(${name}
     ${ARGN}
+    OBJECT
     EXCLUDE_FROM_LIBMLIR
     ENABLE_AGGREGATION
     ADDITIONAL_HEADER_DIRS

mlir/lib/Dialect/GPU/CMakeLists.txt

@@ -57,6 +57,8 @@ add_mlir_dialect_library(MLIRGPUTransforms
   Transforms/SPIRVAttachTarget.cpp
   Transforms/SubgroupReduceLowering.cpp
   Transforms/Utils.cpp
+
+  OBJECT
 
   ADDITIONAL_HEADER_DIRS
   ${MLIR_MAIN_INCLUDE_DIR}/mlir/Dialect/GPU

mlir/lib/Target/LLVM/CMakeLists.txt

@@ -32,6 +32,8 @@ endif()
 add_mlir_dialect_library(MLIRNVVMTarget
   NVVM/Target.cpp
 
+  OBJECT
+
   ADDITIONAL_HEADER_DIRS
   ${MLIR_MAIN_INCLUDE_DIR}/mlir/Dialect/LLVMIR
 
@@ -109,6 +111,8 @@ endif()
 add_mlir_dialect_library(MLIRROCDLTarget
   ROCDL/Target.cpp
 
+  OBJECT
+
   LINK_COMPONENTS
   MCParser
   ${AMDGPU_LIBS}

mlir/tools/mlir-shlib/CMakeLists.txt

@@ -34,6 +34,7 @@ if(LLVM_BUILD_LLVM_DYLIB)
   add_mlir_library(
     MLIR
     SHARED
+    EXCLUDE_FROM_LIBMLIR
     ${INSTALL_WITH_TOOLCHAIN}
     mlir-shlib.cpp
     ${_OBJECTS}