[compiler-rt] Rework the object build support

[phosek]

Summary

The initial implementation didn't properly support cross-compilation
via the runtime build, the updated implementation should address that
by expanding the CMAKE_C_COMPILE_OBJECT variable with correct values.

[smeenai]

This is really nasty, but I'm not sure if there's a better way to do this.

compiler-rt/cmake/Modules/AddCompilerRT.cmake

278 ↗

(On Diff #197489)

I think you mean "CMake 3.9" and not "LLVM 3.9" :)

278 ↗

(On Diff #197489)

Is it okay to drop this part? I don't know how common it is to set COMPILE_FLAGS on sources.

304 ↗

(On Diff #197489)

Would separate_arguments be better here, to handle quoted arguments etc. correctly? (Though I guess the string(REPLACE) on line 282 is potentially screwing up quoted arguments anyway.)

[phosek]

compiler-rt/cmake/Modules/AddCompilerRT.cmake

278 ↗

(On Diff #197489)

I don't think it's very often, but I'm fine including it.

278 ↗

(On Diff #197489)

Yes, but after looking into it a bit I realized that this may not be enough since CMake doesn't allow specifying output names for object libraries so I deleted the comment.

304 ↗

(On Diff #197489)

It seems to be working.

[beanz]

This all looks reasonable to me. It is kinda frustrating that CMake doesn't support any way to control the output name of an object file, or even the install name of one. I suspect that is probably because some of CMake's generation targets (like Xcode) don't give CMake explicit control over output object file names.

compiler-rt/trunk/cmake/Modules/AddCompilerRT.cmake

foreach(libname ${libnames})
     # per-library install rules, so we fall back to the parent target COMPONENT
     if(CMAKE_CONFIGURATION_TYPES AND LIB_PARENT_TARGET)
       set(COMPONENT_OPTION COMPONENT ${LIB_PARENT_TARGET})
     else()
       set(COMPONENT_OPTION COMPONENT ${libname})
     endif()
 
     if(type STREQUAL "OBJECT")
-      string(TOUPPER ${CMAKE_BUILD_TYPE} config)
-      get_property(cflags SOURCE ${sources_${libname}} PROPERTY COMPILE_FLAGS)
-      separate_arguments(cflags)
+      get_property(cflags_${libname} SOURCE ${sources_${libname}} PROPERTY COMPILE_FLAGS)
+      if(CMAKE_C_COMPILER_ID MATCHES Clang AND CMAKE_C_COMPILER_TARGET)
+        list(APPEND cflags_${libname} "-target ${CMAKE_C_COMPILER_TARGET}")
+      endif()
+      string(REPLACE ";" " " extra_cflags_${libname} "${extra_cflags_${libname}}")
+      string(REGEX MATCHALL "<[A-Za-z0-9_]*>" substitutions
+             ${CMAKE_C_COMPILE_OBJECT})
+      set(compile_command_${libname} "${CMAKE_C_COMPILE_OBJECT}")
+      set(output_file_${libname} ${output_name_${libname}}${CMAKE_C_OUTPUT_EXTENSION})
+      foreach(substitution ${substitutions})
+        if(substitution STREQUAL "<CMAKE_C_COMPILER>")
+          string(REPLACE "<CMAKE_C_COMPILER>" "${CMAKE_C_COMPILER}"
+                 compile_command_${libname} ${compile_command_${libname}})
+        elseif(substitution STREQUAL "<OBJECT>")
+          string(REPLACE "<OBJECT>" "${output_dir_${libname}}/${output_file_${libname}}"
+                 compile_command_${libname} ${compile_command_${libname}})
+        elseif(substitution STREQUAL "<SOURCE>")
+          string(REPLACE "<SOURCE>" "${sources_${libname}}"
+                 compile_command_${libname} ${compile_command_${libname}})
+        elseif(substitution STREQUAL "<FLAGS>")
+          string(REPLACE "<FLAGS>" "${CMAKE_C_FLAGS} ${cflags_${libname}} ${extra_cflags_${libname}}"
+                 compile_command_${libname} ${compile_command_${libname}})
+        else()
+          string(REPLACE "${substitution}" "" compile_command_${libname}
+                 ${compile_command_${libname}})
+        endif()
+      endforeach()
+      separate_arguments(compile_command_${libname})
       add_custom_command(
-          OUTPUT ${output_dir_${libname}}/${output_name_${libname}}.o
-          COMMAND ${CMAKE_C_COMPILER} ${sources_${libname}} ${cflags} ${extra_cflags_${libname}} -c -o ${output_dir_${libname}}/${output_name_${libname}}.o
+          OUTPUT ${output_dir_${libname}}/${output_file_${libname}}
+          COMMAND ${compile_command_${libname}}
           DEPENDS ${sources_${libname}}
-          COMMENT "Building C object ${output_name_${libname}}.o")
-      add_custom_target(${libname} DEPENDS ${output_dir_${libname}}/${output_name_${libname}}.o)
-      install(FILES ${output_dir_${libname}}/${output_name_${libname}}.o
+          COMMENT "Building C object ${output_file_${libname}}")
+      add_custom_target(${libname} DEPENDS ${output_dir_${libname}}/${output_file_${libname}})
+      install(FILES ${output_dir_${libname}}/${output_file_${libname}}
         DESTINATION ${install_dir_${libname}}
         ${COMPONENT_OPTION})
     else()
       add_library(${libname} ${type} ${sources_${libname}})
       set_target_compile_flags(${libname} ${extra_cflags_${libname}})
       set_target_link_flags(${libname} ${extra_link_flags_${libname}})
       set_property(TARGET ${libname} APPEND PROPERTY
                    COMPILE_DEFINITIONS ${LIB_DEFS})