[libclc] Add prepare-<triple> targets (#146700)

This target provides a unified build target for all devices under the
single triple. This way a user doesn't have to know device names to
build a specific target's bytecode libraries.

Device names may be considered as internal implementation details as
they are not exposed to users of CMake; users only specify triples to
build. Now, instead of `prepare-{barts,cayman,cedar,cypress}-r600--.bc`,
for example, a user may now build simply `prepare-r600--` and have all
four of those libraries built.

This commit also refactors the CMake somewhat. We were previously
diverging between the SPIR-V and other targets, and duplicating a bit of
logic like the creation of the 'prepare' targets, the targets'
properties, and the installation directory. It's cleaner and hopefully
more robust to share this code between all targets. This commit also
takes this opportunity to improve some comments around this code.

Author: frasercrmck

libclc/cmake/modules/AddLibclc.cmake

@@ -356,55 +356,72 @@ function(add_libclc_builtin_set)
 
   set( builtins_link_lib $<TARGET_PROPERTY:${builtins_link_lib_tgt},TARGET_FILE> )
 
+  # For SPIR-V targets we diverage at this point and generate SPIR-V using the
+  # llvm-spirv tool.
   if( ARG_ARCH STREQUAL spirv OR ARG_ARCH STREQUAL spirv64 )
-    set( spv_suffix ${ARG_ARCH_SUFFIX}.spv )
-    add_custom_command( OUTPUT ${spv_suffix}
-      COMMAND ${llvm-spirv_exe} ${spvflags} -o ${spv_suffix} ${builtins_link_lib}
+    set( obj_suffix ${ARG_ARCH_SUFFIX}.spv )
+    add_custom_command( OUTPUT ${obj_suffix}
+      COMMAND ${llvm-spirv_exe} ${spvflags} -o ${obj_suffix} ${builtins_link_lib}
       DEPENDS ${llvm-spirv_target} ${builtins_link_lib} ${builtins_link_lib_tgt}
     )
-    add_custom_target( "prepare-${spv_suffix}" ALL DEPENDS "${spv_suffix}" )
-    set_target_properties( "prepare-${spv_suffix}" PROPERTIES FOLDER "libclc/Device IR/Prepare" )
-    install( FILES ${CMAKE_CURRENT_BINARY_DIR}/${spv_suffix}
-       DESTINATION "${CMAKE_INSTALL_DATADIR}/clc" )
-
-    return()
-  endif()
+  else()
+    # Non-SPIR-V targets add an extra step to optimize the bytecode
+    set( builtins_opt_lib_tgt builtins.opt.${ARG_ARCH_SUFFIX} )
 
-  set( builtins_opt_lib_tgt builtins.opt.${ARG_ARCH_SUFFIX} )
+    add_custom_command( OUTPUT ${builtins_opt_lib_tgt}.bc
+      COMMAND ${opt_exe} ${ARG_OPT_FLAGS} -o ${builtins_opt_lib_tgt}.bc
+        ${builtins_link_lib}
+      DEPENDS ${opt_target} ${builtins_link_lib} ${builtins_link_lib_tgt}
+    )
+    add_custom_target( ${builtins_opt_lib_tgt}
+      ALL DEPENDS ${builtins_opt_lib_tgt}.bc
+    )
+    set_target_properties( ${builtins_opt_lib_tgt} PROPERTIES
+      TARGET_FILE ${CMAKE_CURRENT_BINARY_DIR}/${builtins_opt_lib_tgt}.bc
+      FOLDER "libclc/Device IR/Opt"
+    )
 
-  # Add opt target
-  add_custom_command( OUTPUT ${builtins_opt_lib_tgt}.bc
-    COMMAND ${opt_exe} ${ARG_OPT_FLAGS} -o ${builtins_opt_lib_tgt}.bc
-      ${builtins_link_lib}
-    DEPENDS ${opt_target} ${builtins_link_lib} ${builtins_link_lib_tgt}
-  )
-  add_custom_target( ${builtins_opt_lib_tgt}
-    ALL DEPENDS ${builtins_opt_lib_tgt}.bc
-  )
-  set_target_properties( ${builtins_opt_lib_tgt} PROPERTIES
-    TARGET_FILE ${CMAKE_CURRENT_BINARY_DIR}/${builtins_opt_lib_tgt}.bc
-    FOLDER "libclc/Device IR/Opt"
-  )
+    set( builtins_opt_lib $<TARGET_PROPERTY:${builtins_opt_lib_tgt},TARGET_FILE> )
 
-  set( builtins_opt_lib $<TARGET_PROPERTY:${builtins_opt_lib_tgt},TARGET_FILE> )
+    set( obj_suffix ${ARG_ARCH_SUFFIX}.bc )
+    add_custom_command( OUTPUT ${obj_suffix}
+      COMMAND ${prepare_builtins_exe} -o ${obj_suffix} ${builtins_opt_lib}
+      DEPENDS ${builtins_opt_lib} ${builtins_opt_lib_tgt} ${prepare_builtins_target} )
+  endif()
 
-  # Add prepare target
-  set( obj_suffix ${ARG_ARCH_SUFFIX}.bc )
-  add_custom_command( OUTPUT ${obj_suffix}
-    COMMAND ${prepare_builtins_exe} -o ${obj_suffix} ${builtins_opt_lib}
-    DEPENDS ${builtins_opt_lib} ${builtins_opt_lib_tgt} ${prepare_builtins_target} )
+  # Add a 'prepare' target
   add_custom_target( prepare-${obj_suffix} ALL DEPENDS ${obj_suffix} )
   set_target_properties( "prepare-${obj_suffix}" PROPERTIES FOLDER "libclc/Device IR/Prepare" )
 
-  # nvptx-- targets don't include workitem builtins, and clspv targets don't
-  # include all OpenCL builtins
+  # Also add a 'prepare' target for the triple. Since a triple may have
+  # multiple devices, ensure we only try to create the triple target once. The
+  # triple's target will build all of the bytecode for its constituent devices.
+  if( NOT TARGET prepare-${ARG_TRIPLE} )
+    add_custom_target( prepare-${ARG_TRIPLE} ALL )
+  endif()
+  add_dependencies( prepare-${ARG_TRIPLE} prepare-${obj_suffix} )
+
+  install(
+    FILES ${CMAKE_CURRENT_BINARY_DIR}/${obj_suffix}
+    DESTINATION "${CMAKE_INSTALL_DATADIR}/clc"
+  )
+
+  # SPIR-V targets can exit early here
+  if( ARG_ARCH STREQUAL spirv OR ARG_ARCH STREQUAL spirv64 )
+    return()
+  endif()
+
+  # Add a test for whether or not the libraries contain unresolved calls which
+  # would usually indicate a build problem. Note that we don't perform this
+  # test for all libclc targets:
+  # * nvptx-- targets don't include workitem builtins
+  # * clspv targets don't include all OpenCL builtins
   if( NOT ARG_ARCH MATCHES "^(nvptx|clspv)(64)?$" )
     add_test( NAME external-calls-${obj_suffix}
       COMMAND ./check_external_calls.sh ${CMAKE_CURRENT_BINARY_DIR}/${obj_suffix} ${LLVM_TOOLS_BINARY_DIR}
       WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR} )
   endif()
 
-  install( FILES ${CMAKE_CURRENT_BINARY_DIR}/${obj_suffix} DESTINATION "${CMAKE_INSTALL_DATADIR}/clc" )
   foreach( a ${ARG_ALIASES} )
     set( alias_suffix "${a}-${ARG_TRIPLE}.bc" )
     add_custom_command(