[Compiler-rt] Emit error if builtins library cannot be found

[kongyi]

Summary

Since setting COMPILER_RT_USE_BUILTINS_LIBRARY would remove -z,defs flag, missing builtins library would continue to build unnoticed. Explicitly emit an error in such case.

[hhb]

compiler-rt/cmake/Modules/AddCompilerRT.cmake

240

Should be "NOTFOUND"?

[mstorsjo]

This broke bootstrapping compiler-rt builtins for me.

When bootstrapping a new toolchain from scratch, we don't have any compiler-rt builtins, so this test will necessarily fail - until the builtins have been compiled and installed.

I can work around it temporarily by not setting COMPILER_RT_USE_BUILTINS_LIBRARY while building the builtins, but if that flag isnt' set, it literally means "we should use libgcc instead of compiler-rt builtins".

I think this kind of fix would make sense:

diff --git a/compiler-rt/cmake/Modules/AddCompilerRT.cmake b/compiler-rt/cmake/Modules/AddCompilerRT.cmake
index 1dde396b1f6..55fd125bac2 100644
--- a/compiler-rt/cmake/Modules/AddCompilerRT.cmake
+++ b/compiler-rt/cmake/Modules/AddCompilerRT.cmake
@@ -231,13 +231,14 @@ function(add_compiler_rt_runtime name type)
         if(WIN32)
           set_output_name(output_name_${libname} ${name}_dynamic ${arch})
         else()
           set_output_name(output_name_${libname} ${name} ${arch})
         endif()
       endif()
-      if(COMPILER_RT_USE_BUILTINS_LIBRARY AND NOT type STREQUAL "OBJECT")
+      if(COMPILER_RT_USE_BUILTINS_LIBRARY AND NOT type STREQUAL "OBJECT" AND 
+         NOT name STREQUAL "clang_rt.builtins")
         get_compiler_rt_target(${arch} target)
         find_compiler_rt_library(builtins ${target} builtins_${libname})
          if(builtins_${libname} STREQUAL "NOTFOUND")
           message(FATAL_ERROR "Cannot find builtins library for the target architecture")
         endif()
       endif()

Because when building the builtins themselves, we can't expect to find builtins, right? (Alternatively the check against clang_rt.builtins could be moved down to the NOTFOUND case.)

[kongyi]

In D79470#2041116, @mstorsjo wrote:

Because when building the builtins themselves, we can't expect to find builtins, right? (Alternatively the check against clang_rt.builtins could be moved down to the NOTFOUND case.)

You're right, we shouldn't fail the build for standalone clang_rt.builtins target. Please submit your change.

[mstorsjo]

In D79470#2041132, @kongyi wrote:

In D79470#2041116, @mstorsjo wrote:

Because when building the builtins themselves, we can't expect to find builtins, right? (Alternatively the check against clang_rt.builtins could be moved down to the NOTFOUND case.)

You're right, we shouldn't fail the build for standalone clang_rt.builtins target. Please submit your change.

Thanks, pushed in 54a85240709ecbcab329fb39af8ba5d6cd565305.

compiler-rt/cmake/Modules/AddCompilerRT.cmake

foreach(arch ${LIB_ARCHS})
           set_output_name(output_name_${libname} ${name}_dynamic ${arch})
         else()
           set_output_name(output_name_${libname} ${name} ${arch})
         endif()
       endif()
       if(COMPILER_RT_USE_BUILTINS_LIBRARY AND NOT type STREQUAL "OBJECT")
         get_compiler_rt_target(${arch} target)
         find_compiler_rt_library(builtins ${target} builtins_${libname})
+        if(builtins_${libname} STREQUAL "NOTFOUND")
+          message(FATAL_ERROR "Cannot find builtins library for the target architecture")
+        endif()
       endif()
       set(sources_${libname} ${LIB_SOURCES})
       format_object_libs(sources_${libname} ${arch} ${LIB_OBJECT_LIBS})
       set(libnames ${libnames} ${libname})
       set(extra_cflags_${libname} ${TARGET_${arch}_CFLAGS} ${NO_LTO_FLAGS} ${NO_PGO_FLAGS} ${LIB_CFLAGS})
       get_compiler_rt_output_dir(${arch} output_dir_${libname})
       get_compiler_rt_install_dir(${arch} install_dir_${libname})
     endforeach()