[Compiler-RT] On Apple Platforms switch to always emitting full debug info

[delcypher]

Summary

Previously the build used -gline-tables-only when COMPILER_RT_DEBUG
was off (default) and -g when COMPILER_RT_DEBUG was on. The end
result of this meant that the release build of the Sanitizer runtimes
were difficult to debug (e.g. information about variables and function
arguments were missing).

Presumably the reason for preferring -gline-tables-only for release
builds was to save space. However, for Apple platforms this doesn't
matter because debug info lives in separate .dSYM files (which aren't
shipped) rather than in the shipped .dylib files.

Now on Apple platforms we always emit full debug info if the compiler
supports it and we emit a fatal error if -g isn't supported.

rdar://79223184

[aralisza]

How come we emit a fatal error if -g isn’t supported?

[delcypher]

In D107501#2926864, @aralisza wrote:

How come we emit a fatal error if -g isn’t supported?

@aralisza
Because I don't want to silently drop debug info. All compilers I'm aware of actually used to build on Apple platforms should support it. If it causes problems we can remove the check.

[aralisza]

Sounds good to me

compiler-rt/CMakeLists.txt

if(MSVC)
   list(APPEND SANITIZER_COMMON_CFLAGS /Z7)
   foreach(var_to_update
     CMAKE_CXX_FLAGS
     CMAKE_CXX_FLAGS_DEBUG
     CMAKE_CXX_FLAGS_RELWITHDEBINFO)
     string(REGEX REPLACE "(^| )/Z[i7I]($| )" " /Z7 "
            "${var_to_update}" "${${var_to_update}}")
   endforeach()
+elseif(APPLE)
+  # On Apple platforms use full debug info (i.e. not `-gline-tables-only`)
+  # for all build types so that the runtime can be debugged.
+  if(NOT COMPILER_RT_HAS_G_FLAG)
+    message(FATAL_ERROR "-g is not supported by host compiler")
+  endif()
+  list(APPEND SANITIZER_COMMON_CFLAGS -g)
 elseif(COMPILER_RT_HAS_GLINE_TABLES_ONLY_FLAG AND NOT COMPILER_RT_DEBUG)
   list(APPEND SANITIZER_COMMON_CFLAGS -gline-tables-only)
 elseif(COMPILER_RT_HAS_G_FLAG)
   list(APPEND SANITIZER_COMMON_CFLAGS -g)
 endif()
 
 if(LLVM_ENABLE_MODULES)
   # Sanitizers cannot be built with -fmodules. The interceptors intentionally