[CMake] Provide an option to use relative paths in debug info

CMake always uses absolute file paths in the generated compiler
invocation which results in absolute file paths being embedded in debug
info. This is undesirable when building a toolchain e.g. on bots as the
debug info may embed the bot source checkout path which is meaningless
anywhere else.

This change introduces the LLVM_USE_RELATIVE_PATHS_IN_DEBUG_INFO which uses
-fdebug-prefix-map (where supported) options to rewrite paths embedded
into debug info with relative ones. Additionally, LLVM_SOURCE_PREFIX can
be used to override the path to source directory with a different one.

Differential Revision: https://reviews.llvm.org/D62622

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@362185 91177308-0d34-0410-b5e6-96231b3b80d8

cmake/modules/HandleLLVMOptions.cmake

@@ -977,3 +977,19 @@ if(macos_signposts_available)
     endif()
   endif()
 endif()
+
+option(LLVM_USE_RELATIVE_PATHS_IN_DEBUG_INFO "Use relative paths in debug info" OFF)
+set(LLVM_SOURCE_PREFIX "" CACHE STRING "Use prefix for sources in debug info")
+
+if(LLVM_USE_RELATIVE_PATHS_IN_DEBUG_INFO)
+  check_c_compiler_flag("-fdebug-prefix-map=foo=bar" SUPPORTS_FDEBUG_PREFIX_MAP)
+  if(LLVM_ENABLE_PROJECTS_USED)
+    get_filename_component(source_root "${LLVM_MAIN_SRC_DIR}/.." ABSOLUTE)
+  else()
+    set(source_root "${LLVM_MAIN_SRC_DIR}")
+  endif()
+  file(RELATIVE_PATH relative_root "${source_root}" "${CMAKE_BINARY_DIR}")
+  append_if(SUPPORTS_FDEBUG_PREFIX_MAP "-fdebug-prefix-map=${CMAKE_BINARY_DIR}=${relative_root}" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+  append_if(SUPPORTS_FDEBUG_PREFIX_MAP "-fdebug-prefix-map=${source_root}/=${LLVM_SOURCE_PREFIX}" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+  add_flag_if_supported("-no-canonical-prefixes" NO_CANONICAL_PREFIXES)
+endif()

cmake/modules/LLVMExternalProjectUtils.cmake

@@ -231,6 +231,8 @@ function(llvm_ExternalProject_Add name source_dir)
                -DLLVM_ENABLE_WERROR=${LLVM_ENABLE_WERROR}
                -DLLVM_HOST_TRIPLE=${LLVM_HOST_TRIPLE}
                -DLLVM_HAVE_LINK_VERSION_SCRIPT=${LLVM_HAVE_LINK_VERSION_SCRIPT}
+               -DLLVM_USE_RELATIVE_PATHS_IN_DEBUG_INFO=${LLVM_USE_RELATIVE_PATHS_IN_DEBUG_INFO}
+               -DLLVM_SOURCE_PREFIX=${LLVM_SOURCE_PREFIX}
                -DPACKAGE_VERSION=${PACKAGE_VERSION}
                -DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE}
                -DCMAKE_MAKE_PROGRAM=${CMAKE_MAKE_PROGRAM}

runtimes/CMakeLists.txt

@@ -375,6 +375,7 @@ else() # if this is included from LLVM's CMake
                              CMAKE_ARGS -DCOMPILER_RT_BUILD_BUILTINS=Off
                                         -DLLVM_INCLUDE_TESTS=${LLVM_INCLUDE_TESTS}
                                         -DLLVM_DEFAULT_TARGET_TRIPLE=${TARGET_TRIPLE}
+                                        -DLLVM_ENABLE_PROJECTS_USED=${LLVM_ENABLE_PROJECTS_USED}
                                         -DLLVM_ENABLE_PER_TARGET_RUNTIME_DIR=ON
                                         -DCMAKE_C_COMPILER_TARGET=${TARGET_TRIPLE}
                                         -DCMAKE_CXX_COMPILER_TARGET=${TARGET_TRIPLE}
@@ -464,6 +465,7 @@ else() # if this is included from LLVM's CMake
                              CMAKE_ARGS -DCOMPILER_RT_BUILD_BUILTINS=Off
                                         -DLLVM_INCLUDE_TESTS=${LLVM_INCLUDE_TESTS}
                                         -DLLVM_DEFAULT_TARGET_TRIPLE=${target}
+                                        -DLLVM_ENABLE_PROJECTS_USED=${LLVM_ENABLE_PROJECTS_USED}
                                         -DLLVM_ENABLE_PER_TARGET_RUNTIME_DIR=ON
                                         -DCMAKE_C_COMPILER_TARGET=${target}
                                         -DCMAKE_CXX_COMPILER_TARGET=${target}