[CMake] Enable the use of -ffile-prefix-map

This handles not paths embedded in debug info, but also in sources.
Since the use of this flag is controlled by an option, rather than
replacing the new option, we add a new option.

Differential Revision: https://reviews.llvm.org/D76018

Author: petrhosek

llvm/cmake/modules/HandleLLVMOptions.cmake

@@ -1019,8 +1019,9 @@ if(macos_signposts_available)
   endif()
 endif()
 
+set(LLVM_SOURCE_PREFIX "" CACHE STRING "Use prefix for sources")
+
 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)
@@ -1034,3 +1035,18 @@ if(LLVM_USE_RELATIVE_PATHS_IN_DEBUG_INFO)
   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()
+
+option(LLVM_USE_RELATIVE_PATHS_IN_FILES "Use relative paths in sources and debug info" OFF)
+
+if(LLVM_USE_RELATIVE_PATHS_IN_FILES)
+  check_c_compiler_flag("-ffile-prefix-map=foo=bar" SUPPORTS_FFILE_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_FFILE_PREFIX_MAP "-ffile-prefix-map=${CMAKE_BINARY_DIR}=${relative_root}" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+  append_if(SUPPORTS_FFILE_PREFIX_MAP "-ffile-prefix-map=${source_root}/=${LLVM_SOURCE_PREFIX}" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+  add_flag_if_supported("-no-canonical-prefixes" NO_CANONICAL_PREFIXES)
+endif()

llvm/cmake/modules/LLVMExternalProjectUtils.cmake

@@ -239,6 +239,7 @@ function(llvm_ExternalProject_Add name source_dir)
                -DLLVM_HOST_TRIPLE=${LLVM_HOST_TRIPLE}
                -DLLVM_HAVE_LINK_VERSION_SCRIPT=${LLVM_HAVE_LINK_VERSION_SCRIPT}
                -DLLVM_USE_RELATIVE_PATHS_IN_DEBUG_INFO=${LLVM_USE_RELATIVE_PATHS_IN_DEBUG_INFO}
+               -DLLVM_USE_RELATIVE_PATHS_IN_FILES=${LLVM_USE_RELATIVE_PATHS_IN_FILES}
                -DLLVM_SOURCE_PREFIX=${LLVM_SOURCE_PREFIX}
                -DPACKAGE_VERSION=${PACKAGE_VERSION}
                -DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE}

llvm/docs/CMake.rst

@@ -631,6 +631,14 @@ LLVM-specific variables
   If enabled, the Z3 constraint solver is activated for the Clang static analyzer.
   A recent version of the z3 library needs to be available on the system.
 
+**LLVM_USE_RELATIVE_PATHS_IN_DEBUG_INFO**:BOOL
+  Rewrite absolute source paths in debug info to relative ones. The source prefix
+  can be adjusted via the LLVM_SOURCE_PREFIX variable.
+
+**LLVM_USE_RELATIVE_PATHS_IN_FILES**:BOOL
+  Rewrite absolute source paths in sources and debug info to relative ones. The
+  source prefix can be adjusted via the LLVM_SOURCE_PREFIX variable.
+
 CMake Caches
 ============