Remove __SHORT_FILE__ macro definition in CMake (#152344)

This per-file macro definition on the command line breaks caching of
modules. See discussion in #150677

Instead we use a constexpr function that processes the __FILE__ macro,
but prefer also the __FILE_NAME__ macro when available (clang/gcc) to spare
compile-time in the frontend.
If the constexpr function isn't const-evaluated, it'll be only evaluated when
printing the debug message.

Author: joker-eph

llvm/cmake/modules/LLVMProcessSources.cmake

@@ -58,21 +58,6 @@ function(llvm_process_sources OUT_VAR)
   set(sources ${ARG_UNPARSED_ARGUMENTS})
   llvm_check_source_file_list(${sources})
 
-  # Don't generate __SHORT_FILE__ on VS builds as it can prevent build parallelisation.
-  if(NOT CMAKE_GENERATOR MATCHES "Visual Studio")
-    foreach(fn ${sources})
-      get_filename_component(suf ${fn} EXT)
-      if("${suf}" STREQUAL ".cpp" OR "${suf}" STREQUAL ".c")
-        get_filename_component(short_name ${fn} NAME)
-        set_property(
-            SOURCE ${fn}
-            APPEND
-            PROPERTY COMPILE_DEFINITIONS __SHORT_FILE__="${short_name}")
-      endif()
-    endforeach()
-  endif()
-
-
   # This adds .td and .h files to the Visual Studio solution:
   add_td_sources(sources)
   find_all_header_files(hdrs "${ARG_ADDITIONAL_HEADER_DIRS}")

llvm/include/llvm/Support/DebugLog.h

@@ -56,6 +56,16 @@ namespace llvm {
   DEBUGLOG_WITH_STREAM_AND_TYPE(llvm::dbgs(), LEVEL, DEBUG_TYPE)
 #define LDBG_LOG_LEVEL_1() LDBG_LOG_LEVEL(1)
 
+// We want the filename without the full path. We are using the __FILE__ macro
+// and a constexpr function to strip the path prefix. We can avoid the frontend
+// repeated evaluation of __FILE__ by using the __FILE_NAME__ when defined
+// (gcc and clang do) which contains the file name already.
+#if defined(__FILE_NAME__)
+#define __LLVM_FILE_NAME__ __FILE_NAME__
+#else
+#define __LLVM_FILE_NAME__ ::llvm::impl::getShortFileName(__FILE__)
+#endif
+
 #define DEBUGLOG_WITH_STREAM_TYPE_FILE_AND_LINE(STREAM, LEVEL, TYPE, FILE,     \
                                                 LINE)                          \
   for (bool _c =                                                               \
@@ -69,17 +79,8 @@ namespace llvm {
 
 #define DEBUGLOG_WITH_STREAM_TYPE_AND_FILE(STREAM, LEVEL, TYPE, FILE)          \
   DEBUGLOG_WITH_STREAM_TYPE_FILE_AND_LINE(STREAM, LEVEL, TYPE, FILE, __LINE__)
-// When __SHORT_FILE__ is not defined, the File is the full path,
-// otherwise __SHORT_FILE__ is defined in CMake to provide the file name
-// without the path prefix.
-#if defined(__SHORT_FILE__)
 #define DEBUGLOG_WITH_STREAM_AND_TYPE(STREAM, LEVEL, TYPE)                     \
-  DEBUGLOG_WITH_STREAM_TYPE_AND_FILE(STREAM, LEVEL, TYPE, __SHORT_FILE__)
-#else
-#define DEBUGLOG_WITH_STREAM_AND_TYPE(STREAM, LEVEL, TYPE)                     \
-  DEBUGLOG_WITH_STREAM_TYPE_AND_FILE(STREAM, LEVEL, TYPE,                      \
-                                     ::llvm::impl::getShortFileName(__FILE__))
-#endif
+  DEBUGLOG_WITH_STREAM_TYPE_AND_FILE(STREAM, LEVEL, TYPE, __LLVM_FILE_NAME__)
 
 namespace impl {
 

llvm/unittests/Support/DebugLogTest.cpp

@@ -6,11 +6,6 @@
 //
 //===----------------------------------------------------------------------===//
 
-// This macro is defined in the LLVM build system, but we undefine it here
-// so that we test at least once in-tree the case where __SHORT_FILE__ is not
-// defined.
-#undef __SHORT_FILE__
-
 #include "llvm/Support/DebugLog.h"
 #include "llvm/ADT/Sequence.h"
 #include "llvm/Support/raw_ostream.h"