dwarf2out: Emit DWARF 6 DW_AT_language_{name,version}

DWARF has voted in recently https://dwarfstd.org/issues/241209.1.html ,
which is basically just a guarantee that the DWARF 6 draft
DW_AT_language_{name,version} attribute codes and content of
https://dwarfstd.org/languages-v6.html can be used as an extension
in DWARF 5 and won't be changed.

So, this patch is an alternative to the
https://gcc.gnu.org/pipermail/gcc-patches/2024-November/669671.html
patch, which had the major problem that it required changing all the
DWARF consumers to be able to debug C17 or later or C++17 or later
sources.
This patch uses still DWARF 5 DW_LANG_C11 or DW_LANG_C_plus_plus_14,
the latest code in DWARF 5 proper, so all DWARF 5 capable consumers
should be able to deal with that, but additionally emits the
DWARF 6 attributes so that newer DWARF consumers can see it isn't
just C++14 but say C++23 or C11 but C23.  Consumers which don't know
those DWARF 6 attributes would just ignore them.  This is like any other
-gno-strict-dwarf extension, except that normally we emit say DWARF 5
codes where possible only after DWARF 5 is released, while in this case
there is a guarantee it can be used before DWARF 6 is released.

2025-01-08  Jakub Jelinek  <jakub@redhat.com>

include/
	* dwarf2.h (enum dwarf_source_language): Fix comment pasto.
	(enum dwarf_source_language_name): New type.
	* dwarf2.def (DW_AT_language_name, DW_AT_language_version): New
	DWARF 6 codes.
gcc/
	* dwarf2out.cc (break_out_comdat_types): Copy over
	DW_AT_language_{name,version} if present.
	(output_skeleton_debug_sections): Remove also
	DW_AT_language_{name,version}.
	(gen_compile_unit_die): For C17, C23, C2Y, C++17, C++20, C++23
	and C++26 emit for -gdwarf-5 -gno-strict-dwarf also
	DW_AT_language_{name,version} attributes.
gcc/testsuite/
	* g++.dg/debug/dwarf2/lang-cpp17.C: Add -gno-strict-dwarf to
	dg-options.  Check also for DW_AT_language_{name,version} values.
	* g++.dg/debug/dwarf2/lang-cpp20.C: Likewise.
	* g++.dg/debug/dwarf2/lang-cpp23.C: New test.

4 files changed, 82 insertions, 16 deletions

diff --git a/gcc/dwarf2out.cc b/gcc/dwarf2out.cc
index 1f6a6ce..8085b8d 100644
--- a/gcc/dwarf2out.cc
+++ b/gcc/dwarf2out.cc
@@ -8755,6 +8755,14 @@ break_out_comdat_types (dw_die_ref die)
         unit = new_die (DW_TAG_type_unit, NULL, NULL);
         add_AT_unsigned (unit, DW_AT_language,
                          get_AT_unsigned (comp_unit_die (), DW_AT_language));
+	if (unsigned lname = get_AT_unsigned (comp_unit_die (),
+					      DW_AT_language_name))
+	  {
+	    add_AT_unsigned (unit, DW_AT_language_name, lname);
+	    add_AT_unsigned (unit, DW_AT_language_version,
+			     get_AT_unsigned (comp_unit_die (),
+					      DW_AT_language_version));
+	  }
 
 	/* Add the new unit's type DIE into the comdat type list.  */
         type_node = ggc_cleared_alloc<comdat_type_node> ();
@@ -11404,6 +11412,8 @@ output_skeleton_debug_sections (dw_die_ref comp_unit,
   /* These attributes will be found in the full debug_info section.  */
   remove_AT (comp_unit, DW_AT_producer);
   remove_AT (comp_unit, DW_AT_language);
+  remove_AT (comp_unit, DW_AT_language_name);
+  remove_AT (comp_unit, DW_AT_language_version);
 
   switch_to_section (debug_skeleton_info_section);
   ASM_OUTPUT_LABEL (asm_out_file, debug_skeleton_info_section_label);
@@ -25318,7 +25328,7 @@ gen_compile_unit_die (const char *filename)
 {
   dw_die_ref die;
   const char *language_string = lang_hooks.name;
-  int language;
+  int language, lname, lversion;
 
   die = new_die (DW_TAG_compile_unit, NULL, NULL);
 
@@ -25366,6 +25376,8 @@ gen_compile_unit_die (const char *filename)
     }
 
   language = DW_LANG_C;
+  lname = 0;
+  lversion = 0;
   if (startswith (language_string, "GNU C")
       && ISDIGIT (language_string[5]))
     {
@@ -25376,11 +25388,28 @@ gen_compile_unit_die (const char *filename)
 	    language = DW_LANG_C99;
 
 	  if (dwarf_version >= 5 /* || !dwarf_strict */)
-	    if (strcmp (language_string, "GNU C11") == 0
-		|| strcmp (language_string, "GNU C17") == 0
-		|| strcmp (language_string, "GNU C23") == 0
-		|| strcmp (language_string, "GNU C2Y") == 0)
-	      language = DW_LANG_C11;
+	    {
+	      if (strcmp (language_string, "GNU C11") == 0)
+		language = DW_LANG_C11;
+	      else if (strcmp (language_string, "GNU C17") == 0)
+		{
+		  language = DW_LANG_C11;
+		  lname = DW_LNAME_C;
+		  lversion = 201710;
+		}
+	      else if (strcmp (language_string, "GNU C23") == 0)
+		{
+		  language = DW_LANG_C11;
+		  lname = DW_LNAME_C;
+		  lversion = 202311;
+		}
+	      else if (strcmp (language_string, "GNU C2Y") == 0)
+		{
+		  language = DW_LANG_C11;
+		  lname = DW_LNAME_C;
+		  lversion = 202500;
+		}
+	    }
 	}
     }
   else if (startswith (language_string, "GNU C++"))
@@ -25392,12 +25421,30 @@ gen_compile_unit_die (const char *filename)
 	    language = DW_LANG_C_plus_plus_11;
 	  else if (strcmp (language_string, "GNU C++14") == 0)
 	    language = DW_LANG_C_plus_plus_14;
-	  else if (strcmp (language_string, "GNU C++17") == 0
-		   || strcmp (language_string, "GNU C++20") == 0
-		   || strcmp (language_string, "GNU C++23") == 0
-		   || strcmp (language_string, "GNU C++26") == 0)
-	    /* For now.  */
-	    language = DW_LANG_C_plus_plus_14;
+	  else if (strcmp (language_string, "GNU C++17") == 0)
+	    {
+	      language = DW_LANG_C_plus_plus_14;
+	      lname = DW_LNAME_C_plus_plus;
+	      lversion = 201703;
+	    }
+	  else if (strcmp (language_string, "GNU C++20") == 0)
+	    {
+	      language = DW_LANG_C_plus_plus_14;
+	      lname = DW_LNAME_C_plus_plus;
+	      lversion = 202002;
+	    }
+	  else if (strcmp (language_string, "GNU C++23") == 0)
+	    {
+	      language = DW_LANG_C_plus_plus_14;
+	      lname = DW_LNAME_C_plus_plus;
+	      lversion = 202302;
+	    }
+	  else if (strcmp (language_string, "GNU C++26") == 0)
+	    {
+	      language = DW_LANG_C_plus_plus_14;
+	      lname = DW_LNAME_C_plus_plus;
+	      lversion = 202400;
+	    }
 	}
     }
   else if (strcmp (language_string, "GNU F77") == 0)
@@ -25441,6 +25488,11 @@ gen_compile_unit_die (const char *filename)
     language = DW_LANG_Ada83;
 
   add_AT_unsigned (die, DW_AT_language, language);
+  if (lname && dwarf_version >= 5 && !dwarf_strict)
+    {
+      add_AT_unsigned (die, DW_AT_language_name, lname);
+      add_AT_unsigned (die, DW_AT_language_version, lversion);
+    }
 
   switch (language)
     {
diff --git a/gcc/testsuite/g++.dg/debug/dwarf2/lang-cpp17.C b/gcc/testsuite/g++.dg/debug/dwarf2/lang-cpp17.C
index a1e3ccc..18f73ee 100644
--- a/gcc/testsuite/g++.dg/debug/dwarf2/lang-cpp17.C
+++ b/gcc/testsuite/g++.dg/debug/dwarf2/lang-cpp17.C
@@ -1,8 +1,10 @@
 // { dg-do compile }
-// { dg-options "-O -std=c++17 -gdwarf-5 -dA" }
+// { dg-options "-O -std=c++17 -gdwarf-5 -dA -gno-strict-dwarf" }
 // { dg-skip-if "AIX DWARF5" { powerpc-ibm-aix* } }
-// For -gdwarf-6 hopefully DW_LANG_C_plus_plus_17
 // DW_LANG_C_plus_plus_14 = 0x0021
+// DW_LNAME_C_plus_plus = 0x0004 201703
 // { dg-final { scan-assembler "0x21\[^\n\r]* DW_AT_language" } } */
+// { dg-final { scan-assembler "0x4\[^\n\r]* DW_AT_language_name" } } */
+// { dg-final { scan-assembler "0x313e7\[^\n\r]* DW_AT_language_version" } } */
 
 int version;
diff --git a/gcc/testsuite/g++.dg/debug/dwarf2/lang-cpp20.C b/gcc/testsuite/g++.dg/debug/dwarf2/lang-cpp20.C
index 62abd61..28eca15 100644
--- a/gcc/testsuite/g++.dg/debug/dwarf2/lang-cpp20.C
+++ b/gcc/testsuite/g++.dg/debug/dwarf2/lang-cpp20.C
@@ -1,8 +1,10 @@
 // { dg-do compile }
-// { dg-options "-O -std=c++20 -gdwarf-5 -dA" }
+// { dg-options "-O -std=c++20 -gdwarf-5 -dA -gno-strict-dwarf" }
 // { dg-skip-if "AIX DWARF5" { powerpc-ibm-aix* } }
-// For -gdwarf-6 hopefully DW_LANG_C_plus_plus_20
 // DW_LANG_C_plus_plus_14 = 0x0021
+// DW_LNAME_C_plus_plus = 0x0004 202002
 // { dg-final { scan-assembler "0x21\[^\n\r]* DW_AT_language" } } */
+// { dg-final { scan-assembler "0x4\[^\n\r]* DW_AT_language_name" } } */
+// { dg-final { scan-assembler "0x31512\[^\n\r]* DW_AT_language_version" } } */
 
 int version;
diff --git a/gcc/testsuite/g++.dg/debug/dwarf2/lang-cpp23.C b/gcc/testsuite/g++.dg/debug/dwarf2/lang-cpp23.C
new file mode 100644
index 0000000..8bcc8f2
--- /dev/null
+++ b/gcc/testsuite/g++.dg/debug/dwarf2/lang-cpp23.C
@@ -0,0 +1,10 @@
+// { dg-do compile }
+// { dg-options "-O -std=c++23 -gdwarf-5 -dA -gno-strict-dwarf" }
+// { dg-skip-if "AIX DWARF5" { powerpc-ibm-aix* } }
+// DW_LANG_C_plus_plus_14 = 0x0021
+// DW_LNAME_C_plus_plus = 0x0004 202302
+// { dg-final { scan-assembler "0x21\[^\n\r]* DW_AT_language" } } */
+// { dg-final { scan-assembler "0x4\[^\n\r]* DW_AT_language_name" } } */
+// { dg-final { scan-assembler "0x3163e\[^\n\r]* DW_AT_language_version" } } */
+
+int version;