[gcc r13-575] c: use CONST_DECL for enumerators in TYPE_VALUES

[gcc r13-575] c: use CONST_DECL for enumerators in TYPE_VALUES

[Marek Polacek]

https://gcc.gnu.org/g:2c05a2d1a8e4697ea95d65c5da601aeae327e7a7

commit r13-575-g2c05a2d1a8e4697ea95d65c5da601aeae327e7a7
Author: Marek Polacek <polacek@redhat.com>
Date:   Tue May 17 13:41:56 2022 -0400

    c: use CONST_DECL for enumerators in TYPE_VALUES
    
    The C and C++ FEs differ in TYPE_VALUES for an enum type: an entry in
    the list in the C++ FE has a CONST_DECL in the TREE_VALUE, but the C FE
    has only the numerical value of the CONST_DECL there.  This has caused
    me some trouble in my PR105497 patch.  Using a CONST_DECL is preferable
    because a CONST_DECL can track more information (e.g., attributes), and
    you can always get the value simply by looking at its DECL_INITIAL.
    
    This turned out to be a trivial change.  One place in godump.cc had to be
    adjusted.  I'm not changing the CONST_DECL check in c_do_switch_warnings
    because I'll be changing it soon in my next patch.  I didn't see any other
    checks that this patch makes redundant.
    
    gcc/c/ChangeLog:
    
            * c-decl.cc (finish_enum): Store the CONST_DECL into TREE_VALUE, not
            its value.
    
    gcc/ChangeLog:
    
            * godump.cc (go_output_typedef): Use the DECL_INITIAL of the TREE_VALUE.

Diff:
---
 gcc/c/c-decl.cc | 4 +++-
 gcc/godump.cc   | 9 +++++----
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/gcc/c/c-decl.cc b/gcc/c/c-decl.cc
index e49879ab286..83655548fc4 100644
--- a/gcc/c/c-decl.cc
+++ b/gcc/c/c-decl.cc
@@ -9253,7 +9253,9 @@ finish_enum (tree enumtype, tree values, tree attributes)
 
 	  DECL_INITIAL (enu) = ini;
 	  TREE_PURPOSE (pair) = DECL_NAME (enu);
-	  TREE_VALUE (pair) = ini;
+	  /* To match the C++ FE, store the CONST_DECL rather than just its
+	     value.  */
+	  TREE_VALUE (pair) = enu;
 	}
 
       TYPE_VALUES (enumtype) = values;
diff --git a/gcc/godump.cc b/gcc/godump.cc
index 2ae0bcc9672..c0f52bbd0f2 100644
--- a/gcc/godump.cc
+++ b/gcc/godump.cc
@@ -1114,6 +1114,7 @@ go_output_typedef (class godump_container *container, tree decl)
 	  struct macro_hash_value *mhval;
 	  void **slot;
 	  char buf[WIDE_INT_PRINT_BUFFER_SIZE];
+	  tree value = DECL_INITIAL (TREE_VALUE (element));
 
 	  name = IDENTIFIER_POINTER (TREE_PURPOSE (element));
 
@@ -1127,12 +1128,12 @@ go_output_typedef (class godump_container *container, tree decl)
 	  if (*slot != NULL)
 	    macro_hash_del (*slot);
 
-	  if (tree_fits_shwi_p (TREE_VALUE (element)))
+	  if (tree_fits_shwi_p (value))
 	    snprintf (buf, sizeof buf, HOST_WIDE_INT_PRINT_DEC,
-		     tree_to_shwi (TREE_VALUE (element)));
-	  else if (tree_fits_uhwi_p (TREE_VALUE (element)))
+		     tree_to_shwi (value));
+	  else if (tree_fits_uhwi_p (value))
 	    snprintf (buf, sizeof buf, HOST_WIDE_INT_PRINT_UNSIGNED,
-		      tree_to_uhwi (TREE_VALUE (element)));
+		      tree_to_uhwi (value));
 	  else
 	    print_hex (wi::to_wide (element), buf);