[gcc/devel/c++-modules] Simplify types of TYPE_VALUES in enumeral types

[Nathan Sidwell]

https://gcc.gnu.org/g:5c8344e7289969e1ee3103beaf9631b284f5ebc3

commit 5c8344e7289969e1ee3103beaf9631b284f5ebc3
Author: Jan Hubicka <jh@suse.cz>
Date:   Tue May 26 10:14:38 2020 +0200

    Simplify types of TYPE_VALUES in enumeral types
    
    streaming code assumes that INTEGER_CST never appears in non-trivial component.
    This is not true and we sometimes stream such components which sort of silently
    works but breaks our IL invariant about tree sharing.  This patch fixes one
    instance of this problem where ENUMERAL_TYPE lists all its valids in TYPE_VALUES
    that with some FEs (like Ada and C++) are having the enumeral type as a type
    while in other FEs (like C) are simple integer types.
    
    I convert them all to integers which also increases chance that they will be
    shared with other integer constants at stream time.
    
    gcc/
    
            * tree.c (free_lang_data_in_type): Simpify types of TYPE_VALUES in
            enumeral types.

Diff:
---
 gcc/tree.c | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/gcc/tree.c b/gcc/tree.c
index 54e471acc89..ea6692476e7 100644
--- a/gcc/tree.c
+++ b/gcc/tree.c
@@ -5556,6 +5556,7 @@ free_lang_data_in_type (tree type, class free_lang_data_d *fld)
     {
       if (TREE_CODE (type) == ENUMERAL_TYPE)
 	{
+	  tree it = NULL_TREE;
 	  ENUM_IS_OPAQUE (type) = 0;
 	  ENUM_IS_SCOPED (type) = 0;
 	  /* Type values are used only for C++ ODR checking.  Drop them
@@ -5568,8 +5569,27 @@ free_lang_data_in_type (tree type, class free_lang_data_d *fld)
 	  /* Simplify representation by recording only values rather
 	     than const decls.  */
 	    for (tree e = TYPE_VALUES (type); e; e = TREE_CHAIN (e))
-	      if (TREE_CODE (TREE_VALUE (e)) == CONST_DECL)
-		TREE_VALUE (e) = DECL_INITIAL (TREE_VALUE (e));
+	      {
+		if (TREE_CODE (TREE_VALUE (e)) == CONST_DECL)
+		  {
+		    TREE_VALUE (e) = DECL_INITIAL (TREE_VALUE (e));
+		    /* We can not stream values whose TREE_TYPE is type itself
+		       because that would create non-trivial CSS.  Canonicalize
+		       them to integer types.  */
+		  }
+		/* Some frontends use ENUMERAL_TYPE to represent the constants.
+		   This leads to nontrivial SCC components containing
+		   INTEGER_CST which is not good for streaming.  Convert them
+		   all to corresponding integer type.  */
+		if (TREE_CODE (TREE_TYPE (TREE_VALUE (e))) != INTEGER_TYPE)
+		  {
+		    if (!it)
+		      it = lang_hooks.types.type_for_size
+			       (TYPE_PRECISION (TREE_TYPE (TREE_VALUE (e))),
+				TYPE_UNSIGNED (TREE_TYPE (TREE_VALUE (e))));
+		    TREE_VALUE (e) = fold_convert (it, TREE_VALUE (e));
+		  }
+	       }
 	}
       free_lang_data_in_one_sizepos (&TYPE_MIN_VALUE (type));
       free_lang_data_in_one_sizepos (&TYPE_MAX_VALUE (type));