[PATCH] Emit DW_AT_const_expr for constexpr variables (take 2)

[Jakub Jelinek]

On Fri, Oct 14, 2016 at 07:31:16PM +0200, Jakub Jelinek wrote:
> This relies on the previous langhook patch (which greatly simplifies it).
> 
> I'm only handling variables for now, DW_AT_const_expr is just weird on
> functions/methods, it is supposed to appear only on
> DW_TAG_inlined_subroutine?
> 
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

This doesn't apply any longer, because Richard removed the origin_die
variable this and following patch need.

Here is an updated version that also reverts part of that change,
bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2016-10-20  Jakub Jelinek  <ja...@redhat.com>

        * dwarf2out.c (gen_variable_die): Emit DW_AT_const_expr attribute
        if needed.  Re-add origin_die variable and its initialization.
cp/
        * cp-objcp-common.c (cp_decl_dwarf_attribute): Handle
        DW_AT_const_expr.
testsuite/
        * g++.dg/debug/dwarf2/constexpr-var-1.C: New test.

--- gcc/dwarf2out.c.jj  2016-10-14 14:37:15.000000000 +0200
+++ gcc/dwarf2out.c     2016-10-14 15:22:57.878078634 +0200
@@ -22247,6 +22247,7 @@ gen_variable_die (tree decl, tree origin
   tree ultimate_origin;
   dw_die_ref var_die;
   dw_die_ref old_die = decl ? lookup_decl_die (decl) : NULL;
+  dw_die_ref origin_die = NULL;
   bool declaration = (DECL_EXTERNAL (decl_or_origin)
                      || class_or_namespace_scope_p (context_die));
   bool specialization_p = false;
@@ -22413,7 +22414,7 @@ gen_variable_die (tree decl, tree origin
   var_die = new_die (tag, context_die, decl);
 
   if (origin != NULL)
-    add_abstract_origin_attribute (var_die, origin);
+    origin_die = add_abstract_origin_attribute (var_die, origin);
 
   /* Loop unrolling can create multiple blocks that refer to the same
      static variable, so we must test for the DW_AT_declaration flag.
@@ -21513,6 +21513,14 @@ gen_variable_die (tree decl, tree origin
     }
   else
     tree_add_const_value_attribute_for_decl (var_die, decl_or_origin);
+
+  if ((dwarf_version >= 4 || !dwarf_strict)
+      && lang_hooks.decls.decl_dwarf_attribute (decl_or_origin,
+                                               DW_AT_const_expr) == 1
+      && !get_AT (var_die, DW_AT_const_expr)
+      && (origin_die == NULL || get_AT (origin_die, DW_AT_const_expr) == NULL)
+      && !specialization_p)
+    add_AT_flag (var_die, DW_AT_const_expr, 1);
 }
 
 /* Generate a DIE to represent a named constant.  */
--- gcc/cp/cp-objcp-common.c.jj 2016-10-14 14:27:56.000000000 +0200
+++ gcc/cp/cp-objcp-common.c    2016-10-14 15:01:27.770495885 +0200
@@ -168,6 +168,11 @@ cp_decl_dwarf_attribute (const_tree decl
        }
       break;
 
+    case DW_AT_const_expr:
+      if (VAR_OR_FUNCTION_DECL_P (decl) && DECL_DECLARED_CONSTEXPR_P (decl))
+       return 1;
+      break;
+
     default:
       break;
     }
--- gcc/testsuite/g++.dg/debug/dwarf2/constexpr-var-1.C.jj      2016-10-14 
15:32:23.323882991 +0200
+++ gcc/testsuite/g++.dg/debug/dwarf2/constexpr-var-1.C 2016-10-14 
15:31:56.000000000 +0200
@@ -0,0 +1,9 @@
+// { dg-do compile }
+// { dg-options "-O -std=c++11 -g -dA -gno-strict-dwarf" }
+// { dg-final { scan-assembler-times " DW_AT_const_expr" 2 } }
+
+constexpr int a = 5;
+struct S
+{
+  static constexpr int b = 6;
+} s;


        Jakub