[C++ Patch] PR 70621 ("[6/7/8 Regression] ICE on invalid code at -O1 and above on x86_64-linux-gnu in record_reference, at cgraphbuild.c:64")

[Paolo Carlini]

Hi,

in this error recovery regression, we ICE only when optimizing, while 
building the cgraph. Avoiding the reported problem seems easy, just 
check the return value of duplicate_decls in start_decl and immediately 
return back error_mark_node. However, while working on the issue, I 
noticed something slightly more interesting, IMO: we have, after the 
relevant duplicate_decls call:

-              if (decl_spec_seq_has_spec_p (declspecs, ds_constexpr)
-                  && !DECL_DECLARED_CONSTEXPR_P (field))
-                error ("%qD declared %<constexpr%> outside its class", 
field);

which I propose to remove. In fact - something I didn't really know - 
for well formed user code, duplicate_decls, near the end, does some 
memcpys which mean that its second argument (would be 'field' in the 
start_decl section we are looking at)  is adjusted to have a 
DECL_DECLARED_CONSTEXPR_P consistent with its first argument. That's of 
course because we want to accept snippets like:

struct A
{
  static const int x;
};

constexpr int A::x = 0;

In turn that means the error above is issued only when something went 
wrong in duplicate_decls in the first place. Thus the above error seems 
at least verbose. However, here in start_decl we are only handling VAR_P 
(decl), thus I don't think the message above even makes sense and could 
be misleading, given snippets like the above. Therefore, I propose to 
remove the diagnostic entirely, which overall also simplifies a patch 
dealing with c++/70621. The below passes testing as-is on x86_64-linux.

Thanks, Paolo.

////////////////////////

/cp
2017-29-08  Paolo Carlini  <paolo.carl...@oracle.com>

        PR c++/70621
        * decl.c (start_decl): Early return error_mark_node if duplicate_decls
        returns it; avoid misleading error message.

/testsuite
2017-29-08  Paolo Carlini  <paolo.carl...@oracle.com>

        PR c++/70621
        * g++.dg/torture/pr70621.C: New.
Index: cp/decl.c
===================================================================
--- cp/decl.c   (revision 251375)
+++ cp/decl.c   (working copy)
@@ -5023,11 +5023,12 @@ start_decl (const cp_declarator *declarator,
                 about this situation, and so we check here.  */
              if (initialized && DECL_INITIALIZED_IN_CLASS_P (field))
                error ("duplicate initialization of %qD", decl);
-             if (duplicate_decls (decl, field, /*newdecl_is_friend=*/false))
+             field = duplicate_decls (decl, field,
+                                      /*newdecl_is_friend=*/false);
+             if (field == error_mark_node)
+               return error_mark_node;
+             else if (field)
                decl = field;
-              if (decl_spec_seq_has_spec_p (declspecs, ds_constexpr)
-                  && !DECL_DECLARED_CONSTEXPR_P (field))
-                error ("%qD declared %<constexpr%> outside its class", field);
            }
        }
       else
Index: testsuite/g++.dg/torture/pr70621.C
===================================================================
--- testsuite/g++.dg/torture/pr70621.C  (revision 0)
+++ testsuite/g++.dg/torture/pr70621.C  (working copy)
@@ -0,0 +1,13 @@
+float foo();
+
+struct A
+{
+  static float x;  // { dg-message "previous declaration" }
+};
+
+double A::x = foo();  // { dg-error "conflicting declaration" }
+
+void bar()
+{
+  A::x = 0;
+}