[gcc/devel/ranger] c++: Fix ICE with implicit operator== [PR94462]

[Aldy Hernandez]

https://gcc.gnu.org/g:467fc7c83abfe8fca8b75defac7c89f6c75bf9d7

commit 467fc7c83abfe8fca8b75defac7c89f6c75bf9d7
Author: Jason Merrill <jason@redhat.com>
Date:   Mon Apr 6 18:19:07 2020 -0400

    c++: Fix ICE with implicit operator== [PR94462]
    
    duplicate_decls assumed that any TREE_ARTIFICIAL function at namespace scope
    was a built-in function, but now in C++20 it's possible to have an
    implicitly declared hidden friend operator==.  We just need to move the
    assert into the if condition.
    
    gcc/cp/ChangeLog
    2020-04-06  Jason Merrill  <jason@redhat.com>
    
            PR c++/94462
            * decl.c (duplicate_decls): Fix handling of DECL_HIDDEN_FRIEND_P.

Diff:
---
 gcc/cp/ChangeLog                           |  5 +++++
 gcc/cp/decl.c                              |  5 +++--
 gcc/testsuite/g++.dg/cpp2a/spaceship-eq9.C | 17 +++++++++++++++++
 3 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index fc75879d14f..02fd9cff79d 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,8 @@
+2020-04-06  Jason Merrill  <jason@redhat.com>
+
+	PR c++/94462
+	* decl.c (duplicate_decls): Fix handling of DECL_HIDDEN_FRIEND_P.
+
 2020-04-04  Marek Polacek  <polacek@redhat.com>
 	    Jason Merrill  <jason@redhat.com>
 
diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index 69a238997b4..a127734af69 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -1451,9 +1451,10 @@ duplicate_decls (tree newdecl, tree olddecl, bool newdecl_is_friend)
 
   /* Check for redeclaration and other discrepancies.  */
   if (TREE_CODE (olddecl) == FUNCTION_DECL
-      && DECL_ARTIFICIAL (olddecl))
+      && DECL_ARTIFICIAL (olddecl)
+      /* A C++20 implicit friend operator== uses the normal path (94462).  */
+      && !DECL_HIDDEN_FRIEND_P (olddecl))
     {
-      gcc_assert (!DECL_HIDDEN_FRIEND_P (olddecl));
       if (TREE_CODE (newdecl) != FUNCTION_DECL)
 	{
 	  /* Avoid warnings redeclaring built-ins which have not been
diff --git a/gcc/testsuite/g++.dg/cpp2a/spaceship-eq9.C b/gcc/testsuite/g++.dg/cpp2a/spaceship-eq9.C
new file mode 100644
index 00000000000..4f5df226410
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/spaceship-eq9.C
@@ -0,0 +1,17 @@
+// PR c++/94462
+// { dg-do compile { target c++2a } }
+
+namespace std {
+  struct strong_ordering { };
+}
+
+namespace Synth {
+  struct B {
+    friend std::strong_ordering operator<=>(B, B) = default;
+  };
+
+  struct C {
+    friend bool operator==(C, C);
+  };
+}
+