https://gcc.gnu.org/g:1788588589a534dd9b732f1ddec10aefd5d689db

commit r15-10577-g1788588589a534dd9b732f1ddec10aefd5d689db
Author: Jakub Jelinek <[email protected]>
Date:   Thu Nov 20 08:19:32 2025 +0100

    c++: Fix error recovery ICE in tsubst_baselink [PR120876]
    
    The following testcase ICEs since r12-6080.  The problem is that
    lookup_fnfields can return NULL_TREE on failure, but the maybe_incomplete
    handling was added before the if (!baselink) handling and assumes that
    baselink is non-NULL (and BASELINK).
    
    The following patch reorders the if (maybe_incomplete) handling with
    if (!baselink).
    
    2025-11-20  Jakub Jelinek  <[email protected]>
    
            PR c++/120876
            * pt.cc (tsubst_baselink): Move maybe_incomplete handling after
            !baselink handling.
    
            * g++.dg/parse/crash81.C: New test.
    
    (cherry picked from commit 6bace0ed49aea613ccd6c4f3c21a9ef0473fe62b)

Diff:
---
 gcc/cp/pt.cc                         | 18 +++++++++---------
 gcc/testsuite/g++.dg/parse/crash81.C | 14 ++++++++++++++
 2 files changed, 23 insertions(+), 9 deletions(-)

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index a245b6ef7490..79195d5b78d8 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -17500,6 +17500,15 @@ tsubst_baselink (tree baselink, tree object_type,
       bool maybe_incomplete = BASELINK_FUNCTIONS_MAYBE_INCOMPLETE_P (baselink);
       baselink = lookup_fnfields (qualifying_scope, name, /*protect=*/1,
                                  complain);
+      if (!baselink)
+       {
+         if ((complain & tf_error)
+             && constructor_name_p (name, qualifying_scope))
+           error ("cannot call constructor %<%T::%D%> directly",
+                  qualifying_scope, name);
+         return error_mark_node;
+       }
+
       if (maybe_incomplete)
        {
          /* Filter out from the new lookup set those functions which didn't
@@ -17513,15 +17522,6 @@ tsubst_baselink (tree baselink, tree object_type,
          BASELINK_FUNCTIONS_MAYBE_INCOMPLETE_P (baselink) = true;
        }
 
-      if (!baselink)
-       {
-         if ((complain & tf_error)
-             && constructor_name_p (name, qualifying_scope))
-           error ("cannot call constructor %<%T::%D%> directly",
-                  qualifying_scope, name);
-         return error_mark_node;
-       }
-
       fns = BASELINK_FUNCTIONS (baselink);
     }
   else
diff --git a/gcc/testsuite/g++.dg/parse/crash81.C 
b/gcc/testsuite/g++.dg/parse/crash81.C
new file mode 100644
index 000000000000..632ab042810a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/parse/crash81.C
@@ -0,0 +1,14 @@
+// PR c++/120876
+// { dg-do compile { target c++11 } }
+
+template <typename T>
+struct S {
+  static bool foo (decltype (bar (T {})));     // { dg-error "'bar' was not 
declared in this scope; did you mean 'baz'\\\?" }
+  static constexpr bool s = foo (0);
+};
+
+void
+baz ()
+{
+  S <int>::s;
+}

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