On 1/21/26 5:04 PM, Jakub Jelinek wrote:
Hi!
The move of the resolves_to_fixed_type_p call earlier in build_base_path
for constexpr virtual inheritance caused the following ICE.
What changed is that in an unevaluated context expr can be a CALL_EXPR with
class type and when it is not a ctor,
resolves_to_fixed_type_p -> fixed_type_or_null
ICEs on it:
if (CLASS_TYPE_P (TREE_TYPE (instance)))
{
/* We missed a build_cplus_new somewhere, likely due to tf_decltype
mishandling. */
gcc_checking_assert (false);
Now, the reason why that worked fine when resolves_to_fixed_type_p was
later in the function is that there was
/* This must happen before the call to save_expr. */
expr = cp_build_addr_expr (expr, complain);
in between the new and old calls to resolves_to_fixed_type_p, and for the
uneval case like that
cp_build_addr_expr -> unary_complex_lvalue -> build_cplus_new
wraps the CALL_EXPR into a TARGET_EXPR already, so the later call
was happy.
Now, none of fixed_type_p, virtual_access or nonnull values are ever
used in the build_base_path uneval path.
if (code == PLUS_EXPR
&& !want_pointer
&& !has_empty
&& !uneval
&& !virtual_access)
return build_simple_base_path (expr, binfo);
doesn't look at it,
if (!want_pointer)
{
rvalue = !lvalue_p (expr);
/* This must happen before the call to save_expr. */
expr = cp_build_addr_expr (expr, complain);
}
else
expr = mark_rvalue_use (expr);
neither, nothing soon after it either and very soon we
if (uneval)
{
expr = build_nop (ptr_target_type, expr);
goto indout;
}
and indout: doesn't use it either.
So, if only uneval expressions have problems with moving the
resolves_to_fixed_type_p call earlier, the following patch fixes
it by just not calling that function at all in the uneval case
because we will not care about the result anyway.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2026-01-21 Jakub Jelinek <[email protected]>
PR c++/123692
* class.cc (build_base_path): Don't call resolves_to_fixed_type_p if
!uneval.
Drop the ! here.
OK with that tweak.
* g++.dg/cpp0x/pr123692.C: New test.
--- gcc/cp/class.cc.jj 2026-01-17 14:35:11.439781766 +0100
+++ gcc/cp/class.cc 2026-01-20 13:36:45.018109244 +0100
@@ -347,7 +347,10 @@ build_base_path (enum tree_code code,
|| processing_template_decl
|| in_template_context);
- fixed_type_p = resolves_to_fixed_type_p (expr, &nonnull);
+ if (!uneval)
+ fixed_type_p = resolves_to_fixed_type_p (expr, &nonnull);
+ else
+ fixed_type_p = 0;
/* Do we need to look in the vtable for the real offset? */
virtual_access = (v_binfo && fixed_type_p <= 0);
--- gcc/testsuite/g++.dg/cpp0x/pr123692.C.jj 2026-01-20 13:42:39.763057828
+0100
+++ gcc/testsuite/g++.dg/cpp0x/pr123692.C 2026-01-20 13:42:18.298423983
+0100
@@ -0,0 +1,9 @@
+// PR c++/123692
+// { dg-do compile { target c++11 } }
+
+struct A { A (int); bool operator == (A); };
+struct B : A { using A::A; };
+B operator - (B, B);
+extern B c;
+extern A d;
+decltype (d == c - 1) x;
Jakub
