[C++ PATCH] Fix ICE in adjust_temp_type (PR c++/87506)

[Jakub Jelinek]

Hi!

I admit this is just a shot in the dark, but I don't see why
one couldn't adjust a type of EMPTY_CLASS_EXPR to EMPTY_CLASS_EXPR
with a different variant of the same type.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

Or, should I drop that
  && TYPE_MAIN_VARIANT (type) == TYPE_MAIN_VARIANT (TREE_TYPE (temp))
part?  We don't really verify something similar for CONSTRUCTORs.

2018-11-16  Jakub Jelinek  <ja...@redhat.com>

        PR c++/87506
        * constexpr.c (adjust_temp_type): Handle EMPTY_CLASS_EXPR.

        * g++.dg/cpp0x/constexpr-87506.C: New test.

--- gcc/cp/constexpr.c.jj       2018-11-16 10:22:18.668258171 +0100
+++ gcc/cp/constexpr.c  2018-11-16 19:24:13.564095334 +0100
@@ -1281,6 +1281,9 @@ adjust_temp_type (tree type, tree temp)
   /* Avoid wrapping an aggregate value in a NOP_EXPR.  */
   if (TREE_CODE (temp) == CONSTRUCTOR)
     return build_constructor (type, CONSTRUCTOR_ELTS (temp));
+  if (TREE_CODE (temp) == EMPTY_CLASS_EXPR
+      && TYPE_MAIN_VARIANT (type) == TYPE_MAIN_VARIANT (TREE_TYPE (temp)))
+    return build0 (EMPTY_CLASS_EXPR, type);
   gcc_assert (scalarish_type_p (type));
   return cp_fold_convert (type, temp);
 }
--- gcc/testsuite/g++.dg/cpp0x/constexpr-87506.C.jj     2018-11-16 
19:32:28.854867665 +0100
+++ gcc/testsuite/g++.dg/cpp0x/constexpr-87506.C        2018-11-16 
19:32:04.705268812 +0100
@@ -0,0 +1,12 @@
+// PR c++/87506
+// { dg-do compile { target c++11 } }
+
+struct A {};
+struct B { constexpr B (const A) {} };
+struct C : B { using B::B; };
+
+void
+foo ()
+{
+  C c (A{});
+}

        Jakub