C++ PATCH for c++/88825 - ICE with bogus function return type deduction

[Marek Polacek]

In this (invalid) testcase the return type deduction failed so FUNCTYPE was
error_mark_node and can_do_nrvo_p crashed.  One way to fix this would be to
check error_operand_p as below.

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

2019-01-13  Marek Polacek  <pola...@redhat.com>

        PR c++/88825 - ICE with bogus function return type deduction.
        * typeck.c (can_do_nrvo_p): Check error_operand_p.

        * g++.dg/cpp1y/auto-fn55.C: New test.

diff --git gcc/cp/typeck.c gcc/cp/typeck.c
index 43d2899a3c4..3d3049cc3a0 100644
--- gcc/cp/typeck.c
+++ gcc/cp/typeck.c
@@ -9342,6 +9342,8 @@ is_std_move_p (tree fn)
 static bool
 can_do_nrvo_p (tree retval, tree functype)
 {
+  if (error_operand_p (functype))
+    return false;
   if (retval)
     STRIP_ANY_LOCATION_WRAPPER (retval);
   tree result = DECL_RESULT (current_function_decl);
diff --git gcc/testsuite/g++.dg/cpp1y/auto-fn55.C 
gcc/testsuite/g++.dg/cpp1y/auto-fn55.C
new file mode 100644
index 00000000000..aea2740e1f5
--- /dev/null
+++ gcc/testsuite/g++.dg/cpp1y/auto-fn55.C
@@ -0,0 +1,8 @@
+// PR c++/88825
+// { dg-do compile { target c++14 } }
+
+auto f () -> auto *
+{
+  int t = 0;
+  return t; // { dg-error "unable to deduce" }
+}