C++ PATCH for c++/80095, ICE with this pointer in NSDMI

[Marek Polacek]

Here we have a reference initialization with NSDMI and *this.  We are crashing
because a PLACEHOLDER_EXPR crept into the gimplifier.

This happens since r218653 where set_up_extended_ref_temp was changed to
use split_nonconstant_init.  As a consequence, cp_gimplify_init_expr might
now be receiving 

  D.2051.p = (void *) &<PLACEHOLDER_EXPR struct A>

instead of 

  D.2051 = {.p = (void *) &<PLACEHOLDER_EXPR struct A>}

where the RHS was a CONSTRUCTOR.  It no longer is, so replace_placeholders is
not called anymore.  It occurred to me that we should use the same check as in
store_init_value (i.e. check that the object to be used in the substitution is
a class), but given what split_nonconstant_init might produce, handle
COMPONENT_REFs specially.

Bootstrapped/regtested on x86_64-linux, ok for trunk and 6?

2017-03-29  Marek Polacek  <pola...@redhat.com>

        PR c++/80095 - ICE with this pointer in NSDMI.
        * cp-gimplify.c (cp_gimplify_init_expr): Call replace_placeholders
        when TO is a class.

        * g++.dg/cpp1y/nsdmi-aggr8.C: New test.

diff --git gcc/cp/cp-gimplify.c gcc/cp/cp-gimplify.c
index 354ae1a..e530daf 100644
--- gcc/cp/cp-gimplify.c
+++ gcc/cp/cp-gimplify.c
@@ -496,7 +496,16 @@ cp_gimplify_init_expr (tree *expr_p)
            TREE_TYPE (from) = void_type_node;
        }
 
-      if (cxx_dialect >= cxx14 && TREE_CODE (sub) == CONSTRUCTOR)
+      /* split_nonconstant_init might've produced something like
+        D.2051.p = (void *) &<PLACEHOLDER_EXPR struct A>
+        in which case we want to substitute the placeholder with
+        D.2051.  */
+      tree op0 = to;
+      while (TREE_CODE (op0) == COMPONENT_REF)
+       op0 = TREE_OPERAND (op0, 0);
+      tree type = TREE_TYPE (op0);
+
+      if (cxx_dialect >= cxx14 && CLASS_TYPE_P (strip_array_types (type)))
        /* Handle aggregate NSDMI.  */
        replace_placeholders (sub, to);
 
diff --git gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr8.C 
gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr8.C
index e69de29..8c99ffb 100644
--- gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr8.C
+++ gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr8.C
@@ -0,0 +1,16 @@
+// PR c++/80095
+// { dg-do compile { target c++14 } }
+
+struct A
+{
+  void* p = this;
+};
+
+void
+foo ()
+{
+  const A& a = A{};
+  A&& a2 = A{};
+  const A& a3{};
+  A&& a4{};
+}

        Marek