We weren't replacing  PLACEHOLDER_EXPR in the following testcase, leading to a
crash in the gimplifier.  The fix seems to be to use replace_placeholders, the
question is where.  These three functions have it:
cp_gimplify_init_expr
store_init_value
build_new_1
But we call neither so I tried adding the call to build_over_call, right
after we create the MODIFY_EXPR with the NSDMI, and that seemed to work
out.

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

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

        PR c++/79796 - ICE with NSDMI and this pointer
        * call.c (build_over_call): Handle NSDMI with a 'this' by calling
        replace_placeholders.

        * g++.dg/cpp0x/nsdmi13.C: New test.

diff --git gcc/cp/call.c gcc/cp/call.c
index dc629b96..b821224 100644
--- gcc/cp/call.c
+++ gcc/cp/call.c
@@ -8047,6 +8047,9 @@ build_over_call (struct z_candidate *cand, int flags, 
tsubst_flags_t complain)
        {
          arg = cp_build_indirect_ref (arg, RO_NULL, complain);
          val = build2 (MODIFY_EXPR, TREE_TYPE (to), to, arg);
+         if (cxx_dialect >= cxx14)
+           /* Handle NSDMI that refer to the object being initialized.  */
+           replace_placeholders (arg, to);
        }
       else
        {
diff --git gcc/testsuite/g++.dg/cpp0x/nsdmi13.C 
gcc/testsuite/g++.dg/cpp0x/nsdmi13.C
index e69de29..2751da3 100644
--- gcc/testsuite/g++.dg/cpp0x/nsdmi13.C
+++ gcc/testsuite/g++.dg/cpp0x/nsdmi13.C
@@ -0,0 +1,13 @@
+// PR c++/79796
+// { dg-do compile { target c++11 } }
+
+struct A
+{
+  A* p = this;
+};
+
+void foo()
+{
+  A a;
+  a = A({});
+}

        Marek

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