[PATCH] c++: ICE with temporary of class type in array DMI [PR109966]

[Marek Polacek <polacek@redhat.com>]

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk/13?

-- >8 --
This ICE started with the fairly complicated r13-765.  We crash in
gimplify_var_or_parm_decl because a stray VAR_DECL leaked there.
The problem is ultimately that potential_prvalue_result_of wasn't
correctly handling arrays and replace_placeholders_for_class_temp_r
replaced a PLACEHOLDER_EXPR in a TARGET_EXPR which is used in the
context of copy elision.  If I have

  M m[2] = { M{""}, M{""} };

then we don't invoke the M(const M&) copy-ctor.  I think the fix is
to detect such a case in potential_prvalue_result_of.

	PR c++/109966

gcc/cp/ChangeLog:

	* typeck2.cc (potential_prvalue_result_of): Add walk_subtrees
	parameter.  Handle initializing an array from a
	brace-enclosed-initializer.
	(replace_placeholders_for_class_temp_r): Pass walk_subtrees down to
	potential_prvalue_result_of.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp1y/nsdmi-aggr20.C: New test.
	* g++.dg/cpp1y/nsdmi-aggr21.C: New test.
---
 gcc/cp/typeck2.cc                         | 27 ++++++++---
 gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr20.C | 17 +++++++
 gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr21.C | 59 +++++++++++++++++++++++
 3 files changed, 96 insertions(+), 7 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr20.C
 create mode 100644 gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr21.C

diff --git a/gcc/cp/typeck2.cc b/gcc/cp/typeck2.cc
index 31198b2f9f5..8b99ce78e9a 100644
--- a/gcc/cp/typeck2.cc
+++ b/gcc/cp/typeck2.cc
@@ -1406,46 +1406,59 @@ digest_init_flags (tree type, tree init, int flags, tsubst_flags_t complain)
      A a = (A{});	      // initializer
      A a = (1, A{});	      // initializer
      A a = true ? A{} : A{};  // initializer
+     A arr[1] = { A{} };      // initializer
      auto x = A{}.x;	      // temporary materialization
      auto x = foo(A{});	      // temporary materialization
 
    FULL_EXPR is the whole expression, SUBOB is its TARGET_EXPR subobject.  */
 
 static bool
-potential_prvalue_result_of (tree subob, tree full_expr)
+potential_prvalue_result_of (tree subob, tree full_expr, int *walk_subtrees)
 {
+#define RECUR(t) potential_prvalue_result_of (subob, t, walk_subtrees)
   if (subob == full_expr)
     return true;
   else if (TREE_CODE (full_expr) == TARGET_EXPR)
     {
       tree init = TARGET_EXPR_INITIAL (full_expr);
       if (TREE_CODE (init) == COND_EXPR)
-	return (potential_prvalue_result_of (subob, TREE_OPERAND (init, 1))
-		|| potential_prvalue_result_of (subob, TREE_OPERAND (init, 2)));
+	return (RECUR (TREE_OPERAND (init, 1))
+		|| RECUR (TREE_OPERAND (init, 2)));
       else if (TREE_CODE (init) == COMPOUND_EXPR)
-	return potential_prvalue_result_of (subob, TREE_OPERAND (init, 1));
+	return RECUR (TREE_OPERAND (init, 1));
       /* ??? I don't know if this can be hit.  */
       else if (TREE_CODE (init) == PAREN_EXPR)
 	{
 	  gcc_checking_assert (false);
-	  return potential_prvalue_result_of (subob, TREE_OPERAND (init, 0));
+	  return RECUR (TREE_OPERAND (init, 0));
 	}
     }
+  /* The array case listed above.  */
+  else if (TREE_CODE (full_expr) == CONSTRUCTOR
+	   && TREE_CODE (TREE_TYPE (full_expr)) == ARRAY_TYPE)
+    for (constructor_elt &e: CONSTRUCTOR_ELTS (full_expr))
+      if (e.value == subob)
+	{
+	  *walk_subtrees = 0;
+	  return true;
+	}
+
   return false;
+#undef RECUR
 }
 
 /* Callback to replace PLACEHOLDER_EXPRs in a TARGET_EXPR (which isn't used
    in the context of guaranteed copy elision).  */
 
 static tree
-replace_placeholders_for_class_temp_r (tree *tp, int *, void *data)
+replace_placeholders_for_class_temp_r (tree *tp, int *walk_subtrees, void *data)
 {
   tree t = *tp;
   tree full_expr = *static_cast<tree *>(data);
 
   /* We're looking for a TARGET_EXPR nested in the whole expression.  */
   if (TREE_CODE (t) == TARGET_EXPR
-      && !potential_prvalue_result_of (t, full_expr))
+      && !potential_prvalue_result_of (t, full_expr, walk_subtrees))
     {
       tree init = TARGET_EXPR_INITIAL (t);
       while (TREE_CODE (init) == COMPOUND_EXPR)
diff --git a/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr20.C b/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr20.C
new file mode 100644
index 00000000000..4796d861e83
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr20.C
@@ -0,0 +1,17 @@
+// PR c++/109966
+// { dg-do compile { target c++14 } }
+
+#define SA(X) static_assert ((X),#X)
+
+struct A {
+  int a;
+  int b = a;
+};
+
+struct B {
+  int x = 0;
+  int y[1]{A{x}.b};
+};
+
+constexpr B b = { };
+SA(b.y[0] == 0);
diff --git a/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr21.C b/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr21.C
new file mode 100644
index 00000000000..efec45bc1a8
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr21.C
@@ -0,0 +1,59 @@
+// PR c++/109966
+// { dg-do compile { target c++14 } }
+
+struct k {
+  k(const char *);
+};
+struct M {
+  k name;
+  int j = 42;
+  int i = j;
+};
+
+M m = M{""};
+
+struct S {
+  M arr1[1]{M{""}};
+  M a1[1] = { (M{""}) };
+  M a2[1] = { (true, M{""}) };
+  M a3[1] = { true ? M{""} : M{""} };
+  M arr2[2]{M{""}, M{""}};
+  M arr3[3]{M{""}, M{""}, M{""}};
+
+  M arr1e[1] = {M{""}};
+  M arr2e[2] = {M{""}, M{""}};
+  M arr3e[3] = {M{""}, M{""}, M{""}};
+
+  M arr1l[1] = { m };
+  M arr2l[2] = { m, m };
+  M arr3l[3] = { m, m, m };
+
+  M m1 = M{""};
+  M m2 = m;
+  M m3{M{""}};
+  M m4 = {M{""}};
+} o;
+
+struct N {
+  N(M);
+};
+
+struct Z {
+  N arr1[1]{ M{""} };
+  N arr2[2]{ M{""}, M{""} };
+  N arr1e[1] = { M{""} };
+  N arr2e[2] = { M{""}, M{""} };
+} z;
+
+struct Y {
+  k name;
+  int j = 42;
+  int i = j;
+  operator M();
+};
+
+struct W {
+  M arr1[1]{ Y{""} };
+  M arr2[2]{ Y{""}, Y{""} };
+  M arr3[3]{ Y{""}, Y{""}, Y{""} };
+} w;

base-commit: 0c179654c3170749f3fb3232f2442fcbc99bffbb
-- 
2.44.0