[C++ PATCH] Fix PLACEHOLDER_EXPR handling (PR c++/79937, PR c++/82410)

Jakub Jelinek jakub@redhat.com
Fri Mar 16 01:06:00 GMT 2018


On Thu, Mar 15, 2018 at 03:33:12PM -0400, Jason Merrill wrote:
> Folding away the INDIRECT_REF is fine.  It's the TARGET_EXPR handling
> that is wrong.

Ah, ok.

> > types of TARGET_EXPR, or ask some langhook whether it is ok to do so
> > (say not ok if find_placeholders (t))?  Or contains_placeholder_p?
> > Though the last one could also affect Ada and could return true even if
> > the PLACEHOLDER_EXPRs are for some nested TARGET_EXPR in it.
> 
> The existing test for whether to collapse a TARGET_EXPR is
> 
>             if (init
>                 && !VOID_TYPE_P (TREE_TYPE (init)))
> 
> so we need this test to fail somehow when the constructor contains
> placeholders, either by adding an additional test (like the ones you
> mention) or by making the initialization void in a way that other
> gimplification knows how to handle.

So what about this?  It uses an unused bit on TARGET_EXPRs rather than
a langhook, but if you prefer a langhook, I can add it.

Tested so far just with
make check-c++-all RUNTESTFLAGS="dg.exp='pr79937* pr82410.C nsdmi*'"

2018-03-15  Jakub Jelinek  <jakub@redhat.com>

	PR c++/79937
	PR c++/82410
	* tree.h (TARGET_EXPR_NO_ELIDE): Define.
	* gimplify.c (gimplify_arg, gimplify_modify_expr_rhs): Don't elide
	TARGET_EXPRs with TARGET_EXPR_NO_ELIDE flag set.

	* cp-tree.h (CONSTRUCTOR_PLACEHOLDER_BOUNDARY): Define.
	(find_placeholder): Declare.
	* tree.c (struct replace_placeholders_t): Add exp member.
	(replace_placeholders_r): Don't walk into ctors with
	CONSTRUCTOR_PLACEHOLDER_BOUNDARY flag set, unless they are equal to
	d->exp.
	(replace_placeholders): Initialize data.exp.
	(find_placeholders_r, find_placeholders): New functions.
	* typeck2.c (process_init_constructor_record,
	process_init_constructor_union): Set CONSTRUCTOR_PLACEHOLDER_BOUNDARY
	if adding NSDMI on which find_placeholder returns true.
	* call.c (build_over_call): Don't call replace_placeholders here.
	* cp-gimplify.c (cp_genericize_r): Set TARGET_EXPR_NO_ELIDE on
	TARGET_EXPRs with CONSTRUCTOR_PLACEHOLDER_BOUNDARY set on
	TARGET_EXPR_INITIAL.
	(cp_fold): Copy over CONSTRUCTOR_PLACEHOLDER_BOUNDARY bit to new
	ctor.

	* g++.dg/cpp1y/pr79937-1.C: New test.
	* g++.dg/cpp1y/pr79937-2.C: New test.
	* g++.dg/cpp1y/pr79937-3.C: New test.
	* g++.dg/cpp1y/pr79937-4.C: New test.
	* g++.dg/cpp1y/pr82410.C: New test.

--- gcc/tree.h.jj	2018-02-22 12:37:02.566387732 +0100
+++ gcc/tree.h	2018-03-15 20:42:57.968858551 +0100
@@ -1197,6 +1197,8 @@ extern tree maybe_wrap_with_location (tr
 #define TARGET_EXPR_SLOT(NODE) TREE_OPERAND_CHECK_CODE (NODE, TARGET_EXPR, 0)
 #define TARGET_EXPR_INITIAL(NODE) TREE_OPERAND_CHECK_CODE (NODE, TARGET_EXPR, 1)
 #define TARGET_EXPR_CLEANUP(NODE) TREE_OPERAND_CHECK_CODE (NODE, TARGET_EXPR, 2)
+/* Don't elide the initialization of TARGET_EXPR_SLOT for this TARGET_EXPR.  */
+#define TARGET_EXPR_NO_ELIDE(NODE) (TARGET_EXPR_CHECK (NODE)->base.private_flag)
 
 /* DECL_EXPR accessor. This gives access to the DECL associated with
    the given declaration statement.  */
--- gcc/gimplify.c.jj	2018-01-18 21:28:49.743301440 +0100
+++ gcc/gimplify.c	2018-03-15 21:06:15.290828320 +0100
@@ -3155,7 +3155,8 @@ gimplify_arg (tree *arg_p, gimple_seq *p
     {
       test = is_gimple_lvalue, fb = fb_either;
       /* Also strip a TARGET_EXPR that would force an extra copy.  */
-      if (TREE_CODE (*arg_p) == TARGET_EXPR)
+      if (TREE_CODE (*arg_p) == TARGET_EXPR
+	  && !TARGET_EXPR_NO_ELIDE (*arg_p))
 	{
 	  tree init = TARGET_EXPR_INITIAL (*arg_p);
 	  if (init
@@ -5211,6 +5212,7 @@ gimplify_modify_expr_rhs (tree *expr_p,
 	    tree init = TARGET_EXPR_INITIAL (*from_p);
 
 	    if (init
+		&& !TARGET_EXPR_NO_ELIDE (*from_p)
 		&& !VOID_TYPE_P (TREE_TYPE (init)))
 	      {
 		*from_p = init;
--- gcc/cp/cp-tree.h.jj	2018-03-15 18:44:21.646300907 +0100
+++ gcc/cp/cp-tree.h	2018-03-15 20:40:49.280818226 +0100
@@ -425,6 +425,7 @@ extern GTY(()) tree cp_global_trees[CPTI
       DECL_VTABLE_OR_VTT_P (in VAR_DECL)
       FUNCTION_RVALUE_QUALIFIED (in FUNCTION_TYPE, METHOD_TYPE)
       CALL_EXPR_REVERSE_ARGS (in CALL_EXPR, AGGR_INIT_EXPR)
+      CONSTRUCTOR_PLACEHOLDER_BOUNDARY (in CONSTRUCTOR)
    6: IDENTIFIER_REPO_CHOSEN (in IDENTIFIER_NODE)
       DECL_CONSTRUCTION_VTABLE_P (in VAR_DECL)
       TYPE_MARKED_P (in _TYPE)
@@ -4144,6 +4145,12 @@ more_aggr_init_expr_args_p (const aggr_i
 #define CONSTRUCTOR_C99_COMPOUND_LITERAL(NODE) \
   (TREE_LANG_FLAG_3 (CONSTRUCTOR_CHECK (NODE)))
 
+/* True if this CONSTRUCTOR contains PLACEHOLDER_EXPRs referencing the
+   CONSTRUCTOR's type not nested inside another CONSTRUCTOR marked with
+   CONSTRUCTOR_PLACEHOLDER_BOUNDARY.  */
+#define CONSTRUCTOR_PLACEHOLDER_BOUNDARY(NODE) \
+  (TREE_LANG_FLAG_5 (CONSTRUCTOR_CHECK (NODE)))
+
 #define DIRECT_LIST_INIT_P(NODE) \
    (BRACE_ENCLOSED_INITIALIZER_P (NODE) && CONSTRUCTOR_IS_DIRECT_INIT (NODE))
 
@@ -7021,6 +7028,7 @@ extern tree array_type_nelts_top		(tree)
 extern tree break_out_target_exprs		(tree);
 extern tree build_ctor_subob_ref		(tree, tree, tree);
 extern tree replace_placeholders		(tree, tree, bool * = NULL);
+extern bool find_placeholders			(tree);
 extern tree get_type_decl			(tree);
 extern tree decl_namespace_context		(tree);
 extern bool decl_anon_ns_mem_p			(const_tree);
--- gcc/cp/tree.c.jj	2018-03-15 18:44:21.661300889 +0100
+++ gcc/cp/tree.c	2018-03-15 20:49:03.518973106 +0100
@@ -3096,6 +3096,7 @@ build_ctor_subob_ref (tree index, tree t
 struct replace_placeholders_t
 {
   tree obj;	    /* The object to be substituted for a PLACEHOLDER_EXPR.  */
+  tree exp;	    /* The outermost exp.  */
   bool seen;	    /* Whether we've encountered a PLACEHOLDER_EXPR.  */
   hash_set<tree> *pset;	/* To avoid walking same trees multiple times.  */
 };
@@ -3134,7 +3135,12 @@ replace_placeholders_r (tree* t, int* wa
       {
 	constructor_elt *ce;
 	vec<constructor_elt,va_gc> *v = CONSTRUCTOR_ELTS (*t);
-	if (d->pset->add (*t))
+	/* Don't walk into CONSTRUCTOR_PLACEHOLDER_BOUNDARY ctors
+	   other than the d->exp one, those have PLACEHOLDER_EXPRs
+	   related to another object.  */
+	if ((CONSTRUCTOR_PLACEHOLDER_BOUNDARY (*t)
+	     && *t != d->exp)
+	    || d->pset->add (*t))
 	  {
 	    *walk_subtrees = false;
 	    return NULL_TREE;
@@ -3192,16 +3198,58 @@ replace_placeholders (tree exp, tree obj
     return exp;
 
   tree *tp = &exp;
-  hash_set<tree> pset;
-  replace_placeholders_t data = { obj, false, &pset };
+  /* Use exp instead of *(type *)&exp.  */
   if (TREE_CODE (exp) == TARGET_EXPR)
     tp = &TARGET_EXPR_INITIAL (exp);
+  hash_set<tree> pset;
+  replace_placeholders_t data = { obj, *tp, false, &pset };
   cp_walk_tree (tp, replace_placeholders_r, &data, NULL);
   if (seen_p)
     *seen_p = data.seen;
   return exp;
 }
 
+/* Callback function for find_placeholders.  */
+
+static tree
+find_placeholders_r (tree *t, int *walk_subtrees, void *)
+{
+  if (TYPE_P (*t) || TREE_CONSTANT (*t))
+    {
+      *walk_subtrees = false;
+      return NULL_TREE;
+    }
+
+  switch (TREE_CODE (*t))
+    {
+    case PLACEHOLDER_EXPR:
+      return *t;
+
+    case CONSTRUCTOR:
+      if (CONSTRUCTOR_PLACEHOLDER_BOUNDARY (*t))
+	*walk_subtrees = false;
+      break;
+
+    default:
+      break;
+    }
+
+  return NULL_TREE;
+}
+
+/* Return true if EXP contains a PLACEHOLDER_EXPR.  Don't walk into
+   ctors with CONSTRUCTOR_PLACEHOLDER_BOUNDARY flag set.  */
+
+bool
+find_placeholders (tree exp)
+{
+  /* This is only relevant for C++14.  */
+  if (cxx_dialect < cxx14)
+    return false;
+
+  return cp_walk_tree_without_duplicates (&exp, find_placeholders_r, NULL);
+}
+
 /* Similar to `build_nt', but for template definitions of dependent
    expressions  */
 
--- gcc/cp/typeck2.c.jj	2018-03-15 18:44:21.661300889 +0100
+++ gcc/cp/typeck2.c	2018-03-15 20:40:49.282818227 +0100
@@ -1470,6 +1470,9 @@ process_init_constructor_record (tree ty
 	    }
 	  /* C++14 aggregate NSDMI.  */
 	  next = get_nsdmi (field, /*ctor*/false, complain);
+	  if (!CONSTRUCTOR_PLACEHOLDER_BOUNDARY (init)
+	      && find_placeholders (next))
+	    CONSTRUCTOR_PLACEHOLDER_BOUNDARY (init) = 1;
 	}
       else if (type_build_ctor_call (TREE_TYPE (field)))
 	{
@@ -1608,10 +1611,11 @@ process_init_constructor_union (tree typ
 	  if (TREE_CODE (field) == FIELD_DECL
 	      && DECL_INITIAL (field) != NULL_TREE)
 	    {
-	      CONSTRUCTOR_APPEND_ELT (CONSTRUCTOR_ELTS (init),
-				      field,
-				      get_nsdmi (field, /*in_ctor=*/false,
-						 complain));
+	      tree val = get_nsdmi (field, /*in_ctor=*/false, complain);
+	      if (!CONSTRUCTOR_PLACEHOLDER_BOUNDARY (init)
+		  && find_placeholders (val))
+		CONSTRUCTOR_PLACEHOLDER_BOUNDARY (init) = 1;
+	      CONSTRUCTOR_APPEND_ELT (CONSTRUCTOR_ELTS (init), field, val);
 	      break;
 	    }
 	}
--- gcc/cp/call.c.jj	2018-03-11 17:48:36.359061434 +0100
+++ gcc/cp/call.c	2018-03-15 21:07:31.781961783 +0100
@@ -8164,8 +8164,6 @@ build_over_call (struct z_candidate *can
 	{
 	  arg = cp_build_fold_indirect_ref (arg);
 	  val = build2 (MODIFY_EXPR, TREE_TYPE (to), to, arg);
-	  /* Handle NSDMI that refer to the object being initialized.  */
-	  replace_placeholders (arg, to);
 	}
       else
 	{
--- gcc/cp/cp-gimplify.c.jj	2018-03-07 22:51:58.742478684 +0100
+++ gcc/cp/cp-gimplify.c	2018-03-15 21:19:27.353619519 +0100
@@ -1515,6 +1515,13 @@ cp_genericize_r (tree *stmt_p, int *walk
 	}
       break;
 
+    case TARGET_EXPR:
+      if (TARGET_EXPR_INITIAL (stmt)
+	  && TREE_CODE (TARGET_EXPR_INITIAL (stmt)) == CONSTRUCTOR
+	  && CONSTRUCTOR_PLACEHOLDER_BOUNDARY (TARGET_EXPR_INITIAL (stmt)))
+	TARGET_EXPR_NO_ELIDE (stmt) = 1;
+      break;
+
     default:
       if (IS_TYPE_OR_DECL_P (stmt))
 	*walk_subtrees = 0;
@@ -2469,7 +2476,11 @@ cp_fold (tree x)
 	      }
 	  }
 	if (nelts)
-	  x = build_constructor (TREE_TYPE (x), nelts);
+	  {
+	    x = build_constructor (TREE_TYPE (x), nelts);
+	    CONSTRUCTOR_PLACEHOLDER_BOUNDARY (x)
+	      = CONSTRUCTOR_PLACEHOLDER_BOUNDARY (org_x);
+	  }
 	break;
       }
     case TREE_VEC:
--- gcc/testsuite/g++.dg/cpp1y/pr79937-1.C.jj	2018-03-15 20:40:49.283818227 +0100
+++ gcc/testsuite/g++.dg/cpp1y/pr79937-1.C	2018-03-15 20:40:49.282818227 +0100
@@ -0,0 +1,23 @@
+// PR c++/79937
+// { dg-do run { target c++14 } }
+
+struct C {};
+
+struct X {
+  unsigned i;
+  unsigned n = i;
+};
+
+C
+bar (X x)
+{
+  if (x.i != 1 || x.n != 1)
+    __builtin_abort ();
+  return {};
+}
+
+int
+main ()
+{
+  C c = bar (X {1});
+}
--- gcc/testsuite/g++.dg/cpp1y/pr79937-2.C.jj	2018-03-15 20:40:49.283818227 +0100
+++ gcc/testsuite/g++.dg/cpp1y/pr79937-2.C	2018-03-15 20:40:49.283818227 +0100
@@ -0,0 +1,24 @@
+// PR c++/79937
+// { dg-do run { target c++14 } }
+
+struct C {};
+
+struct X {
+  unsigned i;
+  unsigned n = i;
+  unsigned m = i;
+};
+
+C
+bar (X x)
+{
+  if (x.i != 1 || x.n != 2 || x.m != 1)
+    __builtin_abort ();
+  return {};
+}
+
+int
+main ()
+{
+  C c = bar (X {1, X {2}.n});
+}
--- gcc/testsuite/g++.dg/cpp1y/pr79937-3.C.jj	2018-03-15 20:40:49.283818227 +0100
+++ gcc/testsuite/g++.dg/cpp1y/pr79937-3.C	2018-03-15 20:40:49.283818227 +0100
@@ -0,0 +1,24 @@
+// PR c++/79937
+// { dg-do run { target c++14 } }
+
+struct X {
+  unsigned i;
+  unsigned n = i;
+  unsigned m = i;
+};
+
+X
+bar (X x)
+{
+  if (x.i != 1 || x.n != 2 || x.m != 1)
+    __builtin_abort ();
+  return x;
+}
+
+int
+main ()
+{
+  X x = bar (X {1, X {2}.n});
+  if (x.i != 1 || x.n != 2 || x.m != 1)
+    __builtin_abort ();
+}
--- gcc/testsuite/g++.dg/cpp1y/pr79937-4.C.jj	2018-03-15 20:40:49.283818227 +0100
+++ gcc/testsuite/g++.dg/cpp1y/pr79937-4.C	2018-03-15 20:40:49.283818227 +0100
@@ -0,0 +1,32 @@
+// PR c++/79937
+// { dg-do run { target c++14 } }
+
+struct X {
+  unsigned i;
+  unsigned n = i;
+};
+
+X
+bar (X x)
+{
+  return x;
+}
+
+struct Y
+{
+  static Y bar (Y y) { return y; }
+  unsigned i;
+  unsigned n = bar (Y{2,i}).n;
+};
+
+int
+main ()
+{
+  X x { 1, bar (X{2}).n };
+  if (x.n != 2)
+    __builtin_abort ();
+
+  Y y { 1 };
+  if (y.n != 1)
+    __builtin_abort ();
+}
--- gcc/testsuite/g++.dg/cpp1y/pr82410.C.jj	2018-03-15 20:40:49.284818227 +0100
+++ gcc/testsuite/g++.dg/cpp1y/pr82410.C	2018-03-15 20:40:49.283818227 +0100
@@ -0,0 +1,16 @@
+// PR c++/82410
+// { dg-do compile { target c++14 } }
+
+int
+main ()
+{
+  struct A {};
+  struct S
+  {
+    int & p;
+    int x = p;
+    operator A () { return {}; }
+  };
+  int l;
+  [] (A) {} (S{l});
+}


	Jakub



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