[C++ PATCH] Partial fix for a recent regression (PR c++/90947)

[Jakub Jelinek <jakub@redhat.com>]

Hi!

The following patch is just a partial fix for a regression introduced
in the PR90947 changes, the testcase is fixed for just C++17/20.
type_initializer_zero_p has been added to the generic code, supposedly
because similar initializer_zerop is in generic code too, but that
means it has a hand-written copy of next_initializable_field which can't
do exactly what next_initializable_field does.

The following patch moves it into the C++ FE which is the only user of that
function and uses next_initializable_field in there.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

I'm afraid I'm lost on how to fix the C++11/14 case, the object
being initialized has std::atomic<int> type, which doesn't have any
direct non-static data members, and has std::__atomic_base<int> as base
class that has some field.  The only FIELD_DECL in std::atomic<int>
is DECL_ARTIFICIAL field for the base class, so next_initializable_field
or the hand-written variant thereof doesn't find any initializable fields
for 11/14.  The initializer is initializer list { {1} } and the function
just returns true if it doesn't find any initializable fields, so in the end
we misoptimize it as { {0} }.

2019-10-22  Jakub Jelinek  <jakub@redhat.com>

	PR c++/90947
	* tree.h (type_initializer_zero_p): Remove.
	* tree.c (type_initializer_zero_p): Remove.
cp/
	* cp-tree.h (type_initializer_zero_p): Declare.
	* decl.c (reshape_init_array_1): Formatting fix.
	* tree.c (type_initializer_zero_p): New function.  Moved from
	../tree.c, use next_initializable_field, formatting fix.

--- gcc/tree.h.jj	2019-09-20 12:25:13.737920929 +0200
+++ gcc/tree.h	2019-10-22 10:07:26.411826804 +0200
@@ -4690,12 +4690,6 @@ extern tree first_field (const_tree);
 extern bool initializer_zerop (const_tree, bool * = NULL);
 extern bool initializer_each_zero_or_onep (const_tree);
 
-/* Analogous to initializer_zerop but also examines the type for
-   which the initializer is being used.  Unlike initializer_zerop,
-   considers empty strings to be zero initializers for arrays and
-   non-zero for pointers.  */
-extern bool type_initializer_zero_p (tree, tree);
-
 extern wide_int vector_cst_int_elt (const_tree, unsigned int);
 extern tree vector_cst_elt (const_tree, unsigned int);
 
--- gcc/tree.c.jj	2019-10-19 09:22:14.830893404 +0200
+++ gcc/tree.c	2019-10-22 10:08:36.501748481 +0200
@@ -11396,73 +11396,6 @@ initializer_each_zero_or_onep (const_tre
     }
 }
 
-/* Given an initializer INIT for a TYPE, return true if INIT is zero
-   so that it can be replaced by value initialization.  This function
-   distinguishes betwen empty strings as initializers for arrays and
-   for pointers (which make it return false).  */
-
-bool
-type_initializer_zero_p (tree type, tree init)
-{
-  if (type  == error_mark_node || init == error_mark_node)
-    return false;
-
-  STRIP_NOPS (init);
-
-  if (POINTER_TYPE_P (type))
-    return TREE_CODE (init) != STRING_CST && initializer_zerop (init);
-
-  if (TREE_CODE (init) != CONSTRUCTOR)
-    return initializer_zerop (init);
-
-  if (TREE_CODE (type) == ARRAY_TYPE)
-    {
-      tree elt_type = TREE_TYPE (type);
-      elt_type = TYPE_MAIN_VARIANT (elt_type);
-      if (elt_type == char_type_node)
-	return initializer_zerop (init);
-
-      tree elt_init;
-      unsigned HOST_WIDE_INT i;
-      FOR_EACH_CONSTRUCTOR_VALUE (CONSTRUCTOR_ELTS (init), i, elt_init)
-	if (!type_initializer_zero_p (elt_type, elt_init))
-	  return false;
-      return true;
-    }
-
-  if (TREE_CODE (type) != RECORD_TYPE)
-    return initializer_zerop (init);
-
-  tree fld = TYPE_FIELDS (type);
-
-  tree fld_init;
-  unsigned HOST_WIDE_INT i;
-  FOR_EACH_CONSTRUCTOR_VALUE (CONSTRUCTOR_ELTS (init), i, fld_init)
-    {
-      /* Advance to the next member, skipping over everything that
-	 canot be initialized (including unnamed bit-fields).  */
-      while (TREE_CODE (fld) != FIELD_DECL
-	     || DECL_ARTIFICIAL (fld)
-	     || (DECL_BIT_FIELD (fld) && !DECL_NAME (fld)))
-	{
-	  fld = DECL_CHAIN (fld);
-	  if (!fld)
-	    return true;
-	  continue;
-	}
-
-      tree fldtype = TREE_TYPE (fld);
-      if (!type_initializer_zero_p (fldtype, fld_init))
-	return false;
-
-      fld = DECL_CHAIN (fld);
-      if (!fld)
-	break;
-    }
-
-  return true;
-}
-
 /* Check if vector VEC consists of all the equal elements and
    that the number of elements corresponds to the type of VEC.
    The function returns first element of the vector
--- gcc/cp/cp-tree.h.jj	2019-10-22 08:15:53.810775827 +0200
+++ gcc/cp/cp-tree.h	2019-10-22 10:10:57.265582861 +0200
@@ -7379,6 +7379,11 @@ extern tree cxx_copy_lang_qualifiers		(c
 
 extern void cxx_print_statistics		(void);
 extern bool maybe_warn_zero_as_null_pointer_constant (tree, location_t);
+/* Analogous to initializer_zerop but also examines the type for
+   which the initializer is being used.  Unlike initializer_zerop,
+   considers empty strings to be zero initializers for arrays and
+   non-zero for pointers.  */
+extern bool type_initializer_zero_p		(tree, tree);
 
 /* in ptree.c */
 extern void cxx_print_xnode			(FILE *, tree, int);
--- gcc/cp/decl.c.jj	2019-10-22 08:57:12.913654620 +0200
+++ gcc/cp/decl.c	2019-10-22 10:13:39.038094034 +0200
@@ -5982,9 +5982,8 @@ reshape_init_array_1 (tree elt_type, tre
       /* Pointers initialized to strings must be treated as non-zero
 	 even if the string is empty.  */
       tree init_type = TREE_TYPE (elt_init);
-      if ((POINTER_TYPE_P (elt_type) != POINTER_TYPE_P (init_type)))
-	last_nonzero = index;
-      else if (!type_initializer_zero_p (elt_type, elt_init))
+      if (POINTER_TYPE_P (elt_type) != POINTER_TYPE_P (init_type)
+	  || !type_initializer_zero_p (elt_type, elt_init))
 	last_nonzero = index;
 
       /* This can happen with an invalid initializer (c++/54501).  */
--- gcc/cp/tree.c.jj	2019-10-19 09:22:16.594866462 +0200
+++ gcc/cp/tree.c	2019-10-22 10:10:29.151015397 +0200
@@ -5527,6 +5527,65 @@ maybe_warn_zero_as_null_pointer_constant
   return false;
 }
 \f
+/* Given an initializer INIT for a TYPE, return true if INIT is zero
+   so that it can be replaced by value initialization.  This function
+   distinguishes betwen empty strings as initializers for arrays and
+   for pointers (which make it return false).  */
+
+bool
+type_initializer_zero_p (tree type, tree init)
+{
+  if (type == error_mark_node || init == error_mark_node)
+    return false;
+
+  STRIP_NOPS (init);
+
+  if (POINTER_TYPE_P (type))
+    return TREE_CODE (init) != STRING_CST && initializer_zerop (init);
+
+  if (TREE_CODE (init) != CONSTRUCTOR)
+    return initializer_zerop (init);
+
+  if (TREE_CODE (type) == ARRAY_TYPE)
+    {
+      tree elt_type = TREE_TYPE (type);
+      elt_type = TYPE_MAIN_VARIANT (elt_type);
+      if (elt_type == char_type_node)
+	return initializer_zerop (init);
+
+      tree elt_init;
+      unsigned HOST_WIDE_INT i;
+      FOR_EACH_CONSTRUCTOR_VALUE (CONSTRUCTOR_ELTS (init), i, elt_init)
+	if (!type_initializer_zero_p (elt_type, elt_init))
+	  return false;
+      return true;
+    }
+
+  if (TREE_CODE (type) != RECORD_TYPE)
+    return initializer_zerop (init);
+
+  tree fld = TYPE_FIELDS (type);
+
+  tree fld_init;
+  unsigned HOST_WIDE_INT i;
+  FOR_EACH_CONSTRUCTOR_VALUE (CONSTRUCTOR_ELTS (init), i, fld_init)
+    {
+      fld = next_initializable_field (fld);
+      if (!fld)
+	return true;
+
+      tree fldtype = TREE_TYPE (fld);
+      if (!type_initializer_zero_p (fldtype, fld_init))
+	return false;
+
+      fld = DECL_CHAIN (fld);
+      if (!fld)
+	break;
+    }
+
+  return true;
+}
+\f
 #if defined ENABLE_TREE_CHECKING && (GCC_VERSION >= 2007)
 /* Complain that some language-specific thing hanging off a tree
    node has been accessed improperly.  */

	Jakub