From: Jason Merrill <jason@redhat.com>
Date: Fri, 22 Jul 2016 03:41:44 +0000 (-0400)
Subject: PR c++/71913 - missing copy elision with new.
X-Git-Tag: releases/gcc-4.9.4~57
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=46bd94f9fd8c396461d2433df72beb8f6762e528;p=thirdparty%2Fgcc.git

PR c++/71913 - missing copy elision with new.

	* call.c (unsafe_copy_elision_p): It's OK to elide when
	initializing an unknown object.

From-SVN: r238619
---

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 5936ea64590b..553c2ba8fc7a 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,9 @@
+2016-07-21  Jason Merrill  <jason@redhat.com>
+
+	PR c++/71913
+	* call.c (unsafe_copy_elision_p): It's OK to elide when
+	initializing an unknown object.
+
 2016-07-20  Jakub Jelinek  <jakub@redhat.com>
 
 	PR c++/71909
diff --git a/gcc/cp/call.c b/gcc/cp/call.c
index d2de2abf503f..59dc3633a74c 100644
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -6757,10 +6757,11 @@ static bool
 unsafe_copy_elision_p (tree target, tree exp)
 {
   tree type = TYPE_MAIN_VARIANT (TREE_TYPE (exp));
-  if (type == CLASSTYPE_AS_BASE (type))
+  /* It's safe to elide the copy for a class with no tail padding.  */
+  if (tree_int_cst_equal (TYPE_SIZE (type), CLASSTYPE_SIZE (type)))
     return false;
-  if (!is_base_field_ref (target)
-      && resolves_to_fixed_type_p (target, NULL))
+  /* It's safe to elide the copy if we aren't initializing a base object.  */
+  if (!is_base_field_ref (target))
     return false;
   tree init = TARGET_EXPR_INITIAL (exp);
   /* build_compound_expr pushes COMPOUND_EXPR inside TARGET_EXPR.  */
diff --git a/gcc/testsuite/g++.dg/init/elide5.C b/gcc/testsuite/g++.dg/init/elide5.C
new file mode 100644
index 000000000000..0a9978ca6615
--- /dev/null
+++ b/gcc/testsuite/g++.dg/init/elide5.C
@@ -0,0 +1,27 @@
+// PR c++/71913
+// { dg-do link { target c++11 } }
+
+void* operator new(unsigned long, void* p) { return p; }
+
+struct IndirectReturn {
+  IndirectReturn() {}
+  // Undefined so we get a link error if the indirect return value is copied
+  IndirectReturn(const IndirectReturn&);
+  IndirectReturn& operator=(const IndirectReturn&) = delete;
+  ~IndirectReturn() {}
+};
+
+IndirectReturn foo() { return IndirectReturn(); }
+
+void bar(void* ptr) {
+  new (ptr) IndirectReturn(foo());
+}
+
+alignas (alignof (IndirectReturn))
+unsigned char c[sizeof(IndirectReturn)];
+
+int main()
+{
+  bar(c);
+}
+