re PR c++/39480 (generated memcpy causes trouble in assignment)

	PR c++/39480
	* call.c (build_over_call): Don't call memcpy if the target is
	the same as the source.

From-SVN: r146011

4 files changed, 57 insertions, 0 deletions

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 905b6e4..d77634d 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,9 @@
+2009-04-09  Jason Merrill  <jason@redhat.com>
+
+	PR c++/39480
+	* call.c (build_over_call): Don't call memcpy if the target is
+	the same as the source.
+
 2009-04-13  Jason Merrill  <jason@redhat.com>
 
 	PR c++/39750
diff --git a/gcc/cp/call.c b/gcc/cp/call.c
index 869146e..ef7c045 100644
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -5396,14 +5396,28 @@ build_over_call (struct z_candidate *cand, int flags, tsubst_flags_t complain)
 	     instead of an explicit call to memcpy.  */
 	
 	  tree arg0, arg1, arg2, t;
+	  tree test = NULL_TREE;
 
 	  arg2 = TYPE_SIZE_UNIT (as_base);
 	  arg1 = arg;
 	  arg0 = cp_build_unary_op (ADDR_EXPR, to, 0, complain);
+
+	  if (!(optimize && flag_tree_ter))
+	    {
+	      /* When TER is off get_pointer_alignment returns 0, so a call
+		 to __builtin_memcpy is expanded as a call to memcpy, which
+		 is invalid with identical args.  When TER is on it is
+		 expanded as a block move, which should be safe.  */
+	      arg0 = save_expr (arg0);
+	      arg1 = save_expr (arg1);
+	      test = build2 (EQ_EXPR, boolean_type_node, arg0, arg1);
+	    }
 	  t = implicit_built_in_decls[BUILT_IN_MEMCPY];
 	  t = build_call_n (t, 3, arg0, arg1, arg2);
 
 	  t = convert (TREE_TYPE (arg0), t);
+	  if (test)
+	    t = build3 (COND_EXPR, TREE_TYPE (t), test, arg0, t);
 	  val = cp_build_indirect_ref (t, 0, complain);
 	}
 
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index d29496f..457aee6 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2009-04-09  Jason Merrill  <jason@redhat.com>
+
+	PR c++/39480
+	* g++.dg/init/copy7.C: New.
+
 2009-04-13  H.J. Lu  <hongjiu.lu@intel.com>
 
 	PR testsuite/39733
diff --git a/gcc/testsuite/g++.dg/init/copy7.C b/gcc/testsuite/g++.dg/init/copy7.C
new file mode 100644
index 0000000..f4364f3
--- /dev/null
+++ b/gcc/testsuite/g++.dg/init/copy7.C
@@ -0,0 +1,32 @@
+// PR c++/39480
+// It isn't always safe to call memcpy with identical arguments.
+// { dg-do run }
+
+extern "C" void abort();
+extern "C" void *
+memcpy(void *dest, void *src, __SIZE_TYPE__ n)
+{
+  abort();
+}
+
+struct A
+{
+  double d[10];
+};
+
+struct B: public A
+{
+  char bc;
+};
+
+B b;
+
+void f(B *a1, B* a2)
+{
+  *a1 = *a2;
+}
+
+int main()
+{
+  f(&b,&b);
+}