re PR c++/43787 (memory copy of empty class (sizeof is one))

	PR c++/43787
gcc:
	* gimplify.c (gimplify_expr): Keep working if gimplify_modify_expr
	returns GS_OK.
	(gimplify_modify_expr_rhs): Return GS_OK if anything changed.
gcc/cp:
	* cp-gimplify.c (cp_gimplify_expr): Remove copies of empty classes.
	* call.c (build_over_call): Don't try to avoid INIT_EXPR copies here.

From-SVN: r159072

gcc/ChangeLog

+2010-05-05  Jason Merrill  <jason@redhat.com>
+
+	PR c++/43787
+	* gimplify.c (gimplify_expr): Keep working if gimplify_modify_expr
+	returns GS_OK.
+	(gimplify_modify_expr_rhs): Return GS_OK if anything changed.
+
 2010-05-05  Alexandre Oliva  <aoliva@redhat.com>
 	    Jakub Jelinek  <jakub@redhat.com>
 

gcc/cp/ChangeLog

+2010-05-05  Jason Merrill  <jason@redhat.com>
+
+	PR c++/43787
+	* cp-gimplify.c (cp_gimplify_expr): Remove copies of empty classes.
+	* call.c (build_over_call): Don't try to avoid INIT_EXPR copies here.
+
 2010-05-04  Paolo Carlini  <paolo.carlini@oracle.com>
 
 	PR c++/43028

gcc/cp/call.c

@@ -5778,20 +5778,8 @@ build_over_call (struct z_candidate *cand, int flags, tsubst_flags_t complain)
 	{
 	  tree to = stabilize_reference (cp_build_indirect_ref (fa, RO_NULL,
 								complain));
-	  tree type = TREE_TYPE (to);
 
-	  if (TREE_CODE (arg) != TARGET_EXPR
-	      && TREE_CODE (arg) != AGGR_INIT_EXPR
-	      && is_really_empty_class (type))
-	    {
-	      /* Avoid copying empty classes.  */
-	      val = build2 (COMPOUND_EXPR, void_type_node, to, arg);
-	      TREE_NO_WARNING (val) = 1;
-	      val = build2 (COMPOUND_EXPR, type, val, to);
-	      TREE_NO_WARNING (val) = 1;
-	    }
-	  else
-	    val = build2 (INIT_EXPR, DECL_CONTEXT (fn), to, arg);
+	  val = build2 (INIT_EXPR, DECL_CONTEXT (fn), to, arg);
 	  return val;
 	}
     }

gcc/cp/cp-gimplify.c

@@ -569,6 +569,26 @@ cp_gimplify_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p)
 	    && !useless_type_conversion_p (TREE_TYPE (op1), TREE_TYPE (op0)))
 	  TREE_OPERAND (*expr_p, 1) = build1 (VIEW_CONVERT_EXPR,
 					      TREE_TYPE (op0), op1);
+
+	else if ((rhs_predicate_for (op0)) (op1)
+		 && !(TREE_CODE (op1) == CALL_EXPR
+		      && CALL_EXPR_RETURN_SLOT_OPT (op1))
+		 && is_really_empty_class (TREE_TYPE (op0)))
+	  {
+	    /* Remove any copies of empty classes.  We check that the RHS
+	       has a simple form so that TARGET_EXPRs and CONSTRUCTORs get
+	       reduced properly, and we leave the return slot optimization
+	       alone because it isn't a copy.
+
+	       Also drop volatile variables on the RHS to avoid infinite
+	       recursion from gimplify_expr trying to load the value.  */
+	    if (!TREE_SIDE_EFFECTS (op1)
+		|| (DECL_P (op1) && TREE_THIS_VOLATILE (op1)))
+	      *expr_p = op0;
+	    else
+	      *expr_p = build2 (COMPOUND_EXPR, TREE_TYPE (*expr_p),
+				op0, op1);
+	  }
       }
       ret = GS_OK;
       break;

gcc/testsuite/ChangeLog

+2010-05-05  Jason Merrill  <jason@redhat.com>
+
+	PR c++/43787
+	* g++.dg/opt/empty1.C: New.
+
 2010-05-05  Janus Weil  <janus@gcc.gnu.org>
 
 	PR fortran/43696

gcc/testsuite/g++.dg/opt/empty1.C

+// PR c++/43787
+// Test that we don't try to copy *x.
+// { dg-do run }
+
+class empty_t {};
+
+int main()
+{
+  empty_t* x = 0;
+  empty_t y = *x;
+}