re PR middle-end/45307 (Stores expanding to no RTL not removed by tree…

re PR middle-end/45307 (Stores expanding to no RTL not removed by tree optimizers, Empty ctors/dtors not eliminated)

	PR c++/45307
	* gimplify.c (gimplify_init_constructor): Just return GS_UNHANDLED
	if ctor is empty.
	(gimplify_modify_expr_rhs): Adjust.

From-SVN: r163380

gcc/ChangeLog

+2010-08-19  Jason Merrill  <jason@redhat.com>
+
+	PR c++/45307
+	* gimplify.c (gimplify_init_constructor): Just return GS_UNHANDLED
+	if ctor is empty.
+	(gimplify_modify_expr_rhs): Adjust.
+
 2010-08-19  Nathan Froyd  <froydnj@codesourcery.com>
 
 	* cfgloop.c (get_loop_body_in_bfs_order): Avoid redundant call to

gcc/cp/ChangeLog

 2010-08-19  Jason Merrill  <jason@redhat.com>
 
+	PR c++/45307
+	* cp-gimplify.c (cp_gimplify_expr): Also remove assignment
+	of empty class CONSTRUCTOR.
+
 	* except.c (pending_noexcept, pending_noexcept_checks): New.
 	(perform_deferred_noexcept_checks): New.
 	(maybe_noexcept_warning): Split from...

gcc/cp/cp-gimplify.c

@@ -575,15 +575,18 @@ cp_gimplify_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p)
 	  TREE_OPERAND (*expr_p, 1) = build1 (VIEW_CONVERT_EXPR,
 					      TREE_TYPE (op0), op1);
 
-	else if ((is_gimple_lvalue (op1) || INDIRECT_REF_P (op1))
-		 && !(TREE_CODE (op1) == CALL_EXPR
-		      && CALL_EXPR_RETURN_SLOT_OPT (op1))
+	else if ((is_gimple_lvalue (op1) || INDIRECT_REF_P (op1)
+		  || (TREE_CODE (op1) == CONSTRUCTOR
+		      && CONSTRUCTOR_NELTS (op1) == 0)
+		  || (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.
+	       has a simple form so that TARGET_EXPRs and non-empty
+	       CONSTRUCTORs get reduced properly, and we leave the return
+	       slot optimization alone because it isn't a copy (FIXME so it
+	       shouldn't be represented as one).
 
 	       Also drop volatile variables on the RHS to avoid infinite
 	       recursion from gimplify_expr trying to load the value.  */

gcc/gimplify.c

@@ -4237,6 +4237,10 @@ gimplify_modify_expr_rhs (tree *expr_p, tree *from_p, tree *to_p,
 	  break;
 
 	case CONSTRUCTOR:
+	  /* If we already made some changes, let the front end have a
+	     crack at this before we break it down.  */
+	  if (ret != GS_UNHANDLED)
+	    break;
 	  /* If we're initializing from a CONSTRUCTOR, break this into
 	     individual MODIFY_EXPRs.  */
 	  return gimplify_init_constructor (expr_p, pre_p, post_p, want_value,

gcc/testsuite/ChangeLog

 2010-08-19  Jason Merrill  <jason@redhat.com>
 
+	* g++.dg/tree-ssa/empty-2.C: New.
+
 	* g++.dg/cpp0x/noexcept09.C: New.
 
 2010-08-19  Daniel Kraft  <d@domob.eu>

gcc/testsuite/g++.dg/tree-ssa/empty-2.C

+// PR c++/45307
+// { dg-options -fdump-tree-gimple }
+
+struct fallible_t { };
+const fallible_t fallible = fallible_t();
+
+// { dg-final { scan-tree-dump-not "fallible" "gimple" } }
+// { dg-final { cleanup-tree-dump "gimple" } }