diff mbox

[Ada] Fix unexpected read of volatile scalar for Out parameter

Message ID 8499959.3HNmPuMVWn@polaris
State New
Headers show

Commit Message

Eric Botcazou Nov. 18, 2013, 10:06 a.m. UTC 
This fixes an old issue in the compiler, whereby it unexpectedly generates a 
read of a volatile variable with scalar type passed as Out parameter to a 
subprogram; the subtlety being that the side-effects of the parameter viewed 
as a name still need to be evaluated prior to the call.

Tested on x86_64-suse-linux, applied on the mainline.


2013-11-18  Eric Botcazou  <ebotcazou@adacore.com>

	* gcc-interface/trans.c (Call_to_gnu): For an Out parameter passed by
	copy and that don't need to be  copied in, only evaluate its address.


2013-11-18  Eric Botcazou  <ebotcazou@adacore.com>

	* gnat.dg/volatile11.adb: New test.
	* gnat.dg/volatile11_pkg.ad[sb]: New helper.
diff mbox

Patch

Index: gcc-interface/trans.c
===================================================================
--- gcc-interface/trans.c	(revision 204913)
+++ gcc-interface/trans.c	(working copy)
@@ -4130,9 +4130,7 @@  Call_to_gnu (Node_Id gnat_node, tree *gn
 	gnu_name
 	  = convert (TREE_TYPE (TYPE_FIELDS (TREE_TYPE (gnu_name))), gnu_name);
 
-      /* If we have not saved a GCC object for the formal, it means it is an
-	 Out parameter not passed by reference and that need not be copied in.
-	 Otherwise, first see if the parameter is passed by reference.  */
+      /* First see if the parameter is passed by reference.  */
       if (is_true_formal_parm && DECL_BY_REF_P (gnu_formal))
 	{
 	  if (Ekind (gnat_formal) != E_In_Parameter)
@@ -4178,6 +4176,9 @@  Call_to_gnu (Node_Id gnat_node, tree *gn
 	  gnu_formal_type = TREE_TYPE (gnu_formal);
 	  gnu_actual = build_unary_op (ADDR_EXPR, gnu_formal_type, gnu_actual);
 	}
+
+      /* Then see if the parameter is an array passed to a foreign convention
+	 subprogram.  */
       else if (is_true_formal_parm && DECL_BY_COMPONENT_PTR_P (gnu_formal))
 	{
 	  gnu_formal_type = TREE_TYPE (gnu_formal);
@@ -4198,6 +4199,8 @@  Call_to_gnu (Node_Id gnat_node, tree *gn
 	     but this is the most likely to work in all cases.  */
 	  gnu_actual = build_unary_op (ADDR_EXPR, gnu_formal_type, gnu_actual);
 	}
+
+      /* Then see if the parameter is passed by descriptor.  */
       else if (is_true_formal_parm && DECL_BY_DESCRIPTOR_P (gnu_formal))
 	{
 	  gnu_actual = convert (gnu_formal_type, gnu_actual);
@@ -4214,6 +4217,8 @@  Call_to_gnu (Node_Id gnat_node, tree *gn
 					 (TREE_TYPE (TREE_TYPE (gnu_formal)),
 					  gnu_actual, gnat_actual));
 	}
+
+      /* Otherwise the parameter is passed by copy.  */
       else
 	{
 	  tree gnu_size;
@@ -4221,11 +4226,18 @@  Call_to_gnu (Node_Id gnat_node, tree *gn
 	  if (Ekind (gnat_formal) != E_In_Parameter)
 	    gnu_name_list = tree_cons (NULL_TREE, gnu_name, gnu_name_list);
 
+	  /* If we didn't create a PARM_DECL for the formal, this means that
+	     it is an Out parameter not passed by reference and that need not
+	     be copied in.  In this case, the value of the actual need not be
+	     read.  However, we still need to make sure that its side-effects
+	     are evaluated before the call, so we evaluate its address.  */
 	  if (!is_true_formal_parm)
 	    {
-	      /* Make sure side-effects are evaluated before the call.  */
 	      if (TREE_SIDE_EFFECTS (gnu_name))
-		append_to_statement_list (gnu_name, &gnu_stmt_list);
+		{
+		  tree addr = build_unary_op (ADDR_EXPR, NULL_TREE, gnu_name);
+		  append_to_statement_list (addr, &gnu_stmt_list);
+		}
 	      continue;
 	    }