Patchwork [Ada] Fix PR ada/47131

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Submitter Eric Botcazou
Date Jan. 4, 2011, 8:56 a.m.
Message ID <201101040956.32642.ebotcazou@adacore.com>
Download mbox | patch
Permalink /patch/77420/
State New
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Comments

Eric Botcazou - Jan. 4, 2011, 8:56 a.m.
This is the failure of ACATS c34011b on SJLJ targets.  We have this kludge in 
Identifier_to_gnu since the Tree-SSA transition:

  /* If we are in an exception handler, force this variable into memory to
     ensure optimization does not remove stores that appear redundant but are
     actually needed in case an exception occurs.

     ??? Note that we need not do this if the variable is declared within the
     handler, only if it is referenced in the handler and declared in an
     enclosing block, but we have no way of testing that right now.

     ??? We used to essentially set the TREE_ADDRESSABLE flag on the variable
     here, but it can now be removed by the Tree aliasing machinery if the
     address of the variable is never taken.  All we can do is to make the
     variable volatile, which might incur the generation of temporaries just
     to access the memory in some circumstances.  This can be avoided for
     variables of non-constant size because they are automatically allocated
     to memory.  There might be no way of allocating a proper temporary for
     them in any case.  We only do this for SJLJ though.  */
  if (VEC_last (tree, gnu_except_ptr_stack)
      && TREE_CODE (gnu_result) == VAR_DECL
      && TREE_CODE (DECL_SIZE_UNIT (gnu_result)) == INTEGER_CST)
    TREE_THIS_VOLATILE (gnu_result) = TREE_SIDE_EFFECTS (gnu_result) = 1;


This turns out to be problematic with recent more stringent consistency checks 
because TREE_THIS_VOLATILE can be set late and thus not propagated in already 
built trees referencing the DECL.

The volatile trick used here is consistent with the setjmp/longjmp semantics 
but we use __builtin_setjmp/__builtin_longjmp to implement the SJLJ scheme.

Tested on i586-suse-linux in SJLJ configuration, applied on the mainline.


2011-01-04  Eric Botcazou  <ebotcazou@adacore.com>

	PR ada/47131
	* gcc-interface/trans.c (Identifier_to_gnu): In SJLJ mode, do not make
	variables that are referenced in exception handlers volatile.

Patch

Index: gcc-interface/trans.c
===================================================================
--- gcc-interface/trans.c	(revision 168416)
+++ gcc-interface/trans.c	(working copy)
@@ -6,7 +6,7 @@ 
  *                                                                          *
  *                          C Implementation File                           *
  *                                                                          *
- *          Copyright (C) 1992-2010, Free Software Foundation, Inc.         *
+ *          Copyright (C) 1992-2011, Free Software Foundation, Inc.         *
  *                                                                          *
  * GNAT is free software;  you can  redistribute it  and/or modify it under *
  * terms of the  GNU General Public License as published  by the Free Soft- *
@@ -980,27 +980,6 @@  Identifier_to_gnu (Node_Id gnat_node, tr
   else
     gnu_result = gnat_to_gnu_entity (gnat_temp, NULL_TREE, 0);
 
-  /* If we are in an exception handler, force this variable into memory to
-     ensure optimization does not remove stores that appear redundant but are
-     actually needed in case an exception occurs.
-
-     ??? Note that we need not do this if the variable is declared within the
-     handler, only if it is referenced in the handler and declared in an
-     enclosing block, but we have no way of testing that right now.
-
-     ??? We used to essentially set the TREE_ADDRESSABLE flag on the variable
-     here, but it can now be removed by the Tree aliasing machinery if the
-     address of the variable is never taken.  All we can do is to make the
-     variable volatile, which might incur the generation of temporaries just
-     to access the memory in some circumstances.  This can be avoided for
-     variables of non-constant size because they are automatically allocated
-     to memory.  There might be no way of allocating a proper temporary for
-     them in any case.  We only do this for SJLJ though.  */
-  if (VEC_last (tree, gnu_except_ptr_stack)
-      && TREE_CODE (gnu_result) == VAR_DECL
-      && TREE_CODE (DECL_SIZE_UNIT (gnu_result)) == INTEGER_CST)
-    TREE_THIS_VOLATILE (gnu_result) = TREE_SIDE_EFFECTS (gnu_result) = 1;
-
   /* Some objects (such as parameters passed by reference, globals of
      variable size, and renamed objects) actually represent the address
      of the object.  In that case, we must do the dereference.  Likewise,