Blame SOURCES/gcc32-c++-unitialized-self-ref.patch

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2004-12-02  Alexandre Oliva  <aoliva@redhat.com>
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	* decl.c (copy_tree_replacing_r, struct replace_node): New.
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	(grok_reference_init): Use them to replace uses of a reference
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	being initialized with a NULL dereference.
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2005-01-03  Jakub Jelinek  <jakub@redhat.com>
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	* g++.dg/other/ref1.C: New test.
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--- gcc/cp/decl.c.jj	2003-03-28 22:03:02.000000000 +0100
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+++ gcc/cp/decl.c	2005-01-03 11:45:24.669972609 +0100
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@@ -1,6 +1,6 @@
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 /* Process declarations and variables for C compiler.
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    Copyright (C) 1988, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000,
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-   2001, 2002, 2003  Free Software Foundation, Inc.
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+   2001, 2002, 2003, 2004  Free Software Foundation, Inc.
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    Contributed by Michael Tiemann (tiemann@cygnus.com)
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 This file is part of GNU CC.
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@@ -7535,6 +7535,30 @@ start_decl_1 (decl)
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     DECL_INITIAL (decl) = NULL_TREE;
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 }
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+static tree copy_tree_replacing_r PARAMS ((tree *, int *, void *));
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+
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+struct replace_node
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+{
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+  tree from, to;
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+};
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+
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+static tree
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+copy_tree_replacing_r (tp, walk_subtrees, data)
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+     tree *tp;
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+     int *walk_subtrees;
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+     void *data;
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+{
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+  struct replace_node *rn = data;
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+
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+  if (*tp != rn->from)
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+    return copy_tree_r (tp, walk_subtrees, NULL);
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+
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+  *tp = rn->to;
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+  *walk_subtrees = 0;
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+
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+  return NULL;
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+}
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+
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 /* Handle initialization of references.
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    These three arguments are from `cp_finish_decl', and have the
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    same meaning here that they do there.
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@@ -7565,6 +7589,35 @@ grok_reference_init (decl, type, init)
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       return NULL_TREE;
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     }
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+  /* Replace occurrences of a reference variable in its own
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+     initializer with a zero-initialized NULL reference.  If we don't
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+     do this and the reference initializer ends up requiring a
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+     temporary (as it almost always will in this case), we'll end up
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+     with the initializer of the temporary referencing the reference
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+     variable before it's in scope, which crashes because we haven't
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+     expanded the reference declaration yet, so its DECL_RTL is NULL.
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+     This is equivalent to zero-initializing the reference variable,
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+     expanding the temporary definition with initializer, then binding
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+     the reference to the temporary, without requiring all the revamp
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+     in reference handling that mainline undergone for GCC 3.4.  It
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+     actually changes behavior a little bit, in that a reference
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+     initialized to itself will now be bound to a NULL reference
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+     instead of getting an indeterminate value, but since using it
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+     before initialization invokes undefined behavior, either way is
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+     fine.  */
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+  if (find_tree (init, decl))
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+    {
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+      struct replace_node rn;
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+
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+      rn.from = decl;
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+      rn.to = build1 (NOP_EXPR, type, integer_zero_node);
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+      
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+      walk_tree (&init, copy_tree_replacing_r, &rn, NULL);
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+
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+      if (warn_uninitialized)
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+	warning ("reference used in its own initializer");
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+    }
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+
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   if (TREE_CODE (init) == TREE_LIST)
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     init = build_compound_expr (init);
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--- gcc/testsuite/g++.dg/other/ref1.C.jj	2005-01-03 11:46:43.005868429 +0100
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+++ gcc/testsuite/g++.dg/other/ref1.C	2005-01-03 11:47:34.475601869 +0100
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@@ -0,0 +1,19 @@
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+// { dg-do compile }
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+// { dg-options "-O2" }
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+
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+struct A
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+{
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+  A ();
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+  ~A ();
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+};
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+
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+extern const A &bar ();
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+extern A baz ();
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+extern int operator!= (const A &x, const A &y);
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+
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+void foo (const A &x)
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+{
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+  /* This has undefined behaviour, as a is used before it is initialized.
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+     Still, we shouldn't ICE on it.  */
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+  const A &a = a != bar () ? x : baz ();
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+}