re PR middle-end/47903 (var-tracking.c: valgrind error)

	PR middle-end/47903
	* real.c (real_arithmetic) <case PLUS_EXPR, MINUS_EXPR,
	MULT_EXPR, RDIV_EXPR>: Clear padding bits in *r first if
	r isn't op0 nor op1.

From-SVN: r170547

gcc/ChangeLog

+2011-02-27  Jakub Jelinek  <jakub@redhat.com>
+
+	PR middle-end/47903
+	* real.c (real_arithmetic) <case PLUS_EXPR, MINUS_EXPR,
+	MULT_EXPR, RDIV_EXPR>: Clear padding bits in *r first if
+	r isn't op0 nor op1.
+
 2011-02-23  Georg-Johann Lay  <avr@gjlay.de>
 
 	* config/avr/avr.md: Remove magic comment for emacs.

gcc/real.c

 /* real.c - software floating point emulation.
    Copyright (C) 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2002,
-   2003, 2004, 2005, 2007, 2008, 2009, 2010 Free Software Foundation, Inc.
+   2003, 2004, 2005, 2007, 2008, 2009, 2010, 2011
+   Free Software Foundation, Inc.
    Contributed by Stephen L. Moshier (moshier@world.std.com).
    Re-written by Richard Henderson <rth@redhat.com>
 
@@ -1009,15 +1010,25 @@ real_arithmetic (REAL_VALUE_TYPE *r, int icode, const REAL_VALUE_TYPE *op0,
   switch (code)
     {
     case PLUS_EXPR:
+      /* Clear any padding areas in *r if it isn't equal to one of the
+	 operands so that we can later do bitwise comparisons later on.  */
+      if (r != op0 && r != op1)
+	memset (r, '\0', sizeof (*r));
       return do_add (r, op0, op1, 0);
 
     case MINUS_EXPR:
+      if (r != op0 && r != op1)
+	memset (r, '\0', sizeof (*r));
       return do_add (r, op0, op1, 1);
 
     case MULT_EXPR:
+      if (r != op0 && r != op1)
+	memset (r, '\0', sizeof (*r));
       return do_multiply (r, op0, op1);
 
     case RDIV_EXPR:
+      if (r != op0 && r != op1)
+	memset (r, '\0', sizeof (*r));
       return do_divide (r, op0, op1);
 
     case MIN_EXPR: