diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 50456696bcb..18dd9dc4a31 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,10 @@
+2008-02-20  Richard Guenther  <rguenther@suse.de>
+
+	* tree.h (fold_real_zero_addition_p): Declare.
+	* fold-const.c (fold_real_zero_addition_p): Export.
+	* tree-ssa-reassoc.c (eliminate_using_constants): Also handle
+	floating-point operations with zero and one.
+
 2008-02-20  Paolo Bonzini  <bonzini@gnu.org>
 
         * doc/install.texi: Correct references to CFLAGS, replacing them
diff --git a/gcc/fold-const.c b/gcc/fold-const.c
index a33b2b07a46..aba71b6bf41 100644
--- a/gcc/fold-const.c
+++ b/gcc/fold-const.c
@@ -134,7 +134,6 @@ static tree extract_muldiv_1 (tree, tree, enum tree_code, tree, bool *);
 static tree fold_binary_op_with_conditional_arg (enum tree_code, tree,
 						 tree, tree,
 						 tree, tree, int);
-static bool fold_real_zero_addition_p (const_tree, const_tree, int);
 static tree fold_mathfn_compare (enum built_in_function, enum tree_code,
 				 tree, tree, tree);
 static tree fold_inf_compare (enum tree_code, tree, tree, tree);
@@ -6426,7 +6425,7 @@ fold_binary_op_with_conditional_arg (enum tree_code code,
    X - 0 is not the same as X because 0 - 0 is -0.  In other rounding
    modes, X + 0 is not the same as X because -0 + 0 is 0.  */
 
-static bool
+bool
 fold_real_zero_addition_p (const_tree type, const_tree addend, int negate)
 {
   if (!real_zerop (addend))
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 4037344d742..7e947ec4b27 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2008-02-20  Richard Guenther  <rguenther@suse.de>
+
+	* gcc.dg/tree-ssa/reassoc-13.c: New testcase.
+
 2008-02-20  Ira Rosen  <irar@il.ibm.com>
 
 	* lib/target-supports.exp (check_effective_target_vect_unpack):
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/reassoc-13.c b/gcc/testsuite/gcc.dg/tree-ssa/reassoc-13.c
new file mode 100644
index 00000000000..4d4dfeb446b
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/reassoc-13.c
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+/* { dg-options "-O -ffast-math -fdump-tree-reassoc1 -fdump-tree-optimized" } */
+
+double foo(double a)
+{
+  double tmp = 5.0;
+  double tmp2 = a + tmp;
+  tmp2 = tmp2 - a;
+  return a + tmp2 - 5.0;
+}
+
+/* { dg-final { scan-tree-dump-not "\\\+ 0.0" "reassoc1" } } */
+/* { dg-final { scan-tree-dump "return a;" "optimized" } } */
+/* { dg-final { cleanup-tree-dump "reassoc1" } } */
+/* { dg-final { cleanup-tree-dump "optimized" } } */
diff --git a/gcc/tree-ssa-reassoc.c b/gcc/tree-ssa-reassoc.c
index a4118c92339..6e6f5f7f442 100644
--- a/gcc/tree-ssa-reassoc.c
+++ b/gcc/tree-ssa-reassoc.c
@@ -39,6 +39,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "langhooks.h"
 #include "pointer-set.h"
 #include "cfgloop.h"
+#include "flags.h"
 
 /*  This is a simple global reassociation pass.  It is, in part, based
     on the LLVM pass of the same name (They do some things more/less
@@ -598,8 +599,10 @@ eliminate_using_constants (enum tree_code opcode,
 			   VEC(operand_entry_t, heap) **ops)
 {
   operand_entry_t oelast = VEC_last (operand_entry_t, *ops);
+  tree type = TREE_TYPE (oelast->op);
 
-  if (oelast->rank == 0 && INTEGRAL_TYPE_P (TREE_TYPE (oelast->op)))
+  if (oelast->rank == 0
+      && (INTEGRAL_TYPE_P (type) || FLOAT_TYPE_P (type)))
     {
       switch (opcode)
 	{
@@ -660,7 +663,11 @@ eliminate_using_constants (enum tree_code opcode,
 	    }
 	  break;
 	case MULT_EXPR:
-	  if (integer_zerop (oelast->op))
+	  if (integer_zerop (oelast->op)
+	      || (FLOAT_TYPE_P (type)
+		  && !HONOR_NANS (TYPE_MODE (type))
+		  && !HONOR_SIGNED_ZEROS (TYPE_MODE (type))
+		  && real_zerop (oelast->op)))
 	    {
 	      if (VEC_length (operand_entry_t, *ops) != 1)
 		{
@@ -675,7 +682,10 @@ eliminate_using_constants (enum tree_code opcode,
 		  return;
 		}
 	    }
-	  else if (integer_onep (oelast->op))
+	  else if (integer_onep (oelast->op)
+		   || (FLOAT_TYPE_P (type)
+		       && !HONOR_SNANS (TYPE_MODE (type))
+		       && real_onep (oelast->op)))
 	    {
 	      if (VEC_length (operand_entry_t, *ops) != 1)
 		{
@@ -690,7 +700,11 @@ eliminate_using_constants (enum tree_code opcode,
 	case BIT_XOR_EXPR:
 	case PLUS_EXPR:
 	case MINUS_EXPR:
-	  if (integer_zerop (oelast->op))
+	  if (integer_zerop (oelast->op)
+	      || (FLOAT_TYPE_P (type)
+		  && (opcode == PLUS_EXPR || opcode == MINUS_EXPR)
+		  && fold_real_zero_addition_p (type, oelast->op,
+						opcode == MINUS_EXPR)))
 	    {
 	      if (VEC_length (operand_entry_t, *ops) != 1)
 		{
diff --git a/gcc/tree.h b/gcc/tree.h
index 99c4aeadab1..f98afe9be80 100644
--- a/gcc/tree.h
+++ b/gcc/tree.h
@@ -4851,6 +4851,8 @@ extern enum tree_code invert_tree_comparison (enum tree_code, bool);
 extern bool tree_expr_nonzero_p (tree);
 extern bool tree_expr_nonzero_warnv_p (tree, bool *);
 
+extern bool fold_real_zero_addition_p (const_tree, const_tree, int);
+
 /* In builtins.c */
 extern tree fold_call_expr (tree, bool);
 extern tree fold_builtin_fputs (tree, tree, bool, bool, tree);