op0_elt = lookup (op0, op0_hash, mode);
op1_elt = lookup (op1, op1_hash, mode);
+ /* If both operands are already equivalent or if they are not in the
+ table but are identical, do nothing. */
+ if ((op0_elt != 0 && op1_elt != 0
+ && op0_elt->first_same_value == op1_elt->first_same_value)
+ || op0 == op1 || rtx_equal_p (op0, op1))
+ return;
+
/* If we aren't setting two things equal all we can do is save this
comparison. Similarly if this is floating-point. In the latter
case, OP1 might be zero and both -0.0 and 0.0 are equal to it.