[Bug tree-optimization/37242] missed FRE opportunity because of signedness of addition

["rguenther at suse dot de" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #11 from rguenther at suse dot de  2008-08-27 20:17 -------
Subject: Re:  missed FRE opportunity because of
 signedness of addition

On Wed, 27 Aug 2008, bonzini at gnu dot org wrote:

> Yet another piece of the puzzle:
> Index: tree-ssa-sccvn.c
> ===================================================================
> --- tree-ssa-sccvn.c    (revision 139423)
> +++ tree-ssa-sccvn.c    (working copy)
> @@ -2052,6 +2052,40 @@ valueize_expr (tree expr)
>    return expr;
>  }
> 
> +static tree
> +make_expression_gimple (tree t)
> +{
> +  enum gimple_rhs_class grc = get_gimple_rhs_class (TREE_CODE (t));
> +  tree op0 = NULL, op1 = NULL;
> +
> +  switch (grc)
> +    {
> +    case GIMPLE_UNARY_RHS:
> +      op0 = TREE_OPERAND (t, 0);
> +      if (!is_gimple_val (op0))
> +        op0 = vn_nary_op_lookup (op0, NULL);
> +      if (op0)
> +        return build1 (TREE_CODE (t), TREE_TYPE (t), op0);

A good idea to lookup this final expression before building it.

> +      break;
> +
> +    case GIMPLE_BINARY_RHS:
> +      op0 = TREE_OPERAND (t, 0);
> +      op1 = TREE_OPERAND (t, 1);
> +      if (!is_gimple_val (op0))
> +        op0 = vn_nary_op_lookup (op0, NULL);
> +      if (!is_gimple_val (op1))
> +        op1 = vn_nary_op_lookup (op1, NULL);
> +      if (op0 && op1)
> +        return build2 (TREE_CODE (t), TREE_TYPE (t), op0, op1);

Likewise.

> +      break;
> +
> +    default:
> +      break;
> +    }
> +
> +  return NULL;
> +}
> +
>  /* Simplify the binary expression RHS, and return the result if
>     simplified. */
> 
> @@ -2100,10 +2134,14 @@ simplify_binary_expression (gimple stmt)
>       of operators of operators (IE (a + b) + (a + c))
>       Otherwise, we will end up with unbounded expressions if
>       fold does anything at all.  */
> -  if (result && valid_gimple_rhs_p (result))
> -    return result;
> +  if (result)
> +    {
> +      STRIP_USELESS_TYPE_CONVERSION (result);
> +      if (!valid_gimple_rhs_p (result))
> +        result = make_expression_gimple (result);
> +    }
> 
> -  return NULL_TREE;
> +  return result;
>  }
> 
>  /* Simplify the unary expression RHS, and return the result if
> @@ -2153,11 +2191,11 @@ simplify_unary_expression (gimple stmt)
>    if (result)
>      {
>        STRIP_USELESS_TYPE_CONVERSION (result);
> -      if (valid_gimple_rhs_p (result))
> -        return result;
> +      if (!valid_gimple_rhs_p (result))
> +        result = make_expression_gimple (result);
>      }
> 
> -  return NULL_TREE;
> +  return result;
>  }
> 
>  /* Try to simplify RHS using equivalences and constant folding.  */
> 
> However it still does not work because the two "unsigned" types do not match.

What do they look like?

Richard.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37242