[PATCH] Fix folding of UBSAN_CHECK_SUB (x, 0) etc.

[Richard Biener]

On Tue, 25 Mar 2014, Jakub Jelinek wrote:

> Hi!
> 
> While working on previous patch, I've noticed a severe omission in the
> -fsanitize=signed-integer-overflow support.  Nothing ever
> folds addition/subtraction of 0 and multiplication by [0,1], none of these
> may ever overflow and thus we can fold them to normal operations and let
> those be folded as normal operations.
> 
> Bootstrapped/regtested on x86_64-linux and i686-linux, tested with
> --with-build-config=bootstrap-ubsan bootstrap on i686-linux, ok for trunk?

I think you only need to adjust gimple_fold_stmt_to_constant_1.

Richard.

> 2014-03-25  Jakub Jelinek  <jakub@redhat.com>
> 
> 	* tree-vrp.c (simplify_internal_call_using_ranges): If only
> 	one range is range_int_cst_p, but not both, at least optimize
> 	addition/subtraction of 0 and multiplication by 0 or 1.
> 
> --- gcc/tree-vrp.c.jj	2014-03-12 10:14:18.000000000 +0100
> +++ gcc/tree-vrp.c	2014-03-24 16:14:50.822674164 +0100
> @@ -9336,31 +9336,58 @@ simplify_internal_call_using_ranges (gim
>    else if (TREE_CODE (op0) == INTEGER_CST)
>      set_value_range_to_value (&vr0, op0, NULL);
>    else
> -    return false;
> +    set_value_range_to_varying (&vr0);
>  
>    if (TREE_CODE (op1) == SSA_NAME)
>      vr1 = *get_value_range (op1);
>    else if (TREE_CODE (op1) == INTEGER_CST)
>      set_value_range_to_value (&vr1, op1, NULL);
>    else
> -    return false;
> +    set_value_range_to_varying (&vr1);
>  
> -  if (!range_int_cst_p (&vr0) || !range_int_cst_p (&vr1))
> -    return false;
> -
> -  tree r1 = int_const_binop (subcode, vr0.min, vr1.min);
> -  tree r2 = int_const_binop (subcode, vr0.max, vr1.max);
> -  if (r1 == NULL_TREE || TREE_OVERFLOW (r1)
> -      || r2 == NULL_TREE || TREE_OVERFLOW (r2))
> -    return false;
> -  if (subcode == MULT_EXPR)
> +  if (!range_int_cst_p (&vr0))
> +    {
> +      /* If one range is VR_ANTI_RANGE, VR_VARYING etc.,
> +	 optimize at least x = y + 0; x = y - 0; x = y * 0;
> +	 and x = y * 1; which never overflow.  */
> +      if (!range_int_cst_p (&vr1))
> +	return false;
> +      if (tree_int_cst_sgn (vr1.min) == -1)
> +	return false;
> +      if (compare_tree_int (vr1.max, subcode == MULT_EXPR) == 1)
> +	return false;
> +    }
> +  else if (!range_int_cst_p (&vr1))
> +    {
> +      /* If one range is VR_ANTI_RANGE, VR_VARYING etc.,
> +	 optimize at least x = 0 + y; x = 0 * y; and x = 1 * y;
> +	 which never overflow.  */
> +      if (subcode == MINUS_EXPR)
> +	return false;
> +      if (!range_int_cst_p (&vr0))
> +	return false;
> +      if (tree_int_cst_sgn (vr0.min) == -1)
> +	return false;
> +      if (compare_tree_int (vr0.max, subcode == MULT_EXPR) == 1)
> +	return false;
> +    }
> +  else
>      {
> -      tree r3 = int_const_binop (subcode, vr0.min, vr1.max);
> -      tree r4 = int_const_binop (subcode, vr0.max, vr1.min);
> -      if (r3 == NULL_TREE || TREE_OVERFLOW (r3)
> -	  || r4 == NULL_TREE || TREE_OVERFLOW (r4))
> +      tree r1 = int_const_binop (subcode, vr0.min, vr1.min);
> +      tree r2 = int_const_binop (subcode, vr0.max, vr1.max);
> +      if (r1 == NULL_TREE || TREE_OVERFLOW (r1)
> +	  || r2 == NULL_TREE || TREE_OVERFLOW (r2))
>  	return false;
> +      if (subcode == MULT_EXPR)
> +	{
> +	  tree r3 = int_const_binop (subcode, vr0.min, vr1.max);
> +	  tree r4 = int_const_binop (subcode, vr0.max, vr1.min);
> +	  if (r3 == NULL_TREE || TREE_OVERFLOW (r3)
> +	      || r4 == NULL_TREE || TREE_OVERFLOW (r4))
> +	    return false;
> +	}
>      }
> +
>    gimple g = gimple_build_assign_with_ops (subcode, gimple_call_lhs (stmt),
>  					   op0, op1);
>    gsi_replace (gsi, g, false);
> 
> 	Jakub
> 
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE / SUSE Labs
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