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Re: [PATCH]Fix computation of offset in ivopt

On 10/18/2013 01:18 PM, Richard Biener wrote:

> Index: gcc/fold-const.c
> ===================================================================
> --- gcc/fold-const.c (revision 203267)
> +++ gcc/fold-const.c (working copy)
> @@ -7270,8 +7270,8 @@ fold_plusminus_mult_expr (location_t loc, enum tre
>        HOST_WIDE_INT int01, int11, tmp;
>        bool swap = false;
>        tree maybe_same;
> -      int01 = TREE_INT_CST_LOW (arg01);
> -      int11 = TREE_INT_CST_LOW (arg11);
> +      int01 = int_cst_value (arg01);
> +      int11 = int_cst_value (arg11);
> this is not correct - it will mishandle all large unsigned numbers.
> The real issue is that we rely on twos-complement arithmetic to work
> when operating on pointer offsets (because we convert them all to
> unsigned sizetype).  That makes interpreting the offsets or expressions
> that compute offsets hard (or impossible in some cases), as you can
> see from the issues in IVOPTs.

I still have patches to keep pointer types in ivopts (using a new
POINTER_PLUSV_EXPR). Would that help in this case? Last time I posted
them they met an unenthusiastic reception so I've never bothered to
repost them.


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