Re: [PATCH] make -Wrestrict for strcat more meaningful (PR 83698)

[Jakub Jelinek <jakub@redhat.com>]

On Tue, Jan 16, 2018 at 01:36:26PM -0700, Martin Sebor wrote:
> --- gcc/gimple-ssa-warn-restrict.c	(revision 256752)
> +++ gcc/gimple-ssa-warn-restrict.c	(working copy)
> @@ -384,6 +384,12 @@ builtin_memref::builtin_memref (tree expr, tree si
>  	  base = SSA_NAME_VAR (base);
>        }
>  
> +  if (DECL_P (base) && TREE_CODE (TREE_TYPE (base)) == ARRAY_TYPE)
> +    {
> +      if (offrange[0] < 0 && offrange[1] > 0)
> +	offrange[0] = 0;
> +    }

Why the 2 nested ifs?

> @@ -1079,14 +1085,35 @@ builtin_access::strcat_overlap ()
>      return false;
>  
>    /* When strcat overlap is certain it is always a single byte:
> -     the terminatinn NUL, regardless of offsets and sizes.  When
> +     the terminating NUL, regardless of offsets and sizes.  When
>       overlap is only possible its range is [0, 1].  */
>    acs.ovlsiz[0] = dstref->sizrange[0] == dstref->sizrange[1] ? 1 : 0;
>    acs.ovlsiz[1] = 1;
> -  acs.ovloff[0] = (dstref->sizrange[0] + dstref->offrange[0]).to_shwi ();
> -  acs.ovloff[1] = (dstref->sizrange[1] + dstref->offrange[1]).to_shwi ();

You use to_shwi many times in the patch, do the callers or something earlier
in this function guarantee that you aren't throwing away any bits (unlike
tree_to_shwi, to_shwi method doesn't ICE, just throws away upper bits).
Especially when you perform additions like here, even if both wide_ints fit
into a shwi, the result might not.

	Jakub