On 9/17/18 4:12 AM, Aldy Hernandez wrote:
> It seems most of the remaining anti range code in
> extract_range_from_unary_expr for CONVERT_EXPR_P is actually dealing
> with non-nullness in practice.
>
> Anti-range handling is mostly handled by canonicalizing anti-ranges into
> its two set constituents (~[10,20] => [MIN,9] U [21,MAX]) and dealing
> with them piece-meal. For that matter, the only way we can reach the
> conversion code in extract_range_from_unary_expr with an anti-range is
> either with a pointer (because pointers are ignored from
> ranges_from_anti_range on purpose), or when converting integers of the
> form ~[SSA, SSA]. I verified this with a bootstrap + tests with some
> specially placed asserts, BTW.
>
> So... if we special handle pointer conversions (both to and fro, as
> opposed to just to), we get rid of any anti-ranges with the exception of
> ~[SSA, SSA] between integers. And anti-ranges of unknown quantities
> (SSAs) will be handled automatically already (courtesy of
> extract_range_into_wide_ints).
>
> I propose we handle pointers at the beginning, and everything else just
> falls into place, with no special code.
>
> As commented in the code, this will pessimize conversions from (char
> *)~[0, 2] to int, because we will forget that the range can also not be
> 1 or 2. But as Jeff commented, we really only care about null or
> non-nullness. Special handling magic pointers with constants IMO is a
> wasted effort. For that matter, I think it was me that added this
> spaghetti a few weeks ago to make sure we handled ~[0,2]. We weren't
> even handling it a short while back :-). Furthermore, in a bootstrap, I
> think we only triggered this twice. And I'm not even sure we make
> further use of anything null/not-null for pointers later on.
>
> This patch simplifies the code, and removes more special handling and
> cryptic comments related to anti-ranges.
>
> Tested with all languages including Ada and Go.
>
> OK for trunk?
>
>
> curr.patch
>
> commit 10406735080ebba81f31b9e7b36247446e07fb69
> Author: Aldy Hernandez <al...@redhat.com>
> Date: Mon Sep 17 11:05:57 2018 +0200
>
> * tree-vrp.c (extract_range_from_unary_expr): Special case all
> pointer conversions.
> Do not do anything special for anti-ranges.
OK.
jeff
