Re: Ping: Re: [patch middle-end]: Fix PR/48814 - [4.4/4.5/4.6/4.7 Regression] Incorrect scalar increment result

[Richard Guenther <richard dot guenther at gmail dot com>]

On Thu, Feb 9, 2012 at 11:53 AM, Richard Guenther
<richard.guenther@gmail.com> wrote:
> On Thu, Feb 9, 2012 at 11:29 AM, Richard Guenther
> <richard.guenther@gmail.com> wrote:
>> On Wed, Feb 8, 2012 at 10:25 PM, Kai Tietz <ktietz70@googlemail.com> wrote:
>>> 2012/1/11 Richard Guenther <richard.guenther@gmail.com>:
>>>>
>>>> count despite being declared volatile and only loaded once in the source
>>>> is loaded twice in gimple. ?If it were a HW register which destroys the
>>>> device after the 2nd load without an intervening store you'd wrecked
>>>> the device ;)
>>>>
>>>> Richard.
>>>
>>> Thanks for explaination. ?I tried to flip order for lhs/rhs in
>>> gimplify_modify_expr & co. ?Issue here is that for some cases we are
>>> relying here on lhs for gimplifying rhs (is_gimple_reg_rhs_or_call vs
>>> is_gimple_mem_rhs_or_call) and this doesn't work for cases in C++
>>> like:
>>>
>>> typedef const unsigned char _Jv_Utf8Const;
>>> typedef __SIZE_TYPE__ uaddr;
>>>
>>> void maybe_adjust_signature (_Jv_Utf8Const *&s, uaddr &special)
>>> {
>>> ?union {
>>> ? ?_Jv_Utf8Const *signature;
>>> ? ?uaddr signature_bits;
>>> ?};
>>> ?signature = s;
>>> ?special = signature_bits & 1;
>>> ?signature_bits -= special;
>>> ?s = signature;
>>> }
>>>
>>> So I modified gimplify_self_mod_expr for post-inc/dec so that we use
>>> following sequence
>>> and add it to pre_p for it:
>>>
>>> tmp = lhs;
>>> lvalue = tmp (+/-) rhs
>>> *expr_p = tmp;
>>
>> As I explained this is the wrong place to fix the PR. ?The issue is not
>> about self-modifying expressions but about evaluating call argument
>> side-effects before side-effects of the lhs.
>
> I am testing the attached instead.

Doesn't work.  Btw, Kai, your patch surely breaks things if you put
the lvalue update into the pre queue.

Consider a simple

 a[i++] = i;

you gimplify that to

  i.0 = i;
  D.1709 = i.0;
  i = D.1709 + 1;
  a[D.1709] = i;

which is wrong.

Seems we are lacking some basic pre-/post-modify testcases ...

Richard.