Re: [PING #2] [PATCH] enhance -Wrestrict to handle string built-ins (PR 78918)

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

On Tue, Aug 1, 2017 at 11:23 AM, Richard Biener
<richard.guenther@gmail.com> wrote:
> On Tue, Aug 1, 2017 at 4:27 AM, Martin Sebor <msebor@gmail.com> wrote:
>> Richard,
>>
>> in discussing this work Jeff mentioned that your comments on
>> the tree-ssa-alias.c parts would be helpful.  When you have
>> a chance could you please give it a once over and let me know
>> if you have any suggestions or concerns?  There are no visible
>> changes to existing clients of the pass, just extensions that
>> are relied on only by the new diagnostics.
>>
>>   https://gcc.gnu.org/ml/gcc-patches/2017-07/msg01264.html
>>
>> I expect to revisit the sprintf %s patch mentioned below and
>> see how to simplify it by taking advantage of the changes
>> implemented here.
>
> Your ptr_deref_alias_decl_p returns true when must_alias is true
> but there is no must-alias relationship.
>
> The ao_ref_init_from_ptr_and_size doesn't belong there.
>
> I dislike all of the changes related to returning an alias "size".
>
> Please keep away from the alias machinery.
>
> Warning during folding is similarly bad design.  Please don't add
> more such things.
>
> Thanks for putting this on my radar though.
> Richard.

Oh, for a constructive comment this all feels like sth for either
sanitizers or a proper static analysis tool.  As I outlined repeatedly
I belive GCC could host a static analysis tool but it surely should
not be interwinded into it's optimization passes or tools.

Richard.

>
>> Thanks
>> Martin
>>
>>
>> On 07/24/2017 09:13 PM, Martin Sebor wrote:
>>>
>>> Ping:
>>>
>>>   https://gcc.gnu.org/ml/gcc-patches/2017-07/msg01264.html
>>>
>>> This change is related to
>>>
>>>   [PATCH] enhance -Wrestrict for sprintf %s arguments
>>>   https://gcc.gnu.org/ml/gcc-patches/2017-07/msg01176.html
>>>
>>> On 07/20/2017 02:45 PM, Martin Sebor wrote:
>>>>
>>>> With more testing (building GDB, Glibc, Busybox, and the Linux
>>>> kernel) I found a few bugs and weaknesses in the initial patch.
>>>> Attached is version 2 that fixes the uncovered problems and makes
>>>> further enhancements to handle more cases.
>>>>
>>>> Martin
>>>>
>>>> On 07/16/2017 05:47 PM, Martin Sebor wrote:
>>>>>
>>>>> Being implemented in the front end, the -Wrestrict warning
>>>>> detects only trivial instances of violations.  The attached
>>>>> patch extends the implementation to the middle-end where
>>>>> data flow and alias analysis can be combined to detect even
>>>>> complex cases of overlap.  This work is independent of but
>>>>> follows on the patch below (waiting for review):
>>>>>
>>>>>   https://gcc.gnu.org/ml/gcc-patches/2017-07/msg00036.html
>>>>>
>>>>> The changes rely on extending the tree-ssa-{alias,structalias}
>>>>> machinery in a simple way to answer the "must-alias" kind of
>>>>> question in addition to the current "may-alias."
>>>>>
>>>>> The rest of the changes are in gimple-fold.c, tree-ssa-strlen.c,
>>>>> and builtins.c.
>>>>>
>>>>> Even though this change makes -Wrestrict a lot more useful, it's
>>>>> not a complete implementation.  Not all built-ins are handled yet
>>>>> (e.g., strncat), and support for user-defined functions is still
>>>>> subject to the limitations of the front end implementation.  To
>>>>> complete the support, handlers for the missing string built-ins
>>>>> will need to be added to tree-ssa-strlen.c, and the remaining
>>>>> bits should be moved from the front end to somewhere in
>>>>> the middle-end (e.g., calls.c).
>>>>>
>>>>> Martin
>>>>
>>>>
>>>
>>