Re: [PATCH v2] fix PR 103143

[Martin Sebor <msebor@gmail.com>]

On 12/6/21 1:14 PM, Jeff Law wrote:
> 
> 
> On 12/6/2021 10:31 AM, Martin Sebor wrote:
>> I have broken up the patch into a series of six.  Attached is
>> part (1), the fix for the typo that causes PR 103143.
>>
>> On 12/3/21 5:00 PM, Jeff Law wrote:
>>>
>>>
>>> On 11/8/2021 7:34 PM, Martin Sebor via Gcc-patches wrote:
>>>> The pointer-query code that implements compute_objsize() that's
>>>> in turn used by most middle end access warnings now has a few
>>>> warts in it and (at least) one bug.  With the exception of
>>>> the bug the warts aren't behind any user-visible bugs that
>>>> I know of but they do cause problems in new code I've been
>>>> implementing on top of it.  Besides fixing the one bug (just
>>>> a typo) the attached patch cleans up these latent issues:
>>>>
>>>> 1) It moves the bndrng member from the access_ref class to
>>>>    access_data.  As a FIXME in the code notes, the member never
>>>>    did belong in the former and only takes up space in the cache.
>>>>
>>>> 2) The compute_objsize_r() function is big, unwieldy, and tedious
>>>>    to step through because of all the if statements that are better
>>>>    coded as one switch statement.  This change factors out more
>>>>    of its code into smaller handler functions as has been suggested
>>>>    and done a few times before.
>>>>
>>>> 3) (2) exposed a few places where I fail to pass the current
>>>>    GIMPLE statement down to ranger.  This leads to worse quality
>>>>    range info, including possible false positives and negatives.
>>>>    I just spotted these problems in code review but I haven't
>>>>    taken the time to come up with test cases.  This change fixes
>>>>    these oversights as well.
>>>>
>>>> 4) The handling of PHI statements is also in one big, hard-to-
>>>>    follow function.  This change moves the handling of each PHI
>>>>    argument into its own handler which merges it into the previous
>>>>    argument.  This makes the code easier to work with and opens it
>>>>    to reuse also for MIN_EXPR and MAX_EXPR.  (This is primarily
>>>>    used to print informational notes after warnings.)
>>>>
>>>> 5) Finally, the patch factors code to dump each access_ref
>>>>    cached by the pointer_query cache out of pointer_query::dump
>>>>    and into access_ref::dump.  This helps with debugging.
>>>>
>>>> These changes should have no user-visible effect and other than
>>>> a regression test for the typo (PR 103143) come with no tests.
>>>> They've been tested on x86_64-linux.
>>> Sigh.  You've identified 6 distinct changes above.  The 5 you've 
>>> enumerated plus a typo fix somewhere.  There's no reason why they 
>>> need to be a single patch and many reasons why they should be a 
>>> series of independent patches.    Combining them into a single patch 
>>> isn't how we do things and it hides the actual bugfix in here.
>>>
>>> Please send a fix for the typo first since that should be able to 
>>> trivially go forward.  Then  a patch for item #1.  That should be 
>>> trivial to review when it's pulled out from teh rest of the patch. 
>>> Beyond that, your choice on ordering, but you need to break this down.
>>>
>>>
>>>
>>>
>>> Jeff
>>>
>>
>>
>> gcc-103413.diff
>>
>> commit 9a5bb7a2b0cdb8654061d9cba543c1408fa7adc9
>> Author: Martin Sebor<msebor@redhat.com>
>> Date:   Sat Dec 4 16:22:07 2021 -0700
>>
>>      Use the recursive form of compute_objsize [PR 103143].
>>      
>>      gcc/ChangeLog:
>>      
>>              PR middle-end/103143
>>              * pointer-query.cc (gimple_call_return_array): Call compute_objsize_r.
>>      
>>      gcc/testsuite/ChangeLog:
>>              PR middle-end/103143
>>              * gcc.dg/Wstringop-overflow-83.c: New test.
> Thanks.  Presumably by going through the public API, qry->depth got 
> reset to 0  and/or we'd get a re-initialized snlim at each call, leading 
> to the infinite recursion?

Yes, each call creates a new ssa_name_limit_t::visited bitmap.
It might be better to make compute_objsize_r() a member of
the same class as the bitmap and also rename it, to make it
harder to make this mistake again.

Martin

> 
> OK for the trunk.  Thanks for breaking this out.
> 
> jeff
>