Re: [GOOGLE] More strict checking for call args

[Dehao Chen <dehao at google dot com>]

On Fri, Jun 7, 2013 at 6:47 AM, Richard Biener
<richard.guenther@gmail.com> wrote:
> On Fri, Jun 7, 2013 at 3:30 PM, Xinliang David Li <davidxl@google.com> wrote:
>> On Fri, Jun 7, 2013 at 2:05 AM, Richard Biener
>> <richard.guenther@gmail.com> wrote:
>>> On Thu, Jun 6, 2013 at 5:10 PM, Dehao Chen <dehao@google.com> wrote:
>>>> Hi, Martin,
>>>>
>>>> Yes, your patch can fix my case. Thanks a lot for the fix.
>>>>
>>>> With the fix, value profiling will still promote the wrong indirect
>>>> call target. Though it will not be inlining, but it results in an
>>>> additional check. How about in check_ic_target, after calling
>>>> gimple_check_call_matching_types, we also check if number of args
>>>> match number of params in target->symbol.decl?
>>>
>>> I wonder what's the point in the gimple_check_call_matching_types check
>>> in the profiling case.  It's at least no longer
>>>
>>> /* Perform sanity check on the indirect call target. Due to race conditions,
>>>    false function target may be attributed to an indirect call site. If the
>>>    call expression type mismatches with the target function's type, expand_call
>>>    may ICE.
>>>
>>> because since the introduction of gimple_call_fntype we will _not_ ICE.
>>>
>>> Thus I argue that check_ic_target should be even removed instead of
>>> enhancing it!
>>>
>>
>> Another reason is what Dehao had mentioned -- wrong target leads to
>> useless transformation.
>
> Sure, but a not wrong in the sense of the predicate does not guarantee
> a useful transformation either.

True, but at least it will filter some obvious bad transformations.

Another important factor is for AutoFDO, which uses source lineno to
map profile to IR. So when the source has changed, it could literally
map anything to an indirect call target. check_ic_target can actually
filter out most of the incorrect targets.

Thanks,
Dehao

>
>>> How does IC profiling determine the called target?  That is, what does it
>>> do when the target is not always the same?  (because the checking code
>>> talks about race conditions for example)
>>
>>
>> The race condition is the happening at instrumentation time -- the
>> indirect call counters are not thread local. We have seen this a lot
>> in the past that a totally bogus target is attributed to a indirect
>> callsite.
>
> So it simply uses whatever function was called last?  Instead of
> using the function that was called most of the time?
>
> Richard.
>
>> thanks,
>>
>> David
>>>
>>> Richard.
>>>
>>>
>>>> Thanks,
>>>> Dehao
>>>>
>>>>
>>>> On Thu, Jun 6, 2013 at 7:11 AM, Martin Jambor <mjambor@suse.cz> wrote:
>>>>>
>>>>> Hi,
>>>>>
>>>>> On Tue, Jun 04, 2013 at 05:19:02PM -0700, Dehao Chen wrote:
>>>>> > attached is a testcase that would cause problem when source has changed:
>>>>> >
>>>>> > $ g++ test.cc -O2 -fprofile-generate -DOLD
>>>>> > $ ./a.out
>>>>> > $ g++ test.cc -O2 -fprofile-use
>>>>> > test.cc:34:1: internal compiler error: in operator[], at vec.h:815
>>>>> >  }
>>>>> >  ^
>>>>> > 0x512740 vec<tree_node*, va_heap, vl_embed>::operator[](unsigned int)
>>>>> > ../../gcc/vec.h:815
>>>>> > 0x512740 vec<tree_node*, va_heap, vl_ptr>::operator[](unsigned int)
>>>>> > ../../gcc/vec.h:1244
>>>>> > 0xf24464 vec<tree_node*, va_heap, vl_embed>::operator[](unsigned int)
>>>>> > ../../gcc/vec.h:815
>>>>> > 0xf24464 vec<tree_node*, va_heap, vl_ptr>::operator[](unsigned int)
>>>>> > ../../gcc/vec.h:1244
>>>>> > 0xf24464 ipa_get_indirect_edge_target_1
>>>>> > ../../gcc/ipa-cp.c:1535
>>>>> > 0x971b9a estimate_edge_devirt_benefit
>>>>> > ../../gcc/ipa-inline-analysis.c:2757
>>>>>
>>>>> Hm, this seems rather like an omission in ipa_get_indirect_edge_target_1.
>>>>> Since it is called also from inlining, we can have parameter count
>>>>> mismatches... and in fact in non-virtual paths of that function we do
>>>>> check that we don't.  Because all callers have to pass known_vals
>>>>> describing all formal parameters of the inline tree root, we should
>>>>> apply the fix below (I've only just started running a bootstrap and
>>>>> testsuite on x86_64, though).
>>>>>
>>>>> OTOH, while I understand that FDO can change inlining sufficiently so
>>>>> that this error occurs, IMHO this should not be caused by outdated
>>>>> profiles but there is somewhere a parameter mismatch in the source.
>>>>>
>>>>> Dehao, can you please check that this patch helps?
>>>>>
>>>>> Richi, if it does and the patch passes bootstrap and tests, is it OK
>>>>> for trunk and 4.8 branch?
>>>>>
>>>>> Thanks and sorry for the trouble,
>>>>>
>>>>> Martin
>>>>>
>>>>>
>>>>> 2013-06-06  Martin Jambor  <mjambor@suse.cz>
>>>>>
>>>>>         * ipa-cp.c (ipa_get_indirect_edge_target_1): Check that param_index is
>>>>>         within bounds at the beginning of the function.
>>>>>
>>>>> Index: src/gcc/ipa-cp.c
>>>>> ===================================================================
>>>>> --- src.orig/gcc/ipa-cp.c
>>>>> +++ src/gcc/ipa-cp.c
>>>>> @@ -1481,7 +1481,8 @@ ipa_get_indirect_edge_target_1 (struct c
>>>>>    tree otr_type;
>>>>>    tree t;
>>>>>
>>>>> -  if (param_index == -1)
>>>>> +  if (param_index == -1
>>>>> +      || known_vals.length () <= (unsigned int) param_index)
>>>>>      return NULL_TREE;
>>>>>
>>>>>    if (!ie->indirect_info->polymorphic)
>>>>> @@ -1516,8 +1517,7 @@ ipa_get_indirect_edge_target_1 (struct c
>>>>>             t = NULL;
>>>>>         }
>>>>>        else
>>>>> -       t = (known_vals.length () > (unsigned int) param_index
>>>>> -            ? known_vals[param_index] : NULL);
>>>>> +       t = NULL;
>>>>>
>>>>>        if (t &&
>>>>>           TREE_CODE (t) == ADDR_EXPR