[GOOGLE] More strict checking for call args

[Xinliang David Li]

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.

The case in reality is very rare -- most of the cases, the
transformation is good.

>
>>> 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?

It uses the most frequent target -- but the target id recorded for the
most frequent target might be corrupted and got mapped to a false
target during profile-use.

David

>
> 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