Re: [GOOGLE] More strict checking for call args

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

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.

>> 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