[PATCH] Proposal on how to fix temporary dtors.

[Manuel Klimek]

Some more context:
It seems like we already need to do that when building the CFG: for the
lifetime extended object we must not emit the destructor at the end of the
full expression, which we currently do.


On Mon, Jul 28, 2014 at 3:03 PM, Manuel Klimek <klimek at google.com> wrote:

> On Mon, Jul 7, 2014 at 10:15 PM, Jordan Rose <jordan_rose at apple.com>
> wrote:
>
>> Ah...then I'm glad we added the assertion. :-) Lifetime-extended
>> temporaries aren't quite implemented correctly yet, but we should probably
>> be removing or not even adding the state when the temporary is
>> lifetime-extended.
>>
>> Unfortunately I don't have this paged in, but there's logic in processing
>> auto destructors to handle this, and a bug (
>> http://llvm.org/bugs/show_bug.cgi?id=19539) about how it's wrong.
>>
>
> Ok, I dug into this a bit, and if I'm not missing something I think it's
> not possible to switch this off without implementing lifetime-extended
> temporaries correctly (or at least a similarly sized implementation effort):
> The only link between the MaterializeTempooraryExpr (which has the
> information whether the lifetime was extended) and the CXXBindTemporaryExpr
> is the underlying object storage. I looked into CodeGen, and if I
> understand it correctly, it looks like it basically stores for the
> destination whether the destructor was already handled (for example from
> the MaterializeTemporary flow). To get that information, I'd guess we need
> to do something similar in the static analyzer.
>
> I hope that my analysis is wrong and you tell me a better way to fix this
> :)
>
> Thanks!
> /Manuel
>
>
>>
>> Jordan
>>
>>
>> On Jul 7, 2014, at 13:13 , Manuel Klimek <klimek at google.com> wrote:
>>
>> Sigh. That triggers in Analysis/dtor.cpp for this CXXBindTemporaryExpr:
>> CXXBindTemporaryExpr 0x3c195d8 'class
>> LifetimeExtension::SaveOnVirtualDestruct' (CXXTemporary 0x3c195d0)
>>  `-CXXTemporaryObjectExpr 0x3c19590 'class
>> LifetimeExtension::SaveOnVirtualDestruct' 'void (void)'
>>
>> I assume something fishy is going on for lifetime extended temporaries...
>>
>>
>> On Mon, Jul 7, 2014 at 8:38 PM, Jordan Rose <jordan_rose at apple.com>
>> wrote:
>>
>>>
>>> On Jul 7, 2014, at 11:37 , Manuel Klimek <klimek at google.com> wrote:
>>>
>>> On Mon, Jul 7, 2014 at 8:05 PM, Jordan Rose <jordan_rose at apple.com>
>>> wrote:
>>>
>>>>
>>>> On Jul 7, 2014, at 10:50 , Manuel Klimek <klimek at google.com> wrote:
>>>>
>>>> On Mon, Jul 7, 2014 at 7:42 PM, Jordan Rose <jordan_rose at apple.com>
>>>> wrote:
>>>>
>>>>>
>>>>> On Jul 7, 2014, at 10:41 , Manuel Klimek <klimek at google.com> wrote:
>>>>>
>>>>> On Mon, Jul 7, 2014 at 7:38 PM, Jordan Rose <jordan_rose at apple.com>
>>>>> wrote:
>>>>>
>>>>>>
>>>>>> On Jul 7, 2014, at 10:37 , Manuel Klimek <klimek at google.com> wrote:
>>>>>>
>>>>>> On Mon, Jul 7, 2014 at 7:29 PM, Jordan Rose <jordan_rose at apple.com>
>>>>>> wrote:
>>>>>>
>>>>>>>
>>>>>>> On Jul 7, 2014, at 10:28 , Manuel Klimek <klimek at google.com> wrote:
>>>>>>>
>>>>>>> On Mon, Jul 7, 2014 at 6:48 PM, Jordan Rose <jordan_rose at apple.com>
>>>>>>> wrote:
>>>>>>>
>>>>>>>> Can you add an assertion at the end of a block that there are no
>>>>>>>> outstanding temporary destructors in the current stack frame? That seems
>>>>>>>> useful.
>>>>>>>>
>>>>>>>
>>>>>>> Do you mean at the end of a VisitBlockDecl?
>>>>>>>
>>>>>>>
>>>>>>> No, during the path-sensitive run, so handleBlockExit.
>>>>>>>
>>>>>>
>>>>>> So you mean at the end of a CFG block? But here we might have
>>>>>> outstanding temporary dtors open (?)
>>>>>>
>>>>>>
>>>>>> Oops, right. Was thinking too much in terms of AST structure. How
>>>>>> about at the end of a function (inlined or not)?
>>>>>>
>>>>>
>>>>> Could we say every time we transition from a block with a temp dtor
>>>>> terminator to a block that does not have a temp dtor terminator (or an
>>>>> unconditional terminator) we check?
>>>>>
>>>>>
>>>>> That sounds correct, but misses the case where we built the CFG wrong
>>>>> (forgetting to add the branch in the correct place and thus never getting
>>>>> to the temp dtor block at all).
>>>>>
>>>>
>>>> Makes sense. Do you have a hint where the right place on function exit
>>>> to check it would be? :)
>>>>
>>>>
>>>> *checks* ExprEngine::processEndOfFunction.
>>>>
>>>
>>> Hm, so we'll need to adjust the data structure to be indexed by stack
>>> frame somehow (use a map) instead of the pair<expr, stack-frame>?
>>>
>>>
>>> Eh, since it's an assertion I'd be fine with just iterating over it in a
>>> helper function. Or better, using std::find_if (if it has proper begin/end
>>> members).
>>>
>>
>>
>>
>
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