Re: [PATCH] tree-sra: Avoid returns of references to SRA candidates

[Richard Biener <rguenther@suse.de>]

> Am 28.11.2023 um 17:59 schrieb Jan Hubicka <hubicka@ucw.cz>:
> 
> 
>> 
>>> On Tue, 28 Nov 2023, Martin Jambor wrote:
>>> 
>>> On Tue, Nov 28 2023, Richard Biener wrote:
>>>> On Mon, 27 Nov 2023, Martin Jambor wrote:
>>>> 
>>>>> Hi,
>>>>> 
>>>>> The enhancement to address PR 109849 contained an importsnt thinko,
>>>>> and that any reference that is passed to a function and does not
>>>>> escape, must also not happen to be aliased by the return value of the
>>>>> function.  This has quickly transpired as bugs PR 112711 and PR
>>>>> 112721.
>>>>> 
>>>>> Just as IPA-modref does a good enough job to allow us to rely on the
>>>>> escaped set of variables, it sems to be doing well also on updating
>>>>> EAF_NOT_RETURNED_DIRECTLY call argument flag which happens to address
>>>>> exactly the situation we need to avoid.  Of course, if a call
>>>>> statement ignores any returned value, we also do not need to check the
>>>>> flag.
>>>> 
>>>> But what about EAF_NOT_RETURNED_INDIRECTLY?  Don't you need to
>>>> verify the parameter doesn't escape through the return at all?
>>>> 
>>> 
>>> I thought EAF_NOT_RETURNED_INDIRECTLY prohibits things like "return
>>> param->next" but those are not a problem (whatever next points to cannot
>>> be an SRA candidate and any ADDR_EXPR storing its address there would
>>> trigger a disqualification or at least an assert).  But I guess I am
>>> wrong, what is actually the exact meaning of the flag?
>> 
>> I thought it's return (x.ptr = param, &x);
>> 
>> so the parameter is reachable from the return value.
>> 
>> But let's Honza answer...
> It is same difference as direct/indirect escape. so it check whether
> values pointed to by arg can be possibly returned.  Indeed maybe we
> should think of better name - the other interpretation did not even
> occur to me, but it makes sense.

So does the directly returned flag cover my interpretation of indirect or is there a hole?

Richard 

> Honza
>> 
>> Richard.