Re: Question on Disable no throw for -flive-patching master option.

["Martin Liška" <mliska@suse.cz>]

Honza: PING^2

On 1/2/19 12:47 PM, Martin Liška wrote:
> Honza: PING
> 
> On 12/6/18 12:16 AM, Qing Zhao wrote:
>> Hi, Honza,
>>
>> I have one question relate to whether to disable nothrow for -flive-patching as following:
>>
>> actually, there are two passes here:
>>
>> 1. local nothrow pass:  in this pass, nothrow attribute is set locally after analyzing every stmt of the function
>> body: 
>>
>> unsigned int
>> pass_nothrow::execute (function *)
>> {
>>   struct cgraph_node *node;
>>   basic_block this_block;
>> …
>>
>> }
>>
>> 2. nothrow propagation pass:  (it’s included in the ipa_pure_const pass as following, propagate the nothrow 
>> attribute along callcgraph)
>>
>> unsigned int
>> pass_ipa_pure_const::
>> execute (function *)
>> {
>>   bool remove_p;
>>
>>   /* Nothrow makes more function to not lead to return and improve
>>      later analysis.  */
>>   propagate_nothrow ();
>>   propagate_malloc ();
>>   remove_p = propagate_pure_const ();
>>
>>   delete funct_state_summaries;
>>   return remove_p ? TODO_remove_functions : 0;
>> }
>>
>> the nothrow propagation pass is included in ipa_pure_const pass, and is guarded by flag_ipa_pure_const, 
>> this flag_ipa_pure_const is disabled when -flive-patching is ON.
>>
>>
>> So, my question is:
>>
>> shall we disable local nothrow pass as well when -flive-patching is ON?
>>
>> my understanding is: we should. 
>>
>> the reason is:   the local nothrow pass is setting the nothrow attribute for the current routine based on its
>> body,  and this “nothrow” attribute will be used  when generating EH code around callsite from the caller
>> of the routine. so the nothrow attribute might impact other routines than the current routine.  as a result,
>> we should disable this pass?
>>
>> what’s your opinion on this?
>>
>> thanks.
>>
>> Qing
>>
>>> On Nov 28, 2018, at 2:24 PM, Qing Zhao <qing.zhao@oracle.com <mailto:qing.zhao@oracle.com>> wrote:
>>>>
>>>> Shall we also disable nothrow or we will worry about C++ only ter?
>>>
>>> This is also mainly for C++ applications, so currently should not be a problem.
>>> But I can add a separate simple patch to add another flag to control nothrow propagation and disable it when -flive-patching is ON.
>>>
>>>>
>>>> Patch is OK,
>>>
>>> thanks for the review.
>>>
>>> I will commit the patch very soon.
>>>
>>> Qing
>>>> thanks!
>>>> Honza
>>