RFR(S): 8228839: Non-CFG nodes have control edges to calls, instead of the call's control projection

[Nils Eliasson]

Hi Vladimir,

I want the workaround in promtly because the issue causes noise in the 
bigapps testing which is really annoying, and might be hiding other 
problems.

The core issue - the PhaseIdealLoop::get_ctrl problem, might turn up 
quite large. Many types of MultiNodes, like calls and Membars are at 
times set incorrectly (often in loopopts). SafepointNodes are a direct 
subclass of MultiNodes but doesn't seem to use a control projection 
anywhere. (But calls that are a subclass of SafepointNodes expect it - 
very confusing).

It is also quite common that the node retrieved from a 
PhaseIdealLoop::get_ctrl(..) is set as control in another node, which 
propagates the problem.

I have tried to sanitize the ctrl-mapping by intercepting all MultiNodes 
(except SafePointNodes and StartNodes) in PhaseIdealLoop::set_ctrl(). 
That seems to solve all downstream issues (without causing new 
problems). But for a permanent fix I need to go through all the call 
sites of set_ctrl() and find out why they don't use the projection.

I also need to investigate why SafepointNodes don't use control 
projections, and what it would take to fix it.

Regards,

Nils


On 2019-08-21 17:36, Vladimir Kozlov wrote:
> Hi Nils,
>
> Did you find in which cases the control edge is set to Call node 
> directly?
>
> Since the fix for JDK 14 we have time to fix it correctly instead of 
> workaround.
>
> Thanks,
> Vladimir
>
> On 8/21/19 3:30 AM, Nils Eliasson wrote:
>> Hi,
>>
>> This is a workaround for the problem that sometimes non-CFG nodes 
>> have their ctrl (PhaseIdealLoop::get_ctrl(n)) set directly to calls, 
>> instead of the call's control projection. I'm working on a patch for 
>> that, but it might end up a bit intrusive. This is a workaround that 
>> simply checks and adjusts for that case.
>>
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8228839
>>
>> Webrev: http://cr.openjdk.java.net/~neliasso/8228839/webrev.01/
>>
>> Please review,
>>
>> // Nils
>>