[14] RFR(S): 8228888: C2 compilation fails with assert "m has strange control"

[Vladimir Kozlov]

On 8/7/19 7:13 AM, Tobias Hartmann wrote:
> Hi,
> 
> please review the following patch:
> https://bugs.openjdk.java.net/browse/JDK-8228888
> http://cr.openjdk.java.net/~thartmann/8228888/webrev.00/

Good.

> 
> I found this while trying to write a regression test for another bug. The assert triggers when OSR
> compiling an infinite loop with two back branches (see StrangeControl.jasm):
> http://cr.openjdk.java.net/~thartmann/8228888/8228888_graph.png
> 
> PhaseIdealLoop::has_local_phi_input() tries to determine if all inputs of n (118 Phi) are block
> local phis. When looking at input m (108 StoreI), the assert fires because m is not a Phi and
> control of m (102 IfFalse) does not dominate control of n (83 Region).
> 
> I think the assert which was added by [1] is too strong. If n is a Phi itself, control of all its
> inputs does not need to dominate its own control.

Correct - loops are examples.

Thanks,
Vladimir

> 
> Thanks,
> Tobias
> 
> [1] https://bugs.openjdk.java.net/browse/JDK-8187822
>