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

[Tobias Hartmann]

Hi,

please review the following patch:
https://bugs.openjdk.java.net/browse/JDK-8228888
http://cr.openjdk.java.net/~thartmann/8228888/webrev.00/

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.

Thanks,
Tobias

[1] https://bugs.openjdk.java.net/browse/JDK-8187822