RFR(XS) 8026940: assert(n->outcnt() != 0 || C->top() == n || n->is_Proj()) failed: No dead instructions after post-alloc

[Niclas Adlertz]

Hi all,

When removing junk phi nodes in post_allocate_copy_removal() we don't check if the inputs of the phi node die.
This results in 'assert(n->outcnt() != 0 || C->top() == n || n->is_Proj()) failed: No dead instructions after post-alloc'.
Fix is to remove input recursively if they go dead.

Tested with JPRT and CTW. Fixes the IeeeRecommendedTests failure.

WEBREV: http://cr.openjdk.java.net/~adlertz/JDK-8026940/webrev00
JBS: https://bugs.openjdk.java.net/browse/JDK-8026940

Kind Regards,
Niclas Adlertz