RFR: sh/jdk11 assert failure because IfNode input is a Phi

[Roland Westrelin]

> http://cr.openjdk.java.net/~roland/shenandoah/LRBafterCallUseBool/webrev.00/

I was trying to write a test case for that bug so I could fix it in
jdk/jdk and then I realized that the fix above was addressing the
consequence of logic that was missing and should have been
backported. So I'd like to back it out and backport what's missing
instead:

http://cr.openjdk.java.net/~roland/shenandoah/LRBafterCallUseBool/webrev.01/

Roland.