private static void coInterferePhiRegisters(
      InterferenceGraph interference, RegisterSpec result, RegisterSpecList sources) {
    int resultReg = result.getReg();
    for (int i = 0; i < sources.size(); ++i) {
      interference.add(resultReg, sources.get(i).getReg());
    }
  }
Ensures that all the phi result registers for all the phis in the same basic block interfere
with each other, and also that a phi's source registers interfere with the result registers
from other phis. This is needed since the dead code remover has allowed through "dead-end phis"
whose results are not used except as local assignments. Without this step, a the result of a
dead-end phi might be assigned the same register as the result of another phi, and the phi
removal move scheduler may generate moves that over-write the live result.

@param ssaMeth {@code non-null;} method to process
@param interference {@code non-null;} interference graph
android/android_framework/dex-maker/src/main/java/com/android/dx/ssa/back/LivenessAnalyzer.java