public void addPhiInsnForReg(RegisterSpec resultSpec) {
    insns.add(0, new PhiInsn(resultSpec, this));
  }
Adds a phi insn to the beginning of this block. This is to be used when the result type or
local-association can be determined at phi insert time.

@param resultSpec {@code non-null;} reg
android/android_framework/dex-maker/src/main/java/com/android/dx/ssa/SsaBasicBlock.java