private void removeFromUseList(SsaInsn insn, RegisterSpecList oldSources) {
    if (oldSources == null) {
      return;
    }

    int szNew = oldSources.size();
    for (int i = 0; i < szNew; i++) {
      if (!useList[oldSources.get(i).getReg()].remove(insn)) {
        throw new RuntimeException("use not found");
      }
    }
  }
Removes a given {@code insn} from the use lists for the given {@code oldSources} (rather than
the sources currently returned by insn.getSources()).

@param insn {@code non-null;} insn in question
@param oldSources {@code null-ok;} registers whose use lists {@code insn} should be removed
    form
android/android_framework/dex-maker/src/main/java/com/android/dx/ssa/SsaMethod.java