public void upgradeToLiteral() {
    RegisterSpecList oldSources = insn.getSources();

    insn = insn.withSourceLiteral();
    getBlock().getParent().onSourcesChanged(this, oldSources);
  }
Upgrades this insn to a version that represents the constant source literally. If the upgrade
is not possible, this does nothing.

@see Insn#withSourceLiteral
android/android_framework/dex-maker/src/main/java/com/android/dx/ssa/NormalSsaInsn.java