Like a byte code is really a Huffman encoding

Simply a minimum Huffman encoding of source code, defined for generic processors.  And a compiler is just that, it is building the expression graph, as a block structure, expanding ll the expression in the source.  Along the way, at any given node, the optimizer notices a frequency of reference, and 'quantizes' that variable to an internal register. It has quite a bit of freedom since today's processors have much internal memory.