"The syntax trees described in section 3.3.1 are not always optimally suitable forcompilation. They contain a lot of redundant information: Parentheses, keywordsused for grouping purposes only, and so on.
Abstract syntax keeps the essence of the structure of the text but omits the irrelevant details. An abstract syntax tree is a tree structure where each node correspondsto one or more nodes in the (concrete) syntax tree"
Gimple + Tree SSA Optimizer
使用vitrual register (可有無限多個registers)
register allocation (virtual register => hard register)