What's special about gcc flags that start with "tree"?

Question

There are a lot of optimization settings starting with tree. Some are:

-ftree-builtin-call-dce
-ftree-ccp
-ftree-ch
-ftree-copyrename
-ftree-dce
-ftree-dominator-opts
-ftree-dse
-ftree-ter

What's special about those flags?

Answer 1

They all work with the tree representation of your source code.

Not sure exactly how GCC does it, but in general a compiler will parse your code and turn it into an abstract syntax tree, parse tree or similar structure. These optimizations work on that tree. Later, the tree will be used to generate the machine code.