GitLab

a function

(for calling convention)

was using nalgebra::DMatrix to implement a graph

1. grow/shrink frame size in the pro/epilogue. Note: though we removed
push/pop for unused callee saved registers, we still reserve frame space
for them. Because we generate spill on frame before we know exactly how
large a space is. The solution is to make spill locations patchable.
2. control flow will combine branches in switch instruction if they all
target the same destination.

(for callee saved regs, we insert push/pop before reg alloc. and
after allocation, remove unnecessary ones)

we never go back to previous passes, since it is not necessary

some refactoring: 1. allows reg alloc using other allocators (other than graph coloring), 2. allows retreat to a previous compilation pass