Compiler
========

This chapter describes the design of the compiler.


Overview
--------

The compiler consists a frontend, mid-end and back-end. The frontend deals with
source file parsing and semantics checking. The mid-end performs optimizations.
This is optional. The back-end generates machine code. The front-end produces
intermediate code. This is a simple representation of the source. The back-end
can accept this kind of representation. This way the compiler is portable and
a front end can be constructed without having to do the rest.

.. graphviz::
  
   digraph x {
   rankdir="LR"
   1 [label="c3 source file"]
   10 [label="c3 front end" ]
   11 [label="language X front end" ]
   20 [label="mid end" ]
   30 [label="back end for X86" ]
   31 [label="back end for ARM" ]
   40 [label="object file"]
   1 -> 10
   10 -> 20 [label="IR-code"]
   11 -> 20 [label="IR-code"]
   20 -> 30 [label="IR-code"]
   20 -> 31 [label="IR-code"]
   30 -> 40
   }

IR-code
-------
The IR-code is implemented in the ir package.

.. autoclass:: ir.Module

.. autoclass:: ir.Function

.. autoclass:: ir.Block

.. autoclass:: ir.Statement

.. autoclass:: ir.Expression

.. # .. inheritance-diagram:: ir.Statement

C3 Front-end
------------

For the front-end a recursive descent parser is created for the c3 language.
This is a subset of the C language with some additional features.

.. graphviz::
  
   digraph c3 {
   rankdir="LR"
   1 [label="source text"]
   10 [label="lexer" ]
   20 [label="parser" ]
   30 [label="semantic checks" ]
   40 [label="code generation"]
   99 [label="IR-code object"]
   1 -> 20
   20 -> 30
   30 -> 40
   40 -> 99
   subgraph rel1 {
    edge [dir=none]
    10 -> 20
   }
   }

.. autoclass:: c3.Builder

.. autoclass:: c3.Parser

.. autoclass:: c3.CodeGenerator

Back-end
--------

The back-end is more complicated. There are several steps to be taken here.

1. Instruction selection
2. register allocation
3. Peep hole optimization?
4. real code generation

.. automodule:: codegen
   :members:

Instruction selection
~~~~~~~~~~~~~~~~~~~~~

The instruction selection phase takes care of scheduling and instruction
selection.  The output of this phase is a one frame per function with a flat
list of abstract machine instructions.

.. autoclass:: irmach.Frame

.. autoclass:: irmach.AbstractInstruction