misc/phases.md

-An incomplete short summary of all the compiler phases & traversals.
+This file holds an incomplete short summary of all the compiler phases & traversals.
 
 If you are reading a traversal you can come here and create or improve a summary of it to improve your and later others understanding of the traversal and the compiler as a whole.
 
 For the full picture of each traversal see the corresponding file in the `src` directory.
 
+The sac compiler operates in many phases. 
+Each phase is a composition of traversals and there are many traversals.
+It is best to work on a need to know basis with the traversals but it is good to have a rough idea of what each phase does.
+
+# Breaking at interesting phases
+
+You can stop at a certain phase by using the `-b` flag.
+For instance `-b 1` will stop after the first phase.
+It is a good idea to write a simple program and run the compiler increasing the number after the `-b` flag to see what each phase does.
+It is also a good idea to run with `-noprelude` to remove the prelude from the output which is introduced in phase 4.
+It is also a good idea to run with `-v 3` to see the names of each traversal in each phase.
+
+Looking before opt (optimizations), currently 10 or ewl and after opt is always interesting.
+After opt if you don't have with loops you can mostly skip to 16 or mem.
+After `mem` the code starts to looks a lot less readable.
+
+The code gen phase (22 or cg) is quite interesting if you do `-b cg` you will get nothing.
+At the end of dm `-b dm` there are only assignments, primitive functions and do-while loops and conditions left.
+(The do-while loops and conditions are reintroduced in ussa:f2l)
+
+With `-b cg:cpl` is an crazy traversal of 10k loc which turns all the assignments and primitive functions into [intermediate code macros]() (CPL)
+At this point the code is actually quite readable again because all the primitive functions applications and assignments are turned into macros.
+
+# Phases 
+
+
+
+
+##  1: Loading SAC program ...
+
+Locate and load the given SAC program source code.
+Run the C preprocessor on the source code.
+Lex and parse it into an ast.
+
+##  2: Preprocessing type patterns ...
+
+Run the type pattern preprocessor on the ast.
+
+##  3: Preprocessing SAC program ...
+
+##  4: Running module system ...
+
+##  5: Simplifying source code ...
+
+##  6: Converting to static single assignment form ...
+
+##  7: Running type inference system ...
+
+##  8: Processing exports ...
+
+##  9: Preparing for code optimization ...
+
+## 10: Enhancing with-loops ...
+
+## 11: Running SAC optimizations ...
+
+## 12: Automatic parallelisation for GPUs skipped.
+
+## 13: Transforming with-loop representation ...
+
+## 14: Running 3rd generation multithreading skipped.
+
+## 15: Introducing task parallelization skipped.
+
+## 16: Introducing memory management instructions ...
+
+## 17: Introduce profiling instruction ...
+
+## 18: Converting from static single assignment form ...
+
+## 19: Running automatic parallelisation skipped.
+
+## 20: Preparing C code generation ...
+
+## 21: Distributed Memory skipped.
+
+## 23: Generating Code ...
+
+
+----
+
+# Traversals 
+
 # Loading SAC program
 
 In this phase the compiler loads the given SAC program.
@@ -191,3 +274,4 @@ To make sure the renaming is consistent with the previous 2 phases the same rena
 ## Hiding struct definition behind typedefs and accessors (hs)
 
 
+#
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