Initial import of l4c

[snipe.git] / README

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 README
 ------
 
 README
 ------
 

-This compiler is a big long chain of modules that transform l3 code into
+This compiler is a big long chain of modules that transform l4 code into

 x86_64 assembly.
 
 x86_64 assembly.
 

-Here is a breakdown of the modules and changes from l2:
+Here is a breakdown of the modules and changes from l3:

 
 

-  * The parser.  The parser was mainly brought in from lab 2, and mainly
-    just a straight-forward extension of the l2 parser.  We added the
-    ability to parse functions, function calls, and variable declarations.
+  * The parser.  The parser was mainly brought in from lab 3, and mainly
+    just a straight-forward extension of the l3 parser.  We changed asops,
+    since they now side-effect and need special properties.  We also added
+    dereferences, arrays, other nice things.
+    
+  * AST utilities.  Some of those now exist to make common operations on raw
+    AST structures less painful.

 
 

-  * The typechecker.  This module is mostly the same as that from l2. It
-    performs function-related typechecking as well now, such as ensuring
-    that the correct number of arguments is supplied in a function call,
-    that there are no multiple definitions of functions, and that there is a
-    main function that takes only one argument.
+  * The typechecker.  The typechecker was significantly revamped.  A
+    'typeof' function was added that did most of the typechecking work;
+    the rest was relatively trivial compared to typeof.  There were many
+    annoying things other than typeof, but typeof was the most interesting
+    to comment on.

 
 

-  * The translator was extended with a CALL.
+  * The translator was extended with support for sizing up structs.  It now
+    is smarter about translating asops.  A MEMORY thingo was added to the
+    Tree, as was ALLOC.

 
 

-  * The munch module was also extended with the ability to munch CALL; a
-    major improvement was made when we realized we could determine what
-    expressions had effects and what had fixed registers. Any expressions
-    that use no fixed registers and have no effects can be reordered during
-    evaluation of a function call's arguments. This enabled us to save a
-    bunch of register-register moves. Saving the caller save registers is
-    left to the liveness analyzer, which we believe results in substantially
-    better code than saving and restoring all caller saves.
+  * The x86/munch modules were extended with support for multiple operand
+    sizes.  This was done in a fashion of extreme type A, and needs to be
+    blasted before the next lab, for it is worthless, terrible, awful, ... A
+    major falling-down of this compiler is that it passes size information
+    around in no less than 235784 different fashions, and the translation
+    between each has caused us no end of grief.  If we had time to rewrite
+    it instead of firefighting broken tests, uh... we would.  Many of our
+    optimizations from last lab needed to be commented out because of this
+    temporary sizing sadness.

 
 

-  * The liveness analyzer remains in more or less the same form, but with
-    substantial performance and cleanliness improvements by replacing lists
-    with maps (via BinaryMapFn) and sets (via ListSetFn). Also, a bug of
-    incredible type A was discovered through much pain and suffering, and
-    promptly fixed; it involved not realizing that a def on one line led to
-    an interference on any succeeding lines. Somehow we got away with this
-    for lab 2. Otherwise, we just explicitly state rules to generate
-    def/use/succ predicates which we then iterate over to find a fixed point
-    for livenesses using the standard rules.
+  * The liveness analyzer was mainly unchanged, but for a few rules.

 
 

-  * The grapher was changed to use the binary map and list set for
-    performance boosts (needed to pass certain large tests, like
-    pine-tree_print.l3). It generates an interference graph from a list of
-    livenesses at each source line.
+  * The grapher was fully unchanged.  Nice.

 
 

-  * The color orderer had no changes.
+  * The color orderer was fully unchanged.  Nice.

 
 

-  * The coloring module was slightly updated to recognize more fixed-color
-    registers. It implements a greedy coloring algorithm.
+  * The coloring module was fully unchanged.  Nice.

 
 

-  * The solidifier was modified to change the callee save system. Now we
-    only save the registers we need to. This improvement was pushed by
-    excessively slow execution time on one of the tests.
+  * The solidifier was modified to deal with the fact that certain things
+    could not be accessed directly.  It, too, has become an unmitigated
+    disaster.  It must deal with all 875847384 of the sizes, and I am sad
+    about this.

 
 

-  * The peepholer is upgraded somewhat; it now eliminates more redundant
-    instructions (such as adding/subtracting 0).
+  * The peepholer lost one form of fail and loss sizing.

 
   * The stringifier is of no interest to you, for it does real things that
     interact with the real world, and that is not of interest to people who
 
   * The stringifier is of no interest to you, for it does real things that
     interact with the real world, and that is not of interest to people who