TODO note in Main about stackification

3 files changed, 15 insertions, 1 deletions

diff --git a/Main.hs b/Main.hs
index c378dde..2173653 100644
--- a/Main.hs
+++ b/Main.hs
@@ -38,6 +38,17 @@ parseOptions' (_, Just _) (_:_) = putStrLn "At most one filename argument expect
 parseOptions :: [String] -> IO (Options, Maybe FilePath)
 parseOptions = parseOptions' (Options False False, Nothing)
 
+-- TODO: Note about stackification. Temporaries need to be pushed before
+-- a call if they're live after it and they could, conceivably, be wrongly
+-- mutated by the called function otherwise. This has a couple of
+-- interesting consequences:
+-- 1. No temporaries ever need to be pushed from the global context, or
+--    "main function", since they can never be wrongly mutated: that
+--    requires re-entering the function in which they were defined, but one
+--    can never re-enter the "main function".
+-- 2. No temporaries ever need to be pushed before a tail call; since no
+--    local variables are live after it (obviously). (Global variables are
+--    covered by point (1.).)
 liveness :: IRProgram -> Map.Map Int [Set.Set Int]
 liveness (IRProgram bbs _ _) =
     let sets = livenessAnalysis bbs bidOf itemsOf outEdges fread fwrite
diff --git a/Util.hs b/Util.hs
index 11b5658..9c3fbf0 100644
--- a/Util.hs
+++ b/Util.hs
@@ -1,5 +1,8 @@
+{-# LANGUAGE TupleSections #-}
 module Util where
 
+import Data.Function (on)
+import Data.List
 import qualified Data.Map.Strict as Map
 
 
diff --git a/lisphs.cabal b/lisphs.cabal
index 3bde869..32aebbe 100644
--- a/lisphs.cabal
+++ b/lisphs.cabal
@@ -13,4 +13,4 @@ executable            lisp
     ghc-options:      -Wall -O2
     build-depends:    base >= 4 && < 5,
                       containers, filepath, mtl, parsec, text
-    other-modules:    AST, Compiler, CompilerMacros, DString, Intermediate, Liveness, Optimiser, Parser, VM
+    other-modules:    AST, Compiler, CompilerMacros, DString, Intermediate, Liveness, Optimiser, Parser, Util, VM