From 7d2013d3f14aa3ab57ed4d3bfb005533fd4cbbed Mon Sep 17 00:00:00 2001
From: Adam Sampson <ats@offog.org>
Date: Tue, 24 Apr 2007 13:03:08 +0000
Subject: [PATCH] Generate more natural replicator loops when base == 0

---
 fco2/GenerateC.hs | 28 +++++++++++++++++++++++++---
 fco2/TODO         |  6 +++---
 2 files changed, 28 insertions(+), 6 deletions(-)

diff --git a/fco2/GenerateC.hs b/fco2/GenerateC.hs
index 33ca75d..ad99778 100644
--- a/fco2/GenerateC.hs
+++ b/fco2/GenerateC.hs
@@ -544,17 +544,39 @@ genReplicator rep body
           body
           tell ["}\n"]
 
+isZero :: A.Expression -> Bool
+isZero (A.ExprLiteral _ (A.Literal _ A.Int (A.IntLiteral _ "0"))) = True
+isZero _ = False
+
 genReplicatorLoop :: A.Replicator -> CGen ()
-genReplicatorLoop (A.For m n base count)
+genReplicatorLoop (A.For m index base count)
+    = if isZero base
+        then genSimpleReplicatorLoop index count
+        else genGeneralReplicatorLoop index base count
+
+genSimpleReplicatorLoop :: A.Name -> A.Expression -> CGen ()
+genSimpleReplicatorLoop index count
+    =  do tell ["int "]
+          genName index
+          tell [" = 0; "]
+          genName index
+          tell [" < "]
+          genExpression count
+          tell ["; "]
+          genName index
+          tell ["++"]
+
+genGeneralReplicatorLoop :: A.Name -> A.Expression -> A.Expression -> CGen ()
+genGeneralReplicatorLoop index base count
     =  do counter <- makeNonce "replicator_count"
           tell ["int ", counter, " = "]
           genExpression count
           tell [", "]
-          genName n
+          genName index
           tell [" = "]
           genExpression base
           tell ["; ", counter, " > 0; ", counter, "--, "]
-          genName n
+          genName index
           tell ["++"]
 
 genReplicatorSize :: A.Replicator -> CGen ()
diff --git a/fco2/TODO b/fco2/TODO
index 4e859d7..b016711 100644
--- a/fco2/TODO
+++ b/fco2/TODO
@@ -46,6 +46,9 @@ works correctly.
 
 ## Passes
 
+Expression simplification -- this should use generics, so that we can have a
+default behaviour that simplifies expressions inside another one.
+
 Output item expressions should be pulled up to variables.
 
 Before code generation, have a pass that resolves all the DATA TYPE .. IS
@@ -64,9 +67,6 @@ Multidimensional array literals won't work.
 We could have genSpec generate {} around specs if it's not immediately inside
 another spec (which'd require some extra boolean arguments to find out).
 
-Replicator loops should be special-cased for when base == 0 to generate the
-sort of loop a C programmer would normally write.
-
 genTopLevel should look at what interface the PROC is actually expecting, like
 occ21 does.