Adjusted the C backend to work with the new step count

backends/GenerateC.hs

@@ -1104,31 +1104,13 @@ cgenReplicatorStart n rep
 cgenReplicatorEnd :: A.Replicator -> CGen ()
 cgenReplicatorEnd rep = tell ["}"]
 
-isZero :: A.Expression -> Bool
-isZero (A.Literal _ A.Int (A.IntLiteral _ "0")) = True
-isZero _ = False
-
 cgenReplicatorLoop :: A.Name -> A.Replicator -> CGen ()
-cgenReplicatorLoop index (A.For m base count)
-    = if isZero base
-        then simple
-        else general
-  where
-    simple :: CGen ()
-    simple
-        =  do tell ["int "]
-              genName index
-              tell ["=0;"]
-              genName index
-              tell ["<"]
-              call genExpression count
-              tell [";"]
-              genName index
-              tell ["++"]
-
-    general :: CGen ()
-    general
-        =  do counter <- csmLift $ makeNonce "replicator_count"
+cgenReplicatorLoop index (A.For m base count step)
+  -- It is now too hard to work out statically if we could make this a
+  -- simple loop (without an additional counter), because step may be
+  -- negative (and that may be determined at run-time.  So we will generate the
+  -- most general loop, and let the C compiler optimise if possibe:
+    =      do counter <- csmLift $ makeNonce "replicator_count"
               tell ["int ", counter, "="]
               call genExpression count
               tell [","]
@@ -1137,7 +1119,8 @@ cgenReplicatorLoop index (A.For m base count)
               call genExpression base
               tell [";", counter, ">0;", counter, "--,"]
               genName index
-              tell ["++"]
+              tell ["+="]
+              call genExpression step
 cgenReplicatorLoop _ _ = cgenMissing "ForEach loops not yet supported in the C backend"
 --}}}
 

backends/GenerateCTest.hs

@@ -450,10 +450,8 @@ testOverArray = TestList $ map testOverArray'
 testReplicator :: Test
 testReplicator = TestList
  [
-  testBothSame "testReplicator 0" "for(int foo=0;foo<10;foo++){" (tcall2 genReplicatorStart foo
-    (A.For emptyMeta (intLiteral 0) (intLiteral 10)))
-  ,testBothSameR "testReplicator 1" "for\\(int ([[:alnum:]_]+)=10,foo=1;\\1>0;\\1--,foo\\+\\+\\)\\{" (tcall2 genReplicatorStart
-    foo (A.For emptyMeta (intLiteral 1) (intLiteral 10)))
+  testBothSameR "testReplicator 1" "for\\(int ([[:alnum:]_]+)=10,foo=1;\\1>0;\\1--,foo\\+=3\\)\\{" (tcall2 genReplicatorStart
+    foo (A.For emptyMeta (intLiteral 1) (intLiteral 10) (intLiteral 3)))
  ]
 
 testDeclaration :: Test