simplify & fix recursion detector

compiler/test/TestCallgraph.kt

@@ -197,10 +197,7 @@ class TestCallgraph: FunSpec({
         callgraph.checkRecursiveCalls(errors)
         errors.errors.size shouldBe 0
         errors.warnings.size shouldBe 4
-        errors.warnings[0] shouldContain "contains recursive subroutine calls"
-        errors.warnings[1] shouldContain "start at"
-        errors.warnings[2] shouldContain "recurse1 at"
-        errors.warnings[3] shouldContain "recurse2 at"
+        errors.warnings[0] shouldContain "contains recursive subroutines"
     }
 
     test("no recursion warning if reference isn't a call") {

compilerAst/src/prog8/compiler/CallGraph.kt

@@ -129,54 +129,35 @@ class CallGraph(private val program: Program, private val allowMissingIdentifier
     }
 
     fun checkRecursiveCalls(errors: IErrorReporter) {
-        val cycles = recursionCycles()
-        if(cycles.any()) {
-            errors.warn("Program contains recursive subroutine calls. These only works in very specific limited scenarios!", cycles[0][0].position)
-            val printed = mutableSetOf<Subroutine>()
-            for(chain in cycles) {
-                if(chain[0] !in printed) {
-                    val chainStr = chain.joinToString(" <-- ") { "${it.name} at ${it.position}" }
-                    errors.warn("Cycle in (a subroutine call in) $chainStr", chain[0].position)
-                    printed.add(chain[0])
-                }
+        val recursiveSubroutines = recursionCycles()
+        if(recursiveSubroutines.any()) {
+            errors.warn("Program contains recursive subroutines. These only works in very specific limited scenarios!", recursiveSubroutines.first().position)
+            for(subroutine in recursiveSubroutines) {
+                errors.warn("recursive subroutine '${subroutine.name}'", subroutine.position)
             }
         }
     }
 
-    private fun recursionCycles(): List<List<Subroutine>> {
-        val chains = mutableListOf<MutableList<Subroutine>>()
+    private fun recursionCycles(): Set<Subroutine> {
+        val cycles = mutableSetOf<Subroutine>()
+
         for(caller in calls.keys) {
-            val visited = calls.keys.associateWith { false }.toMutableMap()
-            val recStack = calls.keys.associateWith { false }.toMutableMap()
-            val chain = mutableListOf<Subroutine>()
-            if(hasCycle(caller, visited, recStack, chain))
-                chains.add(chain)
+            if(hasRecursionCycle(caller))
+                cycles.add(caller)
         }
-        return chains
+        return cycles
     }
 
-    private fun hasCycle(sub: Subroutine, visited: MutableMap<Subroutine, Boolean>, recStack: MutableMap<Subroutine, Boolean>, chain: MutableList<Subroutine>): Boolean {
-        // mark current node as visited and add to recursion stack
-        if(recStack[sub]==true)
-            return true
-        if(visited[sub]==true)
-            return false
-
-        // mark visited and add to recursion stack
-        visited[sub] = true
-        recStack[sub] = true
-
-        // recurse for all neighbours
-        for(called in calls.getValue(sub)) {
-            if(hasCycle(called, visited, recStack, chain)) {
-                chain.add(called)
-                return true
+    private fun hasRecursionCycle(sub: Subroutine): Boolean {
+        val callCloud = calls.getValue(sub).toMutableSet()
+        var previousCloudSize = -1
+        while(callCloud.size > previousCloudSize && sub !in callCloud) {
+            previousCloudSize = callCloud.size
+            for(element in callCloud.toList()) {
+                callCloud.addAll(calls.getValue(element))
             }
         }
-
-        // pop from recursion stack
-        recStack[sub] = false
-        return false
+        return sub in callCloud
     }
 
     fun unused(module: Module) = module !in usedModules

docs/source/todo.rst

@@ -3,8 +3,14 @@ TODO
 
 For next release
 ^^^^^^^^^^^^^^^^
-- can the recursive cycle detector print the actual LINES that do the call?
-
+- what to do with the rouding difference in signed divide by 2 / 4  (double ror)?  it rounds towards minus infinity (so -5 / 2 = -3)
+  while the NON-optimized routine produces -2 .   Virtual machine also produces -3?
+  What rounding do we want?
+- add item to XyzZeropage that enables an option that if zeropage=FULL or KERNALSAFE, moves the cx16 virtual registers to ZP, same location as on x16
+  (can be done on C64 only for now)   Remove those addresses from the ZP free pool = allocate them in ZP like Cx16Zeropage does
+  Adapt the code in AstPreprocessor that relocates the registers as well.
+- for uword pointer variables: allow pointer[uword] array indexing >255 , rewrite it to @(pointer+index)
+  DO NOT allow this for regular array indexing because normal arrays can never exceed size 256
 ...
 
 
@@ -18,13 +24,6 @@ Need help with
 Future Things and Ideas
 ^^^^^^^^^^^^^^^^^^^^^^^
 Compiler:
-
-- add item to XZeropage that enables an option that if zeropage=FULL or KERNALSAFE, moves the cx16 virtual registers to ZP, same location as on x16
-  (can be done on C64 only for now)   Remove those addresses from the ZP free pool = allocate them in ZP like Cx16Zeropage does
-  Adapt the code in AstPreprocessor that relocates the registers as well.
-- for uword pointer variables: allow pointer[uword] array indexing >255 , rewrite it to @(pointer+index)
-  DO NOT allow this for regular array indexing because normal arrays can never exceed size 256
-
 - vm Instruction needs to know what the read-registers/memory are, and what the write-register/memory is.
   this info is needed for more advanced optimizations and later code generation steps.
 - vm: implement remaining sin/cos functions in math.p8

examples/test.p8

@@ -1,16 +1,30 @@
 %import textio
+%import string
 %zeropage basicsafe
 
 main {
     sub start() {
-        ubyte ci
-        ubyte from=10
-        ubyte end=1
-
-        for ci in from to end {
-            txt.print_ub(ci)
-            txt.spc()
-        }
+        word bb = -15
+        bb /= 4
+        txt.print_w(bb)
         txt.nl()
+        bb = 15
+        bb /= 4
+        txt.print_w(bb)
+        txt.nl()
+        uword ubb = 15
+        ubb /= 4
+        txt.print_uw(ubb)
+        txt.nl()
+
+        recurse1()
+    }
+
+    sub recurse1() {
+        recurse2()
+    }
+
+    sub recurse2() {
+        start()
     }
 }