m68k: no longer print recursion warnings

AGENTS.md

@@ -133,7 +133,19 @@ Steps when encountering a compiler crash:
 - **NO EMOJI in user documentation**. Do not use emoji or decorative unicode symbols in documentation files. Functional unicode symbols are acceptable when they serve a clear purpose (e.g., → for arrows, ± for plus-minus, × for multiplication, ° for degrees). Avoid decorative emoji like ❌ ✅ ⚠️ 🎉 etc.
 
 ### Code Style Guidelines
-**Minimal comments when making changes**: When modifying existing code, add only essential comments that explain *why* a change was made or document non-obvious behavior. **Do not add verbose comments** that restate what the code does; let the code speak for itself. Existing extensive comments should be preserved, but new changes should have minimal commentary.
+**Code comments**: Comments are the exception, not the norm. A comment earns its place only by recording
+something the code itself cannot say: the reason for a non-obvious choice, or a constraint that
+a well-meaning future edit would otherwise violate.
+
+- Inline comment inside a function body: 1 line, never more.
+- KDoc on a declaration: 3 lines, unless a genuine non-obvious contract cannot be stated shorter.
+- Never restate the identifier, the type, or what the following line does.
+- Prefer a good name or a well-named function over a comment that explains it.
+
+Before keeping any comment, delete it mentally and ask what the reader loses. If nothing, it goes.
+
+Keep existing comments as they are; do not expand, reword, or reformat them while editing
+nearby lines - unless that would cause inconsistency. 
 
 **Kotlin string `$` handling**: The `$` character is special in Kotlin string literals (string interpolation). If you need a literal `$` character, use Kotlin's `$$"..."` interpolation prefix instead of backslash escaping (`\$`) or `${'$'}`. The `$$"..."` syntax is a fairly recent Kotlin feature that avoids nasty escaping. For example:
 ```kotlin

codeCore/src/prog8/code/core/ICompilationTarget.kt

@@ -87,6 +87,13 @@ interface ICompilationTarget: IStringEncoding, IMemSizer {
     val defaultLauncherType: CbmPrgLauncherType
     val supportsBankedCalls: Boolean
 
+    /**
+     * True when the code generator allocates subroutine locals and per-activation intermediate values
+     * in a stack frame instead of static memory, so a subroutine on a call-graph cycle can have more
+     * than one live activation. False means two live activations would share the same storage.
+     */
+    val supportsStackFrames: Boolean
+
     fun initializeMemoryAreas(compilerOptions: CompilationOptions)
     fun getFloatAsmBytes(num: Number): String
 

codeCore/src/prog8/code/target/Amiga1200Target.kt

@@ -12,6 +12,7 @@ class Amiga1200Target: ICompilationTarget,
 
     override val name = NAME
     override val supportsBankedCalls = true
+    override val supportsStackFrames = true
     override val defaultEncoding = Encoding.ISO
     override val libraryPath = null
     override val customLauncher = emptyList<String>()

codeCore/src/prog8/code/target/Amiga500Target.kt

@@ -12,6 +12,7 @@ class Amiga500Target: ICompilationTarget,
 
     override val name = NAME
     override val supportsBankedCalls = true
+    override val supportsStackFrames = true
     override val defaultEncoding = Encoding.ISO
     override val libraryPath = null
     override val customLauncher = emptyList<String>()

codeCore/src/prog8/code/target/C128Target.kt

@@ -12,6 +12,7 @@ class C128Target: ICompilationTarget,
 
     override val name = NAME
     override val supportsBankedCalls = true
+    override val supportsStackFrames = false
     override val defaultEncoding = Encoding.PETSCII
     override val libraryPath = null
     override val customLauncher = emptyList<String>()

codeCore/src/prog8/code/target/C64Target.kt

@@ -13,6 +13,7 @@ class C64Target: ICompilationTarget,
 
     override val name = NAME
     override val supportsBankedCalls = true
+    override val supportsStackFrames = false
     override val defaultEncoding = Encoding.PETSCII
     override val libraryPath = null
     override val customLauncher = emptyList<String>()

codeCore/src/prog8/code/target/ConfigFileTarget.kt

@@ -19,6 +19,7 @@ class ConfigFileTarget(
     override val supportsBankedCalls: Boolean,
     override val defaultEncoding: Encoding,
     override val cpu: CpuType,
+    override val supportsStackFrames: Boolean,
     override val PROGRAM_LOAD_ADDRESS: UInt,
     override val PROGRAM_MEMTOP_ADDRESS: UInt,
     override val BSSHIGHRAM_START: UInt,
@@ -144,6 +145,7 @@ class ConfigFileTarget(
                 props.getProperty("supports_banked_calls", "false").toBoolean(),
                 Encoding.entries.first { it.prefix==props.getString("encoding") },
                 cpuType,
+                props.getProperty("supports_stack_frames", cpuType.is68k.toString()).toBoolean(),
                 props.getInteger("load_address"),
                 props.getInteger("memtop"),
                 props.getInteger("bss_highram_start"),

codeCore/src/prog8/code/target/Cx16Target.kt

@@ -12,6 +12,7 @@ class Cx16Target: ICompilationTarget,
 
     override val name = NAME
     override val supportsBankedCalls = true
+    override val supportsStackFrames = false
     override val defaultEncoding = Encoding.PETSCII
     override val libraryPath = null
     override val customLauncher = emptyList<String>()

codeCore/src/prog8/code/target/PETTarget.kt

@@ -12,6 +12,7 @@ class PETTarget: ICompilationTarget,
 
     override val name = NAME
     override val supportsBankedCalls = false
+    override val supportsStackFrames = false
     override val defaultEncoding = Encoding.PETSCII
     override val libraryPath = null
     override val customLauncher = emptyList<String>()

codeCore/src/prog8/code/target/Qemu68kTarget.kt

@@ -16,6 +16,7 @@ class Qemu68kTarget: ICompilationTarget,
 
     override val name = NAME
     override val supportsBankedCalls = false
+    override val supportsStackFrames = true
     override val defaultEncoding = Encoding.ISO
     override val libraryPath = null
     override val customLauncher = emptyList<String>()

codeCore/src/prog8/code/target/VMTarget.kt

@@ -12,6 +12,7 @@ class VMTarget: ICompilationTarget,
 
     override val name = NAME
     override val supportsBankedCalls = false
+    override val supportsStackFrames = false
     override val defaultEncoding = Encoding.ISO
     override val libraryPath = null
     override val customLauncher = emptyList<String>()

codeGenM68k/src/prog8/codegen/m68k/M68kCodeGenerator.kt

@@ -29,8 +29,8 @@ class M68kCodeGenerator(val retainSSA: Boolean): ICodeGeneratorBackend {
         }
         irProgram.verifyRegisterTypes(virtualRegisterTypes)
 
-        // Vertical Slice Prototype: stack-frame locals for frameable leaf subroutines
-        StackFrameLayout(irProgram, errors).apply()
+        if (options.compTarget.supportsStackFrames)
+            StackFrameLayout(irProgram, errors).apply()
 
         if (options.dumpVariables)
             dumpVariables(irProgram)

compiler/src/prog8/compiler/Compiler.kt

@@ -717,7 +717,10 @@ private fun postprocessAst(program: Program, errors: IErrorReporter, compilerOpt
     errors.report()
     program.variousCleanups(errors, compilerOptions)
     val callGraph = CallGraph(program)
-    callGraph.checkRecursiveCalls(errors)
+    // on a stack-frame target a recursive subroutine either gets per-activation storage or is
+    // rejected by StackFrameLayout, so there is nothing left to warn about here
+    if(!compilerOptions.compTarget.supportsStackFrames)
+        callGraph.checkRecursiveCalls(errors)
     if(compilerOptions.compTarget.cpu.is68k) {
         checkDeferInReentrantSubroutines(program, callGraph, errors)
         checkFrameAddressEscapes(program, errors)

compiler/test/TestStackFrameLocals.kt

@@ -530,6 +530,34 @@ main {
         otherErrors.errors.size shouldBe 0
     }
 
+    test("recursion warning is only emitted for targets without stack frames") {
+        val src = """
+main {
+    sub rec(ubyte n) -> ubyte {
+        if n == 0 {
+            return 0
+        }
+        return rec(n-1) + 1
+    }
+    sub start() {
+        g = rec(3)
+    }
+    ubyte @shared g
+}
+"""
+        val m68kErrors = ErrorReporterForTests(keepMessagesAfterReporting = true)
+        compileText(Qemu68kTarget(), optimize = false, src, tempdir().toPath(),
+            writeAssembly = false, assemble = false, errors = m68kErrors) shouldNotBe null
+        m68kErrors.errors.size shouldBe 0
+        m68kErrors.warnings.any { it.contains("recursive subroutine") } shouldBe false
+
+        val otherErrors = ErrorReporterForTests(keepMessagesAfterReporting = true)
+        compileText(C64Target(), optimize = false, src, tempdir().toPath(),
+            writeAssembly = false, assemble = false, errors = otherErrors) shouldNotBe null
+        otherErrors.errors.size shouldBe 0
+        otherErrors.warnings.any { it.contains("recursive subroutine") } shouldBe true
+    }
+
     test("slice 3: defer in a recursive subroutine is rejected on m68k only") {
         val src = """
 main {