fixed zp vars 0 initialization

swallow a defer warning for a very common use case

codeGenCpu6502/src/prog8/codegen/cpu6502/ProgramAndVarsGen.kt

@@ -328,10 +328,9 @@ internal class ProgramAndVarsGen(
         if (initializers.isNotEmpty()) {
             asmgen.out("prog8_init_vars\t.block")
             initializers.forEach { assign ->
-                if((assign.value as? PtNumber)?.number != 0.0 || allocator.isZpVar(assign.target.identifier!!.name))
+                val constvalue = assign.value as? PtNumber
+                if(constvalue==null || constvalue.number!=0.0 || allocator.isZpVar(assign.target.identifier!!.name))
                     asmgen.translate(assign)
-                else
-                    throw AssemblyError("non-zp variable should not be initialized to zero; it will be zeroed as part of BSS clear")
                 // the other variables that should be set to zero are done so as part of the BSS section clear.
             }
             asmgen.out("  rts\n  .bend")

codeGenIntermediate/src/prog8/codegen/intermediate/IRCodeGen.kt

@@ -75,7 +75,7 @@ class IRCodeGen(
                         initsToRemove += block to initialization
                     }
                     is PtNumber -> {
-                        require(initValue.number!=0.0) { "variable should not be initialized with 0, it will already be zeroed as part of BSS clear, initializer=$initialization" }
+                        require(initValue.number!=0.0 || variable.zpwish!=ZeropageWish.NOT_IN_ZEROPAGE) {"non-zp variable should not be initialized with 0, it will already be zeroed as part of BSS clear, initializer=$initialization" }
                         variable.setOnetimeInitNumeric(initValue.number)
                         initsToRemove += block to initialization
                     }

codeOptimizers/src/prog8/optimizer/StatementOptimizer.kt

@@ -19,7 +19,7 @@ class StatementOptimizer(private val program: Program,
             val functionName = functionCallStatement.target.nameInSource[0]
             if (functionName in functions.purefunctionNames) {
                 if("ignore_unused" !in parent.definingBlock.options())
-                    errors.info("statement has no effect (function return value is discarded)", functionCallStatement.position)
+                    errors.warn("statement has no effect (function return value is discarded)", functionCallStatement.position)
                 return listOf(IAstModification.Remove(functionCallStatement, parent as IStatementContainer))
             }
         }

compiler/res/prog8lib/c64/graphics.p8

@@ -376,7 +376,7 @@ hline_filled_right   .byte  0, %10000000, %11000000, %11100000, %11110000, %1111
 _ormask     .byte 128, 64, 32, 16, 8, 4, 2, 1
 
 ; note: this can be even faster if we also have a 320 word x-lookup table, but hey, that's a lot of memory.
-; see http://codebase64.org/doku.php?id=base:various_techniques_to_calculate_adresses_fast_common_screen_formats_for_pixel_graphics
+; see https://codebase64.net/doku.php?id=base:various_techniques_to_calculate_adresses_fast_common_screen_formats_for_pixel_graphics
 ; the y lookup tables encodes this formula:  BITMAP_ADDRESS + 320*(py>>3) + (py & 7)    (y from 0..199)
 ; We use the 64tass syntax for range expressions to calculate this table on assembly time.
 

compiler/res/prog8lib/math.asm

@@ -3,7 +3,7 @@
 ;
 ;  some more interesting routines can be found here:
 ;	http://6502org.wikidot.com/software-math
-;	http://codebase64.org/doku.php?id=base:6502_6510_maths
+;	https://codebase64.net/doku.php?id=base:6502_6510_maths
 ;       https://github.com/TobyLobster/multiply_test
 ;       https://github.com/TobyLobster/sqrt_test
 
@@ -353,7 +353,7 @@ _divisor	.word ?
 randword	.proc
 	; -- 16 bit pseudo random number generator into AY
 	;    default seed = $00c2 $1137.  NOTE:  uses self-modifying code so won't work in ROM (use randword_rom instead)
-        ;    routine from https://codebase64.org/doku.php?id=base:x_abc_random_number_generator_8_16_bit
+        ;    routine from https://codebase64.net/doku.php?id=6502_6510_maths:x_abc_random_number_generator_8_16_bit
 		inc x1
 		clc
 x1=*+1
@@ -377,7 +377,7 @@ b1=*+1
 randword_rom	.proc
 	; -- 16 bit pseudo random number generator into AY. Can run from ROM.
 	;    NOTE: you have to set the initial seed using randseed_rom! (a good default seed = $00c2 $1137)
-        ;    routine from https://codebase64.org/doku.php?id=base:x_abc_random_number_generator_8_16_bit
+        ;    routine from https://codebase64.net/doku.php?id=6502_6510_maths:x_abc_random_number_generator_8_16_bit
 		inc  _x1
 		clc
 		lda  _x1

compiler/res/prog8lib/math.p8

@@ -380,7 +380,7 @@ _quadrant_region_to_direction:
 asmsub atan2(ubyte x1 @R0, ubyte y1 @R1, ubyte x2 @R2, ubyte y2 @R3) -> ubyte @A {
     ;; Calculate the angle, in a 256-degree circle, between two points into A.
     ;; The points (x1, y1) and (x2, y2) have to use *unsigned coordinates only* from the positive quadrant in the carthesian plane!
-    ;; https://www.codebase64.org/doku.php?id=base:8bit_atan2_8-bit_angle
+    ;; http://codebase64.net/doku.php?id=base:8bit_atan2_8-bit_angle
     ;; This uses 2 large lookup tables so uses a lot of memory but is super fast.
 
     %asm {{

compiler/res/prog8lib/virtual/diskio.p8

@@ -138,8 +138,8 @@ diskio {
         ;    you can call this multiple times to append more data
         repeat num_bytes {
             %ir {{
-                loadm.w r0,diskio.f_write.bufferpointer
-                loadi.b r99100,r0
+                loadm.w r99000,diskio.f_write.bufferpointer
+                loadi.b r99100,r99000
                 syscall 55 (r99100.b): r99100.b
                 storem.b r99100,$ff02
             }}
@@ -216,12 +216,12 @@ diskio {
     }
 
     ; like save() but omits the 2 byte prg header.
-    sub save_raw(uword filenameptr, uword startaddress, uword savesize) -> bool {
+    sub save_raw(uword filenameptr, uword start_address, uword savesize) -> bool {
         %ir {{
             load.b r99100,1
-            loadm.w r99000,diskio.save.filenameptr
-            loadm.w r99001,diskio.save.start_address
-            loadm.w r99002,diskio.save.savesize
+            loadm.w r99000,diskio.save_raw.filenameptr
+            loadm.w r99001,diskio.save_raw.start_address
+            loadm.w r99002,diskio.save_raw.savesize
             syscall 42 (r99100.b, r99000.w, r99001.w, r99002.w): r99100.b
             returnr.b r99100
         }}

compiler/src/prog8/compiler/Compiler.kt

@@ -468,7 +468,7 @@ private fun processAst(program: Program, errors: IErrorReporter, compilerOptions
     errors.report()
     program.constantFold(errors, compilerOptions)
     errors.report()
-    program.reorderStatements(errors)
+    program.reorderStatements(compilerOptions, errors)
     errors.report()
     program.desugaring(errors, compilerOptions)
     errors.report()

compiler/src/prog8/compiler/astprocessing/AstChecker.kt

@@ -1470,6 +1470,17 @@ internal class AstChecker(private val program: Program,
     }
 
     override fun visit(functionCallStatement: FunctionCallStatement) {
+
+        if(functionCallStatement.target.nameInSource.size==1) {
+            val functionName = functionCallStatement.target.nameInSource[0]
+            if (functionName in program.builtinFunctions.purefunctionNames) {
+                if("ignore_unused" !in functionCallStatement.parent.definingBlock.options()) {
+                    errors.warn("statement has no effect (function return value is discarded)", functionCallStatement.position)
+                    return
+                }
+            }
+        }
+
         // most function calls, even to builtin functions, are still regular FunctionCall nodes here.
         // they get converted to the more specialized node type in BeforeAsmTypecastCleaner
         val targetStatement = functionCallStatement.target.checkFunctionOrLabelExists(program, functionCallStatement, errors)

compiler/src/prog8/compiler/astprocessing/AstExtensions.kt

@@ -20,8 +20,8 @@ internal fun Program.checkValid(errors: IErrorReporter, compilerOptions: Compila
     checker.visit(this)
 }
 
-internal fun Program.reorderStatements(errors: IErrorReporter) {
-    val reorder = StatementReorderer(this, errors)
+internal fun Program.reorderStatements(options: CompilationOptions, errors: IErrorReporter) {
+    val reorder = StatementReorderer(this, options, errors)
     reorder.visit(this)
     if(errors.noErrors()) {
         reorder.applyModifications()

compiler/src/prog8/compiler/astprocessing/SimplifiedAstMaker.kt

@@ -165,8 +165,11 @@ class SimplifiedAstMaker(private val program: Program, private val errors: IErro
             }
         }
 
-        if(srcAssign.origin == AssignmentOrigin.VARINIT && srcAssign.parent is Block && srcAssign.value.constValue(program)?.number==0.0)
-            throw FatalAstException("should not have a redundant block-level variable=0 assignment; it will be zeroed as part of BSS clear")
+        if(srcAssign.origin == AssignmentOrigin.VARINIT && srcAssign.parent is Block && srcAssign.value.constValue(program)?.number==0.0) {
+            val zeropages = srcAssign.target.targetIdentifiers().mapNotNull { it.targetVarDecl()?.zeropage }
+            if(zeropages.any {it==ZeropageWish.NOT_IN_ZEROPAGE})
+                throw FatalAstException("should not have a redundant block-level variable=0 assignment for a non-ZP variable; it will be zeroed as part of BSS clear")
+        }
 
         val assign = PtAssignment(srcAssign.position, srcAssign.origin==AssignmentOrigin.VARINIT)
         val multi = srcAssign.target.multi

compiler/src/prog8/compiler/astprocessing/SimplifiedAstPostprocess.kt

@@ -133,7 +133,7 @@ private fun integrateDefers(subdefers: Map<PtSub, List<PtDefer>>, program: PtPro
         is PtNumber,
         is PtRange,
         is PtString -> true
-        // note that unlike most other times, PtIdentifier IS "complex" this time (it's a variable that might change)
+        is PtIdentifier -> true    // actually PtIdentifier IS "complex" this time (it's a variable that might change) but it's kinda annoying to give a warning message for this very common case
         else -> false
     }
 

compiler/src/prog8/compiler/astprocessing/StatementReorderer.kt

@@ -5,13 +5,11 @@ import prog8.ast.expressions.*
 import prog8.ast.statements.*
 import prog8.ast.walk.AstWalker
 import prog8.ast.walk.IAstModification
-import prog8.code.core.AssociativeOperators
-import prog8.code.core.BaseDataType
-import prog8.code.core.DataType
-import prog8.code.core.IErrorReporter
+import prog8.code.core.*
 
 internal class StatementReorderer(
     val program: Program,
+    val options: CompilationOptions,
     val errors: IErrorReporter
 ) : AstWalker() {
     // Reorders the statements in a way the compiler needs.
@@ -114,11 +112,18 @@ internal class StatementReorderer(
     }
 
     private fun canSkipInitializationWith0(decl: VarDecl): Boolean {
-        // if the variable is declared in a block, we can omit the init with 0 because
+        if(decl.parent is Block) {
+            // if the variable is declared in a block and is NOT in ZEROPAGE, we can omit the init with 0 because
             // the variable will be initialized to zero when the BSS section is cleared as a whole.
-        if(decl.parent is Block)
+            if (decl.zeropage == ZeropageWish.NOT_IN_ZEROPAGE)
                 return true
 
+            // block level zp var that is not in zeropage, doesn't have to be cleared (will be done as part of bss clear at startup)
+            // note: subroutine level var HAS to be cleared because it needs to be zero at every subroutine call!
+            if (decl.zeropage == ZeropageWish.DONTCARE && options.zeropage == ZeropageType.DONTUSE)
+                return true
+        }
+
         // if there is an assignment to the variable below it (regular assign, or For loop),
         // and there is nothing important in between, we can skip the initialization.
         val statements = (decl.parent as? IStatementContainer)?.statements ?: return false

compiler/test/TestBuiltinFunctions.kt

@@ -5,6 +5,7 @@ import io.kotest.engine.spec.tempdir
 import io.kotest.inspectors.shouldForAll
 import io.kotest.matchers.shouldBe
 import io.kotest.matchers.shouldNotBe
+import io.kotest.matchers.string.shouldContain
 import prog8.ast.expressions.NumericLiteral
 import prog8.ast.statements.Assignment
 import prog8.ast.statements.FunctionCallStatement
@@ -13,6 +14,7 @@ import prog8.code.core.BuiltinFunctions
 import prog8.code.core.RegisterOrPair
 import prog8.code.core.isNumeric
 import prog8.code.target.Cx16Target
+import prog8tests.helpers.ErrorReporterForTests
 import prog8tests.helpers.compileText
 
 class TestBuiltinFunctions: FunSpec({
@@ -103,5 +105,31 @@ main {
 
         compileText(Cx16Target(), true, src, outputDir, writeAssembly = true) shouldNotBe null
     }
+
+    test("warning for return value discarding of pure functions") {
+        val src="""
+main {
+    sub start() {
+        word @shared ww = 2222
+
+        abs(ww)
+        sgn(ww)
+        sqrt(ww)
+        min(ww, 0)
+        max(ww, 0)
+        clamp(ww, 0, 319)
+    }
+}"""
+
+        val errors = ErrorReporterForTests(keepMessagesAfterReporting = true)
+        compileText(Cx16Target(), true, src, outputDir, errors=errors, writeAssembly = false) shouldNotBe null
+        errors.warnings.size shouldBe 6
+        errors.warnings[0] shouldContain "statement has no effect"
+        errors.warnings[1] shouldContain "statement has no effect"
+        errors.warnings[2] shouldContain "statement has no effect"
+        errors.warnings[3] shouldContain "statement has no effect"
+        errors.warnings[4] shouldContain "statement has no effect"
+        errors.warnings[5] shouldContain "statement has no effect"
+    }
 })
 

compiler/test/codegeneration/TestVariables.kt

@@ -10,7 +10,10 @@ import prog8.ast.statements.Assignment
 import prog8.ast.statements.AssignmentOrigin
 import prog8.ast.statements.ForLoop
 import prog8.ast.statements.VarDecl
+import prog8.code.ast.PtAssignment
+import prog8.code.ast.PtNumber
 import prog8.code.target.C64Target
+import prog8.code.target.Cx16Target
 import prog8tests.helpers.ErrorReporterForTests
 import prog8tests.helpers.compileText
 
@@ -106,6 +109,7 @@ class TestVariables: FunSpec({
 
     test("global var init with array lookup should sometimes be const") {
         val src="""
+%zeropage dontuse            
 main {
 
     bool[] barray =  [true, false, true, false]
@@ -220,4 +224,85 @@ main {
         (st[5] as Assignment).target.identifier?.nameInSource shouldBe listOf("v1")
         (st[6] as Assignment).target.identifier?.nameInSource shouldBe listOf("v0")
     }
+
+    test("nondirty zp variables should be explicitly initialized to 0") {
+        val src="""
+main {
+    ubyte @shared @requirezp zpvar
+    ubyte @shared @requirezp @dirty dirtyzpvar
+
+    sub start() {
+        ubyte @shared @requirezp zpvar2
+        ubyte @shared @requirezp @dirty dirtyzpvar2
+    }
+}"""
+
+        val result = compileText(Cx16Target(), false, src, outputDir, writeAssembly = true)!!.codegenAst
+
+        val main = result!!.allBlocks().first { it.name=="p8b_main" }
+        main.children.size shouldBe 4
+        val zeroassignlobal =  main.children.single { it is PtAssignment } as PtAssignment
+        (zeroassignlobal.value as PtNumber).number shouldBe 0.0
+        zeroassignlobal.target.identifier!!.name shouldBe "p8b_main.p8v_zpvar"
+
+        val st = result.entrypoint()!!.children
+        st.size shouldBe 4
+        val zeroassign =  st.single { it is PtAssignment } as PtAssignment
+        (zeroassign.value as PtNumber).number shouldBe 0.0
+        zeroassign.target.identifier!!.name shouldBe "p8b_main.p8s_start.p8v_zpvar2"
+    }
+
+    test("nondirty non zp variables in block scope should not be explicitly initialized to 0 (bss clear takes care of it)") {
+        val src="""
+%zeropage dontuse
+
+main {
+    ubyte @shared v1
+    ubyte @shared @dirty dv1
+    sub start() {
+        ubyte @shared v2
+        ubyte @shared @dirty dv2
+    }
+}"""
+
+        val result = compileText(Cx16Target(), false, src, outputDir, writeAssembly = true)!!.codegenAst
+
+        // block level should not be intialized to 0 (will be done by BSS clear)
+        val main = result!!.allBlocks().first { it.name=="p8b_main" }
+        main.children.size shouldBe 3
+        main.children.any { it is PtAssignment } shouldBe false
+
+        // subroutine should be initialized to 0 because that needs to be done on every call to the subroutine
+        val st = result.entrypoint()!!.children
+        st.size shouldBe 4
+        val zeroassign =  st.single { it is PtAssignment } as PtAssignment
+        (zeroassign.value as PtNumber).number shouldBe 0.0
+        zeroassign.target.identifier!!.name shouldBe "p8b_main.p8s_start.p8v_v2"
+    }
+
+    test("nondirty explicit non zp variables in block scope should not be explicitly initialized to 0 (bss clear takes care of it)") {
+        val src="""
+main {
+    ubyte @shared @nozp v1
+    ubyte @shared @dirty @nozp dv1
+    sub start() {
+        ubyte @shared @nozp v2
+        ubyte @shared @dirty @nozp dv2
+    }
+}"""
+
+        val result = compileText(Cx16Target(), false, src, outputDir, writeAssembly = true)!!.codegenAst
+
+        // block level should not be intialized to 0 (will be done by BSS clear)
+        val main = result!!.allBlocks().first { it.name=="p8b_main" }
+        main.children.size shouldBe 3
+        main.children.any { it is PtAssignment } shouldBe false
+
+        // subroutine should be initialized to 0 because that needs to be done on every call to the subroutine
+        val st = result.entrypoint()!!.children
+        st.size shouldBe 4
+        val zeroassign =  st.single { it is PtAssignment } as PtAssignment
+        (zeroassign.value as PtNumber).number shouldBe 0.0
+        zeroassign.target.identifier!!.name shouldBe "p8b_main.p8s_start.p8v_v2"
+    }
 })

docs/docs.iml

@@ -5,7 +5,7 @@
     <content url="file://$MODULE_DIR$">
       <excludeFolder url="file://$MODULE_DIR$/build" />
     </content>
-    <orderEntry type="jdk" jdkName="Python 3.12" jdkType="Python SDK" />
+    <orderEntry type="jdk" jdkName="Python 3" jdkType="Python SDK" />
     <orderEntry type="sourceFolder" forTests="false" />
   </component>
 </module>

docs/source/libraries.rst

@@ -27,7 +27,7 @@ of these library modules automatically as required.
 
 .. note::
     Several algorithms and math routines in Prog8's assembly library files are adapted from
-    code publicly available on https://www.codebase64.org/
+    code publicly available on https://www.codebase64.net/
 
 
 .. _builtinfunctions:

docs/source/software.rst

@@ -65,6 +65,11 @@ Various things:
     and it does it at run time. In this demo a jump table is not only created in the library,
     but also in the main program and copied into the library for its use.
 
+`Additional custom compilation targets (such as VIC-20) <https://github.com/gillham/prog8targets>`_
+    Various custom targets for Prog8 that are not (yet?) part of the Prog8 examples themselves.
+    These additional compilation targets may be in varying state of completeness.
+    Perhaps most recognisable at the time of adding this link, are the various VIC-20 targets.
+
 
 .. image:: _static/curious.png
     :align: center

docs/source/todo.rst

@@ -1,6 +1,10 @@
 TODO
 ====
 
+Since fixing the missing zp-var initialization, programs grew in size again (assem)
+Are there any redundant block-level variable initializations to 0 that we can remove in peephole optimization for example?
+
+
 STRUCTS: are being developed in their own separate branch for now, called "structs".
 Idea is to make it feature complete in the IR/Virtual target, then merge it to master?, and then start building the 6502 code generation for it.
 

examples/test.p8

@@ -1,27 +1,84 @@
+%option no_sysinit
+%zeropage kernalsafe
+%import textio
+%zpallowed 224,255
+
 main {
+    uword @shared @requirezp zpvar1
+    uword @shared @requirezp zpvar2
+    uword @shared @requirezp zpvar3
+    uword @shared @requirezp zpvar4
+    uword @shared @requirezp zpvar5
+    uword @shared @requirezp @dirty dzpvar1
+    uword @shared @requirezp @dirty dzpvar2
+    uword @shared @requirezp @dirty dzpvar3
+    uword @shared @requirezp @dirty dzpvar4
+    uword @shared @requirezp @dirty dzpvar5
+    uword @shared @nozp var1
+    uword @shared @nozp var2
+    uword @shared @nozp var3
+    uword @shared @nozp var4
+    uword @shared @nozp var5
+    uword @shared @nozp @dirty dvar1
+    uword @shared @nozp @dirty dvar2
+    uword @shared @nozp @dirty dvar3
+    uword @shared @nozp @dirty dvar4
+    uword @shared @nozp @dirty dvar5
+
     sub start() {
-        uword uw = 9999
-        word sw = -2222
-        ubyte ub = 42
-        byte sb = -99
-        bool bb = true
+        txt.print("address start of zpvars: ")
+        txt.print_uw(&zpvar1)
+        txt.nl()
+        txt.print("address start of normal vars: ")
+        txt.print_uw(&var1)
+        txt.nl()
 
-        cx16.r0 = uw
-        cx16.r0s = sw
-        cx16.r0L = ub
-        cx16.r0H = ub
-        cx16.r0sL = sb
-        cx16.r0sH = sb
-        cx16.r0bL = bb
-        cx16.r0bH = bb
+        txt.print("non-dirty zp should all be 0: ")
+        txt.print_uw(zpvar1)
+        txt.spc()
+        txt.print_uw(zpvar2)
+        txt.spc()
+        txt.print_uw(zpvar3)
+        txt.spc()
+        txt.print_uw(zpvar4)
+        txt.spc()
+        txt.print_uw(zpvar5)
+        txt.nl()
+        txt.print("non-dirty should all be 0:    ")
+        txt.print_uw(var1)
+        txt.spc()
+        txt.print_uw(var2)
+        txt.spc()
+        txt.print_uw(var3)
+        txt.spc()
+        txt.print_uw(var4)
+        txt.spc()
+        txt.print_uw(var5)
+        txt.nl()
 
-        uw = cx16.r0
-        sw = cx16.r0s
-        ub = cx16.r0L
-        ub = cx16.r0H
-        sb = cx16.r0sL
-        sb = cx16.r0sH
-        bb = cx16.r0bL
-        bb = cx16.r0bH
+        txt.print("dirty zp may be random: ")
+        txt.print_uw(dzpvar1)
+        txt.spc()
+        txt.print_uw(dzpvar2)
+        txt.spc()
+        txt.print_uw(dzpvar3)
+        txt.spc()
+        txt.print_uw(dzpvar4)
+        txt.spc()
+        txt.print_uw(dzpvar5)
+        txt.nl()
+        txt.print("dirty may be random: ")
+        txt.print_uw(dvar1)
+        txt.spc()
+        txt.print_uw(dvar2)
+        txt.spc()
+        txt.print_uw(dvar3)
+        txt.spc()
+        txt.print_uw(dvar4)
+        txt.spc()
+        txt.print_uw(dvar5)
+        txt.nl()
+
+        repeat {}
     }
 }

gradle/wrapper/gradle-wrapper.properties

@@ -1,6 +1,6 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-8.14.2-bin.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.14.3-bin.zip
 networkTimeout=10000
 validateDistributionUrl=true
 zipStoreBase=GRADLE_USER_HOME

intermediate/src/prog8/intermediate/IRInstructions.kt

@@ -11,8 +11,10 @@ Intermediate Representation instructions for the IR Virtual machine.
 
 Specs of the virtual machine this will run on:
 Program to execute is not stored in the system memory, it's just a separate list of instructions.
-65536 virtual registers, 16 bits wide, can also be used as 8 bits. r0-r65535
-65536 virtual floating point registers (64 bits double precision)  fr0-fr65535
+100K virtual registers, 16 bits wide, can also be used as 8 bits. r0-r99999
+    reserved 99000 - 99099 : WORD registers for syscall arguments and response value(s)
+    reserved 99100 - 99199 : BYTE registers for syscall arguments and response value(s)
+100K virtual floating point registers (64 bits double precision)  fr0-fr99999
 65536 bytes of memory. Thus memory pointers (addresses) are limited to 16 bits.
 Value stack, max 128 entries of 1 byte each.
 Status flags: Carry, Zero, Negative.   NOTE: status flags are only affected by the CMP instruction or explicit CLC/SEC,

simpleAst/src/prog8/code/SymbolTable.kt

@@ -200,7 +200,7 @@ class StStaticVariable(name: String,
         // Certain codegens might want to put them back into the variable directly.
         // For strings and arrays this doesn't occur - these are always already specced at creation time.
 
-        require(number!=0.0) { "variable should not be initialized with 0, it will already be zeroed as part of BSS clear" }
+        require(number!=0.0 || zpwish!=ZeropageWish.NOT_IN_ZEROPAGE) { "non-zp variable should not be initialized with 0, it will already be zeroed as part of BSS clear" }
         initializationNumericValue = number
     }