optimized codegen for pointer indexing (read expressions)

codeGenCpu6502/src/prog8/codegen/cpu6502/assignment/AssignmentAsmGen.kt

@@ -72,6 +72,23 @@ internal class AssignmentAsmGen(private val program: Program,
                 val value = assign.source.array!!
                 val elementDt = assign.source.datatype
                 val arrayVarName = asmgen.asmVariableName(value.arrayvar)
+
+                val arrayVarDecl = value.arrayvar.targetVarDecl(program)!!
+                if(arrayVarDecl.datatype==DataType.UWORD) {
+                    // indexing a pointer var instead of a real array or string
+                    if(elementDt !in ByteDatatypes)
+                        throw AssemblyError("non-array var indexing requires bytes dt")
+                    asmgen.loadScaledArrayIndexIntoRegister(value, elementDt, CpuRegister.Y)
+                    if(asmgen.isZpVar(value.arrayvar)) {
+                        asmgen.out("  lda  ($arrayVarName),y")
+                    } else {
+                        asmgen.out("  lda  $arrayVarName |  sta  P8ZP_SCRATCH_W1 |  lda  $arrayVarName+1 |  sta  P8ZP_SCRATCH_W1+1")
+                        asmgen.out("  lda  (P8ZP_SCRATCH_W1),y")
+                    }
+                    assignRegisterByte(assign.target, CpuRegister.A)
+                    return
+                }
+
                 val constIndex = value.indexer.constIndex()
                 if (constIndex!=null) {
                     // constant array index value

codeGenVirtual/src/prog8/codegen/virtual/ExpressionGen.kt

@@ -149,6 +149,20 @@ internal class ExpressionGen(private val codeGen: CodeGen) {
         val code = VmCodeChunk()
         val idxReg = codeGen.vmRegisters.nextFree()
         val arrayLocation = codeGen.allocations.get(arrayIx.variable.targetName)
+
+        if(arrayIx.variable.type==DataType.UWORD) {
+            // indexing a pointer var instead of a real array or string
+            if(eltSize!=1)
+                throw AssemblyError("non-array var indexing requires bytes dt")
+            val pointerReg = codeGen.vmRegisters.nextFree()
+            code += translateExpression(arrayIx.index, idxReg, -1)
+            // TODO introduce LOADIX instruction to skip the ADD (requires 3 registers)
+            code += VmCodeInstruction(Opcode.LOADM, VmDataType.WORD, reg1=pointerReg, value=arrayLocation)
+            code += VmCodeInstruction(Opcode.ADD, VmDataType.WORD, reg1=pointerReg, reg2=idxReg)
+            code += VmCodeInstruction(Opcode.LOADI, vmDt, reg1=resultRegister, reg2=pointerReg)
+            return code
+        }
+
         if(arrayIx.index is PtNumber) {
             // optimized code when index is known - just calculate the memory address here
             val memOffset = (arrayIx.index as PtNumber).number.toInt() * eltSize

compiler/src/prog8/compiler/astprocessing/AstOnetimeTransforms.kt

@@ -45,13 +45,11 @@ internal class AstOnetimeTransforms(private val program: Program) : AstWalker()
                 return if(fcall!=null) {
                     val fname = fcall.target.nameInSource
                     if(fname.size==1 && fname[0] in InplaceModifyingBuiltinFunctions) {
-                        // TODO for now, swap() etc don't work on pointer var indexed args
+                        // TODO for now, swap() etc don't work on pointer var indexed args, so still replace this
                         val memread = DirectMemoryRead(add, arrayIndexedExpression.position)
                         listOf(IAstModification.ReplaceNode(arrayIndexedExpression, memread, parent))
                     } else {
-                        // TODO first candidate for optimization is to remove this:
+                        noModifications
-                        val memread = DirectMemoryRead(add, arrayIndexedExpression.position)
-                        listOf(IAstModification.ReplaceNode(arrayIndexedExpression, memread, parent))
                     }
                 } else {
                     val memread = DirectMemoryRead(add, arrayIndexedExpression.position)

examples/test.p8

@@ -1,5 +1,5 @@
 %import textio
-%zeropage dontuse
+%zeropage basicsafe
 
 
 ; NOTE: meant to test to virtual machine output target (use -target vitual)