better unused variable removal

codeOptimizers/src/prog8/optimizer/UnusedCodeRemover.kt

@@ -107,9 +107,30 @@ class UnusedCodeRemover(private val program: Program,
         if(decl.type==VarDeclType.VAR) {
             val forceOutput = "force_output" in decl.definingBlock.options()
             if (!forceOutput && !decl.autogeneratedDontRemove && !decl.sharedWithAsm && !decl.definingBlock.isInLibrary) {
-                if (callgraph.unused(decl)) {
+                val usages = callgraph.usages(decl)
+                if (usages.isEmpty()) {
                     errors.warn("removing unused variable '${decl.name}'", decl.position)
                     return listOf(IAstModification.Remove(decl, parent as IStatementContainer))
+                } else {
+                    // if all usages are just an assignment to this vardecl
+                    // and it is in regular RAM, then remove the var as well including all assignments
+                    val assignTargets = usages.mapNotNull {
+                        if(it.parent is AssignTarget)
+                                it.parent as AssignTarget
+                        else if(it.parent.parent is AssignTarget)
+                                it.parent.parent as AssignTarget
+                        else null
+                    }.filter {
+                        it.isInRegularRAMof(compTarget.machine)
+                    }
+                    if(assignTargets.size==usages.size) {
+                        errors.warn("removing unused variable '${decl.name}'", decl.position)
+                        return assignTargets.map { it.parent to it.definingScope}.toSet().map {
+                            IAstModification.Remove(it.first, it.second)
+                        } + listOf(
+                            IAstModification.Remove(decl, parent as IStatementContainer)
+                        )
+                    }
                 }
             }
         }

compiler/test/TestCompilerOnRanges.kt

@@ -29,7 +29,7 @@ class TestCompilerOnRanges: FunSpec({
 
     test("testUByteArrayInitializerWithRange_char_to_char") {
         val platform = Cx16Target
-        val result = compileText(platform, true, """
+        val result = compileText(platform, false, """
             main {
                 sub start() {
                     ubyte[] cs = @'a' to 'z' ; values are computed at compile time 

compiler/test/TestOptimization.kt

@@ -93,10 +93,10 @@ class TestOptimization: FunSpec({
             main {
                 sub start() {
                     const ubyte TEST = 10
-                    byte x1 = TEST as byte + 1
-                    byte x2 = 1 + TEST as byte
-                    ubyte y1 = TEST + 1 as byte
-                    ubyte y2 = 1 as byte + TEST
+                    byte @shared x1 = TEST as byte + 1
+                    byte @shared x2 = 1 + TEST as byte
+                    ubyte @shared y1 = TEST + 1 as byte
+                    ubyte @shared y2 = 1 as byte + TEST
                 }
             }
         """
@@ -215,4 +215,29 @@ class TestOptimization: FunSpec({
         val asm = generateAssembly(result1.program)
         asm.valid shouldBe true
     }
+
+    test("unused variable removal") {
+        val src="""
+            main {
+                sub start() {
+                    ubyte unused
+                    ubyte @shared unused_but_shared     ; this one should remain
+                    ubyte usedvar_only_written
+                    usedvar_only_written=2
+                    usedvar_only_written++
+                    ubyte usedvar                       ; and this one too
+                    usedvar = msb(usedvar)
+                }
+            }
+        """
+        val result = compileText(C64Target, optimize=true, src, writeAssembly=false).assertSuccess()
+        result.program.entrypoint.statements.size shouldBe 4       // unused_but_shared decl, unused_but_shared=0,  usedvar decl, usedvar assign
+        val (decl, assign, decl2, assign2) = result.program.entrypoint.statements
+        decl shouldBe instanceOf<VarDecl>()
+        (decl as VarDecl).name shouldBe "unused_but_shared"
+        assign shouldBe instanceOf<Assignment>()
+        decl2 shouldBe instanceOf<VarDecl>()
+        (decl2 as VarDecl).name shouldBe "usedvar"
+        assign2 shouldBe instanceOf<Assignment>()
+    }
 })

compilerInterfaces/src/prog8/compilerinterface/CallGraph.kt

@@ -173,14 +173,18 @@ class CallGraph(private val program: Program) : IAstVisitor {
     }
 
     fun unused(decl: VarDecl): Boolean {
+        // Don't check assembly just for occurrences of variables, if they're not used in prog8 itself, just kill them
+        return usages(decl).isEmpty()
+    }
+
+    fun usages(decl: VarDecl): List<IdentifierReference> {
         if(decl.type!=VarDeclType.VAR || decl.autogeneratedDontRemove || decl.sharedWithAsm)
-            return false
+            return emptyList()
 
         if(decl.definingBlock !in usedBlocks)
-            return false
+            return emptyList()
 
-        val allReferencedVardecls = allIdentifiersAndTargets.filter { it.value is VarDecl }.map { it.value }.toSet()
-        return decl !in allReferencedVardecls // Don't check assembly just for occurrences of variables, if they're not used in prog8 itself, just kill them
+        return allIdentifiersAndTargets.filter { decl===it.value }.map{ it.key.first }
     }
 
     private fun nameInAssemblyCode(name: String) = allAssemblyNodes.any { it.assembly.contains(name) }

examples/test.p8

@@ -5,9 +5,6 @@
 main {
 
     sub start() {
-        ubyte unused                ; TODO FIX : why is this not removed as an unused variable?
-        ubyte @shared unused2
-
         ubyte bb
         uword ww
         ww = not bb or not ww       ; TODO WHY DOES THIS USE STACK EVAL