Local Variables (#584)

effekt/shared/src/main/scala/effekt/generator/llvm/Transformer.scala

@@ -242,6 +242,90 @@ object Transformer {
         shareValues(List(value), freeVariables(rest))
         transform(rest)
 
+      case machine.Var(ref @ machine.Variable(name, machine.Type.Reference(tpe)), init, retType, rest) =>
+        val environment = List(init)
+        val returnAddressName = freshName("returnAddress")
+        val returnValue = freshName("returnValue")
+        val returnType = transform(retType)
+        val parameters = List(Parameter(returnType, returnValue))
+
+        defineLabel(returnAddressName, parameters) {
+          emit(Comment(s"var $name / return address"))
+          popEnvironmentFrom(getStack(), environment)
+          eraseValue(init)
+          val nextReturn = LocalReference(returnAddressType, freshName("returnAddress"))
+          popReturnAddressFrom(getStack(), nextReturn.name)
+          emit(callLabel(nextReturn, List(LocalReference(returnType, returnValue))))
+          RetVoid()
+        }
+
+        val sharerName = freshName("sharer");
+        defineFunction(sharerName, List(Parameter(stackPointerType, "stackPointer"))) {
+          emit(Comment(s"sharer, ${environment.length} free variables"))
+
+          val nextStackPointer = LocalReference(stackPointerType, freshName("stackPointer"));
+          emit(GetElementPtr(nextStackPointer.name, environmentType(environment), LocalReference(stackPointerType, "stackPointer"), List(-1)));
+          loadEnvironmentAt(nextStackPointer, environment);
+
+          shareValues(environment, Set.from(environment));
+          emit(Call("_", Ccc(), VoidType(), shareFrames, List(nextStackPointer)));
+          RetVoid()
+        }
+
+        val eraserName = freshName("eraser");
+        defineFunction(eraserName, List(Parameter(stackPointerType, "stackPointer"))) {
+          emit(Comment(s"eraser, ${environment.length} free variables"))
+
+          val nextStackPointer = LocalReference(stackPointerType, freshName("stackPointer"));
+          emit(GetElementPtr(nextStackPointer.name, environmentType(environment), LocalReference(stackPointerType, "stackPointer"), List(-1)));
+          loadEnvironmentAt(nextStackPointer, environment);
+
+          eraseValues(environment, Set());
+          emit(Call("_", Ccc(), VoidType(), eraseFrames, List(nextStackPointer)));
+          RetVoid()
+        }
+
+        emit(Call(name, Ccc(), referenceType, newReference, List(getStack())))
+
+        shareValues(environment, freeVariables(rest));
+        pushEnvironmentOnto(getStack(), environment);
+        pushReturnAddressOnto(getStack(), returnAddressName, sharerName, eraserName);
+
+        transform(rest)
+
+      case machine.Var(_, _, _, _) => ???
+
+      case machine.LoadVar(name, ref, rest) =>
+        emit(Comment(s"loadvar ${name.name}, reference ${ref.name}"))
+
+        val ptr = freshName(name.name + "_pointer");
+        val ptrRef = LocalReference(PointerType(), ptr)
+        emit(Call(ptr, Ccc(), PointerType(), getVarPointer, List(transform(ref), getStack())))
+
+        // TODO why do we need this?
+        val oldVal = machine.Variable(freshName(ref.name + "_old"), name.tpe)
+        emit(Load(oldVal.name, transform(oldVal.tpe), ptrRef))
+        shareValue(oldVal)
+
+        emit(Load(name.name, transform(name.tpe), ptrRef))
+        eraseValues(List(name), freeVariables(rest))
+        transform(rest)
+
+      case machine.StoreVar(ref, value, rest) =>
+        emit(Comment(s"storevar ${ref.name}, value ${value.name}"))
+
+        val ptr = freshName(ref.name + "pointer");
+        val ptrRef = LocalReference(PointerType(), ptr)
+        emit(Call(ptr, Ccc(), PointerType(), getVarPointer, List(transform(ref), getStack())))
+
+        val oldVal = machine.Variable(freshName(ref.name + "_old"), value.tpe)
+        emit(Load(oldVal.name, transform(oldVal.tpe), ptrRef))
+        eraseValue(oldVal)
+
+        emit(Store(ptrRef, transform(value)))
+        shareValues(List(value), freeVariables(rest))
+        transform(rest)
+
       case machine.PushFrame(frame, rest) =>
         val frameEnvironment = freeVariables(frame).toList;
 
@@ -744,6 +828,9 @@ object Transformer {
   def alloc = ConstantGlobal(PointerType(), "alloc")
   def getPointer = ConstantGlobal(PointerType(), "getPointer")
 
+  def newReference = ConstantGlobal(PointerType(), "newReference")
+  def getVarPointer = ConstantGlobal(PointerType(), "getVarPointer")
+
   def newStack = ConstantGlobal(PointerType(), "newStack");
   def pushStack = ConstantGlobal(PointerType(), "pushStack");
   def popStacks = ConstantGlobal(PointerType(), "popStacks");

effekt/shared/src/main/scala/effekt/machine/Analysis.scala

@@ -35,6 +35,12 @@ def freeVariables(statement: Statement): Set[Variable] =
       Set(ref) ++ freeVariables(rest) -- Set(name)
     case Store(ref, value, rest) =>
       Set(ref, value) ++ freeVariables(rest)
+    case Var(name, init, tpe, rest) => 
+      freeVariables(rest) ++ Set(init) -- Set(name)
+    case LoadVar(name, ref, rest) =>
+      Set(ref) ++ freeVariables(rest) -- Set(name)
+    case StoreVar(ref, value, rest) =>
+      Set(ref, value) ++ freeVariables(rest)
     case PushFrame(frame, rest) =>
       freeVariables(frame) ++ freeVariables(rest)
     case Return(values) =>

effekt/shared/src/main/scala/effekt/machine/PrettyPrinter.scala

@@ -69,6 +69,15 @@ object PrettyPrinter extends ParenPrettyPrinter {
     case Store(reference, value, rest) =>
       "store" <> parens(List(reference, value) map toDoc) <> ";" <> line <> toDoc(rest)
 
+    case Var(name, init, _, rest) =>
+      "var" <+> name <+> "=" <+> toDoc(init) <> ";" <> line <> toDoc(rest)
+
+    case LoadVar(name, reference, rest) =>
+      "let" <+> name <+> "=" <+> "loadVar" <> parens(toDoc(reference)) <> ";" <> line <> toDoc(rest)
+
+    case StoreVar(reference, value, rest) =>
+      "storeVar" <> parens(List(reference, value) map toDoc) <> ";" <> line <> toDoc(rest)
+
     case PushFrame(frame, rest) =>
       "push" <+> toDoc(frame) <> ";" <> line <> toDoc(rest)
 

effekt/shared/src/main/scala/effekt/machine/Transformer.scala

@@ -255,17 +255,16 @@ object Transformer {
         val prompt = Variable(freshName("prompt"), Type.Prompt())
 
         transform(init).run { value =>
-          CurrentPrompt(prompt,
-            Allocate(reference, value, prompt,
-              transform(body)))
+          Var(reference, value, transform(body.tpe),
+            transform(body))
         }
 
       case core.Get(id, capt, tpe) =>
         val stateType = transform(tpe)
         val reference = Variable(transform(id), Type.Reference(stateType))
         val variable = Variable(freshName("get"), stateType)
 
-        Load(variable, reference,
+        LoadVar(variable, reference,
             Return(List(variable)))
 
       case core.Put(id, capt, arg) =>
@@ -274,7 +273,7 @@ object Transformer {
         val variable = Variable(freshName("put"), Positive())
 
         transform(arg).run { value =>
-          Store(reference, value,
+          StoreVar(reference, value,
             Construct(variable, builtins.Unit, List(),
               Return(List(variable))))
         }

effekt/shared/src/main/scala/effekt/machine/Tree.scala

@@ -158,6 +158,21 @@ enum Statement {
   */
   case Store(reference: Variable, value: Variable, rest: Statement)
 
+  /**
+   *  e.g. var x = 42; s
+   */
+  case Var(name: Variable, init: Variable, returnType: Type, rest: Statement)
+
+  /**
+  * e.g. let y = loadVar(x); s
+  */
+  case LoadVar(name: Variable, ref: Variable, rest: Statement)
+
+  /**
+  * e.g. storeVar(x, 42); s
+  */
+  case StoreVar(ref: Variable, value: Variable, rest: Statement)
+
   /**
    * e.g. push { (x, ...) => s }; s
    */

libraries/llvm/rts.ll

@@ -308,6 +308,57 @@ define ptr @getPointer(%Reference %reference, i64 %index, %Stack %stack) {
     ret ptr %pointer
 }
 
+define %Stack @getStack(%Stack %stack, %Prompt %prompt) {
+    %promptPointer = getelementptr %StackValue, %Stack %stack, i64 0, i32 3
+    %thisPrompt = load %Prompt, ptr %promptPointer
+    %found = icmp eq %Prompt %prompt, %thisPrompt
+    br i1 %found, label %done, label %recurse
+
+done:
+    ret %Stack %stack
+
+recurse:
+    %nextStackPointer = getelementptr %StackValue, %Stack %stack, i64 0, i32 4
+    %nextStack = load %Stack, ptr %nextStackPointer
+    %result = call %Stack @getStack(%Stack %nextStack, %Prompt %prompt)
+    ret %Stack %result
+}
+
+define ptr @getVarPointer(%Reference %reference, %Stack %stack) {
+    %prompt32 = extractvalue %Reference %reference, 0
+    %offset32 = extractvalue %Reference %reference, 1
+    %prompt = zext i32 %prompt32 to i64
+    %offset = zext i32 %offset32 to i64
+
+    %targetStack = call %Stack @getStack(%Stack %stack, %Prompt %prompt)
+    %basePointer = getelementptr %StackValue, %Stack %targetStack, i64 0, i32 1, i32 1
+    %base = load %Base, ptr %basePointer
+    %varPointer = getelementptr i8, %Base %base, i64 %offset
+    ret ptr %varPointer
+}
+
+define %Reference @newReference(%Stack %stack) alwaysinline {
+    %stackPointerPointer = getelementptr %StackValue, %Stack %stack, i64 0, i32 1, i32 0
+    %basePointer = getelementptr %StackValue, %Stack %stack, i64 0, i32 1, i32 1
+
+    %stackPointer = load %StackPointer, ptr %stackPointerPointer
+    %base = load %StackPointer, ptr %basePointer
+
+    %intStack = ptrtoint %StackPointer %stackPointer to i64
+    %intBase = ptrtoint %StackPointer %base to i64
+
+    %offset = sub i64 %intStack, %intBase
+    %offset32 = trunc i64 %offset to i32
+
+    %prompt = call %Prompt @currentPrompt(%Stack %stack)
+    %prompt32 = trunc %Prompt %prompt to i32
+
+    %reference..1 = insertvalue %Reference undef, i32 %prompt32, 0
+    %reference = insertvalue %Reference %reference..1, i32 %offset32, 1
+
+    ret %Reference %reference
+}
+
 ; Stack management
 
 define %StackPointer @stackAllocate(%Stack %stack, i64 %n) {