Avoid stack overflow by yielding to trampoline

Author: phischu

libraries/common/io/signal.effekt

@@ -14,10 +14,10 @@ namespace signal {
     """
 }
 
-extern global def unsafeSend[T](signal: Signal[T], value: T): Unit =
+extern async def unsafeSend[T](signal: Signal[T], value: T): Unit =
   llvm """
-    call void @c_signal_send(%Pos ${signal}, %Pos ${value})
-    ret %Pos zeroinitializer
+    call void @c_signal_send(%Pos ${signal}, %Pos ${value}, %Stack %stack)
+    ret void
   """
 
 extern async def unsafeWait[T](signal: Signal[T]): T =

libraries/llvm/io.c

@@ -338,13 +338,15 @@ struct Pos c_signal_make() {
     return (struct Pos) { .tag = 0, .obj = signal, };
 }
 
-void c_signal_send(struct Pos signal, struct Pos value) {
+void c_signal_send(struct Pos signal, struct Pos value, Stack stack) {
     Signal* f = (Signal*)signal.obj;
     switch (f->state) {
         case BEFORE: {
             f->state = SENDING;
             f->payload.value = value;
             erasePositive(signal);
+            // TODO avoid stack overflow without yielding
+            c_yield(stack);
             break;
         }
         case SENDING: {
@@ -354,11 +356,12 @@ void c_signal_send(struct Pos signal, struct Pos value) {
             break;
         }
         case WAITING: {
-            Stack stack = f->payload.stack;
+            Stack other = f->payload.stack;
             f->state = AFTER;
             erasePositive(signal);
-            // TODO this overflows the C stack
-            resume_Pos(stack, value);
+            // TODO avoid stack overflow without yielding
+            c_yield(stack);
+            resume_Pos(other, value);
             break;
         }
         case AFTER: {