compiler: add support for 'go' on func values

This commit allows starting a new goroutine directly from a func value,
not just when the static callee is known.

This is necessary to support the whole time package, not just the
commonly used subset that was compiled with the SimpleDCE pass enabled.

compiler/compiler.go

@@ -1060,32 +1060,47 @@ func (c *Compiler) parseInstr(frame *Frame, instr ssa.Instruction) {
 	case *ssa.Defer:
 		c.emitDefer(frame, instr)
 	case *ssa.Go:
-		if instr.Call.IsInvoke() {
-			c.addError(instr.Pos(), "todo: go on method receiver")
-			return
-		}
-		callee := instr.Call.StaticCallee()
-		if callee == nil {
-			c.addError(instr.Pos(), "todo: go on non-direct function (function pointer, etc.)")
-			return
-		}
-		calleeFn := c.ir.GetFunction(callee)
-
 		// Get all function parameters to pass to the goroutine.
 		var params []llvm.Value
 		for _, param := range instr.Call.Args {
 			params = append(params, c.getValue(frame, param))
 		}
-		if !calleeFn.IsExported() && c.selectScheduler() != "tasks" {
-			// For coroutine scheduling, this is only required when calling an
-			// external function.
-			// For tasks, because all params are stored in a single object, no
-			// unnecessary parameters should be stored anyway.
-			params = append(params, llvm.Undef(c.i8ptrType)) // context parameter
-			params = append(params, llvm.Undef(c.i8ptrType)) // parent coroutine handle
-		}
 
-		c.emitStartGoroutine(calleeFn.LLVMFn, params)
+		// Start a new goroutine.
+		if callee := instr.Call.StaticCallee(); callee != nil {
+			// Static callee is known. This makes it easier to start a new
+			// goroutine.
+			calleeFn := c.ir.GetFunction(callee)
+			if !calleeFn.IsExported() && c.selectScheduler() != "tasks" {
+				// For coroutine scheduling, this is only required when calling
+				// an external function.
+				// For tasks, because all params are stored in a single object,
+				// no unnecessary parameters should be stored anyway.
+				params = append(params, llvm.Undef(c.i8ptrType))            // context parameter
+				params = append(params, llvm.ConstPointerNull(c.i8ptrType)) // parent coroutine handle
+			}
+			c.emitStartGoroutine(calleeFn.LLVMFn, params)
+		} else if !instr.Call.IsInvoke() {
+			// This is a function pointer.
+			// At the moment, two extra params are passed to the newly started
+			// goroutine:
+			//   * The function context, for closures.
+			//   * The parent handle (for coroutines) or the function pointer
+			//     itself (for tasks).
+			funcPtr, context := c.decodeFuncValue(c.getValue(frame, instr.Call.Value), instr.Call.Value.Type().(*types.Signature))
+			params = append(params, context) // context parameter
+			switch c.selectScheduler() {
+			case "coroutines":
+				params = append(params, llvm.ConstPointerNull(c.i8ptrType)) // parent coroutine handle
+			case "tasks":
+				params = append(params, funcPtr)
+			default:
+				panic("unknown scheduler type")
+			}
+			c.emitStartGoroutine(funcPtr, params)
+		} else {
+			c.addError(instr.Pos(), "todo: go on interface call")
+		}
 	case *ssa.If:
 		cond := c.getValue(frame, instr.Cond)
 		block := instr.Block()