compiler: allow larger-than-int values to be sent across a channel

Instead of storing the value to send/receive in the coroutine promise,
store only a pointer in the promise. This simplifies the code a lot and
allows larger value sizes to be sent across a channel.

Unfortunately, this new system has a code size impact. For example,
compiling testdata/channel.go for the BBC micro:bit, there is an
increase in code size from 4776 bytes to 4856 bytes. However, the
improved flexibility and simplicity of the code should be worth it. If
this becomes an issue, we can always refactor the code at a later time.

compiler/channel.go

@@ -12,13 +12,6 @@ import (
 
 // emitMakeChan returns a new channel value for the given channel type.
 func (c *Compiler) emitMakeChan(expr *ssa.MakeChan) (llvm.Value, error) {
-	valueType := c.getLLVMType(expr.Type().(*types.Chan).Elem())
-	if c.targetData.TypeAllocSize(valueType) > c.targetData.TypeAllocSize(c.intType) {
-		// Values bigger than int overflow the data part of the coroutine.
-		// TODO: make the coroutine data part big enough to hold these bigger
-		// values.
-		return llvm.Value{}, c.makeError(expr.Pos(), "todo: channel with values bigger than int")
-	}
 	chanType := c.mod.GetTypeByName("runtime.channel")
 	size := c.targetData.TypeAllocSize(chanType)
 	sizeValue := llvm.ConstInt(c.uintptrType, size, false)
@@ -30,14 +23,27 @@ func (c *Compiler) emitMakeChan(expr *ssa.MakeChan) (llvm.Value, error) {
 // emitChanSend emits a pseudo chan send operation. It is lowered to the actual
 // channel send operation during goroutine lowering.
 func (c *Compiler) emitChanSend(frame *Frame, instr *ssa.Send) {
-	valueType := c.getLLVMType(instr.Chan.Type().(*types.Chan).Elem())
+	valueType := c.getLLVMType(instr.X.Type())
 	ch := c.getValue(frame, instr.Chan)
 	chanValue := c.getValue(frame, instr.X)
 	valueSize := llvm.ConstInt(c.uintptrType, c.targetData.TypeAllocSize(chanValue.Type()), false)
+	coroutine := c.createRuntimeCall("getCoroutine", nil, "")
+
+	// store value-to-send
+	c.builder.SetInsertPointBefore(coroutine.InstructionParent().Parent().EntryBasicBlock().FirstInstruction())
 	valueAlloca := c.builder.CreateAlloca(valueType, "chan.value")
+	c.builder.SetInsertPointBefore(coroutine)
+	c.builder.SetInsertPointAtEnd(coroutine.InstructionParent())
 	c.builder.CreateStore(chanValue, valueAlloca)
 	valueAllocaCast := c.builder.CreateBitCast(valueAlloca, c.i8ptrType, "chan.value.i8ptr")
-	c.createRuntimeCall("chanSendStub", []llvm.Value{llvm.Undef(c.i8ptrType), ch, valueAllocaCast, valueSize}, "")
+
+	// Do the send.
+	c.createRuntimeCall("chanSend", []llvm.Value{coroutine, ch, valueAllocaCast, valueSize}, "")
+
+	// Make sure CoroSplit includes the alloca in the coroutine frame.
+	// This is a bit dirty, but it works (at least in LLVM 8).
+	valueSizeI64 := llvm.ConstInt(c.ctx.Int64Type(), c.targetData.TypeAllocSize(chanValue.Type()), false)
+	c.builder.CreateCall(c.getLifetimeEndFunc(), []llvm.Value{valueSizeI64, valueAllocaCast}, "")
 }
 
 // emitChanRecv emits a pseudo chan receive operation. It is lowered to the
@@ -46,13 +52,21 @@ func (c *Compiler) emitChanRecv(frame *Frame, unop *ssa.UnOp) llvm.Value {
 	valueType := c.getLLVMType(unop.X.Type().(*types.Chan).Elem())
 	valueSize := llvm.ConstInt(c.uintptrType, c.targetData.TypeAllocSize(valueType), false)
 	ch := c.getValue(frame, unop.X)
+	coroutine := c.createRuntimeCall("getCoroutine", nil, "")
+
+	// Allocate memory to receive into.
+	c.builder.SetInsertPointBefore(coroutine.InstructionParent().Parent().EntryBasicBlock().FirstInstruction())
 	valueAlloca := c.builder.CreateAlloca(valueType, "chan.value")
+	c.builder.SetInsertPointBefore(coroutine)
+	c.builder.SetInsertPointAtEnd(coroutine.InstructionParent())
 	valueAllocaCast := c.builder.CreateBitCast(valueAlloca, c.i8ptrType, "chan.value.i8ptr")
-	valueOk := c.builder.CreateAlloca(c.ctx.Int1Type(), "chan.comma-ok.alloca")
+
-	c.createRuntimeCall("chanRecvStub", []llvm.Value{llvm.Undef(c.i8ptrType), ch, valueAllocaCast, valueOk, valueSize}, "")
+	// Do the receive.
+	c.createRuntimeCall("chanRecv", []llvm.Value{coroutine, ch, valueAllocaCast, valueSize}, "")
 	received := c.builder.CreateLoad(valueAlloca, "chan.received")
 	if unop.CommaOk {
-		commaOk := c.builder.CreateLoad(valueOk, "chan.comma-ok")
+		commaOk := c.createRuntimeCall("getTaskPromiseData", []llvm.Value{coroutine}, "chan.commaOk.wide")
+		commaOk = c.builder.CreateTrunc(commaOk, c.ctx.Int1Type(), "chan.commaOk")
 		tuple := llvm.Undef(c.ctx.StructType([]llvm.Type{valueType, c.ctx.Int1Type()}, false))
 		tuple = c.builder.CreateInsertValue(tuple, received, 0, "")
 		tuple = c.builder.CreateInsertValue(tuple, commaOk, 1, "")

compiler/compiler.go

@@ -344,11 +344,9 @@ func (c *Compiler) Compile(mainPath string) []error {
 	realMain.SetLinkage(llvm.ExternalLinkage) // keep alive until goroutine lowering
 	c.mod.NamedFunction("runtime.alloc").SetLinkage(llvm.ExternalLinkage)
 	c.mod.NamedFunction("runtime.free").SetLinkage(llvm.ExternalLinkage)
-	c.mod.NamedFunction("runtime.chanSend").SetLinkage(llvm.ExternalLinkage)
-	c.mod.NamedFunction("runtime.chanRecv").SetLinkage(llvm.ExternalLinkage)
 	c.mod.NamedFunction("runtime.sleepTask").SetLinkage(llvm.ExternalLinkage)
-	c.mod.NamedFunction("runtime.setTaskData").SetLinkage(llvm.ExternalLinkage)
+	c.mod.NamedFunction("runtime.setTaskPromisePtr").SetLinkage(llvm.ExternalLinkage)
-	c.mod.NamedFunction("runtime.getTaskData").SetLinkage(llvm.ExternalLinkage)
+	c.mod.NamedFunction("runtime.getTaskPromisePtr").SetLinkage(llvm.ExternalLinkage)
 	c.mod.NamedFunction("runtime.activateTask").SetLinkage(llvm.ExternalLinkage)
 	c.mod.NamedFunction("runtime.scheduler").SetLinkage(llvm.ExternalLinkage)
 

compiler/goroutine-lowering.go

@@ -62,7 +62,7 @@ package compiler
 //         llvm.suspend(hdl)                       // suspend point
 //         println("some other operation")
 //         var i *int                              // allocate space on the stack for the return value
-//         runtime.setTaskData(hdl, &i)            // store return value alloca in our coroutine promise
+//         runtime.setTaskPromisePtr(hdl, &i)      // store return value alloca in our coroutine promise
 //         bar(hdl)                                // await, pass a continuation (hdl) to bar
 //         llvm.suspend(hdl)                       // suspend point, wait for the callee to re-activate
 //         println("done", *i)
@@ -146,11 +146,9 @@ func (c *Compiler) LowerGoroutines() error {
 	realMain.SetLinkage(llvm.InternalLinkage)
 	c.mod.NamedFunction("runtime.alloc").SetLinkage(llvm.InternalLinkage)
 	c.mod.NamedFunction("runtime.free").SetLinkage(llvm.InternalLinkage)
-	c.mod.NamedFunction("runtime.chanSend").SetLinkage(llvm.InternalLinkage)
-	c.mod.NamedFunction("runtime.chanRecv").SetLinkage(llvm.InternalLinkage)
 	c.mod.NamedFunction("runtime.sleepTask").SetLinkage(llvm.InternalLinkage)
-	c.mod.NamedFunction("runtime.setTaskData").SetLinkage(llvm.InternalLinkage)
+	c.mod.NamedFunction("runtime.setTaskPromisePtr").SetLinkage(llvm.InternalLinkage)
-	c.mod.NamedFunction("runtime.getTaskData").SetLinkage(llvm.InternalLinkage)
+	c.mod.NamedFunction("runtime.getTaskPromisePtr").SetLinkage(llvm.InternalLinkage)
 	c.mod.NamedFunction("runtime.scheduler").SetLinkage(llvm.InternalLinkage)
 
 	return nil
@@ -179,13 +177,13 @@ func (c *Compiler) markAsyncFunctions() (needsScheduler bool, err error) {
 	if !deadlockStub.IsNil() {
 		worklist = append(worklist, deadlockStub)
 	}
-	chanSendStub := c.mod.NamedFunction("runtime.chanSendStub")
+	chanSend := c.mod.NamedFunction("runtime.chanSend")
-	if !chanSendStub.IsNil() {
+	if !chanSend.IsNil() {
-		worklist = append(worklist, chanSendStub)
+		worklist = append(worklist, chanSend)
 	}
-	chanRecvStub := c.mod.NamedFunction("runtime.chanRecvStub")
+	chanRecv := c.mod.NamedFunction("runtime.chanRecv")
-	if !chanRecvStub.IsNil() {
+	if !chanRecv.IsNil() {
-		worklist = append(worklist, chanRecvStub)
+		worklist = append(worklist, chanRecv)
 	}
 
 	if len(worklist) == 0 {
@@ -283,9 +281,6 @@ func (c *Compiler) markAsyncFunctions() (needsScheduler bool, err error) {
 	coroBeginType := llvm.FunctionType(c.i8ptrType, []llvm.Type{c.ctx.TokenType(), c.i8ptrType}, false)
 	coroBeginFunc := llvm.AddFunction(c.mod, "llvm.coro.begin", coroBeginType)
 
-	coroPromiseType := llvm.FunctionType(c.i8ptrType, []llvm.Type{c.i8ptrType, c.ctx.Int32Type(), c.ctx.Int1Type()}, false)
-	coroPromiseFunc := llvm.AddFunction(c.mod, "llvm.coro.promise", coroPromiseType)
-
 	coroSuspendType := llvm.FunctionType(c.ctx.Int8Type(), []llvm.Type{c.ctx.TokenType(), c.ctx.Int1Type()}, false)
 	coroSuspendFunc := llvm.AddFunction(c.mod, "llvm.coro.suspend", coroSuspendType)
 
@@ -297,7 +292,7 @@ func (c *Compiler) markAsyncFunctions() (needsScheduler bool, err error) {
 
 	// Transform all async functions into coroutines.
 	for _, f := range asyncList {
-		if f == sleep || f == deadlockStub || f == chanSendStub || f == chanRecvStub {
+		if f == sleep || f == deadlockStub || f == chanSend || f == chanRecv {
 			continue
 		}
 
@@ -314,7 +309,7 @@ func (c *Compiler) markAsyncFunctions() (needsScheduler bool, err error) {
 			for inst := bb.FirstInstruction(); !inst.IsNil(); inst = llvm.NextInstruction(inst) {
 				if !inst.IsACallInst().IsNil() {
 					callee := inst.CalledValue()
-					if _, ok := asyncFuncs[callee]; !ok || callee == sleep || callee == deadlockStub || callee == chanSendStub || callee == chanRecvStub {
+					if _, ok := asyncFuncs[callee]; !ok || callee == sleep || callee == deadlockStub || callee == chanSend || callee == chanRecv {
 						continue
 					}
 					asyncCalls = append(asyncCalls, inst)
@@ -359,7 +354,7 @@ func (c *Compiler) markAsyncFunctions() (needsScheduler bool, err error) {
 				retvalAlloca = c.builder.CreateAlloca(inst.Type(), "coro.retvalAlloca")
 				c.builder.SetInsertPointBefore(inst)
 				data := c.builder.CreateBitCast(retvalAlloca, c.i8ptrType, "")
-				c.createRuntimeCall("setTaskData", []llvm.Value{frame.taskHandle, data}, "")
+				c.createRuntimeCall("setTaskPromisePtr", []llvm.Value{frame.taskHandle, data}, "")
 			}
 
 			// Suspend.
@@ -404,7 +399,7 @@ func (c *Compiler) markAsyncFunctions() (needsScheduler bool, err error) {
 				// Return this value by writing to the pointer stored in the
 				// parent handle. The parent coroutine has made an alloca that
 				// we can write to to store our return value.
-				returnValuePtr := c.createRuntimeCall("getTaskData", []llvm.Value{parentHandle}, "coro.parentData")
+				returnValuePtr := c.createRuntimeCall("getTaskPromisePtr", []llvm.Value{parentHandle}, "coro.parentData")
 				alloca := c.builder.CreateBitCast(returnValuePtr, llvm.PointerType(inst.Operand(0).Type(), 0), "coro.parentAlloca")
 				c.builder.CreateStore(inst.Operand(0), alloca)
 			default:
@@ -452,6 +447,14 @@ func (c *Compiler) markAsyncFunctions() (needsScheduler bool, err error) {
 		c.builder.CreateUnreachable()
 	}
 
+	// Replace calls to runtime.getCoroutineCall with the coroutine of this
+	// frame.
+	for _, getCoroutineCall := range getUses(c.mod.NamedFunction("runtime.getCoroutine")) {
+		frame := asyncFuncs[getCoroutineCall.InstructionParent().Parent()]
+		getCoroutineCall.ReplaceAllUsesWith(frame.taskHandle)
+		getCoroutineCall.EraseFromParentAsInstruction()
+	}
+
 	// Transform calls to time.Sleep() into coroutine suspend points.
 	for _, sleepCall := range getUses(sleep) {
 		// sleepCall must be a call instruction.
@@ -495,37 +498,11 @@ func (c *Compiler) markAsyncFunctions() (needsScheduler bool, err error) {
 		deadlockCall.EraseFromParentAsInstruction()
 	}
 
-	// Transform calls to runtime.chanSendStub into channel send operations.
+	// Transform calls to runtime.chanSend into channel send operations.
-	for _, sendOp := range getUses(chanSendStub) {
+	for _, sendOp := range getUses(chanSend) {
 		// sendOp must be a call instruction.
 		frame := asyncFuncs[sendOp.InstructionParent().Parent()]
 
-		// Send the value over the channel, or block.
-		sendOp.SetOperand(0, frame.taskHandle)
-		sendOp.SetOperand(sendOp.OperandsCount()-1, c.mod.NamedFunction("runtime.chanSend"))
-
-		// Use taskState.data to store the value to send:
-		//     *(*valueType)(&coroutine.promise().data) = valueToSend
-		//     runtime.chanSend(coroutine, ch)
-		bitcast := sendOp.Operand(2)
-		valueAlloca := bitcast.Operand(0)
-		c.builder.SetInsertPointBefore(valueAlloca)
-		promiseType := c.mod.GetTypeByName("runtime.taskState")
-		promiseRaw := c.builder.CreateCall(coroPromiseFunc, []llvm.Value{
-			frame.taskHandle,
-			llvm.ConstInt(c.ctx.Int32Type(), uint64(c.targetData.PrefTypeAlignment(promiseType)), false),
-			llvm.ConstInt(c.ctx.Int1Type(), 0, false),
-		}, "task.promise.raw")
-		promise := c.builder.CreateBitCast(promiseRaw, llvm.PointerType(promiseType, 0), "task.promise")
-		dataPtr := c.builder.CreateInBoundsGEP(promise, []llvm.Value{
-			llvm.ConstInt(c.ctx.Int32Type(), 0, false),
-			llvm.ConstInt(c.ctx.Int32Type(), 2, false),
-		}, "task.promise.data")
-		sendOp.SetOperand(2, llvm.Undef(c.i8ptrType))
-		valueAlloca.ReplaceAllUsesWith(c.builder.CreateBitCast(dataPtr, valueAlloca.Type(), ""))
-		bitcast.EraseFromParentAsInstruction()
-		valueAlloca.EraseFromParentAsInstruction()
-
 		// Yield to scheduler.
 		c.builder.SetInsertPointBefore(llvm.NextInstruction(sendOp))
 		continuePoint := c.builder.CreateCall(coroSuspendFunc, []llvm.Value{
@@ -538,21 +515,11 @@ func (c *Compiler) markAsyncFunctions() (needsScheduler bool, err error) {
 		sw.AddCase(llvm.ConstInt(c.ctx.Int8Type(), 1, false), frame.cleanupBlock)
 	}
 
-	// Transform calls to runtime.chanRecvStub into channel receive operations.
+	// Transform calls to runtime.chanRecv into channel receive operations.
-	for _, recvOp := range getUses(chanRecvStub) {
+	for _, recvOp := range getUses(chanRecv) {
 		// recvOp must be a call instruction.
 		frame := asyncFuncs[recvOp.InstructionParent().Parent()]
 
-		bitcast := recvOp.Operand(2)
-		commaOk := recvOp.Operand(3)
-		valueAlloca := bitcast.Operand(0)
-
-		// Receive the value over the channel, or block.
-		recvOp.SetOperand(0, frame.taskHandle)
-		recvOp.SetOperand(recvOp.OperandsCount()-1, c.mod.NamedFunction("runtime.chanRecv"))
-		recvOp.SetOperand(2, llvm.Undef(c.i8ptrType))
-		bitcast.EraseFromParentAsInstruction()
-
 		// Yield to scheduler.
 		c.builder.SetInsertPointBefore(llvm.NextInstruction(recvOp))
 		continuePoint := c.builder.CreateCall(coroSuspendFunc, []llvm.Value{
@@ -564,32 +531,6 @@ func (c *Compiler) markAsyncFunctions() (needsScheduler bool, err error) {
 		c.builder.SetInsertPointAtEnd(recvOp.InstructionParent())
 		sw.AddCase(llvm.ConstInt(c.ctx.Int8Type(), 0, false), wakeup)
 		sw.AddCase(llvm.ConstInt(c.ctx.Int8Type(), 1, false), frame.cleanupBlock)
-
-		// The value to receive is stored in taskState.data:
-		//     runtime.chanRecv(coroutine, ch)
-		//     promise := coroutine.promise()
-		//     valueReceived := *(*valueType)(&promise.data)
-		//     ok := promise.commaOk
-		c.builder.SetInsertPointBefore(wakeup.FirstInstruction())
-		promiseType := c.mod.GetTypeByName("runtime.taskState")
-		promiseRaw := c.builder.CreateCall(coroPromiseFunc, []llvm.Value{
-			frame.taskHandle,
-			llvm.ConstInt(c.ctx.Int32Type(), uint64(c.targetData.PrefTypeAlignment(promiseType)), false),
-			llvm.ConstInt(c.ctx.Int1Type(), 0, false),
-		}, "task.promise.raw")
-		promise := c.builder.CreateBitCast(promiseRaw, llvm.PointerType(promiseType, 0), "task.promise")
-		dataPtr := c.builder.CreateInBoundsGEP(promise, []llvm.Value{
-			llvm.ConstInt(c.ctx.Int32Type(), 0, false),
-			llvm.ConstInt(c.ctx.Int32Type(), 2, false),
-		}, "task.promise.data")
-		valueAlloca.ReplaceAllUsesWith(c.builder.CreateBitCast(dataPtr, valueAlloca.Type(), ""))
-		valueAlloca.EraseFromParentAsInstruction()
-		commaOkPtr := c.builder.CreateInBoundsGEP(promise, []llvm.Value{
-			llvm.ConstInt(c.ctx.Int32Type(), 0, false),
-			llvm.ConstInt(c.ctx.Int32Type(), 1, false),
-		}, "task.promise.comma-ok")
-		commaOk.ReplaceAllUsesWith(commaOkPtr)
-		recvOp.SetOperand(3, llvm.Undef(commaOk.Type()))
 	}
 
 	return true, c.lowerMakeGoroutineCalls()

compiler/llvm.go

@@ -22,6 +22,17 @@ func getUses(value llvm.Value) []llvm.Value {
 	return uses
 }
 
+// getLifetimeEndFunc returns the llvm.lifetime.end intrinsic and creates it
+// first if it doesn't exist yet.
+func (c *Compiler) getLifetimeEndFunc() llvm.Value {
+	fn := c.mod.NamedFunction("llvm.lifetime.end.p0i8")
+	if fn.IsNil() {
+		fnType := llvm.FunctionType(c.ctx.VoidType(), []llvm.Type{c.ctx.Int64Type(), c.i8ptrType}, false)
+		fn = llvm.AddFunction(c.mod, "llvm.lifetime.end.p0i8", fnType)
+	}
+	return fn
+}
+
 // splitBasicBlock splits a LLVM basic block into two parts. All instructions
 // after afterInst are moved into a new basic block (created right after the
 // current one) with the given name.

compiler/sizes.go

@@ -113,6 +113,9 @@ func (s *StdSizes) Sizeof(T types.Type) int64 {
 		if k == types.Uintptr {
 			return s.PtrSize
 		}
+		if k == types.UnsafePointer {
+			return s.PtrSize
+		}
 		panic("unknown basic type: " + t.String())
 	case *types.Array:
 		n := t.Len()

src/runtime/chan.go

@@ -39,33 +39,27 @@ const (
 	chanStateClosed
 )
 
-func chanSendStub(caller *coroutine, ch *channel, _ unsafe.Pointer, size uintptr)
-func chanRecvStub(caller *coroutine, ch *channel, _ unsafe.Pointer, _ *bool, size uintptr)
 func deadlockStub()
 
 // chanSend sends a single value over the channel. If this operation can
 // complete immediately (there is a goroutine waiting for a value), it sends the
 // value and re-activates both goroutines. If not, it sets itself as waiting on
 // a value.
-//
+func chanSend(sender *coroutine, ch *channel, value unsafe.Pointer, size uintptr) {
-// The unsafe.Pointer value is used during lowering. During IR generation, it
-// points to the to-be-received value. During coroutine lowering, this value is
-// replaced with a read from the coroutine promise.
-func chanSend(sender *coroutine, ch *channel, _ unsafe.Pointer, size uintptr) {
 	if ch == nil {
 		// A nil channel blocks forever. Do not scheduler this goroutine again.
 		return
 	}
 	switch ch.state {
 	case chanStateEmpty:
+		sender.promise().ptr = value
 		ch.state = chanStateSend
 		ch.blocked = sender
 	case chanStateRecv:
 		receiver := ch.blocked
 		receiverPromise := receiver.promise()
-		senderPromise := sender.promise()
+		memcpy(receiverPromise.ptr, value, size)
-		memcpy(unsafe.Pointer(&receiverPromise.data), unsafe.Pointer(&senderPromise.data), size)
+		receiverPromise.data = 1 // commaOk = true
-		receiverPromise.commaOk = true
 		ch.blocked = receiverPromise.next
 		receiverPromise.next = nil
 		activateTask(receiver)
@@ -76,6 +70,7 @@ func chanSend(sender *coroutine, ch *channel, _ unsafe.Pointer, size uintptr) {
 	case chanStateClosed:
 		runtimePanic("send on closed channel")
 	case chanStateSend:
+		sender.promise().ptr = value
 		sender.promise().next = ch.blocked
 		ch.blocked = sender
 	}
@@ -85,11 +80,7 @@ func chanSend(sender *coroutine, ch *channel, _ unsafe.Pointer, size uintptr) {
 // sender, it receives the value immediately and re-activates both coroutines.
 // If not, it sets itself as available for receiving. If the channel is closed,
 // it immediately activates itself with a zero value as the result.
-//
+func chanRecv(receiver *coroutine, ch *channel, value unsafe.Pointer, size uintptr) {
-// The two unnamed values exist to help during lowering. The unsafe.Pointer
-// points to the value, and the *bool points to the comma-ok value. Both are
-// replaced by reads from the coroutine promise.
-func chanRecv(receiver *coroutine, ch *channel, _ unsafe.Pointer, _ *bool, size uintptr) {
 	if ch == nil {
 		// A nil channel blocks forever. Do not scheduler this goroutine again.
 		return
@@ -97,10 +88,9 @@ func chanRecv(receiver *coroutine, ch *channel, _ unsafe.Pointer, _ *bool, size
 	switch ch.state {
 	case chanStateSend:
 		sender := ch.blocked
-		receiverPromise := receiver.promise()
 		senderPromise := sender.promise()
-		memcpy(unsafe.Pointer(&receiverPromise.data), unsafe.Pointer(&senderPromise.data), size)
+		memcpy(value, senderPromise.ptr, size)
-		receiverPromise.commaOk = true
+		receiver.promise().data = 1 // commaOk = true
 		ch.blocked = senderPromise.next
 		senderPromise.next = nil
 		activateTask(receiver)
@@ -109,14 +99,15 @@ func chanRecv(receiver *coroutine, ch *channel, _ unsafe.Pointer, _ *bool, size
 			ch.state = chanStateEmpty
 		}
 	case chanStateEmpty:
+		receiver.promise().ptr = value
 		ch.state = chanStateRecv
 		ch.blocked = receiver
 	case chanStateClosed:
-		receiverPromise := receiver.promise()
+		memzero(value, size)
-		memzero(unsafe.Pointer(&receiverPromise.data), size)
+		receiver.promise().data = 0 // commaOk = false
-		receiverPromise.commaOk = false
 		activateTask(receiver)
 	case chanStateRecv:
+		receiver.promise().ptr = value
 		receiver.promise().next = ch.blocked
 		ch.blocked = receiver
 	}
@@ -142,8 +133,8 @@ func chanClose(ch *channel, size uintptr) {
 	case chanStateRecv:
 		// The receiver must be re-activated with a zero value.
 		receiverPromise := ch.blocked.promise()
-		memzero(unsafe.Pointer(&receiverPromise.data), size)
+		memzero(receiverPromise.ptr, size)
-		receiverPromise.commaOk = false
+		receiverPromise.data = 0 // commaOk = false
 		activateTask(ch.blocked)
 		ch.state = chanStateClosed
 		ch.blocked = nil

src/runtime/scheduler.go

@@ -49,12 +49,16 @@ func (t *coroutine) promise() *taskState {
 
 func makeGoroutine(*uint8) *uint8
 
+// Compiler stub to get the current goroutine. Calls to this function are
+// removed in the goroutine lowering pass.
+func getCoroutine() *coroutine
+
 // State/promise of a task. Internally represented as:
 //
 //     {i8* next, i1 commaOk, i32/i64 data}
 type taskState struct {
 	next *coroutine
-	commaOk bool // 'comma-ok' flag for channel receive operation
+	ptr  unsafe.Pointer
 	data uint
 }
 
@@ -107,12 +111,22 @@ func activateTask(task *coroutine) {
 	runqueuePushBack(task)
 }
 
-func setTaskData(task *coroutine, value unsafe.Pointer) {
+// getTaskPromisePtr is a helper function to set the current .ptr field of a
-	task.promise().data = uint(uintptr(value))
+// coroutine promise.
+func setTaskPromisePtr(task *coroutine, value unsafe.Pointer) {
+	task.promise().ptr = value
 }
 
-func getTaskData(task *coroutine) unsafe.Pointer {
+// getTaskPromisePtr is a helper function to get the current .ptr field from a
-	return unsafe.Pointer(uintptr(task.promise().data))
+// coroutine promise.
+func getTaskPromisePtr(task *coroutine) unsafe.Pointer {
+	return task.promise().ptr
+}
+
+// getTaskPromiseData is a helper function to get the current .data field of a
+// coroutine promise.
+func getTaskPromiseData(task *coroutine) uint {
+	return task.promise().data
 }
 
 // Add this task to the end of the run queue. May also destroy the task if it's

testdata/channel.go

@@ -20,6 +20,11 @@ func main() {
 	n, ok = <-ch
 	println("recv from closed channel:", n, ok)
 
+	// Test bigger values
+	ch2 := make(chan complex128)
+	go sendComplex(ch2)
+	println("complex128:", <-ch2)
+
 	// Test multi-sender.
 	ch = make(chan int)
 	go fastsender(ch)
@@ -62,6 +67,10 @@ func sender(ch chan int) {
 	close(ch)
 }
 
+func sendComplex(ch chan complex128) {
+	ch <- 7+10.5i
+}
+
 func fastsender(ch chan int) {
 	ch <- 10
 	ch <- 11

testdata/channel.txt

@@ -9,6 +9,7 @@ received num: 6
 received num: 7
 received num: 8
 recv from closed channel: 0 false
+complex128: (+7.000000e+000+1.050000e+001i)
 got n: 10
 got n: 11
 got n: 10