compiler: centralize loads and stores of SSA values

Map, channel, index, and goroutine lowering each create allocas, store
SSA values into them, load results, and emit lifetime intrinsics.

Add helpers for these operations and use runtimeValueResult for runtime
calls that write a value and an optional comma-ok result. The generated
LLVM IR is unchanged.

compiler/channel.go

@@ -30,7 +30,6 @@ func (b *builder) createMakeChan(expr *ssa.MakeChan) llvm.Value {
 // actual channel send operation during goroutine lowering.
 func (b *builder) createChanSend(instr *ssa.Send) {
 	ch := b.getValue(instr.Chan, getPos(instr))
-	chanValue := b.getValue(instr.X, getPos(instr))
 
 	// store value-to-send
 	valueType := b.getLLVMType(instr.X.Type())
@@ -39,8 +38,7 @@ func (b *builder) createChanSend(instr *ssa.Send) {
 	if isZeroSize {
 		valueAlloca = llvm.ConstNull(b.dataPtrType)
 	} else {
-		valueAlloca, valueAllocaSize = b.createTemporaryAlloca(valueType, "chan.value")
-		b.CreateStore(chanValue, valueAlloca)
+		valueAlloca, valueAllocaSize = b.getValueStorage(instr.X, "chan.value")
 	}
 
 	// Allocate buffer for the channel operation.
@@ -65,38 +63,17 @@ func (b *builder) createChanRecv(unop *ssa.UnOp) llvm.Value {
 	valueType := b.getLLVMType(unop.X.Type().Underlying().(*types.Chan).Elem())
 	ch := b.getValue(unop.X, getPos(unop))
 
-	// Allocate memory to receive into.
-	isZeroSize := b.targetData.TypeAllocSize(valueType) == 0
-	var valueAlloca, valueAllocaSize llvm.Value
-	if isZeroSize {
-		valueAlloca = llvm.ConstNull(b.dataPtrType)
-	} else {
-		valueAlloca, valueAllocaSize = b.createTemporaryAlloca(valueType, "chan.value")
-	}
+	result := b.createRuntimeValueResult(valueType, unop.CommaOk, true, "chan")
 
 	// Allocate buffer for the channel operation.
 	channelOp := b.getLLVMRuntimeType("channelOp")
 	channelOpAlloca, channelOpAllocaSize := b.createTemporaryAlloca(channelOp, "chan.op")
 
 	// Do the receive.
-	commaOk := b.createRuntimeCall("chanRecv", []llvm.Value{ch, valueAlloca, channelOpAlloca}, "")
-	var received llvm.Value
-	if isZeroSize {
-		received = llvm.ConstNull(valueType)
-	} else {
-		received = b.CreateLoad(valueType, valueAlloca, "chan.received")
-		b.emitLifetimeEnd(valueAlloca, valueAllocaSize)
-	}
+	commaOk := b.createRuntimeCall("chanRecv", []llvm.Value{ch, result.valuePtr, channelOpAlloca}, "")
+	received := result.finish(b, commaOk, "chan.received")
 	b.emitLifetimeEnd(channelOpAlloca, channelOpAllocaSize)
-
-	if unop.CommaOk {
-		tuple := llvm.Undef(b.ctx.StructType([]llvm.Type{valueType, b.ctx.Int1Type()}, false))
-		tuple = b.CreateInsertValue(tuple, received, 0, "")
-		tuple = b.CreateInsertValue(tuple, commaOk, 1, "")
-		return tuple
-	} else {
-		return received
-	}
+	return received
 }
 
 // createChanClose closes the given channel.
@@ -170,9 +147,7 @@ func (b *builder) createSelect(expr *ssa.Select) llvm.Value {
 		case types.SendOnly:
 			// Store this value in an alloca and put a pointer to this alloca
 			// in the send state.
-			sendValue := b.getValue(state.Send, state.Pos)
-			alloca := llvmutil.CreateEntryBlockAlloca(b.Builder, sendValue.Type(), "select.send.value")
-			b.CreateStore(sendValue, alloca)
+			alloca := b.getSelectSendStorage(state.Send)
 			selectState = b.CreateInsertValue(selectState, alloca, 1, "")
 		default:
 			panic("unreachable")
@@ -280,7 +255,14 @@ func (b *builder) getChanSelectResult(expr *ssa.Extract) llvm.Value {
 		// receive can proceed at a time) so we'll get that alloca, bitcast
 		// it to the correct type, and dereference it.
 		recvbuf := b.selectRecvBuf[expr.Tuple.(*ssa.Select)]
-		typ := b.getLLVMType(expr.Type())
-		return b.CreateLoad(typ, recvbuf, "")
+		return b.loadFromStorage(recvbuf, expr.Type(), "select.received")
 	}
 }
+
+func (b *builder) getSelectSendStorage(value ssa.Value) llvm.Value {
+	typ := b.getLLVMType(value.Type())
+	llvmValue := b.getValue(value, getPos(value))
+	ptr := llvmutil.CreateEntryBlockAlloca(b.Builder, typ, "select.send.value")
+	b.CreateStore(llvmValue, ptr)
+	return ptr
+}