all: add compiler support for interrupts

This commit lets the compiler know about interrupts and allows
optimizations to be performed based on that: interrupts are eliminated
when they appear to be unused in a program. This is done with a new
pseudo-call (runtime/interrupt.New) that is treated specially by the
compiler.

36 files changed, 766 insertions, 199 deletions

diff --git a/compiler/compiler.go b/compiler/compiler.go
index 1217d3d33..b2f803393 100644
--- a/compiler/compiler.go
+++ b/compiler/compiler.go
@@ -217,7 +217,7 @@ func (c *Compiler) Compile(mainPath string) []error {
 				path = path[len(tinygoPath+"/src/"):]
 			}
 			switch path {
-			case "machine", "os", "reflect", "runtime", "runtime/volatile", "sync", "testing", "internal/reflectlite":
+			case "machine", "os", "reflect", "runtime", "runtime/interrupt", "runtime/volatile", "sync", "testing", "internal/reflectlite":
 				return path
 			default:
 				if strings.HasPrefix(path, "device/") || strings.HasPrefix(path, "examples/") {
@@ -828,9 +828,6 @@ func (c *Compiler) parseFunc(frame *Frame) {
 		frame.fn.LLVMFn.SetLinkage(llvm.InternalLinkage)
 		frame.fn.LLVMFn.SetUnnamedAddr(true)
 	}
-	if frame.fn.IsInterrupt() && strings.HasPrefix(c.Triple(), "avr") {
-		frame.fn.LLVMFn.SetFunctionCallConv(85) // CallingConv::AVR_SIGNAL
-	}
 
 	// Some functions have a pragma controlling the inlining level.
 	switch frame.fn.Inline() {
@@ -1314,6 +1311,8 @@ func (c *Compiler) parseCall(frame *Frame, instr *ssa.CallCommon) (llvm.Value, e
 			return c.emitVolatileLoad(frame, instr)
 		case strings.HasPrefix(name, "runtime/volatile.Store"):
 			return c.emitVolatileStore(frame, instr)
+		case name == "runtime/interrupt.New":
+			return c.emitInterruptGlobal(frame, instr)
 		}
 
 		targetFunc := c.ir.GetFunction(fn)
diff --git a/compiler/interrupt.go b/compiler/interrupt.go
new file mode 100644
index 000000000..67cb8eca6
--- /dev/null
+++ b/compiler/interrupt.go
@@ -0,0 +1,92 @@
+package compiler
+
+import (
+	"strconv"
+	"strings"
+
+	"golang.org/x/tools/go/ssa"
+	"tinygo.org/x/go-llvm"
+)
+
+// emitInterruptGlobal creates a new runtime/interrupt.Interrupt struct that
+// will be lowered to a real interrupt during interrupt lowering.
+//
+// This two-stage approach allows unused interrupts to be optimized away if
+// necessary.
+func (c *Compiler) emitInterruptGlobal(frame *Frame, instr *ssa.CallCommon) (llvm.Value, error) {
+	// Get the interrupt number, which must be a compile-time constant.
+	id, ok := instr.Args[0].(*ssa.Const)
+	if !ok {
+		return llvm.Value{}, c.makeError(instr.Pos(), "interrupt ID is not a constant")
+	}
+
+	// Get the func value, which also must be a compile time constant.
+	// Note that bound functions are allowed if the function has a pointer
+	// receiver and is a global. This is rather strict but still allows for
+	// idiomatic Go code.
+	funcValue := c.getValue(frame, instr.Args[1])
+	if funcValue.IsAConstant().IsNil() {
+		// Try to determine the cause of the non-constantness for a nice error
+		// message.
+		switch instr.Args[1].(type) {
+		case *ssa.MakeClosure:
+			// This may also be a bound method.
+			return llvm.Value{}, c.makeError(instr.Pos(), "closures are not supported in interrupt.New")
+		}
+		// Fall back to a generic error.
+		return llvm.Value{}, c.makeError(instr.Pos(), "interrupt function must be constant")
+	}
+
+	// Create a new global of type runtime/interrupt.handle. Globals of this
+	// type are lowered in the interrupt lowering pass.
+	globalType := c.ir.Program.ImportedPackage("runtime/interrupt").Type("handle").Type()
+	globalLLVMType := c.getLLVMType(globalType)
+	globalName := "runtime/interrupt.$interrupt" + strconv.FormatInt(id.Int64(), 10)
+	if global := c.mod.NamedGlobal(globalName); !global.IsNil() {
+		return llvm.Value{}, c.makeError(instr.Pos(), "interrupt redeclared in this program")
+	}
+	global := llvm.AddGlobal(c.mod, globalLLVMType, globalName)
+	global.SetLinkage(llvm.PrivateLinkage)
+	global.SetGlobalConstant(true)
+	global.SetUnnamedAddr(true)
+	initializer := llvm.ConstNull(globalLLVMType)
+	initializer = llvm.ConstInsertValue(initializer, funcValue, []uint32{0})
+	initializer = llvm.ConstInsertValue(initializer, llvm.ConstInt(c.intType, uint64(id.Int64()), true), []uint32{1, 0})
+	global.SetInitializer(initializer)
+
+	// Add debug info to the interrupt global.
+	if c.Debug() {
+		pos := c.ir.Program.Fset.Position(instr.Pos())
+		diglobal := c.dibuilder.CreateGlobalVariableExpression(c.difiles[pos.Filename], llvm.DIGlobalVariableExpression{
+			Name:        "interrupt" + strconv.FormatInt(id.Int64(), 10),
+			LinkageName: globalName,
+			File:        c.getDIFile(pos.Filename),
+			Line:        pos.Line,
+			Type:        c.getDIType(globalType),
+			Expr:        c.dibuilder.CreateExpression(nil),
+			LocalToUnit: false,
+		})
+		global.AddMetadata(0, diglobal)
+	}
+
+	// Create the runtime/interrupt.Interrupt type. It is a struct with a single
+	// member of type int.
+	num := llvm.ConstPtrToInt(global, c.intType)
+	interrupt := llvm.ConstNamedStruct(c.mod.GetTypeByName("runtime/interrupt.Interrupt"), []llvm.Value{num})
+
+	// Add dummy "use" call for AVR, because interrupts may be used even though
+	// they are never referenced again. This is unlike Cortex-M or the RISC-V
+	// PLIC where each interrupt must be enabled using the interrupt number, and
+	// thus keeps the Interrupt object alive.
+	// This call is removed during interrupt lowering.
+	if strings.HasPrefix(c.Triple(), "avr") {
+		useFn := c.mod.NamedFunction("runtime/interrupt.use")
+		if useFn.IsNil() {
+			useFnType := llvm.FunctionType(c.ctx.VoidType(), []llvm.Type{interrupt.Type()}, false)
+			useFn = llvm.AddFunction(c.mod, "runtime/interrupt.use", useFnType)
+		}
+		c.builder.CreateCall(useFn, []llvm.Value{interrupt}, "")
+	}
+
+	return interrupt, nil
+}
diff --git a/compiler/optimizer.go b/compiler/optimizer.go
index 17b782e83..60395edcb 100644
--- a/compiler/optimizer.go
+++ b/compiler/optimizer.go
@@ -57,6 +57,12 @@ func (c *Compiler) Optimize(optLevel, sizeLevel int, inlinerThreshold uint) []er
 		transform.OptimizeStringToBytes(c.mod)
 		transform.OptimizeAllocs(c.mod)
 		transform.LowerInterfaces(c.mod)
+
+		errs := transform.LowerInterrupts(c.mod)
+		if len(errs) > 0 {
+			return errs
+		}
+
 		if c.funcImplementation() == funcValueSwitch {
 			transform.LowerFuncValues(c.mod)
 		}
@@ -100,6 +106,10 @@ func (c *Compiler) Optimize(optLevel, sizeLevel int, inlinerThreshold uint) []er
 		if err != nil {
 			return []error{err}
 		}
+		errs := transform.LowerInterrupts(c.mod)
+		if len(errs) > 0 {
+			return errs
+		}
 	}
 	if c.VerifyIR() {
 		if errs := c.checkModule(); errs != nil {
diff --git a/ir/ir.go b/ir/ir.go
index 9d243bae7..7506400df 100644
--- a/ir/ir.go
+++ b/ir/ir.go
@@ -27,14 +27,13 @@ type Program struct {
 // Function or method.
 type Function struct {
 	*ssa.Function
-	LLVMFn    llvm.Value
-	module    string     // go:wasm-module
-	linkName  string     // go:linkname, go:export, go:interrupt
-	exported  bool       // go:export
-	nobounds  bool       // go:nobounds
-	flag      bool       // used by dead code elimination
-	interrupt bool       // go:interrupt
-	inline    InlineType // go:inline
+	LLVMFn   llvm.Value
+	module   string     // go:wasm-module
+	linkName string     // go:linkname, go:export
+	exported bool       // go:export
+	nobounds bool       // go:nobounds
+	flag     bool       // used by dead code elimination
+	inline   InlineType // go:inline
 }
 
 // Interface type that is at some point used in a type assert (to check whether
@@ -243,18 +242,6 @@ func (f *Function) parsePragmas() {
 				f.inline = InlineHint
 			case "//go:noinline":
 				f.inline = InlineNone
-			case "//go:interrupt":
-				if len(parts) != 2 {
-					continue
-				}
-				name := parts[1]
-				if strings.HasSuffix(name, "_vect") {
-					// AVR vector naming
-					name = "__vector_" + name[:len(name)-5]
-				}
-				f.linkName = name
-				f.exported = true
-				f.interrupt = true
 			case "//go:linkname":
 				if len(parts) != 3 || parts[1] != f.Name() {
 					continue
@@ -288,14 +275,6 @@ func (f *Function) IsExported() bool {
 	return f.exported || f.CName() != ""
 }
 
-// Return true for functions annotated with //go:interrupt. The function name is
-// already customized in LinkName() to hook up in the interrupt vector.
-//
-// On some platforms (like AVR), interrupts need a special compiler flag.
-func (f *Function) IsInterrupt() bool {
-	return f.interrupt
-}
-
 // Return the inline directive of this function.
 func (f *Function) Inline() InlineType {
 	return f.inline
diff --git a/src/machine/board_arduino_nano33_baremetal.go b/src/machine/board_arduino_nano33_baremetal.go
index 829989a16..cb024cd42 100644
--- a/src/machine/board_arduino_nano33_baremetal.go
+++ b/src/machine/board_arduino_nano33_baremetal.go
@@ -2,7 +2,10 @@
 
 package machine
 
-import "device/sam"
+import (
+	"device/sam"
+	"runtime/interrupt"
+)
 
 // UART1 on the Arduino Nano 33 connects to the onboard NINA-W102 WiFi chip.
 var (
@@ -13,11 +16,6 @@ var (
 	}
 )
 
-//go:export SERCOM3_IRQHandler
-func handleUART1() {
-	defaultUART1Handler()
-}
-
 // UART2 on the Arduino Nano 33 connects to the normal TX/RX pins.
 var (
 	UART2 = UART{
@@ -27,11 +25,9 @@ var (
 	}
 )
 
-//go:export SERCOM5_IRQHandler
-func handleUART2() {
-	// should reset IRQ
-	UART2.Receive(byte((UART2.Bus.DATA.Get() & 0xFF)))
-	UART2.Bus.INTFLAG.SetBits(sam.SERCOM_USART_INTFLAG_RXC)
+func init() {
+	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM3, UART1.handleInterrupt)
+	UART2.Interrupt = interrupt.New(sam.IRQ_SERCOM5, UART2.handleInterrupt)
 }
 
 // I2C on the Arduino Nano 33.
diff --git a/src/machine/board_bluepill.go b/src/machine/board_bluepill.go
index 39c7d421f..e6ba49b40 100644
--- a/src/machine/board_bluepill.go
+++ b/src/machine/board_bluepill.go
@@ -2,7 +2,10 @@
 
 package machine
 
-import "device/stm32"
+import (
+	"device/stm32"
+	"runtime/interrupt"
+)
 
 // https://wiki.stm32duino.com/index.php?title=File:Bluepillpinout.gif
 const (
@@ -61,14 +64,12 @@ var (
 	UART0 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    stm32.USART1,
-		IRQVal: stm32.IRQ_USART1,
 	}
 	UART1 = &UART0
 )
 
-//go:export USART1_IRQHandler
-func handleUART1() {
-	UART1.Receive(byte((UART1.Bus.DR.Get() & 0xFF)))
+func init() {
+	UART0.Interrupt = interrupt.New(stm32.IRQ_USART1, UART0.handleInterrupt)
 }
 
 // SPI pins
diff --git a/src/machine/board_circuitplay_express_baremetal.go b/src/machine/board_circuitplay_express_baremetal.go
index 446b1790f..271082e95 100644
--- a/src/machine/board_circuitplay_express_baremetal.go
+++ b/src/machine/board_circuitplay_express_baremetal.go
@@ -2,7 +2,10 @@
 
 package machine
 
-import "device/sam"
+import (
+	"device/sam"
+	"runtime/interrupt"
+)
 
 // UART1 on the Circuit Playground Express.
 var (
@@ -13,9 +16,8 @@ var (
 	}
 )
 
-//go:export SERCOM1_IRQHandler
-func handleUART1() {
-	defaultUART1Handler()
+func init() {
+	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM4, UART1.handleInterrupt)
 }
 
 // I2C on the Circuit Playground Express.
diff --git a/src/machine/board_feather-m0.go b/src/machine/board_feather-m0.go
index 97af7f901..f5fa76a18 100644
--- a/src/machine/board_feather-m0.go
+++ b/src/machine/board_feather-m0.go
@@ -2,7 +2,10 @@
 
 package machine
 
-import "device/sam"
+import (
+	"device/sam"
+	"runtime/interrupt"
+)
 
 // used to reset into bootloader
 const RESET_MAGIC_VALUE = 0xf01669ef
@@ -60,9 +63,8 @@ var (
 	}
 )
 
-//go:export SERCOM1_IRQHandler
-func handleUART1() {
-	defaultUART1Handler()
+func init() {
+	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM1, UART1.handleInterrupt)
 }
 
 // I2C pins
diff --git a/src/machine/board_itsybitsy-m0.go b/src/machine/board_itsybitsy-m0.go
index 3238d2037..ed4f9fa7b 100644
--- a/src/machine/board_itsybitsy-m0.go
+++ b/src/machine/board_itsybitsy-m0.go
@@ -4,6 +4,7 @@ package machine
 
 import (
 	"device/sam"
+	"runtime/interrupt"
 )
 
 // used to reset into bootloader
@@ -62,9 +63,8 @@ var (
 	}
 )
 
-//go:export SERCOM1_IRQHandler
-func handleUART1() {
-	defaultUART1Handler()
+func init() {
+	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM1, UART1.handleInterrupt)
 }
 
 // I2C pins
diff --git a/src/machine/board_nucleof103rb.go b/src/machine/board_nucleof103rb.go
index 1186ce2a6..5e2850f7b 100644
--- a/src/machine/board_nucleof103rb.go
+++ b/src/machine/board_nucleof103rb.go
@@ -2,7 +2,10 @@
 
 package machine
 
-import "device/stm32"
+import (
+	"device/stm32"
+	"runtime/interrupt"
+)
 
 const (
 	PA0  = portA + 0
@@ -100,14 +103,12 @@ var (
 	UART0 = UART{
 		Buffer: NewRingBuffer(),
 		Bus:    stm32.USART2,
-		IRQVal: stm32.IRQ_USART2,
 	}
 	UART2 = &UART0
 )
 
-//go:export USART2_IRQHandler
-func handleUART2() {
-	UART2.Receive(byte((UART2.Bus.DR.Get() & 0xFF)))
+func init() {
+	UART0.Interrupt = interrupt.New(stm32.IRQ_USART2, UART0.handleInterrupt)
 }
 
 // SPI pins
diff --git a/src/machine/board_trinket.go b/src/machine/board_trinket.go
index f2c62160e..b9f2d6864 100644
--- a/src/machine/board_trinket.go
+++ b/src/machine/board_trinket.go
@@ -2,7 +2,10 @@
 
 package machine
 
-import "device/sam"
+import (
+	"device/sam"
+	"runtime/interrupt"
+)
 
 // used to reset into bootloader
 const RESET_MAGIC_VALUE = 0xf01669ef
@@ -51,9 +54,8 @@ var (
 	}
 )
 
-//go:export SERCOM1_IRQHandler
-func handleUART1() {
-	defaultUART1Handler()
+func init() {
+	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM0, UART1.handleInterrupt)
 }
 
 // SPI pins
diff --git a/src/machine/machine_atmega.go b/src/machine/machine_atmega.go
index 83c501e52..16395fe42 100644
--- a/src/machine/machine_atmega.go
+++ b/src/machine/machine_atmega.go
@@ -4,6 +4,7 @@ package machine
 
 import (
 	"device/avr"
+	"runtime/interrupt"
 	"runtime/volatile"
 )
 
@@ -232,6 +233,18 @@ func (uart UART) Configure(config UARTConfig) {
 		config.BaudRate = 9600
 	}
 
+	// Register the UART interrupt.
+	interrupt.New(avr.IRQ_USART_RX, func(intr interrupt.Interrupt) {
+		// Read register to clear it.
+		data := avr.UDR0.Get()
+
+		// Ensure no error.
+		if !avr.UCSR0A.HasBits(avr.UCSR0A_FE0 | avr.UCSR0A_DOR0 | avr.UCSR0A_UPE0) {
+			// Put data from UDR register into buffer.
+			UART0.Receive(byte(data))
+		}
+	})
+
 	// Set baud rate based on prescale formula from
 	// https://www.microchip.com/webdoc/AVRLibcReferenceManual/FAQ_1faq_wrong_baud_rate.html
 	// ((F_CPU + UART_BAUD_RATE * 8L) / (UART_BAUD_RATE * 16L) - 1)
@@ -254,15 +267,3 @@ func (uart UART) WriteByte(c byte) error {
 	avr.UDR0.Set(c) // send char
 	return nil
 }
-
-//go:interrupt USART_RX_vect
-func handleUSART_RX() {
-	// Read register to clear it.
-	data := avr.UDR0.Get()
-
-	// Ensure no error.
-	if !avr.UCSR0A.HasBits(avr.UCSR0A_FE0 | avr.UCSR0A_DOR0 | avr.UCSR0A_UPE0) {
-		// Put data from UDR register into buffer.
-		UART0.Receive(byte(data))
-	}
-}
diff --git a/src/machine/machine_atsamd21.go b/src/machine/machine_atsamd21.go
index c1bb9e632..856ef136b 100644
--- a/src/machine/machine_atsamd21.go
+++ b/src/machine/machine_atsamd21.go
@@ -11,6 +11,7 @@ import (
 	"device/arm"
 	"device/sam"
 	"errors"
+	"runtime/interrupt"
 	"unsafe"
 )
 
@@ -292,9 +293,10 @@ func waitADCSync() {
 
 // UART on the SAMD21.
 type UART struct {
-	Buffer *RingBuffer
-	Bus    *sam.SERCOM_USART_Type
-	SERCOM uint8
+	Buffer    *RingBuffer
+	Bus       *sam.SERCOM_USART_Type
+	SERCOM    uint8
+	Interrupt interrupt.Interrupt
 }
 
 var (
@@ -401,10 +403,7 @@ func (uart UART) Configure(config UARTConfig) error {
 	uart.Bus.INTENSET.Set(sam.SERCOM_USART_INTENSET_RXC)
 
 	// Enable RX IRQ.
-	// IRQ lines are in the same order as SERCOM instance numbers on SAMD21
-	// chips, so the IRQ number can be trivially determined from the SERCOM
-	// number.
-	arm.EnableIRQ(sam.IRQ_SERCOM0 + uint32(uart.SERCOM))
+	uart.Interrupt.Enable()
 
 	return nil
 }
@@ -432,11 +431,12 @@ func (uart UART) WriteByte(c byte) error {
 	return nil
 }
 
-// defaultUART1Handler handles the UART1 IRQ.
-func defaultUART1Handler() {
+// handleInterrupt should be called from the appropriate interrupt handler for
+// this UART instance.
+func (uart *UART) handleInterrupt(interrupt.Interrupt) {
 	// should reset IRQ
-	UART1.Receive(byte((UART1.Bus.DATA.Get() & 0xFF)))
-	UART1.Bus.INTFLAG.SetBits(sam.SERCOM_USART_INTFLAG_RXC)
+	uart.Receive(byte((uart.Bus.DATA.Get() & 0xFF)))
+	uart.Bus.INTFLAG.SetBits(sam.SERCOM_USART_INTFLAG_RXC)
 }
 
 // I2C on the SAMD21.
@@ -1368,7 +1368,8 @@ func (usbcdc USBCDC) Configure(config UARTConfig) {
 	sam.USB_DEVICE.CTRLA.SetBits(sam.USB_DEVICE_CTRLA_ENABLE)
 
 	// enable IRQ
-	arm.EnableIRQ(sam.IRQ_USB)
+	intr := interrupt.New(sam.IRQ_USB, handleUSB)
+	intr.Enable()
 }
 
 func handlePadCalibration() {
@@ -1414,8 +1415,7 @@ func handlePadCalibration() {
 	sam.USB_DEVICE.PADCAL.SetBits(calibTrim << sam.USB_DEVICE_PADCAL_TRIM_Pos)
 }
 
-//go:export USB_IRQHandler
-func handleUSB() {
+func handleUSB(intr interrupt.Interrupt) {
 	// reset all interrupt flags
 	flags := sam.USB_DEVICE.INTFLAG.Get()
 	sam.USB_DEVICE.INTFLAG.Set(flags)
diff --git a/src/machine/machine_atsamd51.go b/src/machine/machine_atsamd51.go
index e23ebf170..e35cb41bc 100644
--- a/src/machine/machine_atsamd51.go
+++ b/src/machine/machine_atsamd51.go
@@ -11,6 +11,7 @@ import (
 	"device/arm"
 	"device/sam"
 	"errors"
+	"runtime/interrupt"
 	"unsafe"
 )
 
@@ -1547,11 +1548,11 @@ func (usbcdc USBCDC) Configure(config UARTConfig) {
 	// enable USB
 	sam.USB_DEVICE.CTRLA.SetBits(sam.USB_DEVICE_CTRLA_ENABLE)
 
-	// enable IRQ
-	arm.EnableIRQ(sam.IRQ_USB_OTHER)
-	arm.EnableIRQ(sam.IRQ_USB_SOF_HSOF)
-	arm.EnableIRQ(sam.IRQ_USB_TRCPT0)
-	arm.EnableIRQ(sam.IRQ_USB_TRCPT1)
+	// enable IRQ at highest priority
+	interrupt.New(sam.IRQ_USB_OTHER, handleUSBIRQ).Enable()
+	interrupt.New(sam.IRQ_USB_SOF_HSOF, handleUSBIRQ).Enable()
+	interrupt.New(sam.IRQ_USB_TRCPT0, handleUSBIRQ).Enable()
+	interrupt.New(sam.IRQ_USB_TRCPT1, handleUSBIRQ).Enable()
 }
 
 func handlePadCalibration() {
@@ -1597,27 +1598,7 @@ func handlePadCalibration() {
 	sam.USB_DEVICE.PADCAL.SetBits(calibTrim << sam.USB_DEVICE_PADCAL_TRIM_Pos)
 }
 
-//go:export USB_OTHER_IRQHandler
-func handleUSBOther() {
-	handleUSBIRQ()
-}
-
-//go:export USB_SOF_HSOF_IRQHandler
-func handleUSBSOFHSOF() {
-	handleUSBIRQ()
-}
-
-//go:export USB_TRCPT0_IRQHandler
-func handleUSBTRCPT0() {
-	handleUSBIRQ()
-}
-
-//go:export USB_TRCPT1_IRQHandler
-func handleUSBTRCPT1() {
-	handleUSBIRQ()
-}
-
-func handleUSBIRQ() {
+func handleUSBIRQ(interrupt.Interrupt) {
 	// reset all interrupt flags
 	flags := sam.USB_DEVICE.INTFLAG.Get()
 	sam.USB_DEVICE.INTFLAG.Set(flags)
diff --git a/src/machine/machine_nrf.go b/src/machine/machine_nrf.go
index 7e12c8a84..0946356b5 100644
--- a/src/machine/machine_nrf.go
+++ b/src/machine/machine_nrf.go
@@ -3,9 +3,9 @@
 package machine
 
 import (
-	"device/arm"
 	"device/nrf"
 	"errors"
+	"runtime/interrupt"
 )
 
 var (
@@ -88,8 +88,9 @@ func (uart UART) Configure(config UARTConfig) {
 	nrf.UART0.INTENSET.Set(nrf.UART_INTENSET_RXDRDY_Msk)
 
 	// Enable RX IRQ.
-	arm.SetPriority(nrf.IRQ_UART0, 0xc0) // low priority
-	arm.EnableIRQ(nrf.IRQ_UART0)
+	intr := interrupt.New(nrf.IRQ_UART0, UART0.handleInterrupt)
+	intr.SetPriority(0xc0) // low priority
+	intr.Enable()
 }
 
 // SetBaudRate sets the communication speed for the UART.
@@ -116,7 +117,7 @@ func (uart UART) WriteByte(c byte) error {
 	return nil
 }
 
-func (uart UART) handleInterrupt() {
+func (uart *UART) handleInterrupt(interrupt.Interrupt) {
 	if nrf.UART0.EVENTS_RXDRDY.Get() != 0 {
 		uart.Receive(byte(nrf.UART0.RXD.Get()))
 		nrf.UART0.EVENTS_RXDRDY.Set(0x0)
diff --git a/src/machine/machine_nrf51.go b/src/machine/machine_nrf51.go
index 6425b2ae2..2c9af2405 100644
--- a/src/machine/machine_nrf51.go
+++ b/src/machine/machine_nrf51.go
@@ -20,11 +20,6 @@ func (uart UART) setPins(tx, rx Pin) {
 	nrf.UART0.PSELRXD.Set(uint32(rx))
 }
 
-//go:export UART0_IRQHandler
-func handleUART0() {
-	UART0.handleInterrupt()
-}
-
 func (i2c I2C) setPins(scl, sda Pin) {
 	i2c.Bus.PSELSCL.Set(uint32(scl))
 	i2c.Bus.PSELSDA.Set(uint32(sda))
diff --git a/src/machine/machine_nrf52.go b/src/machine/machine_nrf52.go
index 392e237c3..b2181770a 100644
--- a/src/machine/machine_nrf52.go
+++ b/src/machine/machine_nrf52.go
@@ -21,11 +21,6 @@ func (uart UART) setPins(tx, rx Pin) {
 	nrf.UART0.PSELRXD.Set(uint32(rx))
 }
 
-//go:export UARTE0_UART0_IRQHandler
-func handleUART0() {
-	UART0.handleInterrupt()
-}
-
 func (i2c I2C) setPins(scl, sda Pin) {
 	i2c.Bus.PSELSCL.Set(uint32(scl))
 	i2c.Bus.PSELSDA.Set(uint32(sda))
diff --git a/src/machine/machine_nrf52840.go b/src/machine/machine_nrf52840.go
index a9dc60cc3..2a76ac27b 100644
--- a/src/machine/machine_nrf52840.go
+++ b/src/machine/machine_nrf52840.go
@@ -77,11 +77,6 @@ func (uart UART) setPins(tx, rx Pin) {
 	nrf.UART0.PSEL.RXD.Set(uint32(rx))
 }
 
-//go:export UARTE0_UART0_IRQHandler
-func handleUART0() {
-	UART0.handleInterrupt()
-}
-
 func (i2c I2C) setPins(scl, sda Pin) {
 	i2c.Bus.PSEL.SCL.Set(uint32(scl))
 	i2c.Bus.PSEL.SDA.Set(uint32(sda))
diff --git a/src/machine/machine_stm32f103xx.go b/src/machine/machine_stm32f103xx.go
index 5e77712f0..6aafb264f 100644
--- a/src/machine/machine_stm32f103xx.go
+++ b/src/machine/machine_stm32f103xx.go
@@ -5,9 +5,9 @@ package machine
 // Peripheral abstraction layer for the stm32.
 
 import (
-	"device/arm"
 	"device/stm32"
 	"errors"
+	"runtime/interrupt"
 )
 
 func CPUFrequency() uint32 {
@@ -111,9 +111,9 @@ func (p Pin) Get() bool {
 
 // UART
 type UART struct {
-	Buffer *RingBuffer
-	Bus    *stm32.USART_Type
-	IRQVal uint32
+	Buffer    *RingBuffer
+	Bus       *stm32.USART_Type
+	Interrupt interrupt.Interrupt
 }
 
 // Configure the UART.
@@ -155,8 +155,8 @@ func (uart UART) Configure(config UARTConfig) {
 	uart.Bus.CR1.Set(stm32.USART_CR1_TE | stm32.USART_CR1_RE | stm32.USART_CR1_RXNEIE | stm32.USART_CR1_UE)
 
 	// Enable RX IRQ
-	arm.SetPriority(uart.IRQVal, 0xc0)
-	arm.EnableIRQ(uart.IRQVal)
+	uart.Interrupt.SetPriority(0xc0)
+	uart.Interrupt.Enable()
 }
 
 // SetBaudRate sets the communication speed for the UART.
@@ -182,6 +182,12 @@ func (uart UART) WriteByte(c byte) error {
 	return nil
 }
 
+// handleInterrupt should be called from the appropriate interrupt handler for
+// this UART instance.
+func (uart *UART) handleInterrupt(interrupt.Interrupt) {
+	uart.Receive(byte((uart.Bus.DR.Get() & 0xFF)))
+}
+
 // SPI on the STM32.
 type SPI struct {
 	Bus *stm32.SPI_Type
diff --git a/src/machine/machine_stm32f407.go b/src/machine/machine_stm32f407.go
index 54c0190d8..c75e38771 100644
--- a/src/machine/machine_stm32f407.go
+++ b/src/machine/machine_stm32f407.go
@@ -5,8 +5,8 @@ package machine
 // Peripheral abstraction layer for the stm32.
 
 import (
-	"device/arm"
 	"device/stm32"
+	"runtime/interrupt"
 )
 
 func CPUFrequency() uint32 {
@@ -203,8 +203,11 @@ func (uart UART) Configure(config UARTConfig) {
 	stm32.USART2.CR1.Set(stm32.USART_CR1_TE | stm32.USART_CR1_RE | stm32.USART_CR1_RXNEIE | stm32.USART_CR1_UE)
 
 	// Enable RX IRQ.
-	arm.SetPriority(stm32.IRQ_USART2, 0xc0)
-	arm.EnableIRQ(stm32.IRQ_USART2)
+	intr := interrupt.New(stm32.IRQ_USART2, func(interrupt.Interrupt) {
+		UART1.Receive(byte((stm32.USART2.DR.Get() & 0xFF)))
+	})
+	intr.SetPriority(0xc0)
+	intr.Enable()
 }
 
 // WriteByte writes a byte of data to the UART.
@@ -215,8 +218,3 @@ func (uart UART) WriteByte(c byte) error {
 	}
 	return nil
 }
-
-//go:export USART2_IRQHandler
-func handleUSART2() {
-	UART1.Receive(byte((stm32.USART2.DR.Get() & 0xFF)))
-}
diff --git a/src/runtime/interrupt/interrupt.go b/src/runtime/interrupt/interrupt.go
new file mode 100644
index 000000000..c37b2c11e
--- /dev/null
+++ b/src/runtime/interrupt/interrupt.go
@@ -0,0 +1,38 @@
+// Package interrupt provides access to hardware interrupts. It provides a way
+// to define interrupts and to enable/disable them.
+package interrupt
+
+// Interrupt provides direct access to hardware interrupts. You can configure
+// this interrupt through this interface.
+//
+// Do not use the zero value of an Interrupt object. Instead, call New to obtain
+// an interrupt handle.
+type Interrupt struct {
+	// Make this number unexported so it cannot be set directly. This provides
+	// some encapsulation.
+	num int
+}
+
+// New is a compiler intrinsic that creates a new Interrupt object. You may call
+// it only once, and must pass constant parameters to it. That means that the
+// interrupt ID must be a Go constant and that the handler must be a simple
+// function: closures are not supported.
+func New(id int, handler func(Interrupt)) Interrupt
+
+// Register is used to declare an interrupt. You should not normally call this
+// function: it is only for telling the compiler about the mapping between an
+// interrupt number and the interrupt handler name.
+func Register(id int, handlerName string) int
+
+// handle is used internally, between IR generation and interrupt lowering. The
+// frontend will create runtime/interrupt.handle objects, cast them to an int,
+// and use that in an Interrupt object. That way the compiler will be able to
+// optimize away all interrupt handles that are never used in a program.
+// This system only works when interrupts need to be enabled before use and this
+// is done only through calling Enable() on this object. If interrups cannot
+// individually be enabled/disabled, the compiler should create a pseudo-call
+// (like runtime/interrupt.use()) that keeps the interrupt alive.
+type handle struct {
+	handler func(Interrupt)
+	Interrupt
+}
diff --git a/src/runtime/interrupt/interrupt_cortexm.go b/src/runtime/interrupt/interrupt_cortexm.go
new file mode 100644
index 000000000..5354be9e0
--- /dev/null
+++ b/src/runtime/interrupt/interrupt_cortexm.go
@@ -0,0 +1,23 @@
+// +build cortexm
+
+package interrupt
+
+import (
+	"device/arm"
+)
+
+// Enable enables this interrupt. Right after calling this function, the
+// interrupt may be invoked if it was already pending.
+func (irq Interrupt) Enable() {
+	arm.EnableIRQ(uint32(irq.num))
+}
+
+// SetPriority sets the interrupt priority for this interrupt. A lower number
+// means a higher priority. Additionally, most hardware doesn't implement all
+// priority bits (only the uppoer bits).
+//
+// Examples: 0xff (lowest priority), 0xc0 (low priority), 0x00 (highest possible
+// priority).
+func (irq Interrupt) SetPriority(priority uint8) {
+	arm.SetPriority(uint32(irq.num), uint32(priority))
+}
diff --git a/src/runtime/runtime_atsamd21.go b/src/runtime/runtime_atsamd21.go
index dbbf8f142..440cd148e 100644
--- a/src/runtime/runtime_atsamd21.go
+++ b/src/runtime/runtime_atsamd21.go
@@ -6,6 +6,7 @@ import (
 	"device/arm"
 	"device/sam"
 	"machine"
+	"runtime/interrupt"
 	"runtime/volatile"
 	"unsafe"
 )
@@ -214,8 +215,14 @@ func initRTC() {
 	sam.RTC_MODE0.CTRL.SetBits(sam.RTC_MODE0_CTRL_ENABLE)
 	waitForSync()
 
-	arm.SetPriority(sam.IRQ_RTC, 0xc0)
-	arm.EnableIRQ(sam.IRQ_RTC)
+	intr := interrupt.New(sam.IRQ_RTC, func(intr interrupt.Interrupt) {
+		// disable IRQ for CMP0 compare
+		sam.RTC_MODE0.INTFLAG.Set(sam.RTC_MODE0_INTENSET_CMP0)
+
+		timerWakeup.Set(1)
+	})
+	intr.SetPriority(0xc0)
+	intr.Enable()
 }
 
 func waitForSync() {
@@ -286,14 +293,6 @@ func timerSleep(ticks uint32) {
 	}
 }
 
-//go:export RTC_IRQHandler
-func handleRTC() {
-	// disable IRQ for CMP0 compare
-	sam.RTC_MODE0.INTFLAG.Set(sam.RTC_MODE0_INTENSET_CMP0)
-
-	timerWakeup.Set(1)
-}
-
 func initUSBClock() {
 	// Turn on clock for USB
 	sam.PM.APBBMASK.SetBits(sam.PM_APBBMASK_USB_)
diff --git a/src/runtime/runtime_atsamd51.go b/src/runtime/runtime_atsamd51.go
index 0b97b2783..7cbcad044 100644
--- a/src/runtime/runtime_atsamd51.go
+++ b/src/runtime/runtime_atsamd51.go
@@ -6,6 +6,7 @@ import (
 	"device/arm"
 	"device/sam"
 	"machine"
+	"runtime/interrupt"
 	"runtime/volatile"
 )
 
@@ -202,8 +203,14 @@ func initRTC() {
 	for sam.RTC_MODE0.SYNCBUSY.HasBits(sam.RTC_MODE0_SYNCBUSY_ENABLE) {
 	}
 
-	arm.SetPriority(sam.IRQ_RTC, 0xc0)
-	arm.EnableIRQ(sam.IRQ_RTC)
+	irq := interrupt.New(sam.IRQ_RTC, func(interrupt.Interrupt) {
+		// disable IRQ for CMP0 compare
+		sam.RTC_MODE0.INTFLAG.SetBits(sam.RTC_MODE0_INTENSET_CMP0)
+
+		timerWakeup.Set(1)
+	})
+	irq.SetPriority(0xc0)
+	irq.Enable()
 }
 
 func waitForSync() {
@@ -271,14 +278,6 @@ func timerSleep(ticks uint32) {
 	}
 }
 
-//go:export RTC_IRQHandler
-func handleRTC() {
-	// disable IRQ for CMP0 compare
-	sam.RTC_MODE0.INTFLAG.SetBits(sam.RTC_MODE0_INTENSET_CMP0)
-
-	timerWakeup.Set(1)
-}
-
 func initUSBClock() {
 	// Turn on clock(s) for USB
 	//MCLK->APBBMASK.reg |= MCLK_APBBMASK_USB;
diff --git a/src/runtime/runtime_nrf.go b/src/runtime/runtime_nrf.go
index c289437d2..50d3e5f2b 100644
--- a/src/runtime/runtime_nrf.go
+++ b/src/runtime/runtime_nrf.go
@@ -6,6 +6,7 @@ import (
 	"device/arm"
 	"device/nrf"
 	"machine"
+	"runtime/interrupt"
 	"runtime/volatile"
 )
 
@@ -43,8 +44,13 @@ func initLFCLK() {
 
 func initRTC() {
 	nrf.RTC1.TASKS_START.Set(1)
-	arm.SetPriority(nrf.IRQ_RTC1, 0xc0) // low priority
-	arm.EnableIRQ(nrf.IRQ_RTC1)
+	intr := interrupt.New(nrf.IRQ_RTC1, func(intr interrupt.Interrupt) {
+		nrf.RTC1.INTENCLR.Set(nrf.RTC_INTENSET_COMPARE0)
+		nrf.RTC1.EVENTS_COMPARE[0].Set(0)
+		rtc_wakeup.Set(1)
+	})
+	intr.SetPriority(0xc0) // low priority
+	intr.Enable()
 }
 
 func putchar(c byte) {
@@ -96,10 +102,3 @@ func rtc_sleep(ticks uint32) {
 		arm.Asm("wfi")
 	}
 }
-
-//go:export RTC1_IRQHandler
-func handleRTC1() {
-	nrf.RTC1.INTENCLR.Set(nrf.RTC_INTENSET_COMPARE0)
-	nrf.RTC1.EVENTS_COMPARE[0].Set(0)
-	rtc_wakeup.Set(1)
-}
diff --git a/src/runtime/runtime_stm32f103xx.go b/src/runtime/runtime_stm32f103xx.go
index 397e3c92f..8c29c264b 100644
--- a/src/runtime/runtime_stm32f103xx.go
+++ b/src/runtime/runtime_stm32f103xx.go
@@ -6,6 +6,7 @@ import (
 	"device/arm"
 	"device/stm32"
 	"machine"
+	"runtime/interrupt"
 	"runtime/volatile"
 )
 
@@ -101,8 +102,9 @@ func initRTC() {
 func initTIM() {
 	stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_TIM3EN)
 
-	arm.SetPriority(stm32.IRQ_TIM3, 0xc3)
-	arm.EnableIRQ(stm32.IRQ_TIM3)
+	intr := interrupt.New(stm32.IRQ_TIM3, handleTIM3)
+	intr.SetPriority(0xc3)
+	intr.Enable()
 }
 
 const asyncScheduler = false
@@ -186,8 +188,7 @@ func timerSleep(ticks uint32) {
 	}
 }
 
-//go:export TIM3_IRQHandler
-func handleTIM3() {
+func handleTIM3(interrupt.Interrupt) {
 	if stm32.TIM3.SR.HasBits(stm32.TIM_SR_UIF) {
 		// Disable the timer.
 		stm32.TIM3.CR1.ClearBits(stm32.TIM_CR1_CEN)
diff --git a/src/runtime/runtime_stm32f407.go b/src/runtime/runtime_stm32f407.go
index 270e1b8a8..fd1be5b43 100644
--- a/src/runtime/runtime_stm32f407.go
+++ b/src/runtime/runtime_stm32f407.go
@@ -6,6 +6,7 @@ import (
 	"device/arm"
 	"device/stm32"
 	"machine"
+	"runtime/interrupt"
 	"runtime/volatile"
 )
 
@@ -121,8 +122,9 @@ var timerWakeup volatile.Register8
 func initTIM3() {
 	stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_TIM3EN)
 
-	arm.SetPriority(stm32.IRQ_TIM3, 0xc3)
-	arm.EnableIRQ(stm32.IRQ_TIM3)
+	intr := interrupt.New(stm32.IRQ_TIM3, handleTIM3)
+	intr.SetPriority(0xc3)
+	intr.Enable()
 }
 
 // Enable the TIM7 clock.(tick count)
@@ -139,8 +141,9 @@ func initTIM7() {
 	// Enable the timer.
 	stm32.TIM7.CR1.SetBits(stm32.TIM_CR1_CEN)
 
-	arm.SetPriority(stm32.IRQ_TIM7, 0xc1)
-	arm.EnableIRQ(stm32.IRQ_TIM7)
+	intr := interrupt.New(stm32.IRQ_TIM7, handleTIM7)
+	intr.SetPriority(0xc1)
+	intr.Enable()
 }
 
 const asyncScheduler = false
@@ -183,8 +186,7 @@ func timerSleep(ticks uint32) {
 	}
 }
 
-//go:export TIM3_IRQHandler
-func handleTIM3() {
+func handleTIM3(interrupt.Interrupt) {
 	if stm32.TIM3.SR.HasBits(stm32.TIM_SR_UIF) {
 		// Disable the timer.
 		stm32.TIM3.CR1.ClearBits(stm32.TIM_CR1_CEN)
@@ -197,8 +199,7 @@ func handleTIM3() {
 	}
 }
 
-//go:export TIM7_IRQHandler
-func handleTIM7() {
+func handleTIM7(interrupt.Interrupt) {
 	if stm32.TIM7.SR.HasBits(stm32.TIM_SR_UIF) {
 		// clear the update flag
 		stm32.TIM7.SR.ClearBits(stm32.TIM_SR_UIF)
diff --git a/tools/gen-device-avr/gen-device-avr.go b/tools/gen-device-avr/gen-device-avr.go
index ac4c8b996..8f9298a21 100755
--- a/tools/gen-device-avr/gen-device-avr.go
+++ b/tools/gen-device-avr/gen-device-avr.go
@@ -260,6 +260,7 @@ func writeGo(outdir string, device *Device) error {
 package {{.pkgName}}
 
 import (
+	"runtime/interrupt"
 	"runtime/volatile"
 	"unsafe"
 )
@@ -277,6 +278,12 @@ const ({{range .interrupts}}
 	IRQ_max = {{.interruptMax}} // Highest interrupt number on this device.
 )
 
+// Map interrupt numbers to function names.
+// These aren't real calls, they're removed by the compiler.
+var ({{range .interrupts}}
+	_ = interrupt.Register(IRQ_{{.Name}}, "__vector_{{.Name}}"){{end}}
+)
+
 // Peripherals.
 var ({{range .peripherals}}
 	// {{.Caption}}
diff --git a/tools/gen-device-svd/gen-device-svd.go b/tools/gen-device-svd/gen-device-svd.go
index cef0365d5..f5aebcfe8 100755
--- a/tools/gen-device-svd/gen-device-svd.go
+++ b/tools/gen-device-svd/gen-device-svd.go
@@ -82,6 +82,7 @@ type Device struct {
 
 type interrupt struct {
 	Name            string
+	HandlerName     string
 	peripheralIndex int
 	Value           int // interrupt number
 	Description     string
@@ -171,12 +172,12 @@ func readSVD(path, sourceURL string) (*Device, error) {
 		groupName := cleanName(periphEl.GroupName)
 
 		for _, interrupt := range periphEl.Interrupts {
-			addInterrupt(interrupts, interrupt.Name, interrupt.Index, description)
+			addInterrupt(interrupts, interrupt.Name, interrupt.Name, interrupt.Index, description)
 			// As a convenience, also use the peripheral name as the interrupt
 			// name. Only do that for the nrf for now, as the stm32 .svd files
 			// don't always put interrupts in the correct peripheral...
 			if len(periphEl.Interrupts) == 1 && strings.HasPrefix(device.Name, "nrf") {
-				addInterrupt(interrupts, periphEl.Name, interrupt.Index, description)
+				addInterrupt(interrupts, periphEl.Name, interrupt.Name, interrupt.Index, description)
 			}
 		}
 
@@ -388,7 +389,7 @@ func readSVD(path, sourceURL string) (*Device, error) {
 	}, nil
 }
 
-func addInterrupt(interrupts map[string]*interrupt, name string, index int, description string) {
+func addInterrupt(interrupts map[string]*interrupt, name, interruptName string, index int, description string) {
 	if _, ok := interrupts[name]; ok {
 		if interrupts[name].Value != index {
 			// Note: some SVD files like the one for STM32H7x7 contain mistakes.
@@ -409,6 +410,7 @@ func addInterrupt(interrupts map[string]*interrupt, name string, index int, desc
 	} else {
 		interrupts[name] = &interrupt{
 			Name:            name,
+			HandlerName:     interruptName + "_IRQHandler",
 			peripheralIndex: len(interrupts),
 			Value:           index,
 			Description:     description,
@@ -619,6 +621,7 @@ func writeGo(outdir string, device *Device) error {
 package {{.pkgName}}
 
 import (
+	"runtime/interrupt"
 	"runtime/volatile"
 	"unsafe"
 )
@@ -628,12 +631,18 @@ const (
 	DEVICE	 = "{{.metadata.name}}"
 )
 
-// Interrupt numbers
+// Interrupt numbers.
 const ({{range .interrupts}}
 	IRQ_{{.Name}} = {{.Value}} // {{.Description}}{{end}}
 	IRQ_max = {{.interruptMax}} // Highest interrupt number on this device.
 )
 
+// Map interrupt numbers to function names.
+// These aren't real calls, they're removed by the compiler.
+var ({{range .interrupts}}
+	_ = interrupt.Register(IRQ_{{.Name}}, "{{.HandlerName}}"){{end}}
+)
+
 // Peripherals.
 var (
 {{range .peripherals}}	{{.Name}} = (*{{.GroupName}}_Type)(unsafe.Pointer(uintptr(0x{{printf "%x" .BaseAddress}}))) // {{.Description}}
@@ -879,7 +888,7 @@ Default_Handler:
 			num++
 		}
 		num++
-		fmt.Fprintf(w, "    .long %s_IRQHandler\n", intr.Name)
+		fmt.Fprintf(w, "    .long %s\n", intr.HandlerName)
 	}
 
 	w.WriteString(`
diff --git a/transform/errors.go b/transform/errors.go
new file mode 100644
index 000000000..226ead28c
--- /dev/null
+++ b/transform/errors.go
@@ -0,0 +1,48 @@
+package transform
+
+import (
+	"go/scanner"
+	"go/token"
+	"path/filepath"
+
+	"tinygo.org/x/go-llvm"
+)
+
+// errorAt returns an error value at the location of the value.
+// The location information may not be complete as it depends on debug
+// information in the IR.
+func errorAt(val llvm.Value, msg string) scanner.Error {
+	return scanner.Error{
+		Pos: getPosition(val),
+		Msg: msg,
+	}
+}
+
+// getPosition returns the position information for the given value, as far as
+// it is available.
+func getPosition(val llvm.Value) token.Position {
+	if !val.IsAInstruction().IsNil() {
+		loc := val.InstructionDebugLoc()
+		if loc.IsNil() {
+			return token.Position{}
+		}
+		file := loc.LocationScope().ScopeFile()
+		return token.Position{
+			Filename: filepath.Join(file.FileDirectory(), file.FileFilename()),
+			Line:     int(loc.LocationLine()),
+			Column:   int(loc.LocationColumn()),
+		}
+	} else if !val.IsAFunction().IsNil() {
+		loc := val.Subprogram()
+		if loc.IsNil() {
+			return token.Position{}
+		}
+		file := loc.ScopeFile()
+		return token.Position{
+			Filename: filepath.Join(file.FileDirectory(), file.FileFilename()),
+			Line:     int(loc.SubprogramLine()),
+		}
+	} else {
+		return token.Position{}
+	}
+}
diff --git a/transform/interrupt.go b/transform/interrupt.go
new file mode 100644
index 000000000..2a0dbe02e
--- /dev/null
+++ b/transform/interrupt.go
@@ -0,0 +1,218 @@
+package transform
+
+import (
+	"fmt"
+	"strings"
+
+	"tinygo.org/x/go-llvm"
+)
+
+// LowerInterrupts creates interrupt handlers for the interrupts created by
+// runtime/interrupt.New.
+//
+// The operation is as follows. The compiler creates the following during IR
+// generation:
+//     * calls to runtime/interrupt.Register that map interrupt IDs to ISR names.
+//     * runtime/interrupt.handle objects that store the (constant) interrupt ID and
+//       interrupt handler func value.
+//
+// This pass then creates the specially named interrupt handler names that
+// simply call the registered handlers. This might seem like it causes extra
+// overhead, but in fact inlining and const propagation will eliminate most if
+// not all of that.
+func LowerInterrupts(mod llvm.Module) []error {
+	var errs []error
+
+	// Discover interrupts. The runtime/interrupt.Register call is a compiler
+	// intrinsic that maps interrupt numbers to handler names.
+	handlerNames := map[int64]string{}
+	for _, call := range getUses(mod.NamedFunction("runtime/interrupt.Register")) {
+		if call.IsACallInst().IsNil() {
+			errs = append(errs, errorAt(call, "expected a call to runtime/interrupt.Register?"))
+			continue
+		}
+
+		num := call.Operand(0)
+		if num.IsAConstant().IsNil() {
+			errs = append(errs, errorAt(call, "non-constant interrupt number?"))
+			continue
+		}
+
+		// extract the interrupt name
+		nameStrGEP := call.Operand(1)
+		if nameStrGEP.IsAConstantExpr().IsNil() || nameStrGEP.Opcode() != llvm.GetElementPtr {
+			errs = append(errs, errorAt(call, "expected a string operand?"))
+			continue
+		}
+		nameStrPtr := nameStrGEP.Operand(0) // note: assuming it's a GEP to the first byte
+		nameStrLen := call.Operand(2)
+		if nameStrPtr.IsAGlobalValue().IsNil() || !nameStrPtr.IsGlobalConstant() || nameStrLen.IsAConstant().IsNil() {
+			errs = append(errs, errorAt(call, "non-constant interrupt name?"))
+			continue
+		}
+
+		// keep track of this name
+		name := string(getGlobalBytes(nameStrPtr)[:nameStrLen.SExtValue()])
+		handlerNames[num.SExtValue()] = name
+
+		// remove this pseudo-call
+		call.ReplaceAllUsesWith(llvm.ConstNull(call.Type()))
+		call.EraseFromParentAsInstruction()
+	}
+
+	ctx := mod.Context()
+	nullptr := llvm.ConstNull(llvm.PointerType(ctx.Int8Type(), 0))
+	builder := ctx.NewBuilder()
+	defer builder.Dispose()
+
+	// Create a function type with the signature of an interrupt handler.
+	fnType := llvm.FunctionType(ctx.VoidType(), nil, false)
+
+	// Collect a slice of interrupt handle objects. The fact that they still
+	// exist in the IR indicates that they could not be optimized away,
+	// therefore we need to make real interrupt handlers for them.
+	var handlers []llvm.Value
+	handleType := mod.GetTypeByName("runtime/interrupt.handle")
+	if !handleType.IsNil() {
+		handlePtrType := llvm.PointerType(handleType, 0)
+		for global := mod.FirstGlobal(); !global.IsNil(); global = llvm.NextGlobal(global) {
+			if global.Type() != handlePtrType {
+				continue
+			}
+			handlers = append(handlers, global)
+		}
+	}
+
+	// Iterate over all handler objects, replacing their ptrtoint uses with a
+	// real interrupt ID and creating an interrupt handler for them.
+	for _, global := range handlers {
+		initializer := global.Initializer()
+		num := llvm.ConstExtractValue(initializer, []uint32{1, 0})
+		name := handlerNames[num.SExtValue()]
+
+		if name == "" {
+			errs = append(errs, errorAt(global, fmt.Sprintf("cannot find interrupt name for number %d", num.SExtValue())))
+			continue
+		}
+
+		// Extract the func value.
+		handlerContext := llvm.ConstExtractValue(initializer, []uint32{0, 0})
+		handlerFuncPtr := llvm.ConstExtractValue(initializer, []uint32{0, 1})
+		if !handlerContext.IsConstant() || !handlerFuncPtr.IsConstant() {
+			// This should have been checked already in the compiler.
+			errs = append(errs, errorAt(global, "func value must be constant"))
+			continue
+		}
+		if !handlerFuncPtr.IsAConstantExpr().IsNil() && handlerFuncPtr.Opcode() == llvm.PtrToInt {
+			// This is a ptrtoint: the IR was created for func lowering using a
+			// switch statement.
+			global := handlerFuncPtr.Operand(0)
+			if global.IsAGlobalValue().IsNil() {
+				errs = append(errs, errorAt(global, "internal error: expected a global for func lowering"))
+				continue
+			}
+			initializer := global.Initializer()
+			if initializer.Type() != mod.GetTypeByName("runtime.funcValueWithSignature") {
+				errs = append(errs, errorAt(global, "internal error: func lowering global has unexpected type"))
+				continue
+			}
+			ptrtoint := llvm.ConstExtractValue(initializer, []uint32{0})
+			if ptrtoint.IsAConstantExpr().IsNil() || ptrtoint.Opcode() != llvm.PtrToInt {
+				errs = append(errs, errorAt(global, "internal error: func lowering global has unexpected func ptr type"))
+				continue
+			}
+			handlerFuncPtr = ptrtoint.Operand(0)
+		}
+		if handlerFuncPtr.Type().TypeKind() != llvm.PointerTypeKind || handlerFuncPtr.Type().ElementType().TypeKind() != llvm.FunctionTypeKind {
+			errs = append(errs, errorAt(global, "internal error: unexpected LLVM types in func value"))
+			continue
+		}
+
+		// Check for an existing interrupt handler, and report it as an error if
+		// there is one.
+		fn := mod.NamedFunction(name)
+		if fn.IsNil() {
+			fn = llvm.AddFunction(mod, name, fnType)
+		} else if fn.Type().ElementType() != fnType {
+			// Don't bother with a precise error message (listing the previsous
+			// location) because this should not normally happen anyway.
+			errs = append(errs, errorAt(global, name+" redeclared with a different signature"))
+			continue
+		} else if !fn.IsDeclaration() {
+			// Interrupt handler was already defined. Check the first
+			// instruction (which should be a call) whether this handler would
+			// be identical anyway.
+			firstInst := fn.FirstBasicBlock().FirstInstruction()
+			if !firstInst.IsACallInst().IsNil() && firstInst.OperandsCount() == 4 && firstInst.CalledValue() == handlerFuncPtr && firstInst.Operand(0) == num && firstInst.Operand(1) == handlerContext {
+				// Already defined and apparently identical, so assume this is
+				// fine.
+				continue
+			}
+
+			errValue := name + " redeclared in this program"
+			fnPos := getPosition(fn)
+			if fnPos.IsValid() {
+				errValue += "\n\tprevious declaration at " + fnPos.String()
+			}
+			errs = append(errs, errorAt(global, errValue))
+			continue
+		}
+
+		// Create the wrapper function which is the actual interrupt handler
+		// that is inserted in the interrupt vector.
+		fn.SetUnnamedAddr(true)
+		fn.SetSection(".text." + name)
+		entryBlock := ctx.AddBasicBlock(fn, "entry")
+		builder.SetInsertPointAtEnd(entryBlock)
+
+		// Set the 'interrupt' flag if needed on this platform.
+		if strings.HasPrefix(mod.Target(), "avr") {
+			// This special calling convention is needed on AVR to save and
+			// restore all clobbered registers, instead of just the ones that
+			// would need to be saved/restored in a normal function call.
+			// Note that the AVR_INTERRUPT calling convention would enable
+			// interrupts right at the beginning of the handler, potentially
+			// leading to lots of nested interrupts and a stack overflow.
+			fn.SetFunctionCallConv(85) // CallingConv::AVR_SIGNAL
+		}
+
+		// Fill the function declaration with the forwarding call.
+		// In practice, the called function will often be inlined which avoids
+		// the extra indirection.
+		builder.CreateCall(handlerFuncPtr, []llvm.Value{num, handlerContext, nullptr}, "")
+		builder.CreateRetVoid()
+
+		// Replace all ptrtoint uses of the global with the interrupt constant.
+		// That can only now be safely done after the interrupt handler has been
+		// created, doing it before the interrupt handler is created might
+		// result in this interrupt handler being optimized away entirely.
+		for _, user := range getUses(global) {
+			if user.IsAConstantExpr().IsNil() || user.Opcode() != llvm.PtrToInt {
+				errs = append(errs, errorAt(global, "internal error: expected a ptrtoint"))
+				continue
+			}
+			user.ReplaceAllUsesWith(num)
+		}
+
+		// The runtime/interrput.handle struct can finally be removed.
+		// It would probably be eliminated anyway by a globaldce pass but it's
+		// better to do it now to be sure.
+		global.EraseFromParentAsGlobal()
+	}
+
+	// Remove now-useless runtime/interrupt.use calls. These are used for some
+	// platforms like AVR that do not need to enable interrupts to use them, so
+	// need another way to keep them alive.
+	// After interrupts have been lowered, this call is useless and would cause
+	// a linker error so must be removed.
+	for _, call := range getUses(mod.NamedFunction("runtime/interrupt.use")) {
+		if call.IsACallInst().IsNil() {
+			errs = append(errs, errorAt(call, "internal error: expected call to runtime/interrupt.use"))
+			continue
+		}
+
+		call.EraseFromParentAsInstruction()
+	}
+
+	return errs
+}
diff --git a/transform/interrupt_test.go b/transform/interrupt_test.go
new file mode 100644
index 000000000..00a199063
--- /dev/null
+++ b/transform/interrupt_test.go
@@ -0,0 +1,24 @@
+package transform
+
+import (
+	"testing"
+
+	"tinygo.org/x/go-llvm"
+)
+
+func TestInterruptLowering(t *testing.T) {
+	t.Parallel()
+	for _, subtest := range []string{"avr", "cortexm"} {
+		t.Run(subtest, func(t *testing.T) {
+			testTransform(t, "testdata/interrupt-"+subtest, func(mod llvm.Module) {
+				errs := LowerInterrupts(mod)
+				if len(errs) != 0 {
+					t.Fail()
+					for _, err := range errs {
+						t.Error(err)
+					}
+				}
+			})
+		})
+	}
+}
diff --git a/transform/testdata/interrupt-avr.ll b/transform/testdata/interrupt-avr.ll
new file mode 100644
index 000000000..1c195634b
--- /dev/null
+++ b/transform/testdata/interrupt-avr.ll
@@ -0,0 +1,33 @@
+target datalayout = "e-P1-p:16:8-i8:8-i16:8-i32:8-i64:8-f32:8-f64:8-n8-a:8"
+target triple = "avr-atmel-none"
+
+%"runtime/interrupt.handle" = type { %runtime.funcValue, %"runtime/interrupt.Interrupt" } %runtime.funcValue = type { i8*, i16 }
+%runtime.typecodeID = type { %runtime.typecodeID*, i16 }
+%runtime.funcValueWithSignature = type { i16, %runtime.typecodeID* }
+%machine.UART = type { %machine.RingBuffer* }
+%machine.RingBuffer = type { [128 x %"runtime/volatile.Register8"], %"runtime/volatile.Register8", %"runtime/volatile.Register8" }
+%"runtime/volatile.Register8" = type { i8 }
+%"runtime/interrupt.Interrupt" = type { i32 }
+
+@"reflect/types.type:func:{named:runtime/interrupt.Interrupt}{}" = external constant %runtime.typecodeID
+@"(machine.UART).Configure$1$withSignature" = internal constant %runtime.funcValueWithSignature { i16 ptrtoint (void (i32, i8*, i8*) addrspace(1)* @"(machine.UART).Configure$1" to i16), %runtime.typecodeID* @"reflect/types.type:func:{named:runtime/interrupt.Interrupt}{}" }
+@"runtime/interrupt.$interrupt18" = private unnamed_addr constant %"runtime/interrupt.handle" { %runtime.funcValue { i8* undef, i16 ptrtoint (%runtime.funcValueWithSignature* @"(machine.UART).Configure$1$withSignature" to i16) }, %"runtime/interrupt.Interrupt" { i32 18 } }
[email protected] = internal global %machine.UART zeroinitializer
+@"device/avr.init$string.18" = internal unnamed_addr constant [17 x i8] c"__vector_USART_RX"
+
+declare void @"(machine.UART).Configure$1"(i32, i8*, i8*) unnamed_addr addrspace(1)
+
+declare i32 @"runtime/interrupt.Register"(i32, i8*, i16, i8*, i8*) addrspace(1)
+
+declare void @"runtime/interrupt.use"(%"runtime/interrupt.Interrupt") addrspace(1)
+
+define void @"(machine.UART).Configure"(%machine.RingBuffer*, i32, i8, i8, i8* %context, i8* %parentHandle) unnamed_addr addrspace(1) {
+  call addrspace(1) void @"runtime/interrupt.use"(%"runtime/interrupt.Interrupt" { i32 ptrtoint (%"runtime/interrupt.handle"* @"runtime/interrupt.$interrupt18" to i32) })
+  ret void
+}
+
+define void @"device/avr.init"(i8* %context, i8* %parentHandle) unnamed_addr addrspace(1) {
+entry:
+  %0 = call addrspace(1) i32 @"runtime/interrupt.Register"(i32 18, i8* getelementptr inbounds ([17 x i8], [17 x i8]* @"device/avr.init$string.18", i32 0, i32 0), i16 17, i8* undef, i8* undef)
+  ret void
+}
diff --git a/transform/testdata/interrupt-avr.out.ll b/transform/testdata/interrupt-avr.out.ll
new file mode 100644
index 000000000..b71c43998
--- /dev/null
+++ b/transform/testdata/interrupt-avr.out.ll
@@ -0,0 +1,35 @@
+target datalayout = "e-P1-p:16:8-i8:8-i16:8-i32:8-i64:8-f32:8-f64:8-n8-a:8"
+target triple = "avr-atmel-none"
+
+%runtime.typecodeID = type { %runtime.typecodeID*, i16 }
+%runtime.funcValueWithSignature = type { i16, %runtime.typecodeID* }
+%machine.UART = type { %machine.RingBuffer* }
+%machine.RingBuffer = type { [128 x %"runtime/volatile.Register8"], %"runtime/volatile.Register8", %"runtime/volatile.Register8" }
+%"runtime/volatile.Register8" = type { i8 }
+%"runtime/interrupt.Interrupt" = type { i32 }
+
+@"reflect/types.type:func:{named:runtime/interrupt.Interrupt}{}" = external constant %runtime.typecodeID
+@"(machine.UART).Configure$1$withSignature" = internal constant %runtime.funcValueWithSignature { i16 ptrtoint (void (i32, i8*, i8*) addrspace(1)* @"(machine.UART).Configure$1" to i16), %runtime.typecodeID* @"reflect/types.type:func:{named:runtime/interrupt.Interrupt}{}" }
[email protected] = internal global %machine.UART zeroinitializer
+@"device/avr.init$string.18" = internal unnamed_addr constant [17 x i8] c"__vector_USART_RX"
+
+declare void @"(machine.UART).Configure$1"(i32, i8*, i8*) unnamed_addr addrspace(1)
+
+declare i32 @"runtime/interrupt.Register"(i32, i8*, i16, i8*, i8*) addrspace(1)
+
+declare void @"runtime/interrupt.use"(%"runtime/interrupt.Interrupt") addrspace(1)
+
+define void @"(machine.UART).Configure"(%machine.RingBuffer*, i32, i8, i8, i8* %context, i8* %parentHandle) unnamed_addr addrspace(1) {
+  ret void
+}
+
+define void @"device/avr.init"(i8* %context, i8* %parentHandle) unnamed_addr addrspace(1) {
+entry:
+  ret void
+}
+
+define avr_signalcc  void @__vector_USART_RX() unnamed_addr addrspace(1) section ".text.__vector_USART_RX" {
+entry:
+  call addrspace(1) void @"(machine.UART).Configure$1"(i32 18, i8* undef, i8* null)
+  ret void
+}
diff --git a/transform/testdata/interrupt-cortexm.ll b/transform/testdata/interrupt-cortexm.ll
new file mode 100644
index 000000000..2c156b5b6
--- /dev/null
+++ b/transform/testdata/interrupt-cortexm.ll
@@ -0,0 +1,38 @@
+target datalayout = "e-m:e-p:32:32-Fi8-i64:64-v128:64:128-a:0:32-n32-S64"
+target triple = "armv7em-none-eabi"
+
+%machine.UART = type { %machine.RingBuffer* }
+%machine.RingBuffer = type { [128 x %"runtime/volatile.Register8"], %"runtime/volatile.Register8", %"runtime/volatile.Register8" }
+%"runtime/volatile.Register8" = type { i8 }
+%"runtime/interrupt.handle" = type { { i8*, void (i32, i8*, i8*)* }, %"runtime/interrupt.Interrupt" }
+%"runtime/interrupt.Interrupt" = type { i32 }
+
+@"runtime/interrupt.$interrupt2" = private unnamed_addr constant %"runtime/interrupt.handle" { { i8*, void (i32, i8*, i8*)* } { i8* bitcast (%machine.UART* @machine.UART0 to i8*), void (i32, i8*, i8*)* @"(*machine.UART).handleInterrupt$bound" }, %"runtime/interrupt.Interrupt" { i32 2 } }
[email protected] = internal global %machine.UART { %machine.RingBuffer* @"machine$alloc.335" }
+@"machine$alloc.335" = internal global %machine.RingBuffer zeroinitializer
+@"device/nrf.init$string.2" = internal unnamed_addr constant [23 x i8] c"UARTE0_UART0_IRQHandler"
+@"device/nrf.init$string.3" = internal unnamed_addr constant [44 x i8] c"SPIM0_SPIS0_TWIM0_TWIS0_SPI0_TWI0_IRQHandler"
+
+declare i32 @"runtime/interrupt.Register"(i32, i8*, i32, i8*, i8*) local_unnamed_addr
+
+declare void @"device/arm.EnableIRQ"(i32, i8* nocapture readnone, i8* nocapture readnone)
+
+declare void @"device/arm.SetPriority"(i32, i32, i8* nocapture readnone, i8* nocapture readnone)
+
+define void @runtime.initAll(i8* nocapture readnone, i8* nocapture readnone) unnamed_addr {
+entry:
+  %2 = call i32 @"runtime/interrupt.Register"(i32 2, i8* getelementptr inbounds ([23 x i8], [23 x i8]* @"device/nrf.init$string.2", i32 0, i32 0), i32 23, i8* undef, i8* undef)
+  %3 = call i32 @"runtime/interrupt.Register"(i32 3, i8* getelementptr inbounds ([44 x i8], [44 x i8]* @"device/nrf.init$string.3", i32 0, i32 0), i32 44, i8* undef, i8* undef)
+  call void @"device/arm.SetPriority"(i32 ptrtoint (%"runtime/interrupt.handle"* @"runtime/interrupt.$interrupt2" to i32), i32 192, i8* undef, i8* undef)
+  call void @"device/arm.EnableIRQ"(i32 ptrtoint (%"runtime/interrupt.handle"* @"runtime/interrupt.$interrupt2" to i32), i8* undef, i8* undef)
+  ret void
+}
+
+define internal void @"(*machine.UART).handleInterrupt$bound"(i32, i8* nocapture %context, i8* nocapture readnone %parentHandle) {
+entry:
+  %unpack.ptr = bitcast i8* %context to %machine.UART*
+  call void @"(*machine.UART).handleInterrupt"(%machine.UART* %unpack.ptr, i32 %0, i8* undef, i8* undef)
+  ret void
+}
+
+declare void @"(*machine.UART).handleInterrupt"(%machine.UART* nocapture, i32, i8* nocapture readnone, i8* nocapture readnone)
diff --git a/transform/testdata/interrupt-cortexm.out.ll b/transform/testdata/interrupt-cortexm.out.ll
new file mode 100644
index 000000000..41fa9a776
--- /dev/null
+++ b/transform/testdata/interrupt-cortexm.out.ll
@@ -0,0 +1,39 @@
+target datalayout = "e-m:e-p:32:32-Fi8-i64:64-v128:64:128-a:0:32-n32-S64"
+target triple = "armv7em-none-eabi"
+
+%machine.UART = type { %machine.RingBuffer* }
+%machine.RingBuffer = type { [128 x %"runtime/volatile.Register8"], %"runtime/volatile.Register8", %"runtime/volatile.Register8" }
+%"runtime/volatile.Register8" = type { i8 }
+
[email protected] = internal global %machine.UART { %machine.RingBuffer* @"machine$alloc.335" }
+@"machine$alloc.335" = internal global %machine.RingBuffer zeroinitializer
+@"device/nrf.init$string.2" = internal unnamed_addr constant [23 x i8] c"UARTE0_UART0_IRQHandler"
+@"device/nrf.init$string.3" = internal unnamed_addr constant [44 x i8] c"SPIM0_SPIS0_TWIM0_TWIS0_SPI0_TWI0_IRQHandler"
+
+declare i32 @"runtime/interrupt.Register"(i32, i8*, i32, i8*, i8*) local_unnamed_addr
+
+declare void @"device/arm.EnableIRQ"(i32, i8* nocapture readnone, i8* nocapture readnone)
+
+declare void @"device/arm.SetPriority"(i32, i32, i8* nocapture readnone, i8* nocapture readnone)
+
+define void @runtime.initAll(i8* nocapture readnone, i8* nocapture readnone) unnamed_addr {
+entry:
+  call void @"device/arm.SetPriority"(i32 2, i32 192, i8* undef, i8* undef)
+  call void @"device/arm.EnableIRQ"(i32 2, i8* undef, i8* undef)
+  ret void
+}
+
+define internal void @"(*machine.UART).handleInterrupt$bound"(i32, i8* nocapture %context, i8* nocapture readnone %parentHandle) {
+entry:
+  %unpack.ptr = bitcast i8* %context to %machine.UART*
+  call void @"(*machine.UART).handleInterrupt"(%machine.UART* %unpack.ptr, i32 %0, i8* undef, i8* undef)
+  ret void
+}
+
+declare void @"(*machine.UART).handleInterrupt"(%machine.UART* nocapture, i32, i8* nocapture readnone, i8* nocapture readnone)
+
+define void @UARTE0_UART0_IRQHandler() unnamed_addr section ".text.UARTE0_UART0_IRQHandler" {
+entry:
+  call void @"(*machine.UART).handleInterrupt$bound"(i32 2, i8* bitcast (%machine.UART* @machine.UART0 to i8*), i8* null)
+  ret void
+}