compiler: always use fat function pointers with context

This reduces complexity in the compiler without affecting binary sizes
too much.

Cortex-M0:   no changes
Linux x64:   no changes
WebAssembly: some testcases (calls, coroutines, map) are slightly bigger

compiler/calls.go

@@ -21,6 +21,9 @@ func (c *Compiler) createRuntimeCall(fnName string, args []llvm.Value, name stri
 		panic("trying to call runtime." + fnName)
 	}
 	fn := c.ir.GetFunction(member.(*ssa.Function))
+	if !fn.IsExported() {
+		args = append(args, llvm.Undef(c.i8ptrType)) // unused context parameter
+	}
 	return c.createCall(fn.LLVMFn, args, name)
 }
 

compiler/compiler.go

@@ -220,8 +220,6 @@ func (c *Compiler) Compile(mainPath string) error {
 	// compiler.
 	c.ir.SimpleDCE()                // remove most dead code
 	c.ir.AnalyseCallgraph()         // set up callgraph
-	c.ir.AnalyseInterfaceConversions() // determine which types are converted to an interface
-	c.ir.AnalyseFunctionPointers()     // determine which function pointer signatures need context
 	c.ir.AnalyseBlockingRecursive() // make all parents of blocking calls blocking (transitively)
 	c.ir.AnalyseGoCalls()           // check whether we need a scheduler
 
@@ -368,7 +366,7 @@ func (c *Compiler) Compile(mainPath string) error {
 	block := c.ctx.AddBasicBlock(initFn.LLVMFn, "entry")
 	c.builder.SetInsertPointAtEnd(block)
 	for _, fn := range c.initFuncs {
-		c.builder.CreateCall(fn, nil, "")
+		c.builder.CreateCall(fn, []llvm.Value{llvm.Undef(c.i8ptrType)}, "")
 	}
 	c.builder.CreateRetVoid()
 
@@ -389,11 +387,10 @@ func (c *Compiler) Compile(mainPath string) error {
 	c.builder.SetInsertPointAtEnd(block)
 	realMain := c.mod.NamedFunction(c.ir.MainPkg().Pkg.Path() + ".main")
 	if c.ir.NeedsScheduler() {
-		coroutine := c.builder.CreateCall(realMain, []llvm.Value{llvm.ConstPointerNull(c.i8ptrType)}, "")
-		scheduler := c.mod.NamedFunction("runtime.scheduler")
-		c.builder.CreateCall(scheduler, []llvm.Value{coroutine}, "")
+		coroutine := c.builder.CreateCall(realMain, []llvm.Value{llvm.ConstPointerNull(c.i8ptrType), llvm.Undef(c.i8ptrType)}, "")
+		c.createRuntimeCall("scheduler", []llvm.Value{coroutine}, "")
 	} else {
-		c.builder.CreateCall(realMain, nil, "")
+		c.builder.CreateCall(realMain, []llvm.Value{llvm.Undef(c.i8ptrType)}, "")
 	}
 	c.builder.CreateRetVoid()
 
@@ -515,17 +512,11 @@ func (c *Compiler) getLLVMType(goType types.Type) (llvm.Type, error) {
 			}
 			paramTypes = append(paramTypes, c.expandFormalParamType(subType)...)
 		}
-		var ptr llvm.Type
-		if c.ir.SignatureNeedsContext(typ) {
 		// make a closure type (with a function pointer type inside):
 		// {context, funcptr}
 		paramTypes = append(paramTypes, c.i8ptrType)
-			ptr = llvm.PointerType(llvm.FunctionType(returnType, paramTypes, false), 0)
+		ptr := llvm.PointerType(llvm.FunctionType(returnType, paramTypes, false), 0)
 		ptr = c.ctx.StructType([]llvm.Type{c.i8ptrType, ptr}, false)
-		} else {
-			// make a simple function pointer
-			ptr = llvm.PointerType(llvm.FunctionType(returnType, paramTypes, false), 0)
-		}
 		return ptr, nil
 	case *types.Slice:
 		elemType, err := c.getLLVMType(typ.Elem())
@@ -706,9 +697,9 @@ func (c *Compiler) parseFuncDecl(f *ir.Function) (*Frame, error) {
 		paramTypes = append(paramTypes, paramTypeFragments...)
 	}
 
-	if c.ir.FunctionNeedsContext(f) {
-		// This function gets an extra parameter: the context pointer (for
-		// closures and bound methods). Add it as an extra paramter here.
+	// Add an extra parameter as the function context. This context is used in
+	// closures and bound methods, but should be optimized away when not used.
+	if !f.IsExported() {
 		paramTypes = append(paramTypes, c.i8ptrType)
 	}
 
@@ -840,10 +831,8 @@ func (c *Compiler) getInterpretedValue(prefix string, value ir.Value) (llvm.Valu
 		}
 		fn := c.ir.GetFunction(value.Elem)
 		ptr := fn.LLVMFn
-		if c.ir.SignatureNeedsContext(fn.Signature) {
 		// Create closure value: {context, function pointer}
 		ptr = c.ctx.ConstStruct([]llvm.Value{llvm.ConstPointerNull(c.i8ptrType), ptr}, false)
-		}
 		return ptr, nil
 
 	case *ir.GlobalValue:
@@ -1128,9 +1117,6 @@ func (c *Compiler) parseFunc(frame *Frame) error {
 	// Load free variables from the context. This is a closure (or bound
 	// method).
 	if len(frame.fn.FreeVars) != 0 {
-		if !c.ir.FunctionNeedsContext(frame.fn) {
-			panic("free variables on function without context")
-		}
 		context := frame.fn.LLVMFn.LastParam()
 		context.SetName("context")
 
@@ -1799,12 +1785,12 @@ func (c *Compiler) parseCall(frame *Frame, instr *ssa.CallCommon, parentHandle l
 			return llvm.Value{}, c.makeError(instr.Pos(), "undefined function: "+targetFunc.LinkName())
 		}
 		var context llvm.Value
-		if c.ir.FunctionNeedsContext(targetFunc) {
 		// This function call is to a (potential) closure, not a regular
 		// function. See whether it is a closure and if so, call it as such.
 		// Else, supply a dummy nil pointer as the last parameter.
-			var err error
-			if mkClosure, ok := instr.Value.(*ssa.MakeClosure); ok {
+		if targetFunc.IsExported() {
+			// don't pass a context parameter
+		} else if mkClosure, ok := instr.Value.(*ssa.MakeClosure); ok {
 			// closure is {context, function pointer}
 			closure, err := c.parseExpr(frame, mkClosure)
 			if err != nil {
@@ -1812,11 +1798,7 @@ func (c *Compiler) parseCall(frame *Frame, instr *ssa.CallCommon, parentHandle l
 			}
 			context = c.builder.CreateExtractValue(closure, 0, "")
 		} else {
-				context, err = c.getZeroValue(c.i8ptrType)
-				if err != nil {
-					return llvm.Value{}, err
-				}
-			}
+			context = llvm.Undef(c.i8ptrType)
 		}
 		return c.parseFunctionCall(frame, instr.Args, targetFunc.LLVMFn, context, c.ir.IsBlocking(targetFunc), parentHandle)
 	}
@@ -1831,14 +1813,11 @@ func (c *Compiler) parseCall(frame *Frame, instr *ssa.CallCommon, parentHandle l
 			return llvm.Value{}, err
 		}
 		// TODO: blocking function pointers (needs analysis)
-		var context llvm.Value
-		if c.ir.SignatureNeedsContext(instr.Signature()) {
 		// 'value' is a closure, not a raw function pointer.
 		// Extract the function pointer and the context pointer.
 		// closure: {context, function pointer}
-			context = c.builder.CreateExtractValue(value, 0, "")
+		context := c.builder.CreateExtractValue(value, 0, "")
 		value = c.builder.CreateExtractValue(value, 1, "")
-		}
 		return c.parseFunctionCall(frame, instr.Args, value, context, false, parentHandle)
 	}
 }
@@ -2016,16 +1995,12 @@ func (c *Compiler) parseExpr(frame *Frame, expr ssa.Value) (llvm.Value, error) {
 		if fn.IsExported() {
 			return llvm.Value{}, c.makeError(expr.Pos(), "cannot use an exported function as value")
 		}
-		ptr := fn.LLVMFn
-		if c.ir.FunctionNeedsContext(fn) {
 		// Create closure for function pointer.
 		// Closure is: {context, function pointer}
-			ptr = c.ctx.ConstStruct([]llvm.Value{
-				llvm.ConstPointerNull(c.i8ptrType),
-				ptr,
-			}, false)
-		}
-		return ptr, nil
+		return c.ctx.ConstStruct([]llvm.Value{
+			llvm.Undef(c.i8ptrType),
+			fn.LLVMFn,
+		}, false), nil
 	case *ssa.Global:
 		if strings.HasPrefix(expr.Name(), "__cgofn__cgo_") || strings.HasPrefix(expr.Name(), "_cgo_") {
 			// Ignore CGo global variables which we don't use.
@@ -2606,15 +2581,12 @@ func (c *Compiler) parseBinOp(op token.Token, typ types.Type, x, y llvm.Value, p
 			return llvm.Value{}, c.makeError(pos, "todo: unknown basic type in binop: "+typ.String())
 		}
 	case *types.Signature:
-		if c.ir.SignatureNeedsContext(typ) {
-			// This is a closure, not a function pointer. Get the underlying
-			// function pointer.
+		// Extract function pointers from the function values (closures).
 		// This is safe: function pointers are generally not comparable
 		// against each other, only against nil. So one or both has to be
-			// nil, so we can ignore the contents of the closure.
+		// nil, so we can ignore the closure context.
 		x = c.builder.CreateExtractValue(x, 1, "")
 		y = c.builder.CreateExtractValue(y, 1, "")
-		}
 		switch op {
 		case token.EQL: // ==
 			return c.builder.CreateICmp(llvm.IntEQ, x, y, ""), nil
@@ -2790,7 +2762,7 @@ func (c *Compiler) parseConst(prefix string, expr *ssa.Const) (llvm.Value, error
 		}
 		// Create a generic nil interface with no dynamic type (typecode=0).
 		fields := []llvm.Value{
-			llvm.ConstInt(c.ctx.Int16Type(), 0, false),
+			llvm.ConstInt(c.uintptrType, 0, false),
 			llvm.ConstPointerNull(c.i8ptrType),
 		}
 		itf := llvm.ConstNamedStruct(c.mod.GetTypeByName("runtime._interface"), fields)
@@ -2979,10 +2951,6 @@ func (c *Compiler) parseMakeClosure(frame *Frame, expr *ssa.MakeClosure) (llvm.V
 		panic("unexpected: MakeClosure without bound variables")
 	}
 	f := c.ir.GetFunction(expr.Fn.(*ssa.Function))
-	if !c.ir.FunctionNeedsContext(f) {
-		// Maybe AnalyseFunctionPointers didn't run?
-		panic("MakeClosure on function signature without context")
-	}
 
 	// Collect all bound variables.
 	boundVars := make([]llvm.Value, 0, len(expr.Bindings))

compiler/defer.go

@@ -14,8 +14,6 @@ package compiler
 //     frames.
 
 import (
-	"go/types"
-
 	"github.com/aykevl/go-llvm"
 	"github.com/aykevl/tinygo/ir"
 	"golang.org/x/tools/go/ssa"
@@ -240,12 +238,10 @@ func (c *Compiler) emitRunDefers(frame *Frame) error {
 				forwardParams = append(forwardParams, forwardParam)
 			}
 
-			if c.ir.SignatureNeedsContext(callback.Method.Type().(*types.Signature)) {
-				// This function takes an extra context parameter. An interface call
-				// cannot also be a closure but we have to supply the parameter
-				// anyway for platforms with a strict calling convention.
+			// Add the context parameter. An interface call cannot also be a
+			// closure but we have to supply the parameter anyway for platforms
+			// with a strict calling convention.
 			forwardParams = append(forwardParams, llvm.Undef(c.i8ptrType))
-			}
 
 			fnPtr, _, err := c.getInvokeCall(frame, callback)
 			if err != nil {
@@ -277,6 +273,10 @@ func (c *Compiler) emitRunDefers(frame *Frame) error {
 				forwardParams = append(forwardParams, forwardParam)
 			}
 
+			// Add the context parameter. We know it is ignored by the receiving
+			// function, but we have to pass one anyway.
+			forwardParams = append(forwardParams, llvm.Undef(c.i8ptrType))
+
 			// Call real function.
 			c.createCall(callback.LLVMFn, forwardParams, "")
 

compiler/interface.go

@@ -304,16 +304,10 @@ func (c *Compiler) getInvokeCall(frame *Frame, instr *ssa.CallCommon) (llvm.Valu
 	if err != nil {
 		return llvm.Value{}, nil, err
 	}
-	if c.ir.SignatureNeedsContext(instr.Method.Type().(*types.Signature)) {
-		// This is somewhat of a hack.
-		// getLLVMType() has created a closure type for us, but we don't
-		// actually want a closure type as an interface call can never be a
-		// closure call. So extract the function pointer type from the
-		// closure.
-		// This happens because somewhere the same function signature is
-		// used in a closure or bound method.
+	// getLLVMType() has created a closure type for us, but we don't actually
+	// want a closure type as an interface call can never be a closure call. So
+	// extract the function pointer type from the closure.
 	llvmFnType = llvmFnType.Subtypes()[1]
-	}
 
 	typecode := c.builder.CreateExtractValue(itf, 0, "invoke.typecode")
 	values := []llvm.Value{
@@ -333,12 +327,9 @@ func (c *Compiler) getInvokeCall(frame *Frame, instr *ssa.CallCommon) (llvm.Valu
 		}
 		args = append(args, val)
 	}
-	if c.ir.SignatureNeedsContext(instr.Method.Type().(*types.Signature)) {
-		// This function takes an extra context parameter. An interface call
-		// cannot also be a closure but we have to supply the nil pointer
-		// anyway.
-		args = append(args, llvm.ConstPointerNull(c.i8ptrType))
-	}
+	// Add the context parameter. An interface call never takes a context but we
+	// have to supply the parameter anyway.
+	args = append(args, llvm.Undef(c.i8ptrType))
 
 	return fnCast, args, nil
 }

docs/internals.rst

@@ -77,14 +77,11 @@ interface
     interface.go for a detailed description of how typeasserts and interface
     calls are implemented.
 
-function pointer
-    A function pointer has two representations: a literal function pointer and a
-    fat function pointer in the form of ``{context, function pointer}``. Which
-    representation is chosen depends on the AnalyseFunctionPointers pass in
-    `ir/passes.go <https://github.com/aykevl/tinygo/blob/master/ir/passes.go>`_:
-    it tries to use a raw function pointer but will use a fat function pointer
-    if there is a closure or bound method somewhere in the program with the
-    exact same signature.
+function value
+    A function value is a fat function pointer in the form of  ``{context,
+    function pointer}`` where context is a pointer which may have any value.
+    The function pointer is expected to be called with the context as the last
+    parameter in all cases.
 
 goroutine
     A goroutine is a linked list of `LLVM coroutines

interp/interp.go

@@ -56,13 +56,14 @@ func Run(mod llvm.Module, targetData llvm.TargetData, debug bool) error {
 	}
 
 	// Do this in a separate step to avoid corrupting the iterator above.
+	undefPtr := llvm.Undef(llvm.PointerType(mod.Context().Int8Type(), 0))
 	for _, call := range initCalls {
 		initName := call.CalledValue().Name()
 		if !strings.HasSuffix(initName, ".init") {
 			return errors.New("expected all instructions in " + name + " to be *.init() calls")
 		}
 		pkgName := initName[:len(initName)-5]
-		_, err := e.Function(call.CalledValue(), nil, pkgName)
+		_, err := e.Function(call.CalledValue(), []Value{&LocalValue{e, undefPtr}}, pkgName)
 		if err == ErrUnreachable {
 			break
 		}

ir/ir.go

@@ -29,8 +29,6 @@ type Program struct {
 	NamedTypes     []*NamedType
 	needsScheduler bool
 	goCalls        []*ssa.Go
-	typesInInterfaces map[string]struct{} // see AnalyseInterfaceConversions
-	fpWithContext     map[string]struct{} // see AnalyseFunctionPointers
 }
 
 // Function or method.
@@ -43,7 +41,6 @@ type Function struct {
 	blocking  bool        // calculated by AnalyseBlockingRecursive
 	flag      bool        // used by dead code elimination
 	interrupt bool        // go:interrupt
-	addressTaken bool        // used as function pointer, calculated by AnalyseFunctionPointers
 	parents   []*Function // calculated by AnalyseCallgraph
 	children  []*Function // calculated by AnalyseCallgraph
 }

ir/passes.go

@@ -17,16 +17,15 @@ import (
 //     String() string
 //     Read([]byte) (int, error)
 func MethodSignature(method *types.Func) string {
-	return method.Name() + Signature(method.Type().(*types.Signature))
+	return method.Name() + signature(method.Type().(*types.Signature))
 }
 
-// Make a readable version of a function (pointer) signature. This string is
-// used internally to match signatures (like in AnalyseFunctionPointers).
+// Make a readable version of a function (pointer) signature.
 // Examples:
 //
 //     () string
 //     (string, int) (int, error)
-func Signature(sig *types.Signature) string {
+func signature(sig *types.Signature) string {
 	s := ""
 	if sig.Params().Len() == 0 {
 		s += "()"
@@ -101,69 +100,6 @@ func (p *Program) AnalyseCallgraph() {
 	}
 }
 
-// Find all types that are put in an interface.
-func (p *Program) AnalyseInterfaceConversions() {
-	// Clear, if AnalyseInterfaceConversions has been called before.
-	p.typesInInterfaces = map[string]struct{}{}
-
-	for _, f := range p.Functions {
-		for _, block := range f.Blocks {
-			for _, instr := range block.Instrs {
-				switch instr := instr.(type) {
-				case *ssa.MakeInterface:
-					name := instr.X.Type().String()
-					if _, ok := p.typesInInterfaces[name]; !ok {
-						p.typesInInterfaces[name] = struct{}{}
-					}
-				}
-			}
-		}
-	}
-}
-
-// Analyse which function pointer signatures need a context parameter.
-// This makes calling function pointers more efficient.
-func (p *Program) AnalyseFunctionPointers() {
-	// Clear, if AnalyseFunctionPointers has been called before.
-	p.fpWithContext = map[string]struct{}{}
-
-	for _, f := range p.Functions {
-		for _, block := range f.Blocks {
-			for _, instr := range block.Instrs {
-				switch instr := instr.(type) {
-				case ssa.CallInstruction:
-					for _, arg := range instr.Common().Args {
-						switch arg := arg.(type) {
-						case *ssa.Function:
-							f := p.GetFunction(arg)
-							f.addressTaken = true
-						}
-					}
-				case *ssa.DebugRef:
-				default:
-					// For anything that isn't a call...
-					for _, operand := range instr.Operands(nil) {
-						if operand == nil || *operand == nil || isCGoInternal((*operand).Name()) {
-							continue
-						}
-						switch operand := (*operand).(type) {
-						case *ssa.Function:
-							f := p.GetFunction(operand)
-							f.addressTaken = true
-						}
-					}
-				}
-				switch instr := instr.(type) {
-				case *ssa.MakeClosure:
-					fn := instr.Fn.(*ssa.Function)
-					sig := Signature(fn.Signature)
-					p.fpWithContext[sig] = struct{}{}
-				}
-			}
-		}
-	}
-}
-
 // Analyse which functions are recursively blocking.
 //
 // Depends on AnalyseCallgraph.
@@ -321,21 +257,3 @@ func (p *Program) IsBlocking(f *Function) bool {
 	}
 	return f.blocking
 }
-
-func (p *Program) FunctionNeedsContext(f *Function) bool {
-	if !f.addressTaken {
-		if f.Signature.Recv() != nil {
-			_, hasInterfaceConversion := p.typesInInterfaces[f.Signature.Recv().Type().String()]
-			if hasInterfaceConversion && p.SignatureNeedsContext(f.Signature) {
-				return true
-			}
-		}
-		return false
-	}
-	return p.SignatureNeedsContext(f.Signature)
-}
-
-func (p *Program) SignatureNeedsContext(sig *types.Signature) bool {
-	_, needsContext := p.fpWithContext[Signature(sig)]
-	return needsContext
-}

src/runtime/panic.go

@@ -2,7 +2,7 @@ package runtime
 
 // trap is a compiler hint that this function cannot be executed. It is
 // translated into either a trap instruction or a call to abort().
-//go:linkname trap llvm.trap
+//go:export llvm.trap
 func trap()
 
 // Builtin function panic(msg), used as a compiler intrinsic.

src/runtime/runtime_unix.go

@@ -6,16 +6,25 @@ import (
 	"unsafe"
 )
 
-func _Cfunc_putchar(c int) int
-func _Cfunc_usleep(usec uint) int
-func _Cfunc_malloc(size uintptr) unsafe.Pointer
-func _Cfunc_abort()
-func _Cfunc_clock_gettime(clk_id uint, ts *timespec)
+//go:export putchar
+func _putchar(c int) int
+
+//go:export usleep
+func usleep(usec uint) int
+
+//go:export malloc
+func malloc(size uintptr) unsafe.Pointer
+
+//go:export abort
+func abort()
+
+//go:export clock_gettime
+func clock_gettime(clk_id uint, ts *timespec)
 
 const heapSize = 1 * 1024 * 1024 // 1MB to start
 
 var (
-	heapStart = uintptr(_Cfunc_malloc(heapSize))
+	heapStart = uintptr(malloc(heapSize))
 	heapEnd   = heapStart + heapSize
 )
 
@@ -45,11 +54,11 @@ func main() int {
 }
 
 func putchar(c byte) {
-	_Cfunc_putchar(int(c))
+	_putchar(int(c))
 }
 
 func sleepTicks(d timeUnit) {
-	_Cfunc_usleep(uint(d) / 1000)
+	usleep(uint(d) / 1000)
 }
 
 // Return monotonic time in nanoseconds.
@@ -57,15 +66,10 @@ func sleepTicks(d timeUnit) {
 // TODO: noescape
 func monotime() uint64 {
 	ts := timespec{}
-	_Cfunc_clock_gettime(CLOCK_MONOTONIC_RAW, &ts)
+	clock_gettime(CLOCK_MONOTONIC_RAW, &ts)
 	return uint64(ts.tv_sec)*1000*1000*1000 + uint64(ts.tv_nsec)
 }
 
 func ticks() timeUnit {
 	return timeUnit(monotime())
 }
-
-func abort() {
-	// panic() exits with exit code 2.
-	_Cfunc_abort()
-}

src/runtime/runtime_wasm.go

@@ -8,16 +8,16 @@ const tickMicros = 1
 
 var timestamp timeUnit
 
-// CommonWA: io_get_stdout
-func _Cfunc_io_get_stdout() int32
+//go:export io_get_stdout
+func io_get_stdout() int32
 
-// CommonWA: resource_write
-func _Cfunc_resource_write(id int32, ptr *uint8, len int32) int32
+//go:export resource_write
+func resource_write(id int32, ptr *uint8, len int32) int32
 
 var stdout int32
 
 func init() {
-	stdout = _Cfunc_io_get_stdout()
+	stdout = io_get_stdout()
 }
 
 //go:export _start
@@ -32,7 +32,7 @@ func cwa_main() {
 }
 
 func putchar(c byte) {
-	_Cfunc_resource_write(stdout, &c, 1)
+	resource_write(stdout, &c, 1)
 }
 
 func sleepTicks(d timeUnit) {

src/runtime/scheduler.go

@@ -31,16 +31,16 @@ const schedulerDebug = false
 // must not be used directly, it is meant to be used as an opaque *i8 in LLVM.
 type coroutine uint8
 
-//go:linkname resume llvm.coro.resume
+//go:export llvm.coro.resume
 func (t *coroutine) resume()
 
-//go:linkname destroy llvm.coro.destroy
+//go:export llvm.coro.destroy
 func (t *coroutine) destroy()
 
-//go:linkname done llvm.coro.done
+//go:export llvm.coro.done
 func (t *coroutine) done() bool
 
-//go:linkname _promise llvm.coro.promise
+//go:export llvm.coro.promise
 func (t *coroutine) _promise(alignment int32, from bool) unsafe.Pointer
 
 // Get the promise belonging to a task.