compiler: simplify interface lowering

This commit simplifies the IR a little bit: instead of calling
pseudo-functions runtime.interfaceImplements and
runtime.interfaceMethod, real declared functions are being called that
are then defined in the interface lowering pass. This should simplify
the interaction between various transformation passes. It also reduces
the number of lines of code, which is generally a good thing.

compiler/interface.go

@@ -47,6 +47,7 @@ func (c *compilerContext) getTypeCode(typ types.Type) llvm.Value {
 		var length int64
 		var methodSet llvm.Value
 		var ptrTo llvm.Value
+		var typeAssert llvm.Value
 		switch typ := typ.(type) {
 		case *types.Named:
 			references = c.getTypeCode(typ.Underlying())
@@ -69,6 +70,9 @@ func (c *compilerContext) getTypeCode(typ types.Type) llvm.Value {
 		}
 		if _, ok := typ.Underlying().(*types.Interface); !ok {
 			methodSet = c.getTypeMethodSet(typ)
+		} else {
+			typeAssert = c.getInterfaceImplementsFunc(typ)
+			typeAssert = llvm.ConstPtrToInt(typeAssert, c.uintptrType)
 		}
 		if _, ok := typ.Underlying().(*types.Pointer); !ok {
 			ptrTo = c.getTypeCode(types.NewPointer(typ))
@@ -87,6 +91,9 @@ func (c *compilerContext) getTypeCode(typ types.Type) llvm.Value {
 		if !ptrTo.IsNil() {
 			globalValue = llvm.ConstInsertValue(globalValue, ptrTo, []uint32{3})
 		}
+		if !typeAssert.IsNil() {
+			globalValue = llvm.ConstInsertValue(globalValue, typeAssert, []uint32{4})
+		}
 		global.SetInitializer(globalValue)
 		global.SetLinkage(llvm.LinkOnceODRLinkage)
 		global.SetGlobalConstant(true)
@@ -193,7 +200,11 @@ func getTypeCodeName(t types.Type) string {
 	case *types.Interface:
 		methods := make([]string, t.NumMethods())
 		for i := 0; i < t.NumMethods(); i++ {
-			methods[i] = t.Method(i).Name() + ":" + getTypeCodeName(t.Method(i).Type())
+			name := t.Method(i).Name()
+			if !token.IsExported(name) {
+				name = t.Method(i).Pkg().Path() + "." + name
+			}
+			methods[i] = name + ":" + getTypeCodeName(t.Method(i).Type())
 		}
 		return "interface:" + "{" + strings.Join(methods, ",") + "}"
 	case *types.Map:
@@ -306,10 +317,9 @@ func (c *compilerContext) getInterfaceMethodSet(typ types.Type) llvm.Value {
 	return llvm.ConstGEP(global, []llvm.Value{zero, zero})
 }
 
-// getMethodSignature returns a global variable which is a reference to an
-// external *i8 indicating the indicating the signature of this method. It is
-// used during the interface lowering pass.
-func (c *compilerContext) getMethodSignature(method *types.Func) llvm.Value {
+// getMethodSignatureName returns a unique name (that can be used as the name of
+// a global) for the given method.
+func (c *compilerContext) getMethodSignatureName(method *types.Func) string {
 	signature := methodSignature(method)
 	var globalName string
 	if token.IsExported(method.Name()) {
@@ -317,6 +327,14 @@ func (c *compilerContext) getMethodSignature(method *types.Func) llvm.Value {
 	} else {
 		globalName = method.Type().(*types.Signature).Recv().Pkg().Path() + ".$methods." + signature
 	}
+	return globalName
+}
+
+// getMethodSignature returns a global variable which is a reference to an
+// external *i8 indicating the indicating the signature of this method. It is
+// used during the interface lowering pass.
+func (c *compilerContext) getMethodSignature(method *types.Func) llvm.Value {
+	globalName := c.getMethodSignatureName(method)
 	signatureGlobal := c.mod.NamedGlobal(globalName)
 	if signatureGlobal.IsNil() {
 		// TODO: put something useful in these globals, such as the method
@@ -345,15 +363,16 @@ func (b *builder) createTypeAssert(expr *ssa.TypeAssert) llvm.Value {
 	commaOk := llvm.Value{}
 	if _, ok := expr.AssertedType.Underlying().(*types.Interface); ok {
 		// Type assert on interface type.
-		// This pseudo call will be lowered in the interface lowering pass to a
-		// real call which checks whether the provided typecode is any of the
-		// concrete types that implements this interface.
+		// This is a call to an interface type assert function.
+		// The interface lowering pass will define this function by filling it
+		// with a type switch over all concrete types that implement this
+		// interface, and returning whether it's one of the matched types.
 		// This is very different from how interface asserts are implemented in
 		// the main Go compiler, where the runtime checks whether the type
 		// implements each method of the interface. See:
 		// https://research.swtch.com/interfaces
-		methodSet := b.getInterfaceMethodSet(expr.AssertedType)
-		commaOk = b.createRuntimeCall("interfaceImplements", []llvm.Value{actualTypeNum, methodSet}, "")
+		fn := b.getInterfaceImplementsFunc(expr.AssertedType)
+		commaOk = b.CreateCall(fn, []llvm.Value{actualTypeNum}, "")
 
 	} else {
 		globalName := "reflect/types.typeid:" + getTypeCodeName(expr.AssertedType)
@@ -420,39 +439,50 @@ func (b *builder) createTypeAssert(expr *ssa.TypeAssert) llvm.Value {
 	}
 }
 
-// getInvokePtr creates an interface function pointer lookup for the specified invoke instruction, using a specified typecode.
-func (b *builder) getInvokePtr(instr *ssa.CallCommon, typecode llvm.Value) llvm.Value {
-	llvmFnType := b.getRawFuncType(instr.Method.Type().(*types.Signature))
-	values := []llvm.Value{
-		typecode,
-		b.getInterfaceMethodSet(instr.Value.Type()),
-		b.getMethodSignature(instr.Method),
+// getMethodsString returns a string to be used in the "tinygo-methods" string
+// attribute for interface functions.
+func (c *compilerContext) getMethodsString(itf *types.Interface) string {
+	methods := make([]string, itf.NumMethods())
+	for i := range methods {
+		methods[i] = c.getMethodSignatureName(itf.Method(i))
 	}
-	fn := b.createRuntimeCall("interfaceMethod", values, "invoke.func")
-	return b.CreateIntToPtr(fn, llvmFnType, "invoke.func.cast")
+	return strings.Join(methods, "; ")
 }
 
-// getInvokeCall creates and returns the function pointer and parameters of an
-// interface call.
-func (b *builder) getInvokeCall(instr *ssa.CallCommon) (llvm.Value, []llvm.Value) {
-	// Call an interface method with dynamic dispatch.
-	itf := b.getValue(instr.Value) // interface
-
-	typecode := b.CreateExtractValue(itf, 0, "invoke.typecode")
-	fnCast := b.getInvokePtr(instr, typecode)
-	receiverValue := b.CreateExtractValue(itf, 1, "invoke.func.receiver")
-
-	args := []llvm.Value{receiverValue}
-	for _, arg := range instr.Args {
-		args = append(args, b.getValue(arg))
+// getInterfaceImplementsfunc returns a declared function that works as a type
+// switch. The interface lowering pass will define this function.
+func (c *compilerContext) getInterfaceImplementsFunc(assertedType types.Type) llvm.Value {
+	fnName := getTypeCodeName(assertedType.Underlying()) + ".$typeassert"
+	llvmFn := c.mod.NamedFunction(fnName)
+	if llvmFn.IsNil() {
+		llvmFnType := llvm.FunctionType(c.ctx.Int1Type(), []llvm.Type{c.uintptrType}, false)
+		llvmFn = llvm.AddFunction(c.mod, fnName, llvmFnType)
+		methods := c.getMethodsString(assertedType.Underlying().(*types.Interface))
+		llvmFn.AddFunctionAttr(c.ctx.CreateStringAttribute("tinygo-methods", methods))
 	}
-	// Add the context parameter. An interface call never takes a context but we
-	// have to supply the parameter anyway.
-	args = append(args, llvm.Undef(b.i8ptrType))
-	// Add the parent goroutine handle.
-	args = append(args, llvm.Undef(b.i8ptrType))
+	return llvmFn
+}
 
-	return fnCast, args
+// getInvokeFunction returns the thunk to call the given interface method. The
+// thunk is declared, not defined: it will be defined by the interface lowering
+// pass.
+func (c *compilerContext) getInvokeFunction(instr *ssa.CallCommon) llvm.Value {
+	fnName := getTypeCodeName(instr.Value.Type().Underlying()) + "." + instr.Method.Name() + "$invoke"
+	llvmFn := c.mod.NamedFunction(fnName)
+	if llvmFn.IsNil() {
+		sig := instr.Method.Type().(*types.Signature)
+		var paramTuple []*types.Var
+		for i := 0; i < sig.Params().Len(); i++ {
+			paramTuple = append(paramTuple, sig.Params().At(i))
+		}
+		paramTuple = append(paramTuple, types.NewVar(token.NoPos, nil, "$typecode", types.Typ[types.Uintptr]))
+		llvmFnType := c.getRawFuncType(types.NewSignature(sig.Recv(), types.NewTuple(paramTuple...), sig.Results(), false)).ElementType()
+		llvmFn = llvm.AddFunction(c.mod, fnName, llvmFnType)
+		llvmFn.AddFunctionAttr(c.ctx.CreateStringAttribute("tinygo-invoke", c.getMethodSignatureName(instr.Method)))
+		methods := c.getMethodsString(instr.Value.Type().Underlying().(*types.Interface))
+		llvmFn.AddFunctionAttr(c.ctx.CreateStringAttribute("tinygo-methods", methods))
+	}
+	return llvmFn
 }
 
 // getInterfaceInvokeWrapper returns a wrapper for the given method so it can be