compiler: refactor func value handling

This commit refactors all func value handling into a new file, which
makes it easier to comprehend it and extend it later.

compiler/func.go

@@ -0,0 +1,189 @@
+package compiler
+
+// This file implements function values and closures. A func value is
+// implemented as a pair of pointers: {context, function pointer}, where the
+// context may be a pointer to a heap-allocated struct containing the free
+// variables, or it may be undef if the function being pointed to doesn't need a
+// context.
+
+import (
+	"go/types"
+
+	"golang.org/x/tools/go/ssa"
+	"tinygo.org/x/go-llvm"
+)
+
+// createFuncValue creates a function value from a raw function pointer with no
+// context.
+func (c *Compiler) createFuncValue(funcPtr llvm.Value) (llvm.Value, error) {
+	// Closure is: {context, function pointer}
+	return c.ctx.ConstStruct([]llvm.Value{
+		llvm.Undef(c.i8ptrType),
+		funcPtr,
+	}, false), nil
+}
+
+// extractFuncScalar returns some scalar that can be used in comparisons. It is
+// a cheap operation.
+func (c *Compiler) extractFuncScalar(funcValue llvm.Value) llvm.Value {
+	return c.builder.CreateExtractValue(funcValue, 1, "")
+}
+
+// extractFuncContext extracts the context pointer from this function value. It
+// is a cheap operation.
+func (c *Compiler) extractFuncContext(funcValue llvm.Value) llvm.Value {
+	return c.builder.CreateExtractValue(funcValue, 0, "")
+}
+
+// decodeFuncValue extracts the context and the function pointer from this func
+// value. This may be an expensive operation.
+func (c *Compiler) decodeFuncValue(funcValue llvm.Value) (funcPtr, context llvm.Value) {
+	context = c.builder.CreateExtractValue(funcValue, 0, "")
+	funcPtr = c.builder.CreateExtractValue(funcValue, 1, "")
+	return
+}
+
+// getFuncType returns the type of a func value given a signature.
+func (c *Compiler) getFuncType(typ *types.Signature) (llvm.Type, error) {
+	rawPtr, err := c.getRawFuncType(typ)
+	if err != nil {
+		return llvm.Type{}, err
+	}
+	return c.ctx.StructType([]llvm.Type{c.i8ptrType, rawPtr}, false), nil
+}
+
+// getRawFuncType returns a LLVM function pointer type for a given signature.
+func (c *Compiler) getRawFuncType(typ *types.Signature) (llvm.Type, error) {
+	// Get the return type.
+	var err error
+	var returnType llvm.Type
+	switch typ.Results().Len() {
+	case 0:
+		// No return values.
+		returnType = c.ctx.VoidType()
+	case 1:
+		// Just one return value.
+		returnType, err = c.getLLVMType(typ.Results().At(0).Type())
+		if err != nil {
+			return llvm.Type{}, err
+		}
+	default:
+		// Multiple return values. Put them together in a struct.
+		// This appears to be the common way to handle multiple return values in
+		// LLVM.
+		members := make([]llvm.Type, typ.Results().Len())
+		for i := 0; i < typ.Results().Len(); i++ {
+			returnType, err := c.getLLVMType(typ.Results().At(i).Type())
+			if err != nil {
+				return llvm.Type{}, err
+			}
+			members[i] = returnType
+		}
+		returnType = c.ctx.StructType(members, false)
+	}
+
+	// Get the parameter types.
+	var paramTypes []llvm.Type
+	if typ.Recv() != nil {
+		recv, err := c.getLLVMType(typ.Recv().Type())
+		if err != nil {
+			return llvm.Type{}, err
+		}
+		if recv.StructName() == "runtime._interface" {
+			// This is a call on an interface, not a concrete type.
+			// The receiver is not an interface, but a i8* type.
+			recv = c.i8ptrType
+		}
+		paramTypes = append(paramTypes, c.expandFormalParamType(recv)...)
+	}
+	for i := 0; i < typ.Params().Len(); i++ {
+		subType, err := c.getLLVMType(typ.Params().At(i).Type())
+		if err != nil {
+			return llvm.Type{}, err
+		}
+		paramTypes = append(paramTypes, c.expandFormalParamType(subType)...)
+	}
+	// All functions take these parameters at the end.
+	paramTypes = append(paramTypes, c.i8ptrType) // context
+	paramTypes = append(paramTypes, c.i8ptrType) // parent coroutine
+
+	// Make a func type out of the signature.
+	return llvm.PointerType(llvm.FunctionType(returnType, paramTypes, false), c.funcPtrAddrSpace), nil
+}
+
+// parseMakeClosure makes a function value (with context) from the given
+// closure expression.
+func (c *Compiler) parseMakeClosure(frame *Frame, expr *ssa.MakeClosure) (llvm.Value, error) {
+	if len(expr.Bindings) == 0 {
+		panic("unexpected: MakeClosure without bound variables")
+	}
+	f := c.ir.GetFunction(expr.Fn.(*ssa.Function))
+
+	// Collect all bound variables.
+	boundVars := make([]llvm.Value, 0, len(expr.Bindings))
+	boundVarTypes := make([]llvm.Type, 0, len(expr.Bindings))
+	for _, binding := range expr.Bindings {
+		// The context stores the bound variables.
+		llvmBoundVar, err := c.parseExpr(frame, binding)
+		if err != nil {
+			return llvm.Value{}, err
+		}
+		boundVars = append(boundVars, llvmBoundVar)
+		boundVarTypes = append(boundVarTypes, llvmBoundVar.Type())
+	}
+	contextType := c.ctx.StructType(boundVarTypes, false)
+
+	// Allocate memory for the context.
+	contextAlloc := llvm.Value{}
+	contextHeapAlloc := llvm.Value{}
+	if c.targetData.TypeAllocSize(contextType) <= c.targetData.TypeAllocSize(c.i8ptrType) {
+		// Context fits in a pointer - e.g. when it is a pointer. Store it
+		// directly in the stack after a convert.
+		// Because contextType is a struct and we have to cast it to a *i8,
+		// store it in an alloca first for bitcasting (store+bitcast+load).
+		contextAlloc = c.builder.CreateAlloca(contextType, "")
+	} else {
+		// Context is bigger than a pointer, so allocate it on the heap.
+		size := c.targetData.TypeAllocSize(contextType)
+		sizeValue := llvm.ConstInt(c.uintptrType, size, false)
+		contextHeapAlloc = c.createRuntimeCall("alloc", []llvm.Value{sizeValue}, "")
+		contextAlloc = c.builder.CreateBitCast(contextHeapAlloc, llvm.PointerType(contextType, 0), "")
+	}
+
+	// Store all bound variables in the alloca or heap pointer.
+	for i, boundVar := range boundVars {
+		indices := []llvm.Value{
+			llvm.ConstInt(c.ctx.Int32Type(), 0, false),
+			llvm.ConstInt(c.ctx.Int32Type(), uint64(i), false),
+		}
+		gep := c.builder.CreateInBoundsGEP(contextAlloc, indices, "")
+		c.builder.CreateStore(boundVar, gep)
+	}
+
+	context := llvm.Value{}
+	if c.targetData.TypeAllocSize(contextType) <= c.targetData.TypeAllocSize(c.i8ptrType) {
+		// Load value (as *i8) from the alloca.
+		contextAlloc = c.builder.CreateBitCast(contextAlloc, llvm.PointerType(c.i8ptrType, 0), "")
+		context = c.builder.CreateLoad(contextAlloc, "")
+	} else {
+		// Get the original heap allocation pointer, which already is an
+		// *i8.
+		context = contextHeapAlloc
+	}
+
+	// Get the function signature type, which is a closure type.
+	// A closure is a tuple of {context, function pointer}.
+	typ, err := c.getFuncType(f.Signature)
+	if err != nil {
+		return llvm.Value{}, err
+	}
+
+	// Create the closure, which is a struct: {context, function pointer}.
+	closure, err := c.getZeroValue(typ)
+	if err != nil {
+		return llvm.Value{}, err
+	}
+	closure = c.builder.CreateInsertValue(closure, f.LLVMFn, 1, "")
+	closure = c.builder.CreateInsertValue(closure, context, 0, "")
+	return closure, nil
+}