build: support comments in functions (#41)

build/context.go

@@ -133,6 +133,11 @@ func (c *Context) Label(name string) {
 	c.activefunc().AddLabel(ir.Label(name))
 }
 
+// Comment adds comment lines to the active function.
+func (c *Context) Comment(lines ...string) {
+	c.activefunc().AddComment(lines...)
+}
+
 func (c *Context) activefunc() *ir.Function {
 	if c.function == nil {
 		c.adderrormessage("no active function")

build/global.go

@@ -125,5 +125,8 @@ func AllocLocal(size int) operand.Mem { return ctx.AllocLocal(size) }
 // Label adds a label to the active function.
 func Label(name string) { ctx.Label(name) }
 
+// Comment adds comment lines to the active function.
+func Comment(lines ...string) { ctx.Comment(lines...) }
+
 // ConstData builds a static data section containing just the given constant.
 func ConstData(name string, v operand.Constant) operand.Mem { return ctx.ConstData(name, v) }

ir/ir.go

@@ -20,6 +20,20 @@ type Label string
 
 func (l Label) node() {}
 
+// Comment represents a multi-line comment.
+type Comment struct {
+	Lines []string
+}
+
+func (c *Comment) node() {}
+
+// NewComment builds a Comment consisting of the provided lines.
+func NewComment(lines ...string) *Comment {
+	return &Comment{
+		Lines: lines,
+	}
+}
+
 // Instruction is a single instruction in a function.
 type Instruction struct {
 	Opcode   string
@@ -176,6 +190,11 @@ func (f *Function) AddLabel(l Label) {
 	f.AddNode(l)
 }
 
+// AddComment adds comment lines to f.
+func (f *Function) AddComment(lines ...string) {
+	f.AddNode(NewComment(lines...))
+}
+
 // AddNode appends a Node to f.
 func (f *Function) AddNode(n Node) {
 	f.Nodes = append(f.Nodes, n)

pass/cfg.go

@@ -11,27 +11,27 @@ import (
 // label name to the following instruction.
 func LabelTarget(fn *ir.Function) error {
 	target := map[ir.Label]*ir.Instruction{}
-	for idx := 0; idx < len(fn.Nodes); idx++ {
-		// Is this a label?
-		lbl, ok := fn.Nodes[idx].(ir.Label)
-		if !ok {
-			continue
-		}
-		// Check for a duplicate label.
-		if _, found := target[lbl]; found {
-			return fmt.Errorf("duplicate label \"%s\"", lbl)
-		}
-		// Advance to next node.
-		if idx == len(fn.Nodes)-1 {
-			return errors.New("function ends with label")
-		}
-		idx++
-		// Should be an instruction.
-		i, ok := fn.Nodes[idx].(*ir.Instruction)
-		if !ok {
-			return errors.New("instruction should follow a label")
+	var empty ir.Label
+	pending := empty
+	for _, node := range fn.Nodes {
+		switch n := node.(type) {
+		case ir.Label:
+			if pending != empty {
+				return errors.New("instruction should follow a label")
+			}
+			pending = n
+			if _, found := target[pending]; found {
+				return fmt.Errorf("duplicate label \"%s\"", pending)
+			}
+		case *ir.Instruction:
+			if pending != empty {
+				target[pending] = n
+				pending = empty
+			}
 		}
-		target[lbl] = i
+	}
+	if pending != empty {
+		return errors.New("function ends with label")
 	}
 	fn.LabelTarget = target
 	return nil

pass/cfg_test.go

@@ -18,6 +18,7 @@ func TestLabelTarget(t *testing.T) {
 	f := ir.NewFunction("happypath")
 	for lbl, i := range expect {
 		f.AddLabel(lbl)
+		f.AddComment("comments should be ignored")
 		f.AddInstruction(i)
 		f.AddInstruction(&ir.Instruction{Opcode: "IDK"})
 	}

printer/goasm.go

@@ -84,6 +84,15 @@ func (p *goasm) function(f *ir.Function) {
 	p.Printf(", %s\n", textsize(f))
 
 	w := p.tabwriter()
+	clear := true
+	flush := func() {
+		w.Flush()
+		w = p.tabwriter()
+		if !clear {
+			p.NL()
+			clear = true
+		}
+	}
 	for _, node := range f.Nodes {
 		switch n := node.(type) {
 		case *ir.Instruction:
@@ -93,10 +102,15 @@ func (p *goasm) function(f *ir.Function) {
 				fmt.Fprintf(w, "\t%s", joinOperands(n.Operands))
 			}
 			fmt.Fprint(w, "\n")
+			clear = false
 		case ir.Label:
-			w.Flush()
-			w = p.tabwriter()
-			p.Printf("\n%s:\n", n)
+			flush()
+			p.Printf("%s:\n", n)
+		case *ir.Comment:
+			flush()
+			for _, line := range n.Lines {
+				p.Printf("\t// %s\n", line)
+			}
 		default:
 			panic("unexpected node type")
 		}

tests/fmt/asm.go

@@ -0,0 +1,26 @@
+// +build ignore
+
+package main
+
+import (
+	. "github.com/mmcloughlin/avo/build"
+	. "github.com/mmcloughlin/avo/reg"
+)
+
+func main() {
+	TEXT("Formatting", NOSPLIT, "func()")
+	Doc("Formatting contains various cases to test the formatter.")
+
+	ADDQ(R8, R8)
+	Comment("One comment line between instructions.")
+	ADDQ(R8, R8)
+
+	Comment("Comment before label.")
+	Label("label")
+	Comment("Comment after label.")
+	ADDQ(R8, R8)
+
+	RET()
+
+	Generate()
+}

tests/fmt/fmt.s

@@ -0,0 +1,16 @@
+// Code generated by command: go run asm.go -out fmt.s -stubs stub.go. DO NOT EDIT.
+
+#include "textflag.h"
+
+// func Formatting()
+TEXT ·Formatting(SB), NOSPLIT, $0
+	ADDQ R8, R8
+
+	// One comment line between instructions.
+	ADDQ R8, R8
+
+	// Comment before label.
+label:
+	// Comment after label.
+	ADDQ R8, R8
+	RET

tests/fmt/gen.go

@@ -0,0 +1,4 @@
+// Package fmt tests assembly printer formatting.
+package fmt
+
+//go:generate go run asm.go -out fmt.s -stubs stub.go