llvm: support building WA source file to an Arduino project

_examples/llvm/arduino_blink.wa

+# Test the llvm backend.
+# Make Arduino's builtin LED blinking.
+# `wa native --target=avr arduino_blink.wa`
+
+#wa:linkname __avr_write_port__
+fn write_port(p i16, v i8)
+
+# Delay a period of time
+var cnt i8
+fn delay(n i32) {
+  for i := i32(0); i < n; i++ {
+    cnt++
+  }
+}
+
+fn main() {
+  # Set Pin #5 (connected with the builtin LED) of Port B to output mode.
+  write_port(0x24, 0x20)
+  for b := 0; ; b++ {
+    if (b % 2) == 0 {
+      # Turn on the LED.
+      write_port(0x25, 0x20)
+    } else {
+      # Turn off the LED.
+      write_port(0x25, 0x00)
+    }
+    # Delay a period of time
+    delay(99999)
+  }
+}

internal/app/app.wa.go

@@ -331,6 +331,12 @@ func (p *App) LLVM(infile string, outfile string, target string, debug bool) err
 	if target != "" {
 		llc = append(llc, "-mtriple", target)
 	}
+	// Add target specific options.
+	switch target {
+	case "avr":
+		llc = append(llc, "-mcpu=atmega328")
+	default:
+	}
 	cmd0 := exec.Command(p.opt.Llc, llc...)
 	cmd0.Stderr = os.Stderr
 	if err := cmd0.Run(); err != nil {
@@ -338,6 +344,35 @@ func (p *App) LLVM(infile string, outfile string, target string, debug bool) err
 		return err
 	}
 
+	// TODO: This is a temporary solution for AVR-Arduino. We generate
+	// an Arduino project instead of an ELF.
+	if target == "avr" {
+		// Create a new directory for the output Arduino project.
+		ext, outdir := path.Ext(outfile), ""
+		if len(ext) > 0 {
+			pos := strings.Index(outfile, ext)
+			outdir = outfile[0:pos]
+		}
+		if err := os.RemoveAll(outdir); err != nil {
+			return err
+		}
+		if err := os.Mkdir(outdir, 0755); err != nil {
+			return err
+		}
+		// Move the assembly file to the project directory.
+		newAsmFile := strings.ReplaceAll(asmfile, ".s", ".S")
+		if err := os.Rename(asmfile, path.Join(outdir, newAsmFile)); err != nil {
+			return err
+		}
+		// Create the project main '.ino' file.
+		inoFile := path.Join(outdir, path.Base(outdir)+".ino")
+		inoStr := "void setup(void) {}\nextern \"C\" { extern void wa_main(void); }\nvoid loop(void) { wa_main(); }\n"
+		if err := os.WriteFile(inoFile, []byte(inoStr), 0644); err != nil {
+			return err
+		}
+		return nil
+	}
+
 	// Invoke command `clang xxx.s -o outfile --target=xxx`.
 	clangArgs := []string{asmfile, "-static", "-o", outfile}
 	if target != "" {

internal/backends/compiler_llvm/compile.go

@@ -56,7 +56,7 @@ func (p *Compiler) Compile(prog *loader.Program) (output string, err error) {
 	}
 
 	// Emit some auxiliary functions.
-	p.output.WriteString("define void @main() {\n")
+	p.output.WriteString("define void @wa_main() {\n")
 	p.output.WriteString("  call void @")
 	p.output.WriteString(getNormalName(prog.SSAMainPkg.Pkg.Path() + ".init()\n"))
 	p.output.WriteString("  call void @")
@@ -67,8 +67,22 @@ func (p *Compiler) Compile(prog *loader.Program) (output string, err error) {
 	// Emit some target specific functions.
 	switch getArch(p.target) {
 	case "", "x86_64", "aarch64":
+		p.output.WriteString("define void @main() {\n")
+		p.output.WriteString("  call void @wa_main()\n")
+		p.output.WriteString("  ret void\n")
+		p.output.WriteString("}\n\n")
 		p.output.WriteString("declare i32 @printf(i8* readonly, ...)\n")
 	case "avr":
+		p.output.WriteString("define void @__avr_write_port__(i16 %0, i8 zeroext %1) {\n")
+		p.output.WriteString("  %3 = inttoptr i16 %0 to i8*\n")
+		p.output.WriteString("  store volatile i8 %1, i8* %3, align 1\n")
+		p.output.WriteString("  ret void\n")
+		p.output.WriteString("}\n\n")
+		p.output.WriteString("define zeroext i8 @__avr_read_port__(i16 %0) {\n")
+		p.output.WriteString("  %2 = inttoptr i16 %0 to i8*\n")
+		p.output.WriteString("  %3 = load volatile i8, i8* %2, align 1\n")
+		p.output.WriteString("  ret i8 %3\n")
+		p.output.WriteString("}\n\n")
 	default:
 	}
 

internal/backends/compiler_llvm/compile_function.go

@@ -12,6 +12,10 @@ import (
 )
 
 func (p *Compiler) compileFunction(fn *ssa.Function) error {
+	if isTargetBuiltin(fn.LinkName(), p.target) || isTargetBuiltin(fn.Name(), p.target) {
+		return nil
+	}
+
 	// Translate return type.
 	var retTyStr string
 	rets := fn.Signature.Results()
@@ -47,10 +51,18 @@ func (p *Compiler) compileFunction(fn *ssa.Function) error {
 	}
 
 	// Emit a proper function name.
-	p.output.WriteString("define ")
+	if len(fn.Blocks) == 0 {
+		p.output.WriteString("declare ")
+	} else {
+		p.output.WriteString("define ")
+	}
 	p.output.WriteString(retTyStr)
 	p.output.WriteString(" @")
-	p.output.WriteString(getNormalName(fn.Pkg.Pkg.Path() + "." + fn.Name()))
+	if len(fn.LinkName()) > 0 {
+		p.output.WriteString(fn.LinkName())
+	} else {
+		p.output.WriteString(getNormalName(fn.Pkg.Pkg.Path() + "." + fn.Name()))
+	}
 	p.output.WriteString("(")
 
 	// Translate arguments.
@@ -70,7 +82,12 @@ func (p *Compiler) compileFunction(fn *ssa.Function) error {
 			p.output.WriteString(", ")
 		}
 	}
-	p.output.WriteString(") {\n")
+	if len(fn.Blocks) == 0 {
+		p.output.WriteString(")\n\n")
+		return nil
+	} else {
+		p.output.WriteString(") {\n")
+	}
 
 	// Translate Go SSA intermediate instructions.
 	for i, b := range fn.Blocks {

internal/backends/compiler_llvm/utils.go

@@ -303,6 +303,7 @@ func getNormalName(name string) string {
 	name = strings.ReplaceAll(name, ".", "__")
 	name = strings.ReplaceAll(name, "$", "__")
 	name = strings.ReplaceAll(name, "/", "__")
+	name = strings.ReplaceAll(name, "#", "__")
 	return name
 }
 
@@ -315,3 +316,24 @@ func getRealType(ty types.Type) types.Type {
 		}
 	}
 }
+
+func isTargetBuiltin(fn string, target string) bool {
+	avr := []string{"__avr_write_port__", "__avr_read_port__"}
+	other := []string{"printf"}
+	var ts []string
+
+	switch getArch(target) {
+	case "avr":
+		ts = avr
+	default:
+		ts = other
+	}
+
+	for _, v := range ts {
+		if v == fn {
+			return true
+		}
+	}
+
+	return false
+}