all: move bootstrapping IR to Go runtime

This has the benefit of not requiring a 'runtime' IR file, so that
complete relocatable files can be built without requiring input IR.
This makes the compiler a lot easier to use without the Makefile.

Code size is not affected.

compiler.go

@@ -348,10 +348,6 @@ func (c *Compiler) Parse(mainPath string, buildTags []string) error {
 	// After all packages are imported, add a synthetic initializer function
 	// that calls the initializer of each package.
 	initFn := c.mod.NamedFunction("runtime.initAll")
-	if initFn.IsNil() {
-		initType := llvm.FunctionType(llvm.VoidType(), nil, false)
-		initFn = llvm.AddFunction(c.mod, "runtime.initAll", initType)
-	}
 	initFn.SetLinkage(llvm.InternalLinkage)
 	block := c.ctx.AddBasicBlock(initFn, "entry")
 	c.builder.SetInsertPointAtEnd(block)
@@ -363,19 +359,18 @@ func (c *Compiler) Parse(mainPath string, buildTags []string) error {
 	// Adjust main function.
 	realMain := c.mod.NamedFunction(c.ir.mainPkg.Pkg.Path() + ".main")
 	if c.ir.NeedsScheduler() {
-		c.mod.NamedFunction("main.main$async").ReplaceAllUsesWith(realMain)
+		c.mod.NamedFunction("runtime.main_mainAsync").ReplaceAllUsesWith(realMain)
 	} else {
-		c.mod.NamedFunction("main.main").ReplaceAllUsesWith(realMain)
+		c.mod.NamedFunction("runtime.main_main").ReplaceAllUsesWith(realMain)
 	}
 
-	// Set functions referenced in runtime.ll to internal linkage, to improve
-	// optimization (hopefully).
-	c.mod.NamedFunction("runtime.scheduler").SetLinkage(llvm.InternalLinkage)
-
 	// Only use a scheduler when necessary.
 	if c.ir.NeedsScheduler() {
 		// Enable the scheduler.
-		c.mod.NamedGlobal("has_scheduler").SetInitializer(llvm.ConstInt(llvm.Int1Type(), 1, false))
+		hasScheduler := c.mod.NamedGlobal("runtime.hasScheduler")
+		hasScheduler.SetInitializer(llvm.ConstInt(llvm.Int1Type(), 1, false))
+		hasScheduler.SetGlobalConstant(true)
+		hasScheduler.SetUnnamedAddr(true)
 	}
 
 	// Initialize runtime type information, for interfaces.
@@ -1104,7 +1099,9 @@ func (c *Compiler) parseFunc(frame *Frame) error {
 	if c.dumpSSA {
 		fmt.Printf("\nfunc %s:\n", frame.fn.fn)
 	}
-	frame.fn.llvmFn.SetLinkage(llvm.InternalLinkage)
+	if !frame.fn.IsExported() {
+		frame.fn.llvmFn.SetLinkage(llvm.InternalLinkage)
+	}
 
 	// Pre-create all basic blocks in the function.
 	for _, block := range frame.fn.fn.DomPreorder() {

ir.go

@@ -35,7 +35,8 @@ type Program struct {
 type Function struct {
 	fn           *ssa.Function
 	llvmFn       llvm.Value
-	linkName     string      // go:linkname pragma
+	linkName     string      // go:linkname or go:export pragma
+	exported     bool        // go:export
 	nobounds     bool        // go:nobounds pragma
 	blocking     bool        // calculated by AnalyseBlockingRecursive
 	flag         bool        // used by dead code elimination
@@ -178,11 +179,22 @@ func (f *Function) parsePragmas() {
 				if hasUnsafeImport(f.fn.Pkg.Pkg) {
 					f.nobounds = true
 				}
+			case "//go:export":
+				if len(parts) != 2 {
+					continue
+				}
+				f.linkName = parts[1]
+				f.exported = true
 			}
 		}
 	}
 }
 
+// Return true iff this function is externally visible.
+func (f *Function) IsExported() bool {
+	return f.exported
+}
+
 // Return the link name for this function.
 func (f *Function) LinkName() string {
 	if f.linkName != "" {

main.go

@@ -30,13 +30,15 @@ func Compile(pkgName, runtimePath, outpath, target string, printIR, dumpSSA bool
 	}
 
 	// Add C/LLVM runtime.
-	runtime, err := llvm.ParseBitcodeFile(runtimePath)
-	if err != nil {
-		return err
-	}
-	err = c.LinkModule(runtime)
-	if err != nil {
-		return err
+	if runtimePath != "" {
+		runtime, err := llvm.ParseBitcodeFile(runtimePath)
+		if err != nil {
+			return err
+		}
+		err = c.LinkModule(runtime)
+		if err != nil {
+			return err
+		}
 	}
 
 	// Compile Go code to IR.

src/runtime/runtime.go

@@ -6,6 +6,39 @@ import (
 
 const Compiler = "tgo"
 
+// The compiler will fill this with calls to the initialization function of each
+// package.
+func initAll()
+
+// These signatures are used to call the correct main function: with scheduling
+// or without scheduling.
+func main_main()
+func main_mainAsync(parent *coroutine) *coroutine
+
+// The compiler will change this to true if there are 'go' statements in the
+// compiled program and turn it into a const.
+var hasScheduler bool
+
+// Entry point for Go. Initialize all packages and call main.main().
+//go:export main
+func main() int {
+	// Run initializers of all packages.
+	initAll()
+
+	// This branch must be optimized away. Only one of the targets must remain,
+	// or there will be link errors.
+	if hasScheduler {
+		// Initialize main and run the scheduler.
+		coro := main_mainAsync(nil)
+		scheduler(coro)
+		return 0
+	} else {
+		// No scheduler is necessary. Call main directly.
+		main_main()
+		return 0
+	}
+}
+
 func Sleep(d Duration) {
 	// This function is treated specially by the compiler: when goroutines are
 	// used, it is transformed into a llvm.coro.suspend() call.

src/runtime/runtime.ll

@@ -1,27 +1,3 @@
 source_filename = "runtime/runtime.ll"
 
-declare void @runtime.initAll()
-declare void @main.main()
-declare i8* @main.main$async(i8*)
-declare void @runtime.scheduler(i8*)
-
-; Will be changed to true if there are 'go' statements in the compiled program.
-@has_scheduler = private unnamed_addr constant i1 false
-
-define i32 @main() {
-    call void @runtime.initAll()
-    %has_scheduler = load i1, i1* @has_scheduler
-    ; This branch will be optimized away. Only one of the targets will remain.
-    br i1 %has_scheduler, label %with_scheduler, label %without_scheduler
-
-with_scheduler:
-    ; Initialize main and run the scheduler.
-    %main = call i8* @main.main$async(i8* null)
-    call void @runtime.scheduler(i8* %main)
-    ret i32 0
-
-without_scheduler:
-    ; No scheduler is necessary. Call main directly.
-    call void @main.main()
-    ret i32 0
-}
+; dummy file

src/runtime/runtime_nrf.c

@@ -29,10 +29,6 @@ void RTC0_IRQHandler() {
 	rtc_wakeup = true;
 }
 
-void _start() {
-	main();
-}
-
 __attribute__((weak))
 void __aeabi_unwind_cpp_pr0() {
 	// dummy, not actually used

src/runtime/runtime_nrf.go

@@ -11,6 +11,11 @@ func _Cfunc_rtc_sleep(ticks uint32)
 
 const Microsecond = 1
 
+//go:export _start
+func _start() {
+	main()
+}
+
 func init() {
 	initUART()
 	initLFCLK()