compiler: Merge the runtime into the Go code, for better code size

Makefile

@@ -12,11 +12,14 @@ LLC = $(LLVM)llc
 
 CFLAGS = -Wall -Werror -Os -g -fno-exceptions -flto -ffunction-sections -fdata-sections $(LLFLAGS)
 
-RUNTIME = build/runtime.bc
+RUNTIME_PARTS = build/runtime.bc
+
+TARGET ?= unix
 
 ifeq ($(TARGET),pca10040)
 GCC = arm-none-eabi-gcc
 LD = arm-none-eabi-ld -T arm.ld
+SIZE = arm-none-eabi-size
 OBJCOPY = arm-none-eabi-objcopy
 LLFLAGS += -target armv7m-none-eabi
 TGOFLAGS += -target $(TARGET)
@@ -26,17 +29,21 @@ CFLAGS += -I$(CURDIR)/lib/nrfx/mdk
 CFLAGS += -I$(CURDIR)/lib/CMSIS/CMSIS/Include
 CFLAGS += -DNRF52832_XXAA
 CFLAGS += -Wno-uninitialized
-RUNTIME += build/runtime_nrf.bc
-RUNTIME += build/system_nrf52.bc
+RUNTIME_PARTS += build/runtime_nrf.bc
+RUNTIME_PARTS += build/system_nrf52.bc
 OBJ += build/startup_nrf51.o # TODO nrf52, see https://bugs.llvm.org/show_bug.cgi?id=31601
 
-else
+else ifeq ($(TARGET),unix)
 # Regular *nix system.
 GCC = gcc
 LD = clang
+SIZE = size
 endif
 
 
+# Make debugging easier by keeping these intermediary files.
+SECONDARY: build/hello.ll build/blinky.ll build/blinky.elf
+
 
 run-hello: build/hello
 	./build/hello
@@ -58,8 +65,8 @@ build/tgo: *.go
 	go build -o build/tgo -i .
 
 # Build textual IR with the Go compiler.
-build/%.ll: src/examples/% src/examples/%/*.go build/tgo src/runtime/*.go
-	./build/tgo $(TGOFLAGS) -printir -o $@ $(subst src/,,$<)
+build/%.o: src/examples/% src/examples/%/*.go build/tgo src/runtime/*.go build/runtime-$(TARGET)-combined.bc
+	./build/tgo $(TGOFLAGS) -printir -runtime build/runtime-$(TARGET)-combined.bc -o $@ $(subst src/,,$<)
 
 # Compile C sources for the runtime.
 build/%.bc: src/runtime/%.c src/runtime/*.h
@@ -76,14 +83,10 @@ build/%.o: lib/nrfx/mdk/gcc_%.S
 	@mkdir -p build
 	clang $(CFLAGS) -c -o $@ $^
 
-# Merge all LLVM files together in a single bitcode file.
-build/%.bc: $(RUNTIME) build/%.ll
+# Merge all runtime LLVM files together in a single bitcode file.
+build/runtime-$(TARGET)-combined.bc: $(RUNTIME_PARTS)
 	$(LINK) -o $@ $^
 
-# Generate an ELF object file from a LLVM bitcode file.
-build/%.o: build/%.bc
-	$(LLC) -filetype=obj -O2 -o $@ $^
-
 # Generate output ELF executable.
 build/%: build/%.o $(OBJ)
 	$(LD) -o $@ $^
@@ -91,6 +94,7 @@ build/%: build/%.o $(OBJ)
 # Generate output ELF for use in objcopy (on a microcontroller).
 build/%.elf: build/%.o $(OBJ)
 	$(LD) -o $@ $^
+	$(SIZE) $@
 
 # Convert executable to Intel hex file (for flashing).
 build/%.hex: build/%.elf

src/runtime/runtime.c

@@ -1,15 +1,19 @@
 
 #include "runtime.h"
+#include <string.h>
 
 void go_main() __asm__("main.main");
 
-void __go_runtime_main() {
-	go_main();
-}
-
-__attribute__((weak))
 int main() {
-	__go_runtime_main();
+	go_main();
 
 	return 0;
 }
+
+__attribute__((weak))
+void * memset(void *s, int c, size_t n) {
+	for (size_t i = 0; i < n; i++) {
+		((uint8_t*)s)[i] = c;
+	}
+	return s;
+}

src/runtime/runtime_nrf.c

@@ -2,6 +2,7 @@
 #include "hal/nrf_uart.h"
 #include "nrf.h"
 #include "runtime.h"
+#include <string.h>
 
 void uart_init(uint32_t pin_tx) {
 	NRF_UART0->ENABLE        = UART_ENABLE_ENABLE_Enabled;
@@ -30,9 +31,7 @@ __attribute__((weak))
 void __aeabi_memclr(uint8_t *dest, size_t n) {
 	// TODO: link with compiler-rt for a better implementation.
 	// For now, use a simple memory zeroer.
-	for (size_t i = 0; i < n; i++) {
-		dest[i] = 0;
-	}
+	memset(dest, 0, n);
 }
 
 __attribute__((weak))

tgo.go

@@ -1033,6 +1033,10 @@ func (c *Compiler) Verify() error {
 	return llvm.VerifyModule(c.mod, 0)
 }
 
+func (c *Compiler) LinkModule(mod llvm.Module) error {
+	return llvm.LinkModules(c.mod, mod)
+}
+
 func (c *Compiler) Optimize(optLevel, sizeLevel int) {
 	builder := llvm.NewPassManagerBuilder()
 	defer builder.Dispose()
@@ -1079,7 +1083,7 @@ func (c *Compiler) EmitObject(path string) error {
 }
 
 // Helper function for Compiler object.
-func Compile(pkgName, outpath, target string, printIR bool) error {
+func Compile(pkgName, runtimePath, outpath, target string, printIR bool) error {
 	var buildTags []string
 	// TODO: put this somewhere else
 	if target == "pca10040" {
@@ -1100,6 +1104,16 @@ func Compile(pkgName, outpath, target string, printIR bool) error {
 		return parseErr
 	}
 
+	// Add C runtime.
+	runtime, err := llvm.ParseBitcodeFile(runtimePath)
+	if err != nil {
+		return err
+	}
+	err = c.LinkModule(runtime)
+	if err != nil {
+		return err
+	}
+
 	if err := c.Verify(); err != nil {
 		return err
 	}
@@ -1119,20 +1133,21 @@ func Compile(pkgName, outpath, target string, printIR bool) error {
 
 func main() {
 	outpath := flag.String("o", "", "output filename")
-	target := flag.String("target", llvm.DefaultTargetTriple(), "LLVM target")
 	printIR := flag.Bool("printir", false, "print LLVM IR after optimizing")
+	runtime := flag.String("runtime", "", "runtime LLVM bitcode files (from C sources)")
+	target := flag.String("target", llvm.DefaultTargetTriple(), "LLVM target")
 
 	flag.Parse()
 
 	if *outpath == "" || flag.NArg() != 1 {
-		fmt.Fprintf(os.Stderr, "usage: %s [-printir] [-target=<target>] -o <output> <input>", os.Args[0])
+		fmt.Fprintf(os.Stderr, "usage: %s [-printir] -runtime=<runtime.bc> [-target=<target>] -o <output> <input>", os.Args[0])
 		flag.PrintDefaults()
 		return
 	}
 
 	os.Setenv("CC", "clang -target=" + *target)
 
-	err := Compile(flag.Args()[0], *outpath, *target, *printIR)
+	err := Compile(flag.Args()[0], *runtime, *outpath, *target, *printIR)
 	if err != nil {
 		fmt.Fprintln(os.Stderr, "error:", err)
 		os.Exit(1)