cmd/internal/obj/arm64: fix branch too far for CBZ (and like)

The assembler backend fixes too-far conditional branches, but only
for BEQ and like. Add a case for CBZ and like.

Fixes #17925.

Change-Id: Ie516e6c5ca165b582367283a0110f7081e00c214
Reviewed-on: https://go-review.googlesource.com/33304
Run-TryBot: Cherry Zhang <cherryyz@google.com>
Reviewed-by: David Chase <drchase@google.com>

src/cmd/internal/obj/arm64/asm7.go

@@ -601,7 +601,7 @@ func span7(ctxt *obj.Link, cursym *obj.LSym) {
 			o = oplook(ctxt, p)
 
 			/* very large branches */
-			if o.type_ == 7 && p.Pcond != nil {
+			if (o.type_ == 7 || o.type_ == 39) && p.Pcond != nil { // 7: BEQ and like, 39: CBZ and like
 				otxt := p.Pcond.Pc - c
 				if otxt <= -(1<<18)+10 || otxt >= (1<<18)-10 {
 					q := ctxt.NewProg()

src/cmd/internal/obj/arm64/asm_test.go

@@ -0,0 +1,62 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package arm64
+
+import (
+	"bytes"
+	"fmt"
+	"internal/testenv"
+	"io/ioutil"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"testing"
+)
+
+// TestLarge generates a very large file to verify that large
+// program builds successfully, in particular, too-far
+// conditional branches are fixed.
+func TestLarge(t *testing.T) {
+	if testing.Short() {
+		t.Skip("Skip in short mode")
+	}
+	testenv.MustHaveGoBuild(t)
+
+	dir, err := ioutil.TempDir("", "testlarge")
+	if err != nil {
+		t.Fatalf("could not create directory: %v", err)
+	}
+	defer os.RemoveAll(dir)
+
+	// generate a very large function
+	buf := bytes.NewBuffer(make([]byte, 0, 7000000))
+	gen(buf)
+
+	tmpfile := filepath.Join(dir, "x.s")
+	err = ioutil.WriteFile(tmpfile, buf.Bytes(), 0644)
+	if err != nil {
+		t.Fatalf("can't write output: %v\n", err)
+	}
+
+	// build generated file
+	cmd := exec.Command(testenv.GoToolPath(t), "tool", "asm", "-o", filepath.Join(dir, "x.o"), tmpfile)
+	cmd.Env = []string{"GOARCH=arm64", "GOOS=linux"}
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Errorf("Build failed: %v, output: %s", err, out)
+	}
+}
+
+// gen generates a very large program, with a very far conditional branch.
+func gen(buf *bytes.Buffer) {
+	fmt.Fprintln(buf, "TEXT f(SB),0,$0-0")
+	fmt.Fprintln(buf, "CBZ R0, label")
+	fmt.Fprintln(buf, "BEQ label")
+	for i := 0; i < 1<<19; i++ {
+		fmt.Fprintln(buf, "MOVD R0, R1")
+	}
+	fmt.Fprintln(buf, "label:")
+	fmt.Fprintln(buf, "RET")
+}