cmd/internal/obj/arm64: fix branch-too-far with TBZ like instructions

The compiler now emits TBZ like instructions, but the assembler's
too-far-branch patch code didn't include that case. Add it.

Fixes #23889.

Change-Id: Ib75f9250c660b9fb652835fbc83263a5d5073dc5
Reviewed-on: https://go-review.googlesource.com/94902
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

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

@@ -728,9 +728,16 @@ func span7(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 			o = c.oplook(p)
 
 			/* very large branches */
-			if (o.type_ == 7 || o.type_ == 39) && p.Pcond != nil { // 7: BEQ and like, 39: CBZ and like
+			if (o.type_ == 7 || o.type_ == 39 || o.type_ == 40) && p.Pcond != nil { // 7: BEQ and like, 39: CBZ and like, 40: TBZ and like
 				otxt := p.Pcond.Pc - pc
-				if otxt <= -(1<<18)+10 || otxt >= (1<<18)-10 {
+				var toofar bool
+				switch o.type_ {
+				case 7, 39: // branch instruction encodes 19 bits
+					toofar = otxt <= -(1<<20)+10 || otxt >= (1<<20)-10
+				case 40: // branch instruction encodes 14 bits
+					toofar = otxt <= -(1<<15)+10 || otxt >= (1<<15)-10
+				}
+				if toofar {
 					q := c.newprog()
 					q.Link = p.Link
 					p.Link = q

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

@@ -52,6 +52,7 @@ func TestLarge(t *testing.T) {
 // 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, "TBZ $5, R0, label")
 	fmt.Fprintln(buf, "CBZ R0, label")
 	fmt.Fprintln(buf, "BEQ label")
 	for i := 0; i < 1<<19; i++ {