Computed goto codegen is inconsistent on aarch64.

[fubark]

Zig Version

0.11.0-dev.1436+59d9afcb5

Steps to Reproduce and Observed Behavior

On compiler explorer with the args -O ReleaseFast -target aarch64-macos.12-none

extern fn foo() void;
extern fn foo2() void;
extern fn foo3() void;

const Op = enum {
 add,
 sub,
 mul,
 ret,
};

export fn eval(insts: [*]const u8) void {
 var pc: usize = 0;
 while (true) {
 switch (@intToEnum(Op, insts[pc])) {
 .add => {
 foo();
 pc += 1;
 continue;
 },
 .sub => {
 foo2();
 pc += 2;
 continue;
 },
 .mul => {
 foo3();
 pc += 3;
 continue;
 },
 .ret => {
 return;
 },
 }
 }
}

Generates the following:

_eval:
 stp x22, x21, [sp, #-48]!
 stp x20, x19, [sp, #16]
 stp x29, x30, [sp, #32]
 mov x19, x0
 mov x20, xzr
 adrp x21, LJTI0_0@PAGE
 add x21, x21, LJTI0_0@PAGEOFF
 b LBB0_2
LBB0_1:
 bl _foo3
 mov w8, #3
 add x20, x20, x8
LBB0_2:
 ldrb w8, [x19, x20]
 and x8, x8, #0x3
 adr x9, LBB0_1
 ldrb w10, [x21, x8]
 add x9, x9, x10, lsl #2
 br x9
LBB0_3:
 bl _foo
 mov w8, #1
 add x20, x20, x8
 b LBB0_2
LBB0_4:
 bl _foo2
 mov w8, #2
 add x20, x20, x8
 b LBB0_2
LBB0_5:
 ldp x29, x30, [sp, #32]
 ldp x20, x19, [sp, #16]
 ldp x22, x21, [sp], #48
 ret
LJTI0_0:
 .byte (LBB0_3-LBB0_1)>>2
 .byte (LBB0_4-LBB0_1)>>2
 .byte (LBB0_1-LBB0_1)>>2
 .byte (LBB0_5-LBB0_1)>>2

Expected Behavior

I expected the codegen to be similar to x86_64 which inlines the jump to the next switch case. Instead on aarch64, it does an indirect jump first and then does the table lookup. Here is the x86_64 output for comparison:

eval:
 push r14
 push rbx
 push rax
 mov r14, rdi
 xor ebx, ebx
 movzx eax, byte ptr [rdi + rbx]
 and eax, 3
 jmp qword ptr [8*rax + .LJTI0_0]
.LBB0_1:
 call foo@PLT
 mov eax, 1
 add rbx, rax
 movzx eax, byte ptr [r14 + rbx]
 and eax, 3
 jmp qword ptr [8*rax + .LJTI0_0]
.LBB0_2:
 call foo2@PLT
 mov eax, 2
 add rbx, rax
 movzx eax, byte ptr [r14 + rbx]
 and eax, 3
 jmp qword ptr [8*rax + .LJTI0_0]
.LBB0_3:
 call foo3@PLT
 mov eax, 3
 add rbx, rax
 movzx eax, byte ptr [r14 + rbx]
 and eax, 3
 jmp qword ptr [8*rax + .LJTI0_0]
.LBB0_4:
 add rsp, 8
 pop rbx
 pop r14
 ret
.LJTI0_0:
 .quad .LBB0_1
 .quad .LBB0_2
 .quad .LBB0_3
 .quad .LBB0_4

[ifreund]

Related: #8220

[xdBronch]

looks like #21257 fixed this
https://godbolt.org/z/31EGc8sz9