codegen quality: std.MultiArrayList(TaggedUnion).get code size increases with field count

[Techatrix]

The implementation of std.MultiArrayList uses an inline else to construct a tagged union from the tag and data which leads to bad code generation in all release modes.

https://godbolt.org/z/7Kxz9q8fG

Show Code

const std = @import("std");

export fn foo(
    list_opaque: *align(@alignOf(std.MultiArrayList(Unwrapped)))std.MultiArrayList(Unwrapped),
) void {
    var list: *std.MultiArrayList(Unwrapped) = @ptrCast(list_opaque);
    std.mem.doNotOptimizeAway(list.get(0));
}

const Tag = std.meta.Tag(Unwrapped);
const Data = @Type(.{
    .@"union" = .{
        .layout = .auto,
        .tag_type = null,
        .fields = std.meta.fields(Unwrapped),
        .decls = &.{},
    },
});

pub const Unwrapped = union(enum) {
    root,
    @"usingnamespace": u32,
    test_decl: extern struct { name_token: u32, block: u32 },
    global_var_decl: extern struct { extra: u32, init: u32 },
    local_var_decl: extern struct { extra: u32, init: u32 },
    simple_var_decl: extern struct { ty: u32, init: u32 },
    aligned_var_decl: extern struct { alignment: u32, init: u32 },
    @"errdefer": extern struct { payload: u32, expr: u32 },
    @"defer": u32,
    @"catch": extern struct { lhs: u32, rhs: u32 },
    field_access: extern struct { lhs: u32, field_name: u32 },
    unwrap_optional: extern struct { lhs: u32, question_mark: u32 },
    equal_equal: extern struct { lhs: u32, rhs: u32 },
    bang_equal: extern struct { lhs: u32, rhs: u32 },
    less_than: extern struct { lhs: u32, rhs: u32 },
    greater_than: extern struct { lhs: u32, rhs: u32 },
    less_or_equal: extern struct { lhs: u32, rhs: u32 },
    greater_or_equal: extern struct { lhs: u32, rhs: u32 },
    assign_mul: extern struct { lhs: u32, rhs: u32 },
    assign_div: extern struct { lhs: u32, rhs: u32 },
    assign_mod: extern struct { lhs: u32, rhs: u32 },
    assign_add: extern struct { lhs: u32, rhs: u32 },
    assign_sub: extern struct { lhs: u32, rhs: u32 },
    assign_shl: extern struct { lhs: u32, rhs: u32 },
    assign_shl_sat: extern struct { lhs: u32, rhs: u32 },
    assign_shr: extern struct { lhs: u32, rhs: u32 },
    assign_bit_and: extern struct { lhs: u32, rhs: u32 },
    assign_bit_xor: extern struct { lhs: u32, rhs: u32 },
    assign_bit_or: extern struct { lhs: u32, rhs: u32 },
    assign_mul_wrap: extern struct { lhs: u32, rhs: u32 },
    assign_add_wrap: extern struct { lhs: u32, rhs: u32 },
    assign_sub_wrap: extern struct { lhs: u32, rhs: u32 },
    assign_mul_sat: extern struct { lhs: u32, rhs: u32 },
    assign_add_sat: extern struct { lhs: u32, rhs: u32 },
    assign_sub_sat: extern struct { lhs: u32, rhs: u32 },
    assign: extern struct { lhs: u32, rhs: u32 },
    assign_destructure: extern struct { extra: u32, init: u32 },
    merge_error_sets: extern struct { lhs: u32, rhs: u32 },
    mul: extern struct { lhs: u32, rhs: u32 },
    div: extern struct { lhs: u32, rhs: u32 },
    mod: extern struct { lhs: u32, rhs: u32 },
    array_mult: extern struct { lhs: u32, rhs: u32 },
    mul_wrap: extern struct { lhs: u32, rhs: u32 },
    mul_sat: extern struct { lhs: u32, rhs: u32 },
    add: extern struct { lhs: u32, rhs: u32 },
    sub: extern struct { lhs: u32, rhs: u32 },
    array_cat: extern struct { lhs: u32, rhs: u32 },
    add_wrap: extern struct { lhs: u32, rhs: u32 },
    sub_wrap: extern struct { lhs: u32, rhs: u32 },
    add_sat: extern struct { lhs: u32, rhs: u32 },
    sub_sat: extern struct { lhs: u32, rhs: u32 },
    shl: extern struct { lhs: u32, rhs: u32 },
    shl_sat: extern struct { lhs: u32, rhs: u32 },
    shr: extern struct { lhs: u32, rhs: u32 },
    bit_and: extern struct { lhs: u32, rhs: u32 },
    bit_xor: extern struct { lhs: u32, rhs: u32 },
    bit_or: extern struct { lhs: u32, rhs: u32 },
    @"orelse": extern struct { lhs: u32, rhs: u32 },
    bool_and: extern struct { lhs: u32, rhs: u32 },
    bool_or: extern struct { lhs: u32, rhs: u32 },
    bool_not: u32,
    negation: u32,
    bit_not: u32,
    negation_wrap: u32,
    address_of: u32,
    @"try": u32,
    @"await": u32,
    optional_type: u32,
    array_type: extern struct { lhs: u32, rhs: u32 },
    array_type_sentinel,
    ptr_type_aligned: extern struct { alignment: u32, elem_type: u32 },
    ptr_type_sentinel: extern struct { sentinel: u32, elem_type: u32 },
    ptr_type: extern struct { extra: u32, elem_type: u32 },
    ptr_type_bit_range: extern struct { extra: u32, elem_type: u32 },
    slice_open: extern struct { lhs: u32, rhs: u32 },
    slice: extern struct { lhs: u32, extra: u32 },
    slice_sentinel: extern struct { lhs: u32, extra: u32 },
    deref: u32,
    array_access: extern struct { lhs: u32, rhs: u32 },
    array_init_one: extern struct { lhs: u32, rhs: u32 },
    array_init_one_comma: extern struct { lhs: u32, rhs: u32 },
    array_init_dot_two: [2]u32,
    array_init_dot_two_comma: [2]u32,
    array_init_dot: extern struct { start: u32, end: u32 },
    array_init_dot_comma: extern struct { start: u32, end: u32 },
    array_init: extern struct { lhs: u32, extra: u32 },
    array_init_comma: extern struct { lhs: u32, extra: u32 },
    struct_init_one: extern struct { lhs: u32, first_field_init: u32 },
    struct_init_one_comma: extern struct { lhs: u32, first_field_init: u32 },
    struct_init_dot_two: [2]u32,
    struct_init_dot_two_comma: [2]u32,
    struct_init_dot: extern struct { start: u32, end: u32 },
    struct_init_dot_comma: extern struct { start: u32, end: u32 },
    struct_init: extern struct { lhs: u32, extra: u32 },
    struct_init_comma: extern struct { lhs: u32, extra: u32 },
    call_one: extern struct { lhs: u32, first_arg: u32 },
    call_one_comma: extern struct { lhs: u32, first_arg: u32 },
    async_call_one: extern struct { lhs: u32, first_arg: u32 },
    async_call_one_comma: extern struct { lhs: u32, first_arg: u32 },
    call: extern struct { lhs: u32, extra: u32 },
    call_comma: extern struct { lhs: u32, extra: u32 },
    async_call: extern struct { lhs: u32, extra: u32 },
    async_call_comma: extern struct { lhs: u32, extra: u32 },
    @"switch": extern struct { lhs: u32, extra: u32 },
    switch_comma: extern struct { lhs: u32, extra: u32 },
    switch_case_one: extern struct { lhs: u32, rhs: u32 },
    switch_case_inline_one: extern struct { lhs: u32, rhs: u32 },
    switch_case: extern struct { extra: u32, rhs: u32 },
    switch_case_inline: extern struct { extra: u32, rhs: u32 },
    switch_range: extern struct { lhs: u32, rhs: u32 },
    while_simple: extern struct { lhs: u32, rhs: u32 },
    while_cont: extern struct { lhs: u32, extra: u32 },
    @"while": extern struct { lhs: u32, rhs: u32 },
    for_simple: extern struct { lhs: u32, rhs: u32 },
    @"for": extern struct { lhs: u32, data: u32 },
    for_range: extern struct { lhs: u32, rhs: u32 },
    if_simple: extern struct { lhs: u32, rhs: u32 },
    @"if": extern struct { lhs: u32, rhs: u32 },
    @"suspend": u32,
    @"resume": u32,
    @"continue": extern struct { label: u32, expr: u32 },
    @"break": extern struct { label: u32, expr: u32 },
    @"return": u32,
    fn_proto_simple: extern struct { first_param_ty: u32, return_type: u32 },
    fn_proto_multi: extern struct { extra: u32, return_type: u32 },
    fn_proto_one: extern struct { extra: u32, return_type: u32 },
    fn_proto: extern struct { extra: u32, return_type: u32 },
    fn_decl: extern struct { fn_prot: u32, body: u32 },
    anyframe_type: extern struct { right_arrow: u32, elem_ty: u32 },
    anyframe_literal,
    char_literal,
    number_literal,
    unreachable_literal,
    identifier,
    enum_literal: u32,
    string_literal,
    multiline_string_literal: extern struct { start: u32, end: u32 },
    grouped_expression: extern struct { expr: u32, r_paren: u32 },
    builtin_call_two: [2]u32,
    builtin_call_two_comma: [2]u32,
    builtin_call: extern struct { start: u32, end: u32 },
    builtin_call_comma: extern struct { start: u32, end: u32 },
    error_set_decl: u32,
    container_decl: extern struct { start: u32, end: u32 },
    container_decl_trailing: extern struct { start: u32, end: u32 },
    container_decl_two: [2]u32,
    container_decl_two_trailing: [2]u32,
    container_decl_arg: extern struct { lhs: u32, extra: u32 },
    container_decl_arg_trailing: extern struct { lhs: u32, extra: u32 },
    tagged_union: extern struct { start: u32, end: u32 },
    tagged_union_trailing: extern struct { start: u32, end: u32 },
    tagged_union_two: [2]u32,
    tagged_union_two_trailing: [2]u32,
    tagged_union_enum_tag: extern struct { lhs: u32, extra: u32 },
    tagged_union_enum_tag_trailing: extern struct { lhs: u32, extra: u32 },
    container_field_init: extern struct { ty: u32, default_init: u32 },
    container_field_align: extern struct { ty: u32, alignment: u32 },
    container_field: extern struct { ty: u32, extra: u32 },
    @"comptime": u32,
    @"nosuspend": u32,
    block_two: [2]u32,
    block_two_semicolon: [2]u32,
    block: extern struct { start: u32, end: u32 },
    block_semicolon: extern struct { start: u32, end: u32 },
    asm_simple: extern struct { lhs: u32, r_paren: u32 },
    @"asm": extern struct { lhs: u32, extra: u32 },
    asm_output: extern struct { lhs: u32, r_paren: u32 },
    asm_input: extern struct { lhs: u32, r_paren: u32 },
    error_value: extern struct { error_token: u32, name: u32 },
    error_union: extern struct { lhs: u32, rhs: u32 },
};

Show Disassembly

$ zig version
0.14.0-dev.2940+d0d5ca2b6
$ zig build-obj foo.zig -OReleaseFast
$ objdump -d foo.o
foo.o:     file format elf64-x86-64

Disassembly of section .text:

0000000000000000 <foo>:
   0:   55                      push   %rbp
   1:   48 89 e5                mov    %rsp,%rbp
   4:   48 8b 07                mov    (%rdi),%rax
   7:   48 8b 4f 10             mov    0x10(%rdi),%rcx
   b:   48 8d 14 c8             lea    (%rax,%rcx,8),%rdx
   f:   48 85 c9                test   %rcx,%rcx
  12:   48 b9 aa aa aa aa aa    movabs $0xaaaaaaaaaaaaaaaa,%rcx
  19:   aa aa aa 
  1c:   48 0f 44 d1             cmove  %rcx,%rdx
  20:   0f b6 12                movzbl (%rdx),%edx
  23:   48 0f 44 c1             cmove  %rcx,%rax
  27:   48 8b 00                mov    (%rax),%rax
  2a:   ff 24 d5 00 00 00 00    jmp    *0x0(,%rdx,8)
  31:   b8 00 00 00 00          mov    $0x0,%eax
  36:   e9 49 08 00 00          jmp    884 <foo+0x884>
  3b:   48 89 45 f0             mov    %rax,-0x10(%rbp)
  3f:   c6 45 f8 03             movb   $0x3,-0x8(%rbp)
  43:   e9 38 08 00 00          jmp    880 <foo+0x880>
  48:   48 89 45 f0             mov    %rax,-0x10(%rbp)
  4c:   c6 45 f8 26             movb   $0x26,-0x8(%rbp)
  50:   e9 2b 08 00 00          jmp    880 <foo+0x880>
  55:   48 89 45 f0             mov    %rax,-0x10(%rbp)
  59:   c6 45 f8 2e             movb   $0x2e,-0x8(%rbp)
  5d:   e9 1e 08 00 00          jmp    880 <foo+0x880>
  62:   48 89 45 f0             mov    %rax,-0x10(%rbp)
  66:   c6 45 f8 0c             movb   $0xc,-0x8(%rbp)
  6a:   e9 11 08 00 00          jmp    880 <foo+0x880>
  6f:   48 89 45 f0             mov    %rax,-0x10(%rbp)
  73:   c6 45 f8 25             movb   $0x25,-0x8(%rbp)
  77:   e9 04 08 00 00          jmp    880 <foo+0x880>
  7c:   48 89 45 f0             mov    %rax,-0x10(%rbp)
  80:   c6 45 f8 14             movb   $0x14,-0x8(%rbp)
  84:   e9 f7 07 00 00          jmp    880 <foo+0x880>
  89:   48 89 45 f0             mov    %rax,-0x10(%rbp)
  8d:   c6 45 f8 16             movb   $0x16,-0x8(%rbp)
  91:   e9 ea 07 00 00          jmp    880 <foo+0x880>
  96:   48 89 45 f0             mov    %rax,-0x10(%rbp)
  9a:   c6 45 f8 3b             movb   $0x3b,-0x8(%rbp)
  9e:   e9 dd 07 00 00          jmp    880 <foo+0x880>
  a3:   48 89 45 f0             mov    %rax,-0x10(%rbp)
  a7:   c6 45 f8 1f             movb   $0x1f,-0x8(%rbp)
  ab:   e9 d0 07 00 00          jmp    880 <foo+0x880>
  b0:   48 89 45 f0             mov    %rax,-0x10(%rbp)
  b4:   c6 45 f8 2f             movb   $0x2f,-0x8(%rbp)
  b8:   e9 c3 07 00 00          jmp    880 <foo+0x880>
  bd:   48 89 45 f0             mov    %rax,-0x10(%rbp)
  c1:   c6 45 f8 55             movb   $0x55,-0x8(%rbp)
  c5:   e9 b6 07 00 00          jmp    880 <foo+0x880>
  ca:   48 89 45 f0             mov    %rax,-0x10(%rbp)
  ce:   c6 45 f8 09             movb   $0x9,-0x8(%rbp)
  d2:   e9 a9 07 00 00          jmp    880 <foo+0x880>
  d7:   89 45 f0                mov    %eax,-0x10(%rbp)
  da:   c6 45 f8 3c             movb   $0x3c,-0x8(%rbp)
  de:   e9 9d 07 00 00          jmp    880 <foo+0x880>
  e3:   48 89 45 f0             mov    %rax,-0x10(%rbp)
  e7:   c6 45 f8 20             movb   $0x20,-0x8(%rbp)
  eb:   e9 90 07 00 00          jmp    880 <foo+0x880>
  f0:   48 89 45 f0             mov    %rax,-0x10(%rbp)
  f4:   c6 45 f8 02             movb   $0x2,-0x8(%rbp)
  f8:   e9 83 07 00 00          jmp    880 <foo+0x880>
  fd:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 101:   c6 45 f8 56             movb   $0x56,-0x8(%rbp)
 105:   e9 76 07 00 00          jmp    880 <foo+0x880>
 10a:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 10e:   c6 45 f8 4e             movb   $0x4e,-0x8(%rbp)
 112:   e9 69 07 00 00          jmp    880 <foo+0x880>
 117:   89 45 f0                mov    %eax,-0x10(%rbp)
 11a:   c6 45 f8 3f             movb   $0x3f,-0x8(%rbp)
 11e:   e9 5d 07 00 00          jmp    880 <foo+0x880>
 123:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 127:   c6 45 f8 0a             movb   $0xa,-0x8(%rbp)
 12b:   e9 50 07 00 00          jmp    880 <foo+0x880>
 130:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 134:   c6 45 f8 0d             movb   $0xd,-0x8(%rbp)
 138:   e9 43 07 00 00          jmp    880 <foo+0x880>
 13d:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 141:   c6 45 f8 5a             movb   $0x5a,-0x8(%rbp)
 145:   e9 36 07 00 00          jmp    880 <foo+0x880>
 14a:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 14e:   c6 45 f8 31             movb   $0x31,-0x8(%rbp)
 152:   e9 29 07 00 00          jmp    880 <foo+0x880>
 157:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 15b:   c6 45 f8 49             movb   $0x49,-0x8(%rbp)
 15f:   e9 1c 07 00 00          jmp    880 <foo+0x880>
 164:   89 45 f0                mov    %eax,-0x10(%rbp)
 167:   c6 45 f8 40             movb   $0x40,-0x8(%rbp)
 16b:   e9 10 07 00 00          jmp    880 <foo+0x880>
 170:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 174:   c6 45 f8 63             movb   $0x63,-0x8(%rbp)
 178:   e9 03 07 00 00          jmp    880 <foo+0x880>
 17d:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 181:   c6 45 f8 0e             movb   $0xe,-0x8(%rbp)
 185:   e9 f6 06 00 00          jmp    880 <foo+0x880>
 18a:   89 45 f0                mov    %eax,-0x10(%rbp)
 18d:   c6 45 f8 01             movb   $0x1,-0x8(%rbp)
 191:   e9 ea 06 00 00          jmp    880 <foo+0x880>
 196:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 19a:   c6 45 f8 5c             movb   $0x5c,-0x8(%rbp)
 19e:   e9 dd 06 00 00          jmp    880 <foo+0x880>
 1a3:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 1a7:   c6 45 f8 11             movb   $0x11,-0x8(%rbp)
 1ab:   e9 d0 06 00 00          jmp    880 <foo+0x880>
 1b0:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 1b4:   c6 45 f8 4c             movb   $0x4c,-0x8(%rbp)
 1b8:   e9 c3 06 00 00          jmp    880 <foo+0x880>
 1bd:   89 45 f0                mov    %eax,-0x10(%rbp)
 1c0:   c6 45 f8 77             movb   $0x77,-0x8(%rbp)
 1c4:   e9 b7 06 00 00          jmp    880 <foo+0x880>
 1c9:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 1cd:   c6 45 f8 51             movb   $0x51,-0x8(%rbp)
 1d1:   e9 aa 06 00 00          jmp    880 <foo+0x880>
 1d6:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 1da:   c6 45 f8 7e             movb   $0x7e,-0x8(%rbp)
 1de:   e9 9d 06 00 00          jmp    880 <foo+0x880>
 1e3:   89 45 f0                mov    %eax,-0x10(%rbp)
 1e6:   c6 45 f8 43             movb   $0x43,-0x8(%rbp)
 1ea:   e9 91 06 00 00          jmp    880 <foo+0x880>
 1ef:   89 45 f0                mov    %eax,-0x10(%rbp)
 1f2:   c6 45 f8 08             movb   $0x8,-0x8(%rbp)
 1f6:   e9 85 06 00 00          jmp    880 <foo+0x880>
 1fb:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 1ff:   c6 45 f8 12             movb   $0x12,-0x8(%rbp)
 203:   e9 78 06 00 00          jmp    880 <foo+0x880>
 208:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 20c:   c6 45 f8 37             movb   $0x37,-0x8(%rbp)
 210:   e9 6b 06 00 00          jmp    880 <foo+0x880>
 215:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 219:   c6 45 f8 1a             movb   $0x1a,-0x8(%rbp)
 21d:   e9 5e 06 00 00          jmp    880 <foo+0x880>
 222:   89 45 f0                mov    %eax,-0x10(%rbp)
 225:   c6 45 f8 3d             movb   $0x3d,-0x8(%rbp)
 229:   e9 52 06 00 00          jmp    880 <foo+0x880>
 22e:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 232:   c6 45 f8 38             movb   $0x38,-0x8(%rbp)
 236:   e9 45 06 00 00          jmp    880 <foo+0x880>
 23b:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 23f:   c6 45 f8 67             movb   $0x67,-0x8(%rbp)
 243:   e9 38 06 00 00          jmp    880 <foo+0x880>
 248:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 24c:   c6 45 f8 59             movb   $0x59,-0x8(%rbp)
 250:   e9 2b 06 00 00          jmp    880 <foo+0x880>
 255:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 259:   c6 45 f8 62             movb   $0x62,-0x8(%rbp)
 25d:   e9 1e 06 00 00          jmp    880 <foo+0x880>
 262:   b8 00 00 00 00          mov    $0x0,%eax
 267:   e9 18 06 00 00          jmp    884 <foo+0x884>
 26c:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 270:   c6 45 f8 74             movb   $0x74,-0x8(%rbp)
 274:   e9 07 06 00 00          jmp    880 <foo+0x880>
 279:   89 45 f0                mov    %eax,-0x10(%rbp)
 27c:   c6 45 f8 3e             movb   $0x3e,-0x8(%rbp)
 280:   e9 fb 05 00 00          jmp    880 <foo+0x880>
 285:   89 45 f0                mov    %eax,-0x10(%rbp)
 288:   c6 45 f8 7a             movb   $0x7a,-0x8(%rbp)
 28c:   e9 ef 05 00 00          jmp    880 <foo+0x880>
 291:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 295:   c6 45 f8 71             movb   $0x71,-0x8(%rbp)
 299:   e9 e2 05 00 00          jmp    880 <foo+0x880>
 29e:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 2a2:   c6 45 f8 5e             movb   $0x5e,-0x8(%rbp)
 2a6:   e9 d5 05 00 00          jmp    880 <foo+0x880>
 2ab:   89 45 f0                mov    %eax,-0x10(%rbp)
 2ae:   c6 45 f8 86             movb   $0x86,-0x8(%rbp)
 2b2:   e9 c9 05 00 00          jmp    880 <foo+0x880>
 2b7:   b8 00 00 00 00          mov    $0x0,%eax
 2bc:   e9 c3 05 00 00          jmp    884 <foo+0x884>
 2c1:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 2c5:   c6 45 f8 1e             movb   $0x1e,-0x8(%rbp)
 2c9:   e9 b2 05 00 00          jmp    880 <foo+0x880>
 2ce:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 2d2:   c6 45 f8 15             movb   $0x15,-0x8(%rbp)
 2d6:   e9 a5 05 00 00          jmp    880 <foo+0x880>
 2db:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 2df:   c6 45 f8 64             movb   $0x64,-0x8(%rbp)
 2e3:   e9 98 05 00 00          jmp    880 <foo+0x880>
 2e8:   89 45 f0                mov    %eax,-0x10(%rbp)
 2eb:   c6 45 f8 8e             movb   $0x8e,-0x8(%rbp)
 2ef:   e9 8c 05 00 00          jmp    880 <foo+0x880>
 2f4:   b8 00 00 00 00          mov    $0x0,%eax
 2f9:   e9 86 05 00 00          jmp    884 <foo+0x884>
 2fe:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 302:   c6 45 f8 22             movb   $0x22,-0x8(%rbp)
 306:   e9 75 05 00 00          jmp    880 <foo+0x880>
 30b:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 30f:   c6 45 f8 27             movb   $0x27,-0x8(%rbp)
 313:   e9 68 05 00 00          jmp    880 <foo+0x880>
 318:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 31c:   c6 45 f8 99             movb   $0x99,-0x8(%rbp)
 320:   e9 5b 05 00 00          jmp    880 <foo+0x880>
 325:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 329:   c6 45 f8 66             movb   $0x66,-0x8(%rbp)
 32d:   e9 4e 05 00 00          jmp    880 <foo+0x880>
 332:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 336:   c6 45 f8 7d             movb   $0x7d,-0x8(%rbp)
 33a:   e9 41 05 00 00          jmp    880 <foo+0x880>
 33f:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 343:   c6 45 f8 9b             movb   $0x9b,-0x8(%rbp)
 347:   e9 34 05 00 00          jmp    880 <foo+0x880>
 34c:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 350:   c6 45 f8 88             movb   $0x88,-0x8(%rbp)
 354:   e9 27 05 00 00          jmp    880 <foo+0x880>
 359:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 35d:   c6 45 f8 79             movb   $0x79,-0x8(%rbp)
 361:   e9 1a 05 00 00          jmp    880 <foo+0x880>
 366:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 36a:   c6 45 f8 34             movb   $0x34,-0x8(%rbp)
 36e:   e9 0d 05 00 00          jmp    880 <foo+0x880>
 373:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 377:   c6 45 f8 6f             movb   $0x6f,-0x8(%rbp)
 37b:   e9 00 05 00 00          jmp    880 <foo+0x880>
 380:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 384:   c6 45 f8 28             movb   $0x28,-0x8(%rbp)
 388:   e9 f3 04 00 00          jmp    880 <foo+0x880>
 38d:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 391:   c6 45 f8 57             movb   $0x57,-0x8(%rbp)
 395:   e9 e6 04 00 00          jmp    880 <foo+0x880>
 39a:   89 45 f0                mov    %eax,-0x10(%rbp)
 39d:   c6 45 f8 9e             movb   $0x9e,-0x8(%rbp)
 3a1:   e9 da 04 00 00          jmp    880 <foo+0x880>
 3a6:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 3aa:   c6 45 f8 30             movb   $0x30,-0x8(%rbp)
 3ae:   e9 cd 04 00 00          jmp    880 <foo+0x880>
 3b3:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 3b7:   c6 45 f8 58             movb   $0x58,-0x8(%rbp)
 3bb:   e9 c0 04 00 00          jmp    880 <foo+0x880>
 3c0:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 3c4:   c6 45 f8 78             movb   $0x78,-0x8(%rbp)
 3c8:   e9 b3 04 00 00          jmp    880 <foo+0x880>
 3cd:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 3d1:   c6 45 f8 a5             movb   $0xa5,-0x8(%rbp)
 3d5:   e9 a6 04 00 00          jmp    880 <foo+0x880>
 3da:   b8 00 00 00 00          mov    $0x0,%eax
 3df:   e9 a0 04 00 00          jmp    884 <foo+0x884>
 3e4:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 3e8:   c6 45 f8 2a             movb   $0x2a,-0x8(%rbp)
 3ec:   e9 8f 04 00 00          jmp    880 <foo+0x880>
 3f1:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 3f5:   c6 45 f8 6d             movb   $0x6d,-0x8(%rbp)
 3f9:   e9 82 04 00 00          jmp    880 <foo+0x880>
 3fe:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 402:   c6 45 f8 69             movb   $0x69,-0x8(%rbp)
 406:   e9 75 04 00 00          jmp    880 <foo+0x880>
 40b:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 40f:   c6 45 f8 9d             movb   $0x9d,-0x8(%rbp)
 413:   e9 68 04 00 00          jmp    880 <foo+0x880>
 418:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 41c:   c6 45 f8 a0             movb   $0xa0,-0x8(%rbp)
 420:   e9 5b 04 00 00          jmp    880 <foo+0x880>
 425:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 429:   c6 45 f8 90             movb   $0x90,-0x8(%rbp)
 42d:   e9 4e 04 00 00          jmp    880 <foo+0x880>
 432:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 436:   c6 45 f8 91             movb   $0x91,-0x8(%rbp)
 43a:   e9 41 04 00 00          jmp    880 <foo+0x880>
 43f:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 443:   c6 45 f8 a7             movb   $0xa7,-0x8(%rbp)
 447:   e9 34 04 00 00          jmp    880 <foo+0x880>
 44c:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 450:   c6 45 f8 10             movb   $0x10,-0x8(%rbp)
 454:   e9 27 04 00 00          jmp    880 <foo+0x880>
 459:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 45d:   c6 45 f8 13             movb   $0x13,-0x8(%rbp)
 461:   e9 1a 04 00 00          jmp    880 <foo+0x880>
 466:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 46a:   c6 45 f8 9a             movb   $0x9a,-0x8(%rbp)
 46e:   e9 0d 04 00 00          jmp    880 <foo+0x880>
 473:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 477:   c6 45 f8 2c             movb   $0x2c,-0x8(%rbp)
 47b:   e9 00 04 00 00          jmp    880 <foo+0x880>
 480:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 484:   c6 45 f8 6a             movb   $0x6a,-0x8(%rbp)
 488:   e9 f3 03 00 00          jmp    880 <foo+0x880>
 48d:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 491:   c6 45 f8 a6             movb   $0xa6,-0x8(%rbp)
 495:   e9 e6 03 00 00          jmp    880 <foo+0x880>
 49a:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 49e:   c6 45 f8 a2             movb   $0xa2,-0x8(%rbp)
 4a2:   e9 d9 03 00 00          jmp    880 <foo+0x880>
 4a7:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 4ab:   c6 45 f8 a8             movb   $0xa8,-0x8(%rbp)
 4af:   e9 cc 03 00 00          jmp    880 <foo+0x880>
 4b4:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 4b8:   c6 45 f8 a9             movb   $0xa9,-0x8(%rbp)
 4bc:   e9 bf 03 00 00          jmp    880 <foo+0x880>
 4c1:   89 45 f0                mov    %eax,-0x10(%rbp)
 4c4:   c6 45 f8 4d             movb   $0x4d,-0x8(%rbp)
 4c8:   e9 b3 03 00 00          jmp    880 <foo+0x880>
 4cd:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 4d1:   c6 45 f8 47             movb   $0x47,-0x8(%rbp)
 4d5:   e9 a6 03 00 00          jmp    880 <foo+0x880>
 4da:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 4de:   c6 45 f8 8a             movb   $0x8a,-0x8(%rbp)
 4e2:   e9 99 03 00 00          jmp    880 <foo+0x880>
 4e7:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 4eb:   c6 45 f8 98             movb   $0x98,-0x8(%rbp)
 4ef:   e9 8c 03 00 00          jmp    880 <foo+0x880>
 4f4:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 4f8:   c6 45 f8 4b             movb   $0x4b,-0x8(%rbp)
 4fc:   e9 7f 03 00 00          jmp    880 <foo+0x880>
 501:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 505:   c6 45 f8 80             movb   $0x80,-0x8(%rbp)
 509:   e9 72 03 00 00          jmp    880 <foo+0x880>
 50e:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 512:   c6 45 f8 5d             movb   $0x5d,-0x8(%rbp)
 516:   e9 65 03 00 00          jmp    880 <foo+0x880>
 51b:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 51f:   c6 45 f8 95             movb   $0x95,-0x8(%rbp)
 523:   e9 58 03 00 00          jmp    880 <foo+0x880>
 528:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 52c:   c6 45 f8 6c             movb   $0x6c,-0x8(%rbp)
 530:   e9 4b 03 00 00          jmp    880 <foo+0x880>
 535:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 539:   c6 45 f8 a4             movb   $0xa4,-0x8(%rbp)
 53d:   e9 3e 03 00 00          jmp    880 <foo+0x880>
 542:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 546:   c6 45 f8 68             movb   $0x68,-0x8(%rbp)
 54a:   e9 31 03 00 00          jmp    880 <foo+0x880>
 54f:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 553:   c6 45 f8 6b             movb   $0x6b,-0x8(%rbp)
 557:   e9 24 03 00 00          jmp    880 <foo+0x880>
 55c:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 560:   c6 45 f8 94             movb   $0x94,-0x8(%rbp)
 564:   e9 17 03 00 00          jmp    880 <foo+0x880>
 569:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 56d:   c6 45 f8 9c             movb   $0x9c,-0x8(%rbp)
 571:   e9 0a 03 00 00          jmp    880 <foo+0x880>
 576:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 57a:   c6 45 f8 a3             movb   $0xa3,-0x8(%rbp)
 57e:   e9 fd 02 00 00          jmp    880 <foo+0x880>
 583:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 587:   c6 45 f8 97             movb   $0x97,-0x8(%rbp)
 58b:   e9 f0 02 00 00          jmp    880 <foo+0x880>
 590:   89 45 f0                mov    %eax,-0x10(%rbp)
 593:   c6 45 f8 9f             movb   $0x9f,-0x8(%rbp)
 597:   e9 e4 02 00 00          jmp    880 <foo+0x880>
 59c:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 5a0:   c6 45 f8 a1             movb   $0xa1,-0x8(%rbp)
 5a4:   e9 d7 02 00 00          jmp    880 <foo+0x880>
 5a9:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 5ad:   c6 45 f8 8b             movb   $0x8b,-0x8(%rbp)
 5b1:   e9 ca 02 00 00          jmp    880 <foo+0x880>
 5b6:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 5ba:   c6 45 f8 89             movb   $0x89,-0x8(%rbp)
 5be:   e9 bd 02 00 00          jmp    880 <foo+0x880>
 5c3:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 5c7:   c6 45 f8 7c             movb   $0x7c,-0x8(%rbp)
 5cb:   e9 b0 02 00 00          jmp    880 <foo+0x880>
 5d0:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 5d4:   c6 45 f8 19             movb   $0x19,-0x8(%rbp)
 5d8:   e9 a3 02 00 00          jmp    880 <foo+0x880>
 5dd:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 5e1:   c6 45 f8 2b             movb   $0x2b,-0x8(%rbp)
 5e5:   e9 96 02 00 00          jmp    880 <foo+0x880>
 5ea:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 5ee:   c6 45 f8 29             movb   $0x29,-0x8(%rbp)
 5f2:   e9 89 02 00 00          jmp    880 <foo+0x880>
 5f7:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 5fb:   c6 45 f8 54             movb   $0x54,-0x8(%rbp)
 5ff:   e9 7c 02 00 00          jmp    880 <foo+0x880>
 604:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 608:   c6 45 f8 93             movb   $0x93,-0x8(%rbp)
 60c:   e9 6f 02 00 00          jmp    880 <foo+0x880>
 611:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 615:   c6 45 f8 53             movb   $0x53,-0x8(%rbp)
 619:   e9 62 02 00 00          jmp    880 <foo+0x880>
 61e:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 622:   c6 45 f8 36             movb   $0x36,-0x8(%rbp)
 626:   e9 55 02 00 00          jmp    880 <foo+0x880>
 62b:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 62f:   c6 45 f8 32             movb   $0x32,-0x8(%rbp)
 633:   e9 48 02 00 00          jmp    880 <foo+0x880>
 638:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 63c:   c6 45 f8 39             movb   $0x39,-0x8(%rbp)
 640:   e9 3b 02 00 00          jmp    880 <foo+0x880>
 645:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 649:   c6 45 f8 33             movb   $0x33,-0x8(%rbp)
 64d:   e9 2e 02 00 00          jmp    880 <foo+0x880>
 652:   b8 00 00 00 00          mov    $0x0,%eax
 657:   e9 28 02 00 00          jmp    884 <foo+0x884>
 65c:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 660:   c6 45 f8 96             movb   $0x96,-0x8(%rbp)
 664:   e9 17 02 00 00          jmp    880 <foo+0x880>
 669:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 66d:   c6 45 f8 70             movb   $0x70,-0x8(%rbp)
 671:   e9 0a 02 00 00          jmp    880 <foo+0x880>
 676:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 67a:   c6 45 f8 7f             movb   $0x7f,-0x8(%rbp)
 67e:   e9 fd 01 00 00          jmp    880 <foo+0x880>
 683:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 687:   c6 45 f8 6e             movb   $0x6e,-0x8(%rbp)
 68b:   e9 f0 01 00 00          jmp    880 <foo+0x880>
 690:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 694:   c6 45 f8 92             movb   $0x92,-0x8(%rbp)
 698:   e9 e3 01 00 00          jmp    880 <foo+0x880>
 69d:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 6a1:   c6 45 f8 8d             movb   $0x8d,-0x8(%rbp)
 6a5:   e9 d6 01 00 00          jmp    880 <foo+0x880>
 6aa:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 6ae:   c6 45 f8 8c             movb   $0x8c,-0x8(%rbp)
 6b2:   e9 c9 01 00 00          jmp    880 <foo+0x880>
 6b7:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 6bb:   c6 45 f8 35             movb   $0x35,-0x8(%rbp)
 6bf:   e9 bc 01 00 00          jmp    880 <foo+0x880>
 6c4:   b8 00 00 00 00          mov    $0x0,%eax
 6c9:   e9 b6 01 00 00          jmp    884 <foo+0x884>
 6ce:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 6d2:   c6 45 f8 8f             movb   $0x8f,-0x8(%rbp)
 6d6:   e9 a5 01 00 00          jmp    880 <foo+0x880>
 6db:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 6df:   c6 45 f8 73             movb   $0x73,-0x8(%rbp)
 6e3:   e9 98 01 00 00          jmp    880 <foo+0x880>
 6e8:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 6ec:   c6 45 f8 18             movb   $0x18,-0x8(%rbp)
 6f0:   e9 8b 01 00 00          jmp    880 <foo+0x880>
 6f5:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 6f9:   c6 45 f8 3a             movb   $0x3a,-0x8(%rbp)
 6fd:   e9 7e 01 00 00          jmp    880 <foo+0x880>
 702:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 706:   c6 45 f8 21             movb   $0x21,-0x8(%rbp)
 70a:   e9 71 01 00 00          jmp    880 <foo+0x880>
 70f:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 713:   c6 45 f8 61             movb   $0x61,-0x8(%rbp)
 717:   e9 64 01 00 00          jmp    880 <foo+0x880>
 71c:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 720:   c6 45 f8 72             movb   $0x72,-0x8(%rbp)
 724:   e9 57 01 00 00          jmp    880 <foo+0x880>
 729:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 72d:   c6 45 f8 2d             movb   $0x2d,-0x8(%rbp)
 731:   e9 4a 01 00 00          jmp    880 <foo+0x880>
 736:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 73a:   c6 45 f8 75             movb   $0x75,-0x8(%rbp)
 73e:   e9 3d 01 00 00          jmp    880 <foo+0x880>
 743:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 747:   c6 45 f8 7b             movb   $0x7b,-0x8(%rbp)
 74b:   e9 30 01 00 00          jmp    880 <foo+0x880>
 750:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 754:   c6 45 f8 60             movb   $0x60,-0x8(%rbp)
 758:   e9 23 01 00 00          jmp    880 <foo+0x880>
 75d:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 761:   c6 45 f8 1b             movb   $0x1b,-0x8(%rbp)
 765:   e9 16 01 00 00          jmp    880 <foo+0x880>
 76a:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 76e:   c6 45 f8 52             movb   $0x52,-0x8(%rbp)
 772:   e9 09 01 00 00          jmp    880 <foo+0x880>
 777:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 77b:   c6 45 f8 5f             movb   $0x5f,-0x8(%rbp)
 77f:   e9 fc 00 00 00          jmp    880 <foo+0x880>
 784:   89 45 f0                mov    %eax,-0x10(%rbp)
 787:   c6 45 f8 41             movb   $0x41,-0x8(%rbp)
 78b:   e9 f0 00 00 00          jmp    880 <foo+0x880>
 790:   89 45 f0                mov    %eax,-0x10(%rbp)
 793:   c6 45 f8 76             movb   $0x76,-0x8(%rbp)
 797:   e9 e4 00 00 00          jmp    880 <foo+0x880>
 79c:   89 45 f0                mov    %eax,-0x10(%rbp)
 79f:   c6 45 f8 42             movb   $0x42,-0x8(%rbp)
 7a3:   e9 d8 00 00 00          jmp    880 <foo+0x880>
 7a8:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 7ac:   c6 45 f8 5b             movb   $0x5b,-0x8(%rbp)
 7b0:   e9 cb 00 00 00          jmp    880 <foo+0x880>
 7b5:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 7b9:   c6 45 f8 44             movb   $0x44,-0x8(%rbp)
 7bd:   e9 be 00 00 00          jmp    880 <foo+0x880>
 7c2:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 7c6:   c6 45 f8 65             movb   $0x65,-0x8(%rbp)
 7ca:   e9 b1 00 00 00          jmp    880 <foo+0x880>
 7cf:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 7d3:   c6 45 f8 0f             movb   $0xf,-0x8(%rbp)
 7d7:   e9 a4 00 00 00          jmp    880 <foo+0x880>
 7dc:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 7e0:   c6 45 f8 4a             movb   $0x4a,-0x8(%rbp)
 7e4:   e9 97 00 00 00          jmp    880 <foo+0x880>
 7e9:   b8 00 00 00 00          mov    $0x0,%eax
 7ee:   e9 91 00 00 00          jmp    884 <foo+0x884>
 7f3:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 7f7:   c6 45 f8 23             movb   $0x23,-0x8(%rbp)
 7fb:   e9 80 00 00 00          jmp    880 <foo+0x880>
 800:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 804:   c6 45 f8 4f             movb   $0x4f,-0x8(%rbp)
 808:   eb 76                   jmp    880 <foo+0x880>
 80a:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 80e:   c6 45 f8 50             movb   $0x50,-0x8(%rbp)
 812:   eb 6c                   jmp    880 <foo+0x880>
 814:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 818:   c6 45 f8 1c             movb   $0x1c,-0x8(%rbp)
 81c:   eb 62                   jmp    880 <foo+0x880>
 81e:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 822:   c6 45 f8 17             movb   $0x17,-0x8(%rbp)
 826:   eb 58                   jmp    880 <foo+0x880>
 828:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 82c:   c6 45 f8 48             movb   $0x48,-0x8(%rbp)
 830:   eb 4e                   jmp    880 <foo+0x880>
 832:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 836:   c6 45 f8 07             movb   $0x7,-0x8(%rbp)
 83a:   eb 44                   jmp    880 <foo+0x880>
 83c:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 840:   c6 45 f8 24             movb   $0x24,-0x8(%rbp)
 844:   eb 3a                   jmp    880 <foo+0x880>
 846:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 84a:   c6 45 f8 46             movb   $0x46,-0x8(%rbp)
 84e:   eb 30                   jmp    880 <foo+0x880>
 850:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 854:   c6 45 f8 1d             movb   $0x1d,-0x8(%rbp)
 858:   eb 26                   jmp    880 <foo+0x880>
 85a:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 85e:   c6 45 f8 05             movb   $0x5,-0x8(%rbp)
 862:   eb 1c                   jmp    880 <foo+0x880>
 864:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 868:   c6 45 f8 0b             movb   $0xb,-0x8(%rbp)
 86c:   eb 12                   jmp    880 <foo+0x880>
 86e:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 872:   c6 45 f8 06             movb   $0x6,-0x8(%rbp)
 876:   eb 08                   jmp    880 <foo+0x880>
 878:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 87c:   c6 45 f8 04             movb   $0x4,-0x8(%rbp)
 880:   48 8d 45 f0             lea    -0x10(%rbp),%rax
 884:   8b 48 08                mov    0x8(%rax),%ecx
 887:   89 4d e8                mov    %ecx,-0x18(%rbp)
 88a:   48 8b 00                mov    (%rax),%rax
 88d:   48 89 45 e0             mov    %rax,-0x20(%rbp)
 891:   8b 45 e8                mov    -0x18(%rbp),%eax
 894:   89 45 f8                mov    %eax,-0x8(%rbp)
 897:   48 8b 45 e0             mov    -0x20(%rbp),%rax
 89b:   48 89 45 f0             mov    %rax,-0x10(%rbp)
 89f:   48 8d 45 f0             lea    -0x10(%rbp),%rax
 8a3:   48 89 45 d0             mov    %rax,-0x30(%rbp)
 8a7:   48 8d 45 d0             lea    -0x30(%rbp),%rax
 8ab:   48 89 45 d8             mov    %rax,-0x28(%rbp)
 8af:   5d                      pop    %rbp
 8b0:   c3                      ret

[rohlem]

The inline else is used to transfer data from one union type (the input type U1)
to another with identical fields (the untagged union type U2 used to store the payload)
via switch(tag) {inline else => |t| @unionInit(U1, @tagName(t), @field(u2, @tagName(t))}.

The main cause of this is the current formulation of @unionInit,
which in status-quo kind of forces separating the initialization into separate branches:

• The second parameter is a comptime []u8.
  If this also accepted the union's tag type, the value could be runtime-provided.
  The compiler could share common code between union states with similar initialization logic.
  • EDIT: I assume the main reason that it wasn't initially written this way is that untagged unions
    currently don't have a tag type associated.
    We could keep only accepting the tag type for tagged unions,
    but since this is about a codegen improvement that untagged unions could also benefit from,
    I personally think we should always generate a tag type,
    and specially track in @typeInfo/std.builtin.Type whether a union type is tagged or not in a separate field.
• The third parameter must be an initialization expression for the provided field type.
  This forces the field type to be comptime-known at this point.
  If the compiler instead also allowed an argument that is itself a union with corresponding states
  (where each payload is a valid initialization expression for the target union's corr. state payload),
  the compiler could runtime-switch based on the second argument (also allowed to be runtime-known, see previous point).
  • EDIT: I think missing states in the third argument's type should always lead to a compile error.
    We could also treat them as unreachable, meaning they add an assertion that
    the tag in the second argument never indicates that state,
    however that is already modellable via uninstantiable (noreturn-like) states.

With these changes / enhancements, the transfer could look like @unionInit(U1, @as(U1Tag, u2), u2).
(Maybe the cast could be unnecessary: @unionInit(U1, u2, u2) / @unionInit(U1, tag, u2).)
If they are too intrusive / complex to pack into the same builtin, we could of course
name this new variant something else for now, like @unionTransfer, or @unionInit2.

[tauoverpi]

Possibly stupid question but is it safe to @memcpy the union value to the location given union(enum) consistently places the tag (at the end iirc) and each value is forced to occupy the memory of the largest member (remaining space is undefined if present)? To avoid paying for large copies this can be split among size classes chosen at comptime.

[rohlem]

@tauoverpi I think a userland solution like that would work in status-quo in most cases
(since not all eventually-intended safety mechanisms are implemented yet).
Arguably though, the codegen of the intended mechanism provided by the language shouldn't be worse than a userland hack/workaround.