lobsters:

```
Top-20 calls to C functions from JIT code (79.9% of total 97,004,883):
                             rb_vm_opt_send_without_block: 19,874,212 (20.5%)
                                rb_vm_setinstancevariable:  9,774,841 (10.1%)
                                              rb_ivar_get:  9,358,866 ( 9.6%)
                                             rb_hash_aref:  6,828,948 ( 7.0%)
                                               rb_vm_send:  6,441,551 ( 6.6%)
                                          rb_vm_env_write:  5,375,989 ( 5.5%)
                                        rb_vm_invokesuper:  3,037,836 ( 3.1%)
                                               Module#===:  2,562,446 ( 2.6%)
                                             rb_ary_entry:  2,354,546 ( 2.4%)
                                             Kernel#is_a?:  1,424,092 ( 1.5%)
                               rb_vm_opt_getconstant_path:  1,344,923 ( 1.4%)
                                           Thread.current:  1,300,822 ( 1.3%)
                                     rb_zjit_defined_ivar:  1,222,613 ( 1.3%)
                                        rb_vm_invokeblock:  1,184,555 ( 1.2%)
                                                 Hash#[]=:  1,061,969 ( 1.1%)
                                              rb_ary_push:  1,024,987 ( 1.1%)
                                          rb_ary_new_capa:    904,003 ( 0.9%)
                                        rb_str_buf_append:    833,782 ( 0.9%)
                               rb_class_allocate_instance:    822,626 ( 0.8%)
                                               Hash#fetch:    755,913 ( 0.8%)
```

railsbench:

```
Top-20 calls to C functions from JIT code (74.8% of total 189,170,268):
               rb_vm_opt_send_without_block: 29,870,307 (15.8%)
                  rb_vm_setinstancevariable: 17,631,199 ( 9.3%)
                               rb_hash_aref: 16,928,890 ( 8.9%)
                                rb_ivar_get: 14,441,240 ( 7.6%)
                            rb_vm_env_write: 11,571,001 ( 6.1%)
                                 rb_vm_send: 11,153,457 ( 5.9%)
                          rb_vm_invokesuper:  7,568,267 ( 4.0%)
                                 Module#===:  6,065,923 ( 3.2%)
                                   Hash#[]=:  2,842,990 ( 1.5%)
                               rb_ary_entry:  2,766,125 ( 1.5%)
                                rb_ary_push:  2,722,079 ( 1.4%)
                          rb_vm_invokeblock:  2,594,398 ( 1.4%)
                             Thread.current:  2,560,129 ( 1.4%)
                             rb_str_getbyte:  1,965,627 ( 1.0%)
                               Kernel#is_a?:  1,961,815 ( 1.0%)
                 rb_vm_opt_getconstant_path:  1,863,678 ( 1.0%)
                      rb_hash_new_with_size:  1,796,456 ( 0.9%)
                 rb_class_allocate_instance:  1,785,043 ( 0.9%)
                              String#empty?:  1,713,414 ( 0.9%)
                            rb_ary_new_capa:  1,678,834 ( 0.9%)
```

shipit:

```
Top-20 calls to C functions from JIT code (83.4% of total 182,402,821):
                             rb_vm_opt_send_without_block: 45,753,484 (25.1%)
                                              rb_ivar_get: 21,020,650 (11.5%)
                                rb_vm_setinstancevariable: 17,528,603 ( 9.6%)
                                             rb_hash_aref: 11,892,856 ( 6.5%)
                                               rb_vm_send: 11,723,471 ( 6.4%)
                                          rb_vm_env_write: 10,434,452 ( 5.7%)
                                               Module#===:  4,225,048 ( 2.3%)
                                        rb_vm_invokesuper:  3,705,906 ( 2.0%)
                                           Thread.current:  3,337,603 ( 1.8%)
                                             rb_ary_entry:  3,114,378 ( 1.7%)
                                                 Hash#[]=:  2,509,912 ( 1.4%)
                                             Array#empty?:  2,282,994 ( 1.3%)
                                        rb_vm_invokeblock:  2,210,511 ( 1.2%)
                                               Hash#fetch:  2,017,960 ( 1.1%)
                                                    _bi20:  1,975,147 ( 1.1%)
                                     rb_zjit_defined_ivar:  1,897,127 ( 1.0%)
                               rb_vm_opt_getconstant_path:  1,813,294 ( 1.0%)
                                          rb_ary_new_capa:  1,615,406 ( 0.9%)
                                             Kernel#is_a?:  1,567,854 ( 0.9%)
                               rb_class_allocate_instance:  1,560,035 ( 0.9%)
```

Thanks to @eregon for the idea.

Co-authored-by: Jacob Denbeaux <jacob.denbeaux@shopify.com>
Co-authored-by: Alan Wu <XrXr@users.noreply.github.com>

This implements Shopify#854:

- Splits boot-time and enable-time initialization,
  tracks progress with `InitializationState` enum

- Introduces `RubyVM::ZJIT.enable` Ruby method for
  enabling the JIT lazily, if not already enabled

- Introduces `--zjit-disable` flag, which can be
  used alongside the other `--zjit-*` flags but
  prevents enabling the JIT at boot time

- Adds ZJIT infra to support JIT hooks, but this
  is not currently exercised (Shopify/ruby#667)

Left for future enhancements:

- Support kwargs for overriding the CLI flags in
  `RubyVM::ZJIT.enable`

Closes Shopify#854

* ZJIT: Add HIR for CCallWithFrame

* ZJIT: Update stats to count not inlined cfunc calls

* ZJIT: Stops optimizing SendWithoutBlock when TracePoint is activated

* ZJIT: Fallback to SendWithoutBlock when CCallWithFrame has too many args

* ZJIT: Rename cfun -> cfunc

Add side exit tracing functionality for ZJIT