ZJIT: Speed up Rails benchmarks

[k0kubun]

This issue aims to make ZJIT as fast as YJIT on the following benchmarks in yjit-bench:

• railsbench
• lobsters
• shipit

activerecord and erubi-rails should also be improved. But it's nice to focus on realistic, whole-application benchmarks.

Burndown list

Reduce side exits

ratio_in_zjit is still 72%. This should be the top priority until we increase it to 98-99% or more. When it's low, it not only becomes slower due to cache thrashing but also randomly misses already-implemented optimizations.

We should look at "side exit reasons" and its sub-categories like "compile error reasons" and "unhandled YARV insns", and fix the ones that happen most frequently.

• 37.5%: register_spill_on_* ZJIT: Support spilling in the register allocator #716 (@k0kubun)
• 15.5%: guard_type_failure ZJIT: guard_type_failure happens too frequently on lobsters #771 (not assigned)
• 13.9%: guard_shape_failure ZJIT: guard_shape_failure happens too frequently on ruby-bench #727 (not assigned)
• 6.7%: block_param_proxy_not_iseq_or_ifunc ZJIT: Fix block_param_proxy_not_iseq_or_ifunc exits #772 (not assigned)

Reduce dynamic sends

Method calls are a major source of potential speedups. Even if you fully materialize a frame like YJIT does, they can still be a lot faster than the interpreter (at least as fast as YJIT) by reducing memory reads and removing function calls.

We should look at "send fallback reasons" and its sub-categories like "not optimized instructions" and "not optimized method types", and fix the ones that happen most frequently.

• 20.4%: send_without_block_cfunc_not_variadic ZJIT: Support calls to non-leaf C functions #759 (@st0012)
• 19.4%: send_without_block_polymorphic ZJIT: send_without_block_polymorphic happens too frequently #776 (not assigned)
• 18.3%: opt_aref
  • ZJIT: Specialize #[] into an rb_hash_aref call if a profiled type is Hash #793 (not assigned)
  • ZJIT: Specialize #[] into ArrayArefFixnum if a profiled type is Array #792 (not assigned)
• 14.6%: send ZJIT: Support compiling Send without dynamic dispatch #777 (@st0012)

Reduce things slower than YJIT

There are overheads in ZJIT that YJIT doesn't have. To make ZJIT faster than YJIT, we need to remove them, or at least minimize their impact.

• Avoid spilling the same thing into two different (VM and C) stacks (@k0kubun)
• ZJIT: Avoid reloading locals on send that are not referenced by blockiseq #774 (not assigned)
• ZJIT: Consider using SP register for reloading locals #769 (not assigned)

ZJIT stats

ZJIT stats on lobsters as of 2025-10-17

***ZJIT: Printing ZJIT statistics on exit***
Top-20 not inlined C methods (61.1% of total 10,568,483):
                               Kernel#is_a?: 1,030,761 ( 9.8%)
                                  String#<<:   851,954 ( 8.1%)
                                   Hash#[]=:   742,941 ( 7.0%)
                              Regexp#match?:   399,888 ( 3.8%)
                                  Hash#key?:   349,146 ( 3.3%)
                         String#start_with?:   334,961 ( 3.2%)
                         Kernel#respond_to?:   316,527 ( 3.0%)
                 ObjectSpace::WeakKeyMap#[]:   238,978 ( 2.3%)
                              TrueClass#===:   235,771 ( 2.2%)
                             FalseClass#===:   231,144 ( 2.2%)
                             Array#include?:   211,385 ( 2.0%)
                                 Hash#fetch:   204,702 ( 1.9%)
                        Kernel#block_given?:   181,797 ( 1.7%)
                                 Kernel#dup:   179,341 ( 1.7%)
                             BasicObject#!=:   175,997 ( 1.7%)
                                 String.new:   166,696 ( 1.6%)
                            Kernel#kind_of?:   165,600 ( 1.6%)
                                  String#==:   157,735 ( 1.5%)
                      Process.clock_gettime:   144,992 ( 1.4%)
                                 Array#any?:   138,310 ( 1.3%)
Top-20 not annotated C methods (62.1% of total 10,723,378):
                               Kernel#is_a?: 1,212,652 (11.3%)
                                  String#<<:   851,954 ( 7.9%)
                                   Hash#[]=:   743,120 ( 6.9%)
                              Regexp#match?:   399,888 ( 3.7%)
                                  Hash#key?:   349,146 ( 3.3%)
                         String#start_with?:   334,961 ( 3.1%)
                         Kernel#respond_to?:   316,527 ( 3.0%)
                 ObjectSpace::WeakKeyMap#[]:   238,978 ( 2.2%)
                              TrueClass#===:   235,771 ( 2.2%)
                             FalseClass#===:   231,144 ( 2.2%)
                             Array#include?:   211,385 ( 2.0%)
                                 Hash#fetch:   204,702 ( 1.9%)
                        Kernel#block_given?:   191,666 ( 1.8%)
                                 Kernel#dup:   179,348 ( 1.7%)
                             BasicObject#!=:   176,181 ( 1.6%)
                                 String.new:   166,696 ( 1.6%)
                            Kernel#kind_of?:   165,634 ( 1.5%)
                                  String#==:   163,667 ( 1.5%)
                      Process.clock_gettime:   144,992 ( 1.4%)
                                 Array#any?:   138,310 ( 1.3%)
Top-2 not optimized method types for send (100.0% of total 72,318):
  cfunc: 48,055 (66.4%)
   iseq: 24,263 (33.6%)
Top-6 not optimized method types for send_without_block (100.0% of total 4,523,682):
       iseq: 2,271,935 (50.2%)
    bmethod:   985,636 (21.8%)
  optimized:   949,704 (21.0%)
      alias:   310,747 ( 6.9%)
       null:     5,106 ( 0.1%)
      cfunc:       554 ( 0.0%)
Top-13 not optimized instructions (100.0% of total 4,293,170):
             invokesuper: 2,373,404 (55.3%)
             invokeblock:   811,926 (18.9%)
             sendforward:   505,452 (11.8%)
                  opt_eq:   451,754 (10.5%)
                opt_plus:    74,404 ( 1.7%)
               opt_minus:    36,228 ( 0.8%)
  opt_send_without_block:    21,791 ( 0.5%)
                 opt_neq:     7,231 ( 0.2%)
                opt_mult:     6,752 ( 0.2%)
                  opt_or:     3,753 ( 0.1%)
                  opt_lt:       348 ( 0.0%)
                  opt_ge:        91 ( 0.0%)
                  opt_gt:        36 ( 0.0%)
Top-9 send fallback reasons (100.0% of total 25,480,950):
                send_without_block_polymorphic: 9,722,492 (38.2%)
                              send_no_profiles: 5,894,788 (23.1%)
  send_without_block_not_optimized_method_type: 4,523,682 (17.8%)
                     not_optimized_instruction: 4,293,170 (16.8%)
                send_without_block_no_profiles:   948,972 ( 3.7%)
                send_not_optimized_method_type:    72,318 ( 0.3%)
       send_without_block_cfunc_array_variadic:    15,134 ( 0.1%)
                      obj_to_string_not_string:     9,765 ( 0.0%)
       send_without_block_direct_too_many_args:       629 ( 0.0%)
Top-9 unhandled YARV insns (100.0% of total 690,950):
         expandarray: 328,490 (47.5%)
        checkkeyword: 190,694 (27.6%)
    getclassvariable:  59,901 ( 8.7%)
  invokesuperforward:  49,503 ( 7.2%)
       getblockparam:  49,119 ( 7.1%)
   opt_duparray_send:  11,978 ( 1.7%)
         getconstant:     952 ( 0.1%)
          checkmatch:     290 ( 0.0%)
                once:      23 ( 0.0%)
Top-3 compile error reasons (100.0% of total 3,718,619):
  register_spill_on_alloc: 3,418,255 (91.9%)
  register_spill_on_ccall:   182,018 ( 4.9%)
        exception_handler:   118,346 ( 3.2%)
Top-17 side exit reasons (100.0% of total 10,860,358):
                        compile_error: 3,718,619 (34.2%)
                   guard_type_failure: 2,638,914 (24.3%)
                  guard_shape_failure: 1,917,205 (17.7%)
                  unhandled_yarv_insn:   690,950 ( 6.4%)
  block_param_proxy_not_iseq_or_ifunc:   535,789 ( 4.9%)
                      unhandled_kwarg:   455,348 ( 4.2%)
                unknown_newarray_send:   314,788 ( 2.9%)
     patchpoint_stable_constant_names:   235,469 ( 2.2%)
                      unhandled_splat:   122,071 ( 1.1%)
        patchpoint_no_singleton_class:   109,652 ( 1.0%)
                   unhandled_hir_insn:    76,397 ( 0.7%)
          patchpoint_method_redefined:    21,590 ( 0.2%)
           block_param_proxy_modified:    19,193 ( 0.2%)
              patchpoint_no_ep_escape:     3,765 ( 0.0%)
               obj_to_string_fallback:       566 ( 0.0%)
               guard_type_not_failure:        22 ( 0.0%)
                            interrupt:        20 ( 0.0%)
                             send_count: 68,203,448
                     dynamic_send_count: 25,480,950 (37.4%)
                   optimized_send_count: 42,722,498 (62.6%)
              iseq_optimized_send_count: 18,587,492 (27.3%)
      inline_cfunc_optimized_send_count: 13,566,523 (19.9%)
non_variadic_cfunc_optimized_send_count:  7,904,314 (11.6%)
    variadic_cfunc_optimized_send_count:  2,664,169 ( 3.9%)
dynamic_getivar_count:                        7,365,994
dynamic_setivar_count:                        7,244,999
compiled_iseq_count:                              4,796
failed_iseq_count:                                  447
compile_time:                                     779ms
profile_time:                                       8ms
gc_time:                                           11ms
invalidation_time:                                 75ms
vm_write_pc_count:                           63,634,930
vm_write_sp_count:                           62,291,157
vm_write_locals_count:                       62,291,157
vm_write_stack_count:                        62,291,157
vm_write_to_parent_iseq_local_count:            292,458
vm_read_from_parent_iseq_local_count:         6,599,701
code_region_bytes:                           22,970,368
side_exit_count:                             10,860,358
total_insn_count:                           517,605,935
vm_insn_count:                              162,979,594
zjit_insn_count:                            354,626,341
ratio_in_zjit:                                    68.5%

ZJIT stats on railsbench as of 2025-10-17

***ZJIT: Printing ZJIT statistics on exit***
Top-20 not inlined C methods (63.9% of total 22,558,282):
                                   Hash#[]=: 1,700,237 ( 7.5%)
                                  String#<<: 1,494,022 ( 6.6%)
                               Kernel#is_a?: 1,429,926 ( 6.3%)
                              Regexp#match?: 1,235,064 ( 5.5%)
                         Kernel#respond_to?: 1,198,251 ( 5.3%)
                                  Hash#key?: 1,087,406 ( 4.8%)
                             String#setbyte:   810,022 ( 3.6%)
                                  Integer#^:   766,624 ( 3.4%)
                        Kernel#block_given?:   603,613 ( 2.7%)
                                  String#==:   590,408 ( 2.6%)
                                 String.new:   482,204 ( 2.1%)
                                Hash#delete:   455,288 ( 2.0%)
                             BasicObject#!=:   428,771 ( 1.9%)
                                 Hash#fetch:   408,621 ( 1.8%)
                         String#ascii_only?:   373,915 ( 1.7%)
                 ObjectSpace::WeakKeyMap#[]:   287,957 ( 1.3%)
                               NilClass#===:   277,244 ( 1.2%)
                               Kernel#Array:   269,590 ( 1.2%)
                                 Array#join:   260,047 ( 1.2%)
                             Array#include?:   247,816 ( 1.1%)
Top-20 not annotated C methods (64.6% of total 22,425,847):
                                   Hash#[]=: 1,700,416 ( 7.6%)
                               Kernel#is_a?: 1,515,668 ( 6.8%)
                                  String#<<: 1,494,022 ( 6.7%)
                              Regexp#match?: 1,235,064 ( 5.5%)
                         Kernel#respond_to?: 1,198,251 ( 5.3%)
                                  Hash#key?: 1,087,406 ( 4.8%)
                             String#setbyte:   810,022 ( 3.6%)
                                  Integer#^:   766,624 ( 3.4%)
                        Kernel#block_given?:   603,613 ( 2.7%)
                                  String#==:   601,114 ( 2.7%)
                                 String.new:   482,204 ( 2.2%)
                                Hash#delete:   455,288 ( 2.0%)
                             BasicObject#!=:   428,876 ( 1.9%)
                                 Hash#fetch:   408,621 ( 1.8%)
                         String#ascii_only?:   373,915 ( 1.7%)
                 ObjectSpace::WeakKeyMap#[]:   287,957 ( 1.3%)
                               NilClass#===:   277,244 ( 1.2%)
                               Kernel#Array:   269,590 ( 1.2%)
                             Array#include?:   247,816 ( 1.1%)
                                 Kernel#dup:   239,887 ( 1.1%)
Top-2 not optimized method types for send (100.0% of total 186,159):
   iseq: 112,747 (60.6%)
  cfunc:  73,412 (39.4%)
Top-6 not optimized method types for send_without_block (100.0% of total 8,142,248):
       iseq: 3,464,671 (42.6%)
  optimized: 2,632,884 (32.3%)
    bmethod: 1,290,701 (15.9%)
      alias:   706,020 ( 8.7%)
       null:    47,942 ( 0.6%)
      cfunc:        30 ( 0.0%)
Top-11 not optimized instructions (100.0% of total 8,394,873):
             invokesuper: 5,602,274 (66.7%)
             invokeblock: 1,764,936 (21.0%)
             sendforward:   551,832 ( 6.6%)
                  opt_eq:   441,959 ( 5.3%)
                opt_plus:    31,635 ( 0.4%)
  opt_send_without_block:     1,163 ( 0.0%)
                  opt_lt:       372 ( 0.0%)
                opt_mult:       251 ( 0.0%)
                  opt_ge:       193 ( 0.0%)
                 opt_neq:       149 ( 0.0%)
                  opt_or:       109 ( 0.0%)
Top-8 send fallback reasons (100.0% of total 40,619,436):
                send_without_block_polymorphic: 12,933,921 (31.8%)
                              send_no_profiles:  9,033,636 (22.2%)
                     not_optimized_instruction:  8,394,873 (20.7%)
  send_without_block_not_optimized_method_type:  8,142,248 (20.0%)
                send_without_block_no_profiles:  1,709,913 ( 4.2%)
       send_without_block_cfunc_array_variadic:    215,046 ( 0.5%)
                send_not_optimized_method_type:    186,159 ( 0.5%)
                      obj_to_string_not_string:      3,640 ( 0.0%)
Top-9 unhandled YARV insns (100.0% of total 1,604,456):
    getclassvariable: 458,136 (28.6%)
       getblockparam: 455,921 (28.4%)
        checkkeyword: 265,425 (16.5%)
  invokesuperforward: 239,383 (14.9%)
         expandarray: 137,305 ( 8.6%)
         getconstant:  48,100 ( 3.0%)
          checkmatch:     149 ( 0.0%)
                once:      23 ( 0.0%)
   opt_duparray_send:      14 ( 0.0%)
Top-3 compile error reasons (100.0% of total 5,570,130):
  register_spill_on_alloc: 4,994,130 (89.7%)
        exception_handler:   356,784 ( 6.4%)
  register_spill_on_ccall:   219,216 ( 3.9%)
Top-16 side exit reasons (100.0% of total 12,412,191):
                        compile_error: 5,570,130 (44.9%)
                  unhandled_yarv_insn: 1,604,456 (12.9%)
                  guard_shape_failure: 1,462,883 (11.8%)
                   guard_type_failure:   845,891 ( 6.8%)
  block_param_proxy_not_iseq_or_ifunc:   765,968 ( 6.2%)
                      unhandled_kwarg:   658,341 ( 5.3%)
                      unhandled_splat:   446,990 ( 3.6%)
     patchpoint_stable_constant_names:   397,594 ( 3.2%)
                unknown_newarray_send:   332,740 ( 2.7%)
                   unhandled_hir_insn:   160,205 ( 1.3%)
          patchpoint_method_redefined:   106,687 ( 0.9%)
           block_param_proxy_modified:    59,589 ( 0.5%)
               obj_to_string_fallback:       553 ( 0.0%)
              patchpoint_no_ep_escape:       155 ( 0.0%)
                            interrupt:         8 ( 0.0%)
        patchpoint_no_singleton_class:         1 ( 0.0%)
                             send_count: 133,391,539
                     dynamic_send_count:  40,619,436 (30.5%)
                   optimized_send_count:  92,772,103 (69.5%)
              iseq_optimized_send_count:  39,936,536 (29.9%)
      inline_cfunc_optimized_send_count:  30,277,285 (22.7%)
non_variadic_cfunc_optimized_send_count:  16,755,937 (12.6%)
    variadic_cfunc_optimized_send_count:   5,802,345 ( 4.3%)
dynamic_getivar_count:                       10,980,323
dynamic_setivar_count:                       12,962,722
compiled_iseq_count:                              2,530
failed_iseq_count:                                  245
compile_time:                                     402ms
profile_time:                                      19ms
gc_time:                                           33ms
invalidation_time:                                  4ms
vm_write_pc_count:                          125,997,735
vm_write_sp_count:                          122,927,105
vm_write_locals_count:                      122,927,105
vm_write_stack_count:                       122,927,105
vm_write_to_parent_iseq_local_count:            385,461
vm_read_from_parent_iseq_local_count:        11,266,484
code_region_bytes:                           12,156,928
side_exit_count:                             12,412,191
total_insn_count:                           866,779,936
vm_insn_count:                              216,821,024
zjit_insn_count:                            649,958,912
ratio_in_zjit:                                    75.0%

[k0kubun]

As of Aug 21st #622 (comment), the ZJIT speedup is:

Details

interp: ruby 3.5.0dev (2025-08-21T20:05:47Z master 5076e88f35) +PRISM [x86_64-linux]
yjit: ruby 3.5.0dev (2025-08-21T20:05:47Z master 5076e88f35) +YJIT +PRISM [x86_64-linux]
zjit: ruby 3.5.0dev (2025-08-21T20:05:47Z master 5076e88f35) +ZJIT +PRISM [x86_64-linux]

-----------------  -----------  ----------  ---------  ----------  ---------  ----------  ------------  ------------  -----------  -----------
bench              interp (ms)  stddev (%)  yjit (ms)  stddev (%)  zjit (ms)  stddev (%)  yjit 1st itr  zjit 1st itr  interp/yjit  interp/zjit
lobsters           834.6        0.2         490.7      1.4         849.5      0.4         0.708         0.789         1.701        0.982
railsbench         1937.9       0.9         1014.4     2.5         1965.6     0.7         1.392         0.951         1.910        0.986
shipit             1563.8       1.3         696.2      4.0         1628.3     1.4         1.078         0.849         2.246        0.960
-----------------  -----------  ----------  ---------  ----------  ---------  ----------  ------------  ------------  -----------  -----------

[k0kubun]

Current ZJIT stats on lobsters w/ ratio_in_zjit: 61.8%

Details

***ZJIT: Printing ZJIT statistics on exit***
compilation failure reasons:
  hir_compile: 646 (67.1%)
  asm_compile: 317 (32.9%)
dynamic_send_count:  9,987,581
compiled_iseq_count: 6,393
compilation_failure: 963
compile_time:        5,142ms
profile_time:        58ms
gc_time:             69ms
invalidation_time:   11ms
code_region_bytes:   7,716,864
side_exit_count:     3,443,669
total_insn_count:    167,468,218
vm_insn_count:       63,937,908
zjit_insn_count:     103,530,310
ratio_in_zjit:       61.8%
Top-20 side exit reasons (99.9% of all 36):
     compilation_failure: 1,921,990 (35.8%)
  opt_send_without_block:   961,569 (17.9%)
             invokesuper:   612,320 (11.4%)
      getblockparamproxy:   556,271 (10.4%)
             invokeblock:   339,194 ( 6.3%)
    opt_getconstant_path:   222,008 ( 4.1%)
               opt_nil_p:   197,201 ( 3.7%)
                    send:   135,798 ( 2.5%)
            checkkeyword:    88,575 ( 1.7%)
             expandarray:    80,198 ( 1.5%)
       opt_newarray_send:    63,092 ( 1.2%)
                 opt_not:    49,949 ( 0.9%)
       opt_case_dispatch:    48,082 ( 0.9%)
                  opt_eq:    47,818 ( 0.9%)
                   throw:    15,811 ( 0.3%)
        getclassvariable:     9,905 ( 0.2%)
             objtostring:     7,274 ( 0.1%)
           getblockparam:     3,393 ( 0.1%)
                 opt_neq:     1,563 ( 0.0%)
                 opt_and:       928 ( 0.0%)
Top-10 specific side exit reasons (100.0% of all 10):
     compilation_failure: 1,921,990 (35.8%)
          unknown_opcode: 1,740,199 (32.4%)
      guard_type_failure: 1,158,450 (21.6%)
              patchpoint:   233,490 ( 4.4%)
       unknown_call_type:   225,102 ( 4.2%)
   unknown_newarray_send:    63,092 ( 1.2%)
   unhandled_instruction:    15,956 ( 0.3%)
  obj_to_string_fallback:     7,274 ( 0.1%)
  unhandled_defined_type:        84 ( 0.0%)
               interrupt:        22 ( 0.0%)

[k0kubun]

Monthly check-in on lobsters stats w/ ratio_in_zjit: 71.7%

Details

***ZJIT: Printing ZJIT statistics on exit***
Top-5 dynamic send types (100.0% of total 13,978,308):
  send_without_block: 10,632,067 (76.1%)
                send:  2,038,059 (14.6%)
         invokesuper:    675,358 ( 4.8%)
         invokeblock:    411,217 ( 2.9%)
        send_forward:    221,607 ( 1.6%)
Top-7 send fallback unspecialized def_types (100.0% of total 3,997,763):
      cfunc: 2,392,653 (59.8%)
       iseq:   756,317 (18.9%)
  optimized:   360,258 ( 9.0%)
    bmethod:   339,080 ( 8.5%)
      alias:    77,616 ( 1.9%)
    attrset:    69,318 ( 1.7%)
       null:     2,521 ( 0.1%)
Top-2 dynamic send types (100.0% of total 3,416,261):
  polymorphic: 2,718,923 (79.6%)
  no_profiles:   697,338 (20.4%)
Top-9 unhandled YARV insns (100.0% of total 224,988):
        checkkeyword: 87,913 (39.1%)
         expandarray: 79,925 (35.5%)
  invokesuperforward: 22,296 ( 9.9%)
       getblockparam: 15,375 ( 6.8%)
   opt_duparray_send: 10,141 ( 4.5%)
    getclassvariable:  8,693 ( 3.9%)
         getconstant:    328 ( 0.1%)
          checkmatch:    290 ( 0.1%)
                once:     27 ( 0.0%)
Top-3 compile error reasons (100.0% of total 1,079,916):
  register_spill_on_alloc: 966,618 (89.5%)
  register_spill_on_ccall:  93,008 ( 8.6%)
        exception_handler:  20,290 ( 1.9%)
Top-14 side exit reasons (100.0% of total 2,774,537):
                        compile_error: 1,079,916 (38.9%)
                   guard_type_failure:   424,544 (15.3%)
                  guard_shape_failure:   382,566 (13.8%)
                  unhandled_yarv_insn:   224,988 ( 8.1%)
  block_param_proxy_not_iseq_or_ifunc:   183,317 ( 6.6%)
                      unhandled_kwarg:   154,583 ( 5.6%)
                           patchpoint:   140,024 ( 5.0%)
                unknown_newarray_send:   125,041 ( 4.5%)
                      unhandled_splat:    31,139 ( 1.1%)
                   unhandled_hir_insn:    16,384 ( 0.6%)
           block_param_proxy_modified:    11,686 ( 0.4%)
               obj_to_string_fallback:       308 ( 0.0%)
               guard_type_not_failure:        22 ( 0.0%)
                            interrupt:        19 ( 0.0%)
dynamic_send_count:                   13,978,308
compiled_iseq_count:                  4,108
failed_iseq_count:                    360
compile_time:                         6,081ms
profile_time:                         56ms
gc_time:                              25ms
invalidation_time:                    16ms
vm_write_pc_count:                    22,735,938
vm_write_sp_count:                    22,266,134
vm_write_locals_count:                22,266,134
vm_write_stack_count:                 22,266,134
vm_write_to_parent_iseq_local_count:  116,533
vm_read_from_parent_iseq_local_count: 2,607,996
code_region_bytes:                    7,741,440
side_exit_count:                      2,774,537
total_insn_count:                     166,381,287
vm_insn_count:                        47,026,175
zjit_insn_count:                      119,355,112
ratio_in_zjit:                        71.7%

[k0kubun]

added a burn-down list to the issue description.

[k0kubun]

Closing since Max split this into three issues:

• ZJIT: lobsters perf burndown #833
• ZJIT: railsbench perf burndown #834
• ZJIT: shipit perf burndown #835