Differentiate T_ARRAY and array subclasses

[tenderlove]

This commit teaches the YJIT context the difference between Arrays (objects with type T_ARRAY and class rb_cArray) vs Array subclasses (objects with type T_ARRAY but not class rb_cArray). It uses this information to reduce the number of guards emitted when using jit_guard_known_klass with rb_cArray, notably opt_aref

[noahgibbs]

This sounds like a useful thing. Certainly I had good luck with the same change to strings. Have you run any benchmarks on it?

[maximecb]

Looks like a good idea 👍

Could you include the output of --yjit-stats on railsbench before/after, and quickly benchmark railsbench and liquid-render? I don't expect to see a perf difference but the stats should change a bit, particularly inline code size.

[k0kubun]

Could you include the output of --yjit-stats on railsbench before/after

reminder: You can see this one on CI

Before

https://github.com/ruby/ruby/actions/runs/3878313771/jobs/6614355505

***YJIT: Printing YJIT statistics on exit***
method call exit reasons: 
               iseq_has_rest     109180 (31.4%)
                 iseq_zsuper      45902 (13.2%)
         args_splat_non_iseq      36456 (10.5%)
                   block_arg      32966 ( 9.5%)
            iseq_arity_error      28523 ( 8.2%)
         iseq_ruby2_keywords      24631 ( 7.1%)
              iseq_has_no_kw      17853 ( 5.1%)
         iseq_splat_with_opt      15316 ( 4.4%)
            args_splat_cfunc      13841 ( 4.0%)
                    kw_splat      12611 ( 3.6%)
    iseq_missing_optional_kw       3942 ( 1.1%)
             iseq_has_kwrest       3229 ( 0.9%)
               iseq_has_post       1958 ( 0.6%)
              refined_method        812 ( 0.2%)
       cfunc_ruby_array_varg        469 ( 0.1%)
                    keywords         90 ( 0.0%)
               zsuper_method          5 ( 0.0%)
invokeblock exit reasons: 
               ifunc       5691 (59.0%)
     iseq_arg0_splat       2000 (20.7%)
                proc       1848 (19.2%)
    iseq_tag_changed         76 ( 0.8%)
              symbol         32 ( 0.3%)
invokesuper exit reasons: 
         block       4716 (99.6%)
    me_changed         21 ( 0.4%)
leave exit reasons: 
        interp_return    1699583 (98.1%)
    start_pc_non_zero      33361 ( 1.9%)
         se_interrupt         38 ( 0.0%)
getblockparamproxy exit reasons: 
    block_param_modified         77 (100.0%)
getinstancevariable exit reasons:
    (all relevant counters are zero)
setinstancevariable exit reasons:
    (all relevant counters are zero)
opt_aref exit reasons: 
    (all relevant counters are zero)
expandarray exit reasons: 
            splat       9944 (100.0%)
    rhs_too_small          4 ( 0.0%)
opt_getinlinecache exit reasons: 
    miss          2 (100.0%)
invalidation reasons: 
          method_lookup        316 (60.4%)
    constant_state_bump        149 (28.5%)
       constant_ic_fill         58 (11.1%)
bindings_allocations:         154
bindings_set:                   0
compiled_iseq_count:         2168
compiled_block_count:       19986
compiled_branch_count:      34954
block_next_count:            7062
defer_count:                 6618
freed_iseq_count:              35
invalidation_count:           523
constant_state_bumps:           0
inline_code_size:         2014869
outlined_code_size:       2014448
freed_code_size:                0
code_region_size:         4042752
yjit_alloc_size:         40497128
live_page_count:              247
freed_page_count:               0
code_gc_count:                  0
num_gc_obj_refs:            15879
object_shape_count:          2407
side_exit_count:           434463
total_exit_count:         2134046
total_insns_count:       88045532
vm_insns_count:           7341981
yjit_insns_count:        81138014
ratio_in_yjit:              91.7%
avg_len_in_yjit:             37.8
Top-20 most frequent exit ops (100.0% of exits):
    opt_send_without_block:     130268 (30.0%)
               invokesuper:     115611 (26.6%)
                      send:     101733 (23.4%)
               invokeblock:      36200 (8.3%)
                  opt_aref:      14024 (3.2%)
                     throw:      10460 (2.4%)
               expandarray:       9948 (2.3%)
             setlocal_WC_0:       8148 (1.9%)
                    opt_eq:       4966 (1.1%)
        getblockparamproxy:       2176 (0.5%)
                 opt_nil_p:        325 (0.1%)
               objtostring:        286 (0.1%)
                checkmatch:        154 (0.0%)
      opt_getconstant_path:         63 (0.0%)
                      once:         58 (0.0%)
                     leave:         38 (0.0%)
               opt_empty_p:          2 (0.0%)
                  opt_ltlt:          1 (0.0%)
                  opt_aset:          1 (0.0%)
          opt_regexpmatch2:          1 (0.0%)
itr #1: 6657ms

After

https://github.com/ruby/ruby/actions/runs/3885204101/jobs/6628783596

***YJIT: Printing YJIT statistics on exit***
method call exit reasons: 
               iseq_has_rest     109182 (31.4%)
                 iseq_zsuper      45902 (13.2%)
         args_splat_non_iseq      36456 (10.5%)
                   block_arg      32965 ( 9.5%)
            iseq_arity_error      28523 ( 8.2%)
         iseq_ruby2_keywords      24632 ( 7.1%)
              iseq_has_no_kw      17853 ( 5.1%)
         iseq_splat_with_opt      15316 ( 4.4%)
            args_splat_cfunc      13841 ( 4.0%)
                    kw_splat      12611 ( 3.6%)
    iseq_missing_optional_kw       3942 ( 1.1%)
             iseq_has_kwrest       3229 ( 0.9%)
               iseq_has_post       1958 ( 0.6%)
              refined_method        812 ( 0.2%)
       cfunc_ruby_array_varg        469 ( 0.1%)
                    keywords         90 ( 0.0%)
               zsuper_method          5 ( 0.0%)
invokeblock exit reasons: 
               ifunc       5691 (59.0%)
     iseq_arg0_splat       2000 (20.7%)
                proc       1848 (19.2%)
    iseq_tag_changed         76 ( 0.8%)
              symbol         32 ( 0.3%)
invokesuper exit reasons: 
         block       4716 (99.6%)
    me_changed         21 ( 0.4%)
leave exit reasons: 
        interp_return    1699600 (98.1%)
    start_pc_non_zero      33361 ( 1.9%)
         se_interrupt         26 ( 0.0%)
getblockparamproxy exit reasons: 
    block_param_modified         77 (100.0%)
getinstancevariable exit reasons:
    (all relevant counters are zero)
setinstancevariable exit reasons:
    (all relevant counters are zero)
opt_aref exit reasons: 
    (all relevant counters are zero)
expandarray exit reasons: 
            splat       9944 (100.0%)
    rhs_too_small          4 ( 0.0%)
opt_getinlinecache exit reasons: 
    miss          2 (100.0%)
invalidation reasons: 
          method_lookup        311 (59.9%)
    constant_state_bump        150 (28.9%)
       constant_ic_fill         58 (11.2%)
bindings_allocations:         154
bindings_set:                   0
compiled_iseq_count:         2169
compiled_block_count:       19995
compiled_branch_count:      34907
block_next_count:            7066
defer_count:                 6616
freed_iseq_count:              35
invalidation_count:           519
constant_state_bumps:           0
inline_code_size:         2013729
outlined_code_size:       2011354
freed_code_size:                0
code_region_size:         4030464
yjit_alloc_size:         40456410
live_page_count:              246
freed_page_count:               0
code_gc_count:                  0
num_gc_obj_refs:            15810
object_shape_count:          2408
side_exit_count:           434447
total_exit_count:         2134047
total_insns_count:       88047082
vm_insns_count:           7341642
yjit_insns_count:        81139887
ratio_in_yjit:              91.7%
avg_len_in_yjit:             37.8
Top-19 most frequent exit ops (100.0% of exits):
    opt_send_without_block:     130259 (30.0%)
               invokesuper:     115616 (26.6%)
                      send:     101733 (23.4%)
               invokeblock:      36199 (8.3%)
                  opt_aref:      14027 (3.2%)
                     throw:      10460 (2.4%)
               expandarray:       9948 (2.3%)
             setlocal_WC_0:       8148 (1.9%)
                    opt_eq:       4966 (1.1%)
        getblockparamproxy:       2176 (0.5%)
                 opt_nil_p:        325 (0.1%)
               objtostring:        285 (0.1%)
                checkmatch:        154 (0.0%)
      opt_getconstant_path:         63 (0.0%)
                      once:         58 (0.0%)
                     leave:         26 (0.0%)
               opt_empty_p:          2 (0.0%)
                  opt_ltlt:          1 (0.0%)
          opt_regexpmatch2:          1 (0.0%)
itr #1: 6346ms

[maximecb]

Well done!