YJIT: Add a live ISeq counter

It's an estimator for application size and could be used as a
compilation heuristic later.

Co-authored-by: Maxime Chevalier-Boisvert <maxime.chevalierboisvert@shopify.com>
Co-authored-by: Takashi Kokubun <takashikkbn@gmail.com>

common.mk

@@ -3429,6 +3429,7 @@ compile.$(OBJEXT): {$(VPATH)}vm_callinfo.h
 compile.$(OBJEXT): {$(VPATH)}vm_core.h
 compile.$(OBJEXT): {$(VPATH)}vm_debug.h
 compile.$(OBJEXT): {$(VPATH)}vm_opts.h
+compile.$(OBJEXT): {$(VPATH)}yjit.h
 complex.$(OBJEXT): $(CCAN_DIR)/check_type/check_type.h
 complex.$(OBJEXT): $(CCAN_DIR)/container_of/container_of.h
 complex.$(OBJEXT): $(CCAN_DIR)/list/list.h

compile.c

@@ -39,6 +39,7 @@
 #include "vm_core.h"
 #include "vm_callinfo.h"
 #include "vm_debug.h"
+#include "yjit.h"
 
 #include "builtin.h"
 #include "insns.inc"
@@ -1019,6 +1020,11 @@ rb_iseq_translate_threaded_code(rb_iseq_t *iseq)
     }
     FL_SET((VALUE)iseq, ISEQ_TRANSLATED);
 #endif
+
+#if USE_YJIT
+    rb_yjit_live_iseq_count++;
+#endif
+
     return COMPILE_OK;
 }
 

iseq.c

@@ -168,6 +168,8 @@ rb_iseq_free(const rb_iseq_t *iseq)
         rb_rjit_free_iseq(iseq); /* Notify RJIT */
 #if USE_YJIT
         rb_yjit_iseq_free(body->yjit_payload);
+        RUBY_ASSERT(rb_yjit_live_iseq_count > 0);
+        rb_yjit_live_iseq_count--;
 #endif
         ruby_xfree((void *)body->iseq_encoded);
         ruby_xfree((void *)body->insns_info.body);

yjit.h

@@ -27,6 +27,7 @@
 // Expose these as declarations since we are building YJIT.
 extern uint64_t rb_yjit_call_threshold;
 extern uint64_t rb_yjit_cold_threshold;
+extern uint64_t rb_yjit_live_iseq_count;
 void rb_yjit_incr_counter(const char *counter_name);
 bool rb_yjit_enabled_p(void);
 bool rb_yjit_compile_new_iseqs(void);

yjit.rb

@@ -316,6 +316,7 @@ module RubyVM::YJIT
       out.puts "bindings_allocations:  " + format_number(13, stats[:binding_allocations])
       out.puts "bindings_set:          " + format_number(13, stats[:binding_set])
       out.puts "compilation_failure:   " + format_number(13, compilation_failure) if compilation_failure != 0
+      out.puts "live_iseq_count:       " + format_number(13, stats[:live_iseq_count])
       out.puts "compiled_iseq_entry:   " + format_number(13, stats[:compiled_iseq_entry])
       out.puts "cold_iseq_entry:       " + format_number_pct(13, stats[:cold_iseq_entry], stats[:compiled_iseq_entry] + stats[:cold_iseq_entry])
       out.puts "compiled_iseq_count:   " + format_number(13, stats[:compiled_iseq_count])

yjit/src/stats.rs

@@ -14,6 +14,10 @@ use crate::cruby::*;
 use crate::options::*;
 use crate::yjit::yjit_enabled_p;
 
+/// A running total of how many ISeqs are in the system.
+#[no_mangle]
+pub static mut rb_yjit_live_iseq_count: u64 = 0;
+
 /// A middleware to count Rust-allocated bytes as yjit_alloc_size.
 #[global_allocator]
 static GLOBAL_ALLOCATOR: StatsAlloc = StatsAlloc { alloc_size: AtomicUsize::new(0) };
@@ -635,6 +639,8 @@ fn rb_yjit_gen_stats_dict(context: bool) -> VALUE {
 
         // VM instructions count
         hash_aset_usize!(hash, "vm_insns_count", rb_vm_insns_count as usize);
+
+        hash_aset_usize!(hash, "live_iseq_count", rb_yjit_live_iseq_count as usize);
     }
 
     // If we're not generating stats, put only default counters