ZJIT: Add --zjit-stats (#14034)

zjit.rb

@@ -1,6 +1,61 @@
+# frozen_string_literal: true
+
+# This module allows for introspection of \ZJIT, CRuby's just-in-time compiler.
+# Everything in the module is highly implementation specific and the API might
+# be less stable compared to the standard library.
+#
+# This module may not exist if \ZJIT does not support the particular platform
+# for which CRuby is built.
 module RubyVM::ZJIT
-  # Assert that any future ZJIT compilation will return a function pointer
-  def self.assert_compiles
-    Primitive.rb_zjit_assert_compiles
+  # Avoid calling a Ruby method here to avoid interfering with compilation tests
+  if Primitive.rb_zjit_stats_enabled_p
+    at_exit { print_stats }
+  end
+end
+
+class << RubyVM::ZJIT
+  # Return ZJIT statistics as a Hash
+  def stats
+    stats = Primitive.rb_zjit_stats
+
+    if stats.key?(:vm_insns_count) && stats.key?(:zjit_insns_count)
+      stats[:total_insns_count] = stats[:vm_insns_count] + stats[:zjit_insns_count]
+      stats[:ratio_in_zjit] = 100.0 * stats[:zjit_insns_count] / stats[:total_insns_count]
+    end
+
+    stats
+  end
+
+  # Get the summary of ZJIT statistics as a String
+  def stats_string
+    buf = +''
+    stats = self.stats
+
+    [
+      :total_insns_count,
+      :vm_insns_count,
+      :zjit_insns_count,
+      :ratio_in_zjit,
+    ].each do |key|
+      value = stats[key]
+      if key == :ratio_in_zjit
+        value = '%0.1f%%' % value
+      end
+      buf << "#{'%-18s' % "#{key}:"} #{value}\n"
+    end
+    buf
+  end
+
+  # Assert that any future ZJIT compilation will return a function pointer
+  def assert_compiles # :nodoc:
+    Primitive.rb_zjit_assert_compiles
+  end
+
+  # :stopdoc:
+  private
+
+  # Print ZJIT stats
+  def print_stats
+    $stderr.write stats_string
   end
 end