ZJIT: Add RubyVM::ZJIT.enabled? (ruby#14159)

Co-authored-by: Max Bernstein <tekknolagi@gmail.com>

Author: k0kubun

test/ruby/test_zjit.rb

@@ -9,6 +9,15 @@
 return unless JITSupport.zjit_supported?
 
 class TestZJIT < Test::Unit::TestCase
+  def test_enabled
+    assert_runs 'false', <<~RUBY, zjit: false
+      RubyVM::ZJIT.enabled?
+    RUBY
+    assert_runs 'true', <<~RUBY, zjit: true
+      RubyVM::ZJIT.enabled?
+    RUBY
+  end
+
   def test_call_itself
     assert_compiles '42', <<~RUBY, call_threshold: 2
       def test = 42.itself
@@ -1547,14 +1556,23 @@ def assert_runs(expected, test_script, insns: [], assert_compiles: false, **opts
   end
 
   # Run a Ruby process with ZJIT options and a pipe for writing test results
-  def eval_with_jit(script, call_threshold: 1, num_profiles: 1, stats: false, debug: true, timeout: 1000, pipe_fd:)
-    args = [
-      "--disable-gems",
-      "--zjit-call-threshold=#{call_threshold}",
-      "--zjit-num-profiles=#{num_profiles}",
-    ]
-    args << "--zjit-stats" if stats
-    args << "--zjit-debug" if debug
+  def eval_with_jit(
+    script,
+    call_threshold: 1,
+    num_profiles: 1,
+    zjit: true,
+    stats: false,
+    debug: true,
+    timeout: 1000,
+    pipe_fd:
+  )
+    args = ["--disable-gems"]
+    if zjit
+      args << "--zjit-call-threshold=#{call_threshold}"
+      args << "--zjit-num-profiles=#{num_profiles}"
+      args << "--zjit-stats" if stats
+      args << "--zjit-debug" if debug
+    end
     args << "-e" << script_shell_encode(script)
     pipe_r, pipe_w = IO.pipe
     # Separate thread so we don't deadlock when

zjit.rb

@@ -14,7 +14,12 @@ module RubyVM::ZJIT
 end
 
 class << RubyVM::ZJIT
-  # Return ZJIT statistics as a Hash
+  # Check if \ZJIT is enabled
+  def enabled?
+    Primitive.cexpr! 'RBOOL(rb_zjit_enabled_p)'
+  end
+
+  # Return \ZJIT statistics as a Hash
   def stats
     stats = Primitive.rb_zjit_stats
 
@@ -26,7 +31,7 @@ def stats
     stats
   end
 
-  # Get the summary of ZJIT statistics as a String
+  # Get the summary of \ZJIT statistics as a String
   def stats_string
     buf = +''
     stats = self.stats