Prevent enabling yjit when zjit enabled (rubyGH-13358)

`ruby --yjit --zjit` already warns and exits, but it was still possible
to enable both with `ruby --zjit -e 'RubyVM:YJIT.enable`.

This commit prevents that with a warning and an early return. (We could
also exit, but that seems a bit unfriendly once we're already running
the program.)

Co-authored-by: ywenc <[email protected]>

Author: composerinteralia

common.mk

@@ -21737,6 +21737,7 @@ yjit.$(OBJEXT): {$(VPATH)}vm_sync.h
 yjit.$(OBJEXT): {$(VPATH)}yjit.c
 yjit.$(OBJEXT): {$(VPATH)}yjit.h
 yjit.$(OBJEXT): {$(VPATH)}yjit.rbinc
+yjit.$(OBJEXT): {$(VPATH)}zjit.h
 zjit.$(OBJEXT): $(CCAN_DIR)/check_type/check_type.h
 zjit.$(OBJEXT): $(CCAN_DIR)/container_of/container_of.h
 zjit.$(OBJEXT): $(CCAN_DIR)/list/list.h

test/ruby/test_yjit.rb

@@ -166,6 +166,11 @@ def test_yjit_enable_with_invalid_runtime_mem_size_option
     end
   end
 
+  if JITSupport.zjit_supported?
+    def test_yjit_enable_with_zjit_enabled
+      assert_in_out_err(['--zjit'], 'puts RubyVM::YJIT.enable', ['false'], ['Only one JIT can be enabled at the same time.'])
+    end
+  end
 
   def test_yjit_stats_and_v_no_error
     _stdout, stderr, _status = invoke_ruby(%w(-v --yjit-stats), '', true, true)

yjit.c

@@ -29,6 +29,7 @@
 #include "iseq.h"
 #include "ruby/debug.h"
 #include "internal/cont.h"
+#include "zjit.h"
 
 // For mmapp(), sysconf()
 #ifndef _WIN32

yjit.rb

@@ -48,6 +48,11 @@ def self.reset_stats!
   def self.enable(stats: false, log: false, mem_size: nil, call_threshold: nil)
     return false if enabled?
 
+    if Primitive.cexpr! 'RBOOL(rb_zjit_enabled_p)'
+      warn("Only one JIT can be enabled at the same time.")
+      return false
+    end
+
     if mem_size
       raise ArgumentError, "mem_size must be a Integer" unless mem_size.is_a?(Integer)
       raise ArgumentError, "mem_size must be between 1 and 2048 MB" unless (1..2048).include?(mem_size)

zjit.h

@@ -14,6 +14,7 @@ void rb_zjit_profile_enable(const rb_iseq_t *iseq);
 void rb_zjit_bop_redefined(int redefined_flag, enum ruby_basic_operators bop);
 void rb_zjit_invalidate_ep_is_bp(const rb_iseq_t *iseq);
 #else
+#define rb_zjit_enabled_p false
 static inline void rb_zjit_compile_iseq(const rb_iseq_t *iseq, rb_execution_context_t *ec, bool jit_exception) {}
 static inline void rb_zjit_profile_insn(enum ruby_vminsn_type insn, rb_execution_context_t *ec) {}
 static inline void rb_zjit_profile_enable(const rb_iseq_t *iseq) {}