Cleanup diff against upstream. Add comments

I did a `git diff --stat` against upstream and looked at all the files
that are outside of YJIT to come up with these minor changes.

iseq.h

@@ -315,8 +315,6 @@ VALUE rb_iseq_defined_string(enum defined_type type);
 /* vm.c */
 VALUE rb_iseq_local_variables(const rb_iseq_t *iseq);
 
-NOINLINE(void rb_yjit_empty_func_with_ec(rb_control_frame_t *cfp, rb_execution_context_t *ec));
-
 RUBY_SYMBOL_EXPORT_END
 
 #endif /* RUBY_ISEQ_H */

mjit.h

@@ -193,6 +193,7 @@ mjit_exec(rb_execution_context_t *ec)
     RB_DEBUG_COUNTER_INC(mjit_frame_VM2JT);
 #  endif
     RB_DEBUG_COUNTER_INC(mjit_exec_call_func);
+    // Under SystemV x64 calling convention
     // ec -> RDI
     // cfp -> RSI
     return func(ec, ec->cfp);

proc.c

@@ -347,7 +347,7 @@ rb_binding_alloc(VALUE klass)
     VALUE obj;
     rb_binding_t *bind;
     obj = TypedData_Make_Struct(klass, rb_binding_t, &ruby_binding_data_type, bind);
-#if RUBY_DEBUG
+#if YJIT_STATS
     rb_yjit_collect_binding_alloc();
 #endif
     return obj;
@@ -614,7 +614,7 @@ bind_local_variable_set(VALUE bindval, VALUE sym, VALUE val)
 	env = VM_ENV_ENVVAL_PTR(vm_block_ep(&bind->block));
     }
 
-#if RUBY_DEBUG
+#if YJIT_STATS
     rb_yjit_collect_binding_set();
 #endif
 

tool/ruby_vm/models/instructions.rb

@@ -18,6 +18,5 @@ RubyVM::Instructions = RubyVM::BareInstructions.to_a + \
                        RubyVM::OperandsUnifications.to_a + \
                        RubyVM::InstructionsUnifications.to_a
 
-
 require_relative 'trace_instructions'
 RubyVM::Instructions.freeze

vm_exec.c

@@ -93,13 +93,8 @@ vm_exec_core(rb_execution_context_t *ec, VALUE initial)
 #define USE_MACHINE_REGS 1
 
 #elif defined(__GNUC__) && defined(__powerpc64__)
-#if 0
     DECL_SC_REG(const VALUE *, pc, "14");
     DECL_SC_REG(rb_control_frame_t *, cfp, "15");
-#else
-    register rb_control_frame_t *reg_cfp;
-    const VALUE *reg_pc;
-#endif
 #define USE_MACHINE_REGS 1
 
 #elif defined(__GNUC__) && defined(__aarch64__)

vm_insnhelper.c

@@ -4808,6 +4808,8 @@ vm_ic_update(const rb_iseq_t *iseq, IC ic, VALUE val, const VALUE *reg_ep)
     ruby_vm_const_missing_count = 0;
     RB_OBJ_WRITE(iseq, &ic->entry, ice);
 #ifndef MJIT_HEADER
+    // MJIT and YJIT can't be on at the same time, so there is no need to
+    // notify YJIT about changes to the IC when running inside MJIT code.
     rb_yjit_constant_ic_update(iseq, ic);
 #endif
 }