YJIT: implement side chain fallback for setlocal to avoid exiting (#8227)

* YJIT: implement side chain fallback for setlocal to avoid exiting

* Update yjit/src/codegen.rs

Co-authored-by: Takashi Kokubun <takashikkbn@gmail.com>

---------

Co-authored-by: Takashi Kokubun <takashikkbn@gmail.com>

test/ruby/test_yjit.rb

@@ -661,7 +661,7 @@ class TestYJIT < Test::Unit::TestCase
 
   def test_send_block
     # Setlocal_wc_0 sometimes side-exits on write barrier
-    assert_compiles(<<~'RUBY', result: "b:n/b:y/b:y/b:n", exits: { :setlocal_WC_0 => 0..1 })
+    assert_compiles(<<~'RUBY', result: "b:n/b:y/b:y/b:n")
       def internal_method(&b)
         "b:#{block_given? ? "y" : "n"}"
       end

vm_core.h

@@ -1758,6 +1758,7 @@ rb_thread_t * ruby_thread_from_native(void);
 int ruby_thread_set_native(rb_thread_t *th);
 int rb_vm_control_frame_id_and_class(const rb_control_frame_t *cfp, ID *idp, ID *called_idp, VALUE *klassp);
 void rb_vm_rewind_cfp(rb_execution_context_t *ec, rb_control_frame_t *cfp);
+void rb_vm_env_write(const VALUE *ep, int index, VALUE v);
 VALUE rb_vm_bh_to_procval(const rb_execution_context_t *ec, VALUE block_handler);
 
 void rb_vm_register_special_exception_str(enum ruby_special_exceptions sp, VALUE exception_class, VALUE mesg);

vm_insnhelper.c

@@ -505,6 +505,12 @@ vm_env_write(const VALUE *ep, int index, VALUE v)
     }
 }
 
+void
+rb_vm_env_write(const VALUE *ep, int index, VALUE v)
+{
+    vm_env_write(ep, index, v);
+}
+
 VALUE
 rb_vm_bh_to_procval(const rb_execution_context_t *ec, VALUE block_handler)
 {

yjit/bindgen/src/main.rs

@@ -283,6 +283,7 @@ fn main() {
         .blocklist_type("rb_control_frame_struct")
         .opaque_type("rb_control_frame_struct")
         .allowlist_function("rb_vm_bh_to_procval")
+        .allowlist_function("rb_vm_env_write")
         .allowlist_function("rb_vm_ep_local_ep")
         .allowlist_type("vm_special_object_type")
         .allowlist_var("VM_ENV_DATA_INDEX_SPECVAL")

yjit/src/codegen.rs

@@ -1546,8 +1546,7 @@ fn gen_expandarray(
 
     let array_opnd = asm.stack_opnd(0);
 
-    // num is the number of requested values. If there aren't enough in the
-    // array then we're going to push on nils.
+    // If the array operand is nil, just push on nils
     if asm.ctx.get_opnd_type(array_opnd.into()) == Type::Nil {
         asm.stack_pop(1); // pop after using the type info
         // special case for a, b = nil pattern
@@ -1762,6 +1761,7 @@ fn gen_getlocal_wc1(
 fn gen_setlocal_generic(
     jit: &mut JITState,
     asm: &mut Assembler,
+    ocb: &mut OutlinedCb,
     ep_offset: u32,
     level: u32,
 ) -> Option<CodegenStatus> {
@@ -1770,6 +1770,29 @@ fn gen_setlocal_generic(
     // Load environment pointer EP at level
     let ep_opnd = gen_get_ep(asm, level);
 
+    // Fallback because of write barrier
+    if asm.ctx.get_chain_depth() > 0
+    {
+        // Save the PC and SP because it runs GC
+        jit_prepare_routine_call(jit, asm);
+
+        // Pop the value to write from the stack
+        let value_opnd = asm.stack_pop(1);
+
+        // void rb_vm_env_write(const VALUE *ep, int index, VALUE v)
+        let index = -(ep_offset as i64);
+        asm.ccall(
+            rb_vm_env_write as *const u8,
+            vec![
+                ep_opnd,
+                index.into(),
+                value_opnd,
+            ]
+        );
+
+        return Some(KeepCompiling);
+    }
+
     // Write barriers may be required when VM_ENV_FLAG_WB_REQUIRED is set, however write barriers
     // only affect heap objects being written. If we know an immediate value is being written we
     // can skip this check.
@@ -1783,7 +1806,15 @@ fn gen_setlocal_generic(
         asm.test(flags_opnd, VM_ENV_FLAG_WB_REQUIRED.into());
 
         // if (flags & VM_ENV_FLAG_WB_REQUIRED) != 0
-        asm.jnz(Target::side_exit(Counter::setlocal_wb_required));
+        assert!(asm.ctx.get_chain_depth() == 0);
+        jit_chain_guard(
+            JCC_JNZ,
+            jit,
+            asm,
+            ocb,
+            1,
+            Counter::setlocal_wb_required,
+        );
     }
 
     if level == 0 {
@@ -1804,29 +1835,29 @@ fn gen_setlocal_generic(
 fn gen_setlocal(
     jit: &mut JITState,
     asm: &mut Assembler,
-    _ocb: &mut OutlinedCb,
+    ocb: &mut OutlinedCb,
 ) -> Option<CodegenStatus> {
     let idx = jit.get_arg(0).as_u32();
     let level = jit.get_arg(1).as_u32();
-    gen_setlocal_generic(jit, asm, idx, level)
+    gen_setlocal_generic(jit, asm, ocb, idx, level)
 }
 
 fn gen_setlocal_wc0(
     jit: &mut JITState,
     asm: &mut Assembler,
-    _ocb: &mut OutlinedCb,
+    ocb: &mut OutlinedCb,
 ) -> Option<CodegenStatus> {
     let idx = jit.get_arg(0).as_u32();
-    gen_setlocal_generic(jit, asm, idx, 0)
+    gen_setlocal_generic(jit, asm, ocb, idx, 0)
 }
 
 fn gen_setlocal_wc1(
     jit: &mut JITState,
     asm: &mut Assembler,
-    _ocb: &mut OutlinedCb,
+    ocb: &mut OutlinedCb,
 ) -> Option<CodegenStatus> {
     let idx = jit.get_arg(0).as_u32();
-    gen_setlocal_generic(jit, asm, idx, 1)
+    gen_setlocal_generic(jit, asm, ocb, idx, 1)
 }
 
 // new hash initialized from top N values

yjit/src/cruby_bindings.inc.rs

@@ -1166,6 +1166,7 @@ extern "C" {
     pub static mut rb_block_param_proxy: VALUE;
     pub fn rb_vm_ep_local_ep(ep: *const VALUE) -> *const VALUE;
     pub fn rb_iseq_path(iseq: *const rb_iseq_t) -> VALUE;
+    pub fn rb_vm_env_write(ep: *const VALUE, index: ::std::os::raw::c_int, v: VALUE);
     pub fn rb_vm_bh_to_procval(ec: *const rb_execution_context_t, block_handler: VALUE) -> VALUE;
     pub fn rb_vm_frame_method_entry(
         cfp: *const rb_control_frame_t,