YJIT: Skip setlocal WB check for immediate values (#6122)

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.

yjit/src/codegen.rs

@@ -1565,10 +1565,15 @@ fn gen_setlocal_wc0(
 
     let slot_idx = jit_get_arg(jit, 0).as_i32();
     let local_idx = slot_to_local_idx(jit.get_iseq(), slot_idx).as_usize();
+    let value_type = ctx.get_opnd_type(StackOpnd(0));
 
     // Load environment pointer EP (level 0) from CFP
     gen_get_ep(cb, REG0, 0);
 
+    // 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.
+    if !value_type.is_imm() {
         // flags & VM_ENV_FLAG_WB_REQUIRED
         let flags_opnd = mem_opnd(
             64,
@@ -1582,10 +1587,10 @@ fn gen_setlocal_wc0(
 
         // if (flags & VM_ENV_FLAG_WB_REQUIRED) != 0
         jnz_ptr(cb, side_exit);
+    }
 
     // Set the type of the local variable in the context
-    let temp_type = ctx.get_opnd_type(StackOpnd(0));
+    ctx.set_local_type(local_idx, value_type);
-    ctx.set_local_type(local_idx, temp_type);
 
     // Pop the value to write from the stack
     let stack_top = ctx.stack_pop(1);
@@ -1606,9 +1611,15 @@ fn gen_setlocal_generic(
     local_idx: i32,
     level: u32,
 ) -> CodegenStatus {
+    let value_type = ctx.get_opnd_type(StackOpnd(0));
+
     // Load environment pointer EP at level
     gen_get_ep(cb, REG0, level);
 
+    // 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.
+    if !value_type.is_imm() {
         // flags & VM_ENV_FLAG_WB_REQUIRED
         let flags_opnd = mem_opnd(
             64,
@@ -1622,6 +1633,7 @@ fn gen_setlocal_generic(
 
         // if (flags & VM_ENV_FLAG_WB_REQUIRED) != 0
         jnz_ptr(cb, side_exit);
+    }
 
     // Pop the value to write from the stack
     let stack_top = ctx.stack_pop(1);