YJIT: Generate side exits as late as possible (#7612)

* YJIT: Generate side exits late as possible

* YJIT: s/for_stack_size/with_stack_size/

* YJIT: s/get_counter/exit_counter/

yjit/src/core.rs

@@ -1516,6 +1516,16 @@ impl Context {
         self.stack_size
     }
 
+    /// Create a new Context instance with a given stack_size and sp_offset adjusted
+    /// accordingly. This is useful when you want to virtually rewind a stack_size for
+    /// generating a side exit while considering past sp_offset changes on gen_save_sp.
+    pub fn with_stack_size(&self, stack_size: u8) -> Context {
+        let mut ctx = self.clone();
+        ctx.sp_offset -= (ctx.get_stack_size() as isize - stack_size as isize) as i8;
+        ctx.stack_size = stack_size;
+        ctx
+    }
+
     pub fn get_sp_offset(&self) -> i8 {
         self.sp_offset
     }