fix: 修复无 else 块时冗余指令跳转问题

crates/oxide_compiler/src/counter.rs

@@ -33,7 +33,9 @@ impl Compiler {
                 self.count_statement(&ifs.consequent, ctx);
                 ctx.alloc_reg(); // result register
                 ctx.projected_pc += 1; // LOAD_VAR result <- consequent
-                ctx.projected_pc += 1; // JMP (skip else)
+                if ifs.alternate.is_some() {
+                    ctx.projected_pc += 1; // JMP (skip else)
+                }
                 ctx.label_map.insert(else_label, ctx.projected_pc);
                 if let Some(alt_stmt) = &ifs.alternate {
                     self.count_statement(alt_stmt, ctx);
@@ -173,7 +175,7 @@ impl Compiler {
                         LogicalOperator::And => Label::TernaryEnd(id),
                         LogicalOperator::Or => Label::TernaryElse(id),
                         LogicalOperator::Coalesce => {
-                            return;
+                            unreachable!()
                         }
                     };
                     ctx.label_map.insert(skip_label, ctx.projected_pc);

crates/oxide_compiler/src/emitter.rs

@@ -93,9 +93,12 @@ impl Compiler {
                     ));
                 }
 
-                let end_pos = ctx.label_map[&end_label];
-                let offset = (end_pos as isize) - (ctx.bytecode.len() as isize);
-                ctx.emit(opcode::encode_jmp(offset as i16));
+                let has_alt = ifs.alternate.is_some();
+                if has_alt {
+                    let end_pos = ctx.label_map[&end_label];
+                    let offset = (end_pos as isize) - (ctx.bytecode.len() as isize);
+                    ctx.emit(opcode::encode_jmp(offset as i16));
+                }
 
                 if let Some(alt) = &ifs.alternate {
                     let alt_reg = self.emit_statement(alt, ctx)?;