将uintptru\t转换为bool会使SSO基准测试速度减慢几倍

考虑下面实现的类(基本上是为了MCVE) (假设是little endian、64位指针等):

class String {
   char* data_;
   bool sso() const { return reinterpret_cast<uintptr_t>(data_) & 1; }     
 public:
    String(const char * arg = "") {
       auto len = strlen(arg);
       if (len > 6) {
          data_ = new char[len + 1];
          memcpy(data_, arg, len + 1);
       } 
       else {
          data_ = reinterpret_cast<char*>((uintptr_t)1);
          memcpy(reinterpret_cast<char*>(&data_) + 1, arg, len + 1);
       }            
   }  
   ~String() { if (sso() == false) delete data_; }
// ~String() { if (reinterpret_cast<uintptr_t>(data_) & 1 == 0) delete data_; }
};

static void CreateShort(benchmark::State& state) {    
   for (auto _ : state) {    
      String s("hello");
      benchmark::DoNotOptimize(s); 
   }  
}

快5.7倍

• 基准链接: http://quick-bench.com/wZhYuffRc1LMwFJ4rx4Xxy330Sw
• 导柱连杆: https://godbolt.org/z/dAUI_u

与叮当声,没有区别,这两个变种是快速的。

问题是转换成 bool

~String() { if ((bool)(reinterpret_cast<uintptr_t>(data_) & 1) == false) delete data_; }