您的标志之一是:

--with-default-libstdcxx-abi=gcc4-compatible

GCC4不支持小字符串优化.

and GCC4 does not support small string optimzation.

GCC5开始支持它. isocpp 指出:

GCC5 started supporting it. isocpp states:

默认情况下，使用小字符串优化而不是写时复制引用计数来启用std :: string的新实现.

A new implementation of std::string is enabled by default, using the small string optimization instead of copy-on-write reference counting.

支持我的主张.

此外，浏览std :: string 时提到:

如我们所见，较旧的libstdc ++实现了写时复制功能，因此它使 他们没有利用小对象优化的感觉.

As we see, older libstdc++ implements copy-on-write, and so it makes sense for them to not utilize small objects optimization.

然后当GCC5出现时，他更改上下文.

and then he changes context, when GCC5 comes in play.