gcc5.1的新libstdc++可能会分配大量堆内存

valgrind在使用gcc5.1, g++ ./a.cpp，

int main () {}

valgrind表示，valgrind ./a.out

==32037== HEAP SUMMARY:
==32037==     in use at exit: 72,704 bytes in 1 blocks
==32037==   total heap usage: 1 allocs, 0 frees, 72,704 bytes allocated
==32037== 
==32037== LEAK SUMMARY:
==32037==    definitely lost: 0 bytes in 0 blocks
==32037==    indirectly lost: 0 bytes in 0 blocks
==32037==      possibly lost: 0 bytes in 0 blocks
==32037==    still reachable: 72,704 bytes in 1 blocks
==32037==         suppressed: 0 bytes in 0 blocks
==32037== Rerun with --leak-check=full to see details of leaked memory
==32037== 
==32037== For counts of detected and suppressed errors, rerun with: -v
==32037== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 5 from 5)

对于c程序，valgrind不会报告内存泄漏和内存分配。此外，对于gcc5.0和gcc4.9.2, valgrind报告没有内存泄漏，也没有内存分配。那么，我猜gcc5.1的新libstdc++是原因。

我的问题是如何减少这种巨大的内存分配，这可能是在libstdc++。实际上，这个用-O3编译的空c++程序的执行时间比一个空c程序的执行时间要长几毫秒(不含systime)。