码

这是代码：

#include <iostream>
 
constexpr unsigned long divisors(unsigned long n,unsigned long c)
{
    // This is supposed to sum 1 anytime a divisor shows up
    // in the recursion
    return !c ? 0 : !(n % c) + divisors(n,c - 1);
}
 
int main()
{
    // Here I print the number of divisors of 9 numbers! (from 1 to 9)
    for (unsigned long i = 1; i < 10; ++i)
        std::cout << i << " has " << divisors(i,i) << " divisors" << std::endl;
}

正确的行为

这是使用的编译命令,以及程序在正常情况下显示的正确和预期输出：

clang++ -O2 -std=c++11 -stdlib=libc++ -lcxxrt -ldl sample.cpp -o sample
./sample 
1 has 1 divisors
2 has 2 divisors
3 has 2 divisors
4 has 3 divisors
5 has 2 divisors
6 has 4 divisors
7 has 2 divisors
8 has 4 divisors
9 has 3 divisors

行为不正确

这是用于生成提供错误输出的二进制文件的命令行.请注意,唯一的更改是优化标志(-O2到-O3.)

clang++ -O3 -std=c++11 -stdlib=libc++ -lcxxrt -ldl sample.cpp -o sample
./sample 
1 has 1 divisors
2 has 2 divisors
3 has 2 divisors
4 has 1 divisors
5 has 2 divisors
6 has 3 divisors
7 has 2 divisors
8 has 2 divisors
9 has 2 divisors

编辑

我已经更新到了行李箱,铿锵声版本3.4(行李箱183073).这种行为不再重现,应该已经以某种方式修复了.谁知道它是什么问题,如果有一个实际验证和修复,请随时提供答案.如果没有验证,则可能发生回归.