const在这里允许(理论上)优化吗? [英] Does const allow for (theoretical) optimization here?
问题描述
请考虑以下代码段:
void foo(const int&);
int bar();
int test1()
{
int x = bar();
int y = x;
foo(x);
return x - y;
}
int test2()
{
const int x = bar();
const int y = x;
foo(x);
return x - y;
}
在我对标准的理解中，test2中的foo不允许x和y进行更改，而在test1中的foo不能对其进行更改(例如，const_cast从const int&中删除const，因为所引用的对象实际上不是test1中的const).
In my understanding of the standard, neither x nor y are allowed to be changed by foo in test2, whereas they could be changed by foo in test1 (with e.g. a const_cast to remove const from the const int& because the referenced objects aren't actually const in test1).
现在，无论gcc，clang还是MSVC都似乎都没有将test2优化为foo(bar()); return 0;，而且我可以理解，他们不想浪费优化，而将这种优化传递给实践的人很少.
Now, neither gcc nor clang nor MSVC seem to optimize test2 to foo(bar()); return 0;, and I can understand that they do not want to waste optimization passes on an optimization that only rarely applies in practice.
但是我至少对我对这种情况的理解是正确的，还是我缺少在test2中修改x的某种合法方法?
But am I at least correct in my understanding of this situation, or am I missing some legal way for x to be modified in test2?
