在内联时,是否有任何C++编译器删除if语句总是保持相同的答案？

Question

如果我有以下功能:

void foo(DoThisSometimes, DoThisAlways)
{
  if (DoThisSometimes == 1)
    {
      //Do stuff
    }
  //Do other stuff
{

内联代码调用此函数DoThisSometimes为0,是否有任何编译器会从内联函数中删除这部分代码:

if (DoThisSometimes == 1)
    {
      //Do stuff
    }

Answer 1

一个体面的编译器当然应该做这个优化,而GCC确实如此.以下来源:

#include <cstdio>

inline void foo(bool maybe)
{
    if (maybe) {
        printf("Maybe\n");
    }
    printf("Always\n");
}

int main()
{
    foo(true);
    foo(false);
}

编译(优化-O3)到:

0000000000400410 <main>:
  400410:   48 83 ec 08             sub    $0x8,%rsp
  400414:   bf e4 05 40 00          mov    $0x4005e4,%edi
  400419:   e8 d2 ff ff ff          callq  4003f0 <puts@plt>
  40041e:   bf ea 05 40 00          mov    $0x4005ea,%edi
  400423:   e8 c8 ff ff ff          callq  4003f0 <puts@plt>
  400428:   bf ea 05 40 00          mov    $0x4005ea,%edi
  40042d:   e8 be ff ff ff          callq  4003f0 <puts@plt>
  400432:   31 c0                   xor    %eax,%eax
  400434:   48 83 c4 08             add    $0x8,%rsp
  400438:   c3                      retq   
  400439:   0f 1f 00                nopl   (%rax)

puts无条件地召唤三次.