c - gcc -Wall -Wuninitialized 不会对未初始化的变量发出警告

Question

gcc 版本 - gcc (Ubuntu 4.8.4-2ubuntu1~14.04.1) 4.8.4

使用 -Wall -Wuninitialized 编译以下代码会按预期抛出警告警告:“test”在此函数中使用未初始化 [-Wuninitialized]

#include<stdio.h>
#include<stdlib.h>

void check (int test )
{
   printf("%d",test);
}

int
main()
{
   int test;
   check(test);
   return 0;
}

但是使用 -Wall -Wuninitialized 编译下面的代码不会抛出警告

#include<stdio.h>
#include<stdlib.h>

void check (int test )
{
   printf("%d",test);
}

int
main()
{
   int test;
   int condition = 0;

   if(condition == 27)
      test = 10;

   check(test);
   return 0;
}

它不应该发出警告吗？它与编译器优化有关吗？

Answer 1

What an user understands as a false positive may be different for the particular user. Some users are interested in cases that are hidden because of actions of the optimizers combined with the current environment. However, many users aren't, since that case is hidden because it cannot arise in the compiled code. The canonical example is (MM05):

int x;
if (f ())
x = 3;
return x;

where 'f' always return non-zero for the current environment, and thus, it may be optimised away. Here, a group of users would like to get an uninitialized warning since 'f' may return zero when compiled elsewhere. Yet, other group of users would consider spurious a warning about a situation that cannot arise in the executable being compiled.

https://gcc.gnu.org/wiki/Better_Uninitialized_Warnings#Proposal

---

编辑:MMO5 已经修复

https://gcc.gnu.org/wiki/Better_Uninitialized_Warnings#MM05