[Bug c/46853] gcc fails to warn about uninitialized variable

[gcc-bugs at nospam dot pz.podzone.net]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46853

--- Comment #2 from gcc-bugs at nospam dot pz.podzone.net 2010-12-09 08:36:46 
UTC ---
The variable can be optimised away in the WHILE_LOOP test case so in effect the
variable 'foo' is never used uninitialised.

However with the FOR_LOOP test case it is not possible to optimise away the
variable 'foo' and it is unclear what value the function will eventually
return.

In theory the for loop and the variable 'i' could be optimised away, but I
doubt gcc actually does this.  However imagine that gcc did so then the
FOR_LOOP test case should generate the same warning as the basic test case, but
it does not.

Is it unreasonable to expect gcc to warn about uninitialised use of the
variable in such cases where it is not optimised away?

[Bug c/46853] New: gcc fails to warn about uninitialized variable

[gcc-bugs at nospam dot pz.podzone.net]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46853

   Summary: gcc fails to warn about uninitialized variable
   Product: gcc
   Version: 4.4.5
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: gcc-b...@nospam.pz.podzone.net


With the code below gcc warns of uninitialised variable only when not nested in
a loop.

The test case is simple enough. I think gcc should be able to check for this.  

The 'FOR_LOOP' test case has also been checked with GNU C (GCC) version 4.4.3
(arm-unknown-elf), and gcc (Debian 4.4.5-8) 4.4.5, with the same behaviour as
below.

$ cat gcc_test.c
int func(void);

int main(void)
{
  int foo;

  foo = func();

  return foo;
}

int func(void)
{
  int foo;

#if defined (FOR_LOOP)

  int i;

  for (i = 0; i  5; i++)

#elif defined (WHILE_LOOP)

  while(1)

#endif

  {
if (foo == 0x00)/* uninitialised use */
{
  foo = 0xFF;
}
  }

  return foo;
}
$ gcc gcc_test.c -Os -Wall -Wextra -Wuninitialized
gcc_test.c: In function `func':
gcc_test.c:29: warning: `foo' is used uninitialized in this function
$ gcc gcc_test.c -Os -Wall -Wextra -Wuninitialized -DFOR_LOOP
$ gcc gcc_test.c -Os -Wall -Wextra -Wuninitialized -DWHILE_LOOP
$ gcc --version
gcc (GCC) 4.3.4 20090804 (release) 1
Copyright (C) 2008 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$