https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69975
Bug ID: 69975
Summary: Missing uninitilized warning / optimized to use wrong
value
Product: gcc
Version: 5.3.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: jan.sm...@alcatel-lucent.com
Target Milestone: ---
#include <stdio.h>
int X;
int foo(int yyy, int zzz)
{
int xxx;
if (yyy)
{
printf("in y\n");
xxx = 5;
}
if (zzz)
{
printf("in x\n");
X = xxx;
}
return X;
}
int main(void)
{
printf("got %d\n", foo(0,1));
return 0;
}
$ gcc test-uninit.c -o /tmp/bla -O1 -Wall -Wuninitialized && /tmp/bla
in x
got 5
$ gcc test-uninit.c -o /tmp/bla -O0 -Wall -Wuninitialized && /tmp/bla
in x
got 0
I would have expected random garbage from the stack, but never ever '5'.
(which makes it seem as if the (yyy) condition was true.)
And this should really give a compile time warning.
If this is considered undefined behaviour, then it is not cought by
-fsanitize=undefined in GCC 5.3
