http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52609
--- Comment #2 from Pawel Sikora <pluto at agmk dot net> 2012-03-18 09:32:03
UTC ---
(In reply to comment #1)
> >accessing unsigned* via float* looks buggy
>
> It does not have to be if the original argument was originally of type float.
> Aliasing is not about type of pointers but the type which is used to access
> and
> such.
ok, here's an updated testcase:
$ cat alias-bug.c
unsigned buffer[1];
float bug1( unsigned u )
{
buffer[0]=u;
return *(float*)(&buffer[0]); // warning.
}
float bug2( unsigned u )
{
buffer[0]=u;
float* ptr=(float*)&buffer[0];
return *ptr; // missed strict aliasing warning.
}
gcc repots warning only for bug1() and misses warning for bug2():
$ gcc -Wall -Wstrict-aliasing=3 -O2 alias-bug.c -c
alias-bug.c: In function 'bug1':
alias-bug.c:6:2: warning: dereferencing type-punned pointer will break
strict-aliasing rules [-Wstrict-aliasing]
