Hi,
The following cobe generates a warning "dereferencing type-punned
pointer will break strict-aliasing rules" in function foo(). When I
add an intermediate variable (as in function bar()) the warning
disappears.
#include <stdint.h>
typedef struct blob_St {
uint32_t length;
char data[0] __attribute__ ((aligned (sizeof (uint32_t))));;
} blob_t;
int
foo (blob_t *arg)
{
return *(uint32_t*)arg->data == 10;
}
int
bar (blob_t *arg)
{
uint32_t *tmp;
tmp = (uint32_t*)arg->data;
return *tmp == 10;
}
This code was compiled using 'gcc -c -Wall test.c -O2'. With gcc
version 4.4 I get the error, with versions 4.3 and 4.1 I don't.
My questions are:
1. Why does the error disappear when I use an intermediate variable?
2. Do I run the risk of generating incorrent code if using an
intermediate variable and compiling with strict aliasing?
Thank you.
/A
