https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86259
--- Comment #5 from Vladimir Panteleev <gcc at thecybershadow dot net> ---
(In reply to Andrew Pinski from comment #2)
> Note gcc thinks strlen(s) is less than or equal to 3 as s is really T.s
> which is an array of 4 in size and there for the last element has to be a
> null char.
Hmm. Here is a simpler example which illustrates this:
/////////////////// test.c ///////////////////
#include <stdio.h>
#include <string.h>
struct S
{
int x[1];
};
union U
{
struct S arr[64];
char s[256];
};
int main()
{
union U u;
strcpy(u.s, "abcdefghijklmnopqrstuvwxyz");
size_t len = strlen((char*)&u.arr[1].x);
puts(len > 10 ? "YES" : "NO");
return 0;
}
//////////////////////////////////////////////
This prints "NO" with -O1 and above. clang always prints "YES".
Are you sure this is an optimization the compiler is allowed to make, though? I
would think that the explicit cast to char* removes all bets as to how long the
string really is.
