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Re: Altivec + 16 byte alignment
On 11-Feb-2003, Mike Stump <mstump@apple.com> wrote:
> On Tuesday, February 11, 2003, at 11:59 AM, John David Anglin wrote:
> > Another issue is GCC's alignment attribute is silently ignored for
> > stack locals and the documentation doesn't say that.
>
> Let us agree that this is just a bug, or at least a bug for CPUs that
> have hard requirements of say 16 bytes (Altivec, SSE) and the user asks
> for 16 byte alignment and we silently only do 8 byte alignment.
Please let us agree that this is just a bug, regardless of the CPU's
requirements. The alignment declaration might be used by the programmer
to ensure that the lower bits are available for use as tag bits.
For example, the following program should result in either success
or a compile error (if the requested alignment is not supported).
But IMHO it should not result in an assertion failure.
#include <assert.h>
#define ALIGN 32
int main() {
char c __attribute__((aligned(ALIGN)));
assert ((((unsigned long) &c) & (ALIGN - 1)) == 0);
return 0;
}
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