Re: aliasing revisited

[Ian Lance Taylor <iant at google dot com>]

Brian Budge <brian.budge@gmail.com> writes:

> simd4f is a wrapper on __m128, and "m_leftRep" is an array of
> uint32_t.  I realize that I could just create a simd4f array for "c",
> perform the first loop, and then put a union in the second loop.  This
> would require at least one extra write per uint32_t though.  Is there
> any way of specifying that "c" aliases "m_leftRep"?  Or am I stuck
> with the union?

I don't know if this answers your question, because I don't know
precisely what you mean by a wrapper, but note that __m128 is magical: a
pointer to __m128 is permitted to alias other pointers.  This is
essentially required by the Intel docs.  It is implemented by giving
__m128 the "may_alias" attribute, q.v.

Ian