https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91154
--- Comment #32 from Uroš Bizjak <ubizjak at gmail dot com> ---
(In reply to H.J. Lu from comment #31)
> > No, IMO IRA should be "fixed" to avoid stack temporary and (based on some
> > cost metric) use direct move for paradoxical subregs.
>
> The problem is
>
> /* Moves between SSE and integer units are expensive. */
> if (SSE_CLASS_P (class1) != SSE_CLASS_P (class2))
>
> /* ??? By keeping returned value relatively high, we limit the number
> of moves between integer and SSE registers for all targets.
> Additionally, high value prevents problem with x86_modes_tieable_p(),
> where integer modes in SSE registers are not tieable
> because of missing QImode and HImode moves to, from or between
> MMX/SSE registers. */
> return MAX (8, SSE_CLASS_P (class1)
> ? ix86_cost->hard_register.sse_to_integer
> : ix86_cost->hard_register.integer_to_sse);
>
> The minimum cost of moves between SSE and integer units is 8.
I guess this should be reviewed. This is from reload time, nowadays we never
actually disable sse <-> int moves, we use preferred_for_{speed,size}
attributes. Also, at least for TARGET_MMX_WITH_SSE targets, we can change the
penalty for MMX moves.
These sort of changes should be backed by runtime benchmark results.
Thanks for heads up, but let's take this cost issue elsewhere.
