Hi!
On Wed, Aug 25, 2021 at 08:23:32PM -0400, David Edelsohn wrote:
> rs6000: inline ldouble __gcc_qsub
>
> While performing some tests of IEEE 128 float for PPC64LE, Michael
> Meissner noticed that __gcc_qsub is substantially slower than
> __gcc_qadd. __gcc_qsub valls __gcc_add with the second operand
("calls", "__gcc_qadd")
> negated. Because the functions normally are invoked through
> libgcc shared object, the extra PLT overhead has a large impact
> on the overall time of the function. Instead of trying to be
> fancy with function decorations to prevent interposition, this
> patch inlines the definition of __gcc_qadd into __gcc_qsub with
> the negation propagated through the function.
Looks good to me, and it is a good way to resolve this. This code is
too old (and unimportant) to do serious engineering on. If we want
any serious optimisation on it we should do that at tree level (why does
that not happen yet anyway?), and inline all of this. This patch is
really just to make benchmark results saner ;-)
Thanks David!
Segher
