On Wed, May 05, 2021 at 01:45:29PM +0200, Marc Glisse wrote:
> On Tue, 4 May 2021, Jakub Jelinek via Gcc-patches wrote:
>
> > 2) the pr94589-2.C testcase should be matching just 12 times each, but runs
> > into operator>=(strong_ordering, unspecified) being defined as
> > (_M_value&1)==_M_value
> > rather than _M_value>=0. When not honoring NaNs, the 2 case should be
> > unreachable and so (_M_value&1)==_M_value is then equivalent to _M_value>=0,
> > but is not a single use but two uses. I'll need to pattern match that case
> > specially.
>
> Somewhere in RTL (_M_value&1)==_M_value is turned into (_M_value&-2)==0,
> that could be worth doing already in GIMPLE.
Apparently it is
/* Simplify eq/ne (and/ior x y) x/y) for targets with a BICS instruction or
constant folding if x/y is a constant. */
if ((code == EQ || code == NE)
&& (op0code == AND || op0code == IOR)
&& !side_effects_p (op1)
&& op1 != CONST0_RTX (cmp_mode))
{
/* Both (eq/ne (and x y) x) and (eq/ne (ior x y) y) simplify to
(eq/ne (and (not y) x) 0). */
...
/* Both (eq/ne (and x y) y) and (eq/ne (ior x y) x) simplify to
(eq/ne (and (not x) y) 0). */
Yes, doing that on GIMPLE for the case where the not argument is constant
would simplify the phiopt follow-up (it would be single imm use then).
Jakub
