match.pd: Optimize (x & y) == x into (x & ~y) == 0 [PR94589]

> 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).

On Thu, May 06, 2021 at 09:42:41PM +0200, Marc Glisse wrote:
> We can probably do it in 2 steps, first something like
>
> (for cmp (eq ne)
>  (simplify
>   (cmp (bit_and:c @0 @1) @0)
>   (cmp (@0 (bit_not! @1)) { build_zero_cst (TREE_TYPE (@0)); })))
>
> to get rid of the double use, and then simplify X&C==0 to X<=~C if C is a
> mask 111...000 (I thought we already had a function to detect such masks, or
> the 000...111, but I can't find them anymore).

Ok, here is the first step then.

2021-05-12  Jakub Jelinek  <jakub@redhat.com>
	    Marc Glisse  <marc.glisse@inria.fr>

	PR tree-optimization/94589
	* match.pd ((X & Y) == X -> (X & ~Y) == 0,
	(X | Y) == Y -> (X & ~Y) == 0): New GIMPLE simplifications.

	* gcc.dg/tree-ssa/pr94589-1.c: New test.

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