[Bug tree-optimization/101650] New: (len | N) == len is transformed to len & N != 0

[Bug tree-optimization/101650] New: (len | N) == len is transformed to len & N != 0

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101650

            Bug ID: 101650
           Summary: (len | N) == len is transformed to len & N != 0
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---

While looking at PR 101590, I noticed this one.
#include <stddef.h>

const size_t N = 4;

bool foo(size_t len) {
        size_t newlen = len | N;
        return newlen == len;
}


(for cmp  (NE EQ)
     icmp (EQ NE)
 (simplify
  (cmp (bit_ior @0 INTEGER_CST@1) @0)
  (icmp (bit_and @0 @1) ({ build_zero_cst (TREE_TYPE (@0)); })
 )
)

This is already done for bit_and.

[Bug tree-optimization/101650] (len | N) == len is transformed to len & N != 0

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101650

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2021-07-27
           Assignee|unassigned at gcc dot gnu.org      |pinskia at gcc dot gnu.org
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=101590

[Bug tree-optimization/101650] (len | N) == len is transformed to len & N != 0

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101650

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 101591 has been marked as a duplicate of this bug. ***

[Bug tree-optimization/101650] (len | N) == len is transformed to len & N != 0

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101650

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
So the pattern which we have currently matching (X | Y) == Y does this:
 /* (X | Y) == Y becomes (X & ~Y) == 0.  */
 (simplify
  (cmp:c (bit_ior:c @0 @1) @1)
  (cmp (bit_and @0 (bit_not! @1)) { build_zero_cst (TREE_TYPE (@0)); }))

So adding:
 /* (Y | CST) == Y becomes (Y & CST) != 0.  */
 (simplify
  (cmp:c (bit_ior @1 INTEGER_CST@0) @1)
  (icmp (bit_and @1 @0) { build_zero_cst (TREE_TYPE (@0)); }))

Is needed.