[Bug tree-optimization/96237] New: Failure to recognize and pattern composed of and+or after shift

[Bug tree-optimization/96237] New: Failure to recognize and pattern composed of and+or after shift

[gabravier at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96237

            Bug ID: 96237
           Summary: Failure to recognize and pattern composed of and+or
                    after shift
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gabravier at gmail dot com
  Target Milestone: ---

unsigned char f(unsigned char x)
{
    auto a = (x >> 3) & 1;
    if (x & 16)
        a |= 2;
    if (x & 32)
        a |= 4;
    return a;
}

This can be optimized to `return (x >> 3) & 7;`. This transformation is done by
LLVM, but not by GCC.

[Bug tree-optimization/96237] Failure to recognize and pattern composed of and+or after shift

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96237

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement

[Bug tree-optimization/96237] Failure to recognize and pattern composed of and+or after shift

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96237

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2020-07-19

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
if (x & 16)
        a |= 2;

Maybe should be transformed into:
a |= ((x >> 4) & 0x1) << 1;
Which in turn should be transformed into:
a |= ((x & 0x10) >> 3);


    if (x & 32)
        a |= 4;
gets transformed into:
a |= ((x & 0x20) >> 3);

And:
a |= ((x & 0x40) >> 3);
a |= ((x & 0x20) >> 3);
Into:
a |= ((x & 0x60) >> 3);
Or:
a |= ((x >> 3) & 0x6);

Combine that with:
a = (x >> 3) & 1;
gets us:
a |= ((x >> 3) & 0x7);

Hopefully I did that correctly.

[Bug tree-optimization/96237] Failure to recognize and pattern composed of and+or after shift

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96237

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |pinskia at gcc dot gnu.org
             Status|NEW                         |ASSIGNED

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I am going to implement the match patterns needed.

Something like:
(for bitop (bit_and bit_ior)
 (simplify
  (cond @0 (bitop @1 integer_power2@2) @1)
  (bitop @1 (lshift @0 ({ log2(@2); }) ))))

Note log2 here is just psedu-code :).

[Bug tree-optimization/96237] Failure to recognize and pattern composed of and+or after shift

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96237

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #2)
> I am going to implement the match patterns needed.

This is just expanding:
/* (zero_one != 0) ? z <op> y : y -> ((typeof(y))zero_one * z) <op> y */

Patterns not to just zero_one but rather integer_power2 which I am going to do
the week after next.