[Bug tree-optimization/106244] New: Failure to optimize (1 << x) & 1 to `x == 0` if separated into multiple statements

[Bug tree-optimization/106244] New: Failure to optimize (1 << x) & 1 to `x == 0` if separated into multiple statements

[gabravier at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106244

            Bug ID: 106244
           Summary: Failure to optimize (1 << x) & 1 to `x == 0` if
                    separated into multiple statements
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gabravier at gmail dot com
  Target Milestone: ---

#include <stdint.h>

int8_t f(int8_t x)
{
    int8_t sh = 1 << x;
    return sh & 1;
}

This can be optimized to `return x == 0;`. This transformation is done by LLVM,
but not by GCC.

PS: For some reason GCC manages to do this optimization if I replace `f` with
`return (1 << x) & 1;` instead of having it spelled out in 2 statements.

[Bug tree-optimization/106244] Failure to optimize (1 << x) & 1 to `x == 0` if separated into multiple statements

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106244

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2022-07-10
     Ever confirmed|0                           |1
           Severity|normal                      |enhancement
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Actually it is not optimized if it was in one statement:
int8_t f1(int8_t x)
{
    return ((int8_t)(1 << x)) & 1;
}

The IR has:
  _4 = (int) x_1(D);
  _5 = 1 << _4;
  sh_6 = (int8_t) _5;
  _7 = sh_6 & 1;

We optimize directly "(1 << x) & 1" but not with a cast.