[Bug tree-optimization/122563] New: Redundant computation around x & (-x)

[fxue at os dot amperecomputing.com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122563

            Bug ID: 122563
           Summary: Redundant computation around x & (-x)
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: fxue at os dot amperecomputing.com
  Target Milestone: ---

"x & (-x)" is to get a value of power of 2, (or zero value), which has same LSB
as "x". Any prior computation that does not change LSB, is redundant regarding
to the expression "x & (-x)", for example:

int foo(int x, int m, int n)
{
   x *= (2 * m + 1);  // could be eliminated
   x |= x << n;       // could be eliminated 

   return x & (-x);
}