[llvm-bugs] [Bug 50545] New: Failure to optimize loop of and by progressively bigger operand to single and+select

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=50545

            Bug ID: 50545
           Summary: Failure to optimize loop of and by progressively
                    bigger operand to single and+select
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Loop Optimizer
          Assignee: unassignedbugs at nondot.org
          Reporter: gabravier at gmail.com
                CC: llvm-bugs at lists.llvm.org

int f(int c)
{
    int i = 1;
    while ((c & i)) {
        c &= i;
        i <<= 1;
    }
    return c;
}

This can be optimized to `return (c & 1) == 0 ? c : (c & 1);`. This
transformation is done by GCC, but not by LLVM.

Godbolt comparison: https://godbolt.org/z/oTxbxv5fo
alive2 comparison: https://alive2.llvm.org/ce/z/oDxuS4

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