[llvm-bugs] [Bug 48524] New: Failure to optimize simple bitwise pattern

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=48524

            Bug ID: 48524
           Summary: Failure to optimize simple bitwise pattern
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: gabravier at gmail.com
                CC: llvm-bugs at lists.llvm.org

int f1(int n)
{
    return n - (((n > 63) ? n : 63) & -64);
}

This can be optimized to `return (n <= 63) ? n : (n & 63);` (and presumably the
same optimization should be doable with other powers of 2).

PS: I found this optimization while looking at how this :

int f1(int n)
{
    while (n >= 64)
        n -= 64;

    return n;
}

is optimized. LLVM outputs the first example I gave here, while GCC outputs the
optimization I gave here.

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