[llvm-bugs] [Bug 47593] New: Failure to optimize bitwise not pattern

via llvm-bugs llvm-bugs at lists.llvm.org
Mon Sep 21 03:48:38 PDT 2020


            Bug ID: 47593
           Summary: Failure to optimize bitwise not 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 a, int b)
    return ~(a | b) | (~a & b);

This can be optimized to `return ~a;`. This optimization is done by GCC, but
not by LLVM.

See also comparison here : https://godbolt.org/z/vqTW4a

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