[llvm-bugs] [Bug 50094] New: (popcount(x) ^ popcount(y)) & 1 - > (popcount(x ^ y)) & 1

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=50094

            Bug ID: 50094
           Summary: (popcount(x) ^ popcount(y)) & 1 - > (popcount(x ^ y))
                    & 1
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: david.bolvansky at gmail.com
                CC: llvm-bugs at lists.llvm.org

Original pattern: (__builtin_parity(x) ^ __builtin_parity(y))

LLVM rewrites it as: (__builtin_popcount(x) ^ __builtin_popcount(y)) & 1

----------------------------------------
define i32 @src(i32 %0, i32 %1) noread nowrite nofree {
%2:
  %3 = ctpop i32 %0
  %4 = ctpop i32 %1
  %5 = xor i32 %4, %3
  %6 = and i32 %5, 1
  ret i32 %6
}
=>
define i32 @tgt(i32 %0, i32 %1) noread nowrite nofree {
%2:
  %3 = xor i32 %1, %0
  %4 = ctpop i32 %3
  %5 = and i32 %4, 1
  ret i32 %5
}
Transformation seems to be correct!

parity_xor(unsigned int, unsigned int):                       #
@parity_xor(unsigned int, unsigned int)
        popcnt  ecx, edi
        popcnt  eax, esi
        xor     eax, ecx
        and     eax, 1
        ret
tgt(unsigned int, unsigned int):                               # @tgt(unsigned
int, unsigned int)
        xor     edi, esi
        popcnt  eax, edi
        and     eax, 1
        ret

https://godbolt.org/z/v3h361fz7

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