[llvm-bugs] [Bug 50141] New: Missing trunc(ctpop(zext(x))) -> ctpop(x) fold

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=50141

            Bug ID: 50141
           Summary: Missing trunc(ctpop(zext(x))) -> ctpop(x) fold
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: llvm-dev at redking.me.uk
                CC: david.bolvansky at gmail.com, lebedev.ri at gmail.com,
                    llvm-bugs at lists.llvm.org, nikita.ppv at gmail.com,
                    spatel+llvm at rotateright.com

https://simd.godbolt.org/z/EcP4en5KG

#include <x86intrin.h>

__v8hu ctpop_int(__v8hu x) {
    return (__v8hu) {
        (unsigned short)__builtin_popcount( x[0] ),
        (unsigned short)__builtin_popcount( x[1] ),
        (unsigned short)__builtin_popcount( x[2] ),
        (unsigned short)__builtin_popcount( x[3] ),
        (unsigned short)__builtin_popcount( x[4] ),
        (unsigned short)__builtin_popcount( x[5] ),
        (unsigned short)__builtin_popcount( x[6] ),
        (unsigned short)__builtin_popcount( x[7] )
    };
}

define <8 x i16> @ctpop_int(<8 x i16> %0){
  %2 = zext <8 x i16> %0 to <8 x i32>
  %3 = call <8 x i32> @llvm.ctpop.v8i32(<8 x i32> %2)
  %4 = trunc <8 x i32> %3 to <8 x i16>
  ret <8 x i16> %4
}
declare <8 x i32> @llvm.ctpop.v8i32(<8 x i32>)

We should be able to just use a @llvm.ctpop.v8i16 call

Not sure if the trunc is vital, or whether we should also allow the fold:

    ctpop(zext(x)) -> zext(ctpop(x))

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