[llvm-bugs] [Bug 52056] New: Regressed popcnt of unsigned short

via llvm-bugs llvm-bugs at lists.llvm.org
Sun Oct 3 15:27:18 PDT 2021


            Bug ID: 52056
           Summary: Regressed popcnt of unsigned short
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: david.bolvansky at gmail.com
                CC: craig.topper at gmail.com, llvm-bugs at lists.llvm.org,
                    llvm-dev at redking.me.uk, pengfei.wang at intel.com,
                    spatel+llvm at rotateright.com

int pc(unsigned short a) { return __builtin_popcount(a); }

LLVM trunk
pc(unsigned short):                                 # @pc(unsigned short)
        popcntw %di, %ax
        movzwl  %ax, %eax

LLVM 12:
pc(unsigned short):                                 # @pc(unsigned short)
        popcntl %edi, %eax

pc(unsigned short):                                 # @pc(unsigned short)
        popcntl %edi, %eax

Maybe the solution is to add i16 -> i32 handling here in X86ISelLowering ?

   if (Subtarget.hasPOPCNT()) {
     setOperationPromotedToType(ISD::CTPOP, MVT::i8, MVT::i32);
   } else { ....


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