[X86] Don't use popcnt for parity if only bits 7:0 of the input can be non-zero.

Without popcnt we had a special case for using the parity flag from a single test i8 test instruction if only bits 7:0 could be non-zero. That special case is still useful when we have popcnt.

To reach this special case, we enable custom lowering of parity for i16/i32/i64 even when popcnt is enabled. The check for POPCNT being enabled is now after the special case in LowerPARITY.

Fixes PR52093

Differential Revision: https://reviews.llvm.org/D111249

Author: topperc

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -425,6 +425,10 @@ X86TargetLowering::X86TargetLowering(const X86TargetMachine &TM,
   setTruncStoreAction(MVT::f128, MVT::f16, Expand);
 
   setOperationAction(ISD::PARITY, MVT::i8, Custom);
+  setOperationAction(ISD::PARITY, MVT::i16, Custom);
+  setOperationAction(ISD::PARITY, MVT::i32, Custom);
+  if (Subtarget.is64Bit())
+    setOperationAction(ISD::PARITY, MVT::i64, Custom);
   if (Subtarget.hasPOPCNT()) {
     setOperationPromotedToType(ISD::CTPOP, MVT::i8, MVT::i32);
   } else {
@@ -435,11 +439,6 @@ X86TargetLowering::X86TargetLowering(const X86TargetMachine &TM,
       setOperationAction(ISD::CTPOP        , MVT::i64  , Expand);
     else
       setOperationAction(ISD::CTPOP        , MVT::i64  , Custom);
-
-    setOperationAction(ISD::PARITY, MVT::i16, Custom);
-    setOperationAction(ISD::PARITY, MVT::i32, Custom);
-    if (Subtarget.is64Bit())
-      setOperationAction(ISD::PARITY, MVT::i64, Custom);
   }
 
   setOperationAction(ISD::READCYCLECOUNTER , MVT::i64  , Custom);
@@ -30469,6 +30468,10 @@ static SDValue LowerPARITY(SDValue Op, const X86Subtarget &Subtarget,
     return DAG.getNode(ISD::ZERO_EXTEND, DL, VT, Setnp);
   }
 
+  // If we have POPCNT, use the default expansion.
+  if (Subtarget.hasPOPCNT())
+    return SDValue();
+
   if (VT == MVT::i64) {
     // Xor the high and low 16-bits together using a 32-bit operation.
     SDValue Hi = DAG.getNode(ISD::TRUNCATE, DL, MVT::i32,