[llvm] [X86] SimplifyDemandedBitsForTargetNode - add handling for VPMADD52L/VPMADD52H (PR #155494)

[Simon Pilgrim via llvm-commits]

================
@@ -44957,6 +44957,23 @@ bool X86TargetLowering::SimplifyDemandedBitsForTargetNode(
     Known.Zero.setLowBits(Known2.countMinTrailingZeros());
     return false;
   }
+  case X86ISD::VPMADD52L:
+  case X86ISD::VPMADD52H: {
+    KnownBits KnownOp0, KnownOp1;
+    SDValue Op0 = Op.getOperand(0);
+    SDValue Op1 = Op.getOperand(1);
+    //  Only demand the lower 52-bits of operands 0 / 1 (and all 64-bits of
+    //  operand 2).
+    APInt Low52Bits = APInt::getLowBitsSet(BitWidth, 52);
+    if (SimplifyDemandedBits(Op0, Low52Bits, OriginalDemandedElts, KnownOp0,
+                             TLO, Depth + 1))
+      return true;
+
+    if (SimplifyDemandedBits(Op1, Low52Bits, OriginalDemandedElts, KnownOp1,
+                             TLO, Depth + 1))
+      return true;
----------------
RKSimon wrote:

Add a TODO for knownbits as well 

https://github.com/llvm/llvm-project/pull/155494