[llvm] [ValueTracking][X86] Compute KnownBits for phadd/phsub (PR #92429)

[Simon Pilgrim via llvm-commits]

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@@ -37262,6 +37262,27 @@ void X86TargetLowering::computeKnownBitsForTargetNode(const SDValue Op,
     }
     break;
   }
+  case X86ISD::HADD: {
+    Known = DAG.computeKnownBits(Op.getOperand(0), DemandedElts, Depth + 1);
+    KnownBits Known2 =
+        DAG.computeKnownBits(Op.getOperand(1), DemandedElts, Depth + 1);
+
+    Known = KnownBits::computeForAddSub(true, false, false, Known, Known)
+                .intersectWith(KnownBits::computeForAddSub(true, false, false,
+                                                           Known2, Known2));
+    break;
+  }
+  case X86ISD::HSUB: {
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RKSimon wrote:

You can merge HADD/HSUB cases and call `computeForAddSub(Opc == X86ISD::HADD, ...)`

https://github.com/llvm/llvm-project/pull/92429