[llvm] added ISD::VECTOR_COMPRESS handling in computeKnownBits/ComputeNumSign… (PR #159692)

[Jay Foad via llvm-commits]

================
@@ -4792,6 +4813,19 @@ unsigned SelectionDAG::ComputeNumSignBits(SDValue Op, const APInt &DemandedElts,
     }
     return Tmp;
 
+  case ISD::VECTOR_COMPRESS: {
+    SDValue Vec = Op.getOperand(0);
+    SDValue Mask = Op.getOperand(1);
+    SDValue PassThru = Op.getOperand(2);
+    // If PassThru is undefined, early out.
+    if (PassThru.isUndef())
+      return 1;
+    Tmp = ComputeNumSignBits(Vec, Depth + 1);
+    Tmp2 = ComputeNumSignBits(PassThru, Depth + 1);
----------------
jayfoad wrote:

You can make the early-out more generic:
```suggestion
    Tmp = ComputeNumSignBits(PassThru, Depth + 1);
    if (Tmp == 1)
      return 1;
    Tmp2 = ComputeNumSignBits(Vec, Depth + 1);
```

https://github.com/llvm/llvm-project/pull/159692