[llvm] [DAG] ISD::matchUnaryPredicate / matchUnaryFpPredicate / matchBinaryPredicate - add DemandedElts variant (PR #183013)

[via llvm-commits]

================
@@ -361,8 +361,14 @@ bool ISD::matchUnaryPredicateImpl(SDValue Op,
       ISD::SPLAT_VECTOR != Op.getOpcode())
     return false;
 
+  if (ISD::SPLAT_VECTOR == Op.getOpcode() && DemandedElts == 0)
+    return true;
+
   EVT SVT = Op.getValueType().getScalarType();
   for (unsigned i = 0, e = Op.getNumOperands(); i != e; ++i) {
+    if (!DemandedElts[i])
----------------
VachanVY wrote:

<details> 

`Op = [2, 2, 2, 2]` `DemandedElts = [0, 0, 1, 0]`

For splat vectors `e = Op.getNumOperands()` is `1`, we never really get to check the demanded lane if we don't have `ISD::SPLAT_VECTOR != Op.getOpcode()`

So when a normal vector and not demanded lane then skip the check

```cpp
if (ISD::SPLAT_VECTOR == Op.getOpcode() && !DemandedElts)
    return true;
```

We are sure that if it is Splat vector atleast one lane is sure to be demanded due to early return before itself as above.

</details>

https://github.com/llvm/llvm-project/pull/183013