[llvm] [SLP]Cost-based choice of the i1 reduction form (PR #223163)

[Matt Arsenault via llvm-commits]

================
@@ -32219,27 +32234,66 @@ class HorizontalReduction {
     return {ReducedSubTree, ResNegated};
   }
 
+  /// Emits an i1 reduction in the cheaper of the plain and the bitcast-based
+  /// form. Returns nullptr if not an i1 reduction handled here.
+  Value *emitI1Reduction(Value *VectorizedValue, IRBuilderBase &Builder,
+                         const TargetTransformInfo &TTI,
+                         TTI::CastContextHint Ctx, Type *DestTy, Value *Start) {
+    auto *FTy = cast<FixedVectorType>(VectorizedValue->getType());
+    bool IsAdd = RdxKind == RecurKind::Add &&
+                 DestTy->getScalarType() != FTy->getScalarType();
+    bool IsBoolLogic =
+        (RdxKind == RecurKind::And || RdxKind == RecurKind::Or) &&
+        DestTy->getScalarType() == FTy->getScalarType();
+    if (Start || FTy->getScalarType() != Builder.getInt1Ty() ||
----------------
arsenm wrote:

```suggestion
    if (Start || !FTy->getScalarType()->isIntegerTy(1) ||
```

https://github.com/llvm/llvm-project/pull/223163