[llvm] [SLP][REVEC] Make getAltInstrMask and getGatherCost vectorize vector instructions. (PR #99461)

[Alexey Bataev via llvm-commits]

================
@@ -11388,7 +11393,8 @@ InstructionCost BoUpSLP::getGatherCost(ArrayRef<Value *> VL, bool ForPoisonSrc,
     }
 
     DuplicateNonConst = true;
-    ShuffledElements.setBit(I);
+    for (unsigned J = 0; J != ScalarTyNumElements; ++J)
+      ShuffledElements.setBit(I * ScalarTyNumElements + J);
----------------
alexey-bataev wrote:

```suggestion
    ShuffledElements.setBit(I * ScalarTyNumElements, I * ScalarTyNumElements + ScalarTyNumElements);
```

https://github.com/llvm/llvm-project/pull/99461