The following vector api tests fail (computing incorrect results) after JDK-8293409.
```
TEST: jdk/incubator/vector/Long256VectorTests.java
TEST: jdk/incubator/vector/Float128VectorTests.java
TEST: jdk/incubator/vector/FloatMaxVectorTests.java
TEST: jdk/incubator/vector/Int256VectorTests.java
TEST: jdk/incubator/vector/Double256VectorTests.java
TEST: jdk/incubator/vector/Float64VectorTests.java
TEST: jdk/incubator/vector/LongMaxVectorTests.java
TEST: jdk/incubator/vector/Short128VectorTests.java
TEST: jdk/incubator/vector/Short64VectorTests.java
TEST: jdk/incubator/vector/Float256VectorTests.java
TEST: jdk/incubator/vector/Double128VectorTests.java
TEST: jdk/incubator/vector/DoubleMaxVectorTests.java
TEST: jdk/incubator/vector/Short256VectorTests.java
TEST: jdk/incubator/vector/Int128VectorTests.java
TEST: jdk/incubator/vector/ShortMaxVectorTests.java
TEST: jdk/incubator/vector/IntMaxVectorTests.java
TEST: jdk/incubator/vector/Long128VectorTests.java
TEST: jdk/incubator/vector/Int64VectorTests.java
```

To fix the bug, the generate_iota_indices also needs to be updated.