[llvm] [VPlan] First step towards VPlan cost modeling. (PR #92555)

[via llvm-commits]

jeanPerier wrote:

> Reverted for now in [f1f3c34](https://github.com/llvm/llvm-project/commit/f1f3c34b4770437bdb022737918603b4bbeb523e). Would still be good to get the reproducer from @jeanPerier for flang and from @dklimkin for tensorflow/XLA if possible. I believe they are distinct from the other issue mentioned here.

Thanks for reverting. I was able to reduce one of the crash compiling a Fortran application to the Fortran program below.

I attach the related LLVM IR, you can reproduce the crash starting from the Fortran IR with `clang -Ofast -c`: [fortran_crash.ll.txt](https://github.com/user-attachments/files/15952980/fortran_crash.ll.txt)

```
subroutine foo(mask, matrix, n, m, k)
  implicit none
  integer :: n, m, k
  real(8) :: matrix(n, m)
  logical :: mask(n, m)
  where (mask(:, k))
      matrix(:,k) = 1._8
  elsewhere
      matrix(:,k) = 0._8
  end where
end subroutine
```

https://github.com/llvm/llvm-project/pull/92555