Rollup merge of #141252 - dianqk:gvn-repeat-index, r=saethlin

gvn: bail out unavoidable non-ssa locals in repeat

Fixes #141251.

We cannot transform `*elem` to `array[idx1]` in the following code, as `idx1` has already been modified.

```rust
    mir! {
        let array;
        let elem;
        {
            array = [*val; 5];
            elem = &array[idx1];
            idx1 = idx2;
            RET = *elem;
            Return()
        }
    }
```

Perhaps I could transform it to `array[0]`, but I prefer the conservative approach.

r? mir-opt

Author: tgross35