Rollup merge of #140115 - dianqk:gvn-matchbr, r=oli-obk

mir-opt: execute MatchBranchSimplification after GVN

This can provide more opportunities for MatchBranchSimplification.

Currently, rustc does not optimize the following code into a single statement at mir-opt, and this PR fixes the first case.

```rust
pub fn match1(c: bool, v1: i32, v2: i32) -> i32 {
    if c { v1 - v2 } else { v1 - v2 }
}

pub fn match2(c: bool, v1: i32) -> i32 {
    if c { v1 - 1 } else { v1 - 1 }
}
```

https://rust.godbolt.org/z/Y8xPMjrfM

r? mir-opt

Author: GuillaumeGomez