[llvm] [FastISel] Support unreachable with NoTrapAfterNoReturn (PR #118296)

[Nikita Popov via llvm-commits]

nikic wrote:

> LGTM. Was there any concrete use case where this caused a noticeable amount of fallbacks?

Yes, this is one of the more common cause of fallbacks for Rust code. For the test case I'm looking at the distribution looks like this:

```
array(7) {
  ["invoke"]=>
  int(7870)
  ["unreachable"]=>
  int(3160)
  ["landingpad"]=>
  int(630)
  ["args"]=>
  int(566)
  ["ret"]=>
  int(397)
  ["other"]=>
  int(324)
  ["switch"]=>
  int(237)
}
```

https://github.com/llvm/llvm-project/pull/118296