[llvm] [LV] Remove common extends and selects in CSE (PR #147731)

[David Sherwood via llvm-commits]

================
@@ -804,6 +804,10 @@ int FunctionComparator::cmpOperations(const Instruction *L,
         return Res;
     }
   }
+  if (const CastInst *Cast = dyn_cast<CastInst>(L)) {
----------------
david-arm wrote:

Perhaps I'm missing something here, but I'm surprised this isn't already caught by

```
  if (int Res = cmpTypes(L->getType(), R->getType()))
    return Res;
```

above? Wouldn't `L->getType()` be equivalent to `Cast->getDestTy()`?

https://github.com/llvm/llvm-project/pull/147731