Before this patch, InstCombine hung because it replaced a value with a
more complex one:
```
%sel = select i1 %cmp, i32 %smax, i32 0 ->
%sel = select i1 %cmp, i32 %masked, i32 0 ->
%sel = select i1 %cmp, i32 %smax, i32 0 ->
...
```
This patch makes this replacement more conservative. It only performs
the replacement iff the new value is one of the operands of the original
value.
Closes https://github.com/llvm/llvm-project/issues/142405.
5e2dcfe42c