ab1dbcecd6
While we could emit such a tautological `select`, it will stick around until the next instsimplify invocation, which may happen after we count the cost of this redundant `select`. Which is precisely what happens with loop vectorization legality checks, and that artificially increases the cost of said checks, which is bad. There is prior art for this in `IRBuilderBase::CreateAnd()`/`IRBuilderBase::CreateOr()`. Refs. https://reviews.llvm.org/D109368#3089809