[LV] Never widen an induction variable.

[LV] Never widen an induction variable.

There's no need to widen canonical induction variables. It's just as efficient to create a *new*, wide, induction variable.

Consider, if we widen an indvar, then we'll have to truncate it before its uses anyway (1 trunc). If we create a new indvar instead, we'll have to truncate that instead (1 trunc) [besides which IndVars should go and clean up our mess after us anyway on principle].

This lets us remove a ton of special-casing code.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@246631 91177308-0d34-0410-b5e6-96231b3b80d8