If IVUpdateMayOverflow is false, we proved that the induction increment
cannot overflow in the vector loop. This allows setting NUW in some
cases when folding the tail.
PR: https://github.com/llvm/llvm-project/pull/111758
In LoopVectorizationCostModel::getInstructionCost(), when the condition
canTruncateToMinimalBitwidth() is satisfied, for a trunc, the source
type is computed as the smallest type of the source vector and the
destination vector, and the destination type is computed as the largest
type of the instruction and destination type. This is clearly a logical
error, as the original source vector type could be smaller than the
original destination vector type, and the trunc semantics are broken
because we're attempting to widen.
Fixes#47665.
