Update optimizeForVFAndUF to completely remove the vector loop region
when possible. At the moment, we cannot remove the region if it contains
* widened IVs: the recipe is needed to generate the step vector
* reductions: ComputeReductionResults requires the reduction phi recipe
for codegen.
Both cases can be addressed by more explicit modeling.
The patch also includes a number of updates to allow executing VPlans
without a vector loop region.
Depends on https://github.com/llvm/llvm-project/pull/110004
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.
