Add a new PtrAdd opcode to VPInstruction that corresponds to
IRBuilder::CreatePtrAdd, which creates a GEP with source element type
i8.
This is then used to model scalarizing VPWidenPointerInductionRecipe by
introducing scalar-steps to model the index increment followed by a
PtrAdd.
Note that PtrAdd needs to be able to generate code for only the first
lane or for all lanes. This may warrant introducing a separate recipe
for scalarizing that can be created without relying on the underlying
IR.
Depends on https://github.com/llvm/llvm-project/pull/80271
PR: https://github.com/llvm/llvm-project/pull/83068
Some optimizations are apply after UF and VF have been chosen. This
patch adds an extra print of the final VPlan just before
codegen/execution.
In the future, there will be additional transforms that are applied
later (interleaving for example).
PR: https://github.com/llvm/llvm-project/pull/82269
