Update VPlan to populate VPIRFlags during VPInstruction construction and
use it when creating widened recipes, instead of constructing VPIRFlags
from the underlying IR instruction each time. The VPRecipeWithIRFlags
constructor taking an underlying instruction and setting the flags based
on it has been removed.

This centralizes initial VPIRFlags creation and ensures flags are
consistently available throughout VPlan transformations and makes sure
we don't accidentally re-add flags from the underlying instruction that
already got dropped during transformations.

Follow-up to https://github.com/llvm/llvm-project/pull/167253, which did
the same for VPIRMetadata.

Should be NFC w.r.t. to the generated IR.

PR: https://github.com/llvm/llvm-project/pull/168450

This reverts commit 62d1a080e69e3c5e98840e000135afa7c688a77b.

This appears to be causing some runtime failures on RISCV
https://lab.llvm.org/buildbot/#/builders/210/builds/5221

Building on top of https://github.com/llvm/llvm-project/pull/148817,
introduce a new abstract LastActiveLane opcode that gets lowered to
Not(Mask) → FirstActiveLane(NotMask) → Sub(result, 1).

When folding the tail, update all extracts for uses outside the loop the
extract the value of the last actice lane.

See also https://github.com/llvm/llvm-project/issues/148603

PR: https://github.com/llvm/llvm-project/pull/149042

Rename onlyFirst(Lane|Part)Used to usesFirst(Lane|Part)Only, in line
with usesScalars, for clarity.

Add getConstantInt helper methods to VPlan to simplify the common
pattern of creating constant integer live-ins.

Suggested as follow-up in
https://github.com/llvm/llvm-project/pull/164127.

Split off from https://github.com/llvm/llvm-project/pull/156262.

Similar to VPRegionBlock::getCanonicalIV, add helper to get the type of
the canonical IV, in preparation for removing VPCanonicalIVPHIRecipe.

PR: https://github.com/llvm/llvm-project/pull/164127

Add a new Unpack VPInstruction (name to be improved) to explicitly
extract scalars values from vectors.

Test changes are movements of the extracts: they are no generated
together and also directly after the producer.

Depends on https://github.com/llvm/llvm-project/pull/155102 (included in
PR)

PR: https://github.com/llvm/llvm-project/pull/155670

Add m_FirstActiveLane, to slightly simplify pattern matching in
preparation for https://github.com/llvm/llvm-project/pull/149042.

The canonical IV is tied to region blocks; move getCanonicalIV there and
update all users.

PR: https://github.com/llvm/llvm-project/pull/163020