[qt/clang/llvm]: Summary of bulk changes made

Git repository change summary for qt/clang/llvm
Pushed by mirror-service into branch 'upstream/users/gandhi56/sandbox-vectorizer/topdown-vec'.
Changed from 7c7949ff481e74a8ef0f817ab4e1da1f2d864e9e to 6c01528e0b3bad3348753818e613892d66622257
Acknowledgement was received that this change introduces only existing code that has been pushed to another public open source repository.

This change contains the following new commits:

Git commit 6c01528e0b3bad3348753818e613892d66622257 by Anshil Gandhi on 17/07/2026 at 17:55..
[SBVec] Add top-down vectorization to the unified Sandbox Vectorizer

Extend the Sandbox Vectorizer's `bottom-up-vec` pass so a single
implementation can vectorize in either direction, and add the top-down
strategy that walks def-use chains forward from a seed.

Direction selection
--------------------
The pass direction is chosen from the Region's auxiliary pass argument:
"bottom-up" (or empty, the default) and "top-down" map onto a
SchedDirection, and any other value is rejected with a fatal usage error.
The vectorizer always runs in the same direction as the scheduler.

Top-down traversal
------------------
Bottom-up starts from a seed slice (e.g. stores to consecutive addresses)
and recurses into operands. Top-down instead starts from a seed of
consecutive loads and recurses into *users*:

- vectorizeRec() registers the current bundle's vector (pre-order) before
  recursing, so instructions are marked vectorized as soon as they are
  claimed. This prevents sibling user bundles from claiming the same
  instruction and guarantees termination.
- VecUtils::getNextUserBundles() drives the walk. For each user of lane 0
  it tries to assemble a matching user for every remaining lane, requiring
  the same opcode, type, parent block, and operand-usage indices, and
  claiming each instruction at most once. Only complete bundles (one user
  per lane) are returned.
- A non-Widen legality result stops the walk down that path: the bundle is
  left scalar and no action is recorded. DiamondReuse results cannot occur
  top-down because already-vectorized users are skipped, so a bundle never
  contains an instruction already in InstrMaps.

Operand and external-use handling
---------------------------------
Because a user bundle is emitted after its operand bundle, emitVectors()
looks up each operand's vector in InstrMaps and creates a pack when the
operand was not vectorized. emitUnpacksForExternalUses() now redirects
only the genuinely external (non-vectorized) uses via replaceUsesWithIf(),
instead of a blanket replaceAllUsesWith() that would corrupt the operands
of user bundles not yet emitted. Scheduling is currently skipped for the
top-down direction (TODO).

Refactoring
-----------
Unify the two strategies to avoid code duplication: introduce a shared
BundleTy alias, move user-bundle collection into VecUtils (with unit
tests), and thread the direction through legality checks and vector
emission.

Co-authored-by: Cursor <[email protected]>
https://invent.kde.org/qt/clang/llvm/-/commit/6c01528e0b3bad3348753818e613892d66622257