[PATCH] D116479: [VPlan] Introduce and use ExitCheckAndBranch VPInstruction.

[Florian Hahn via Phabricator via llvm-commits]

fhahn added inline comments.


================
Comment at: llvm/lib/Transforms/Vectorize/VPlan.cpp:932
+  // and check to VectorLatchBB.
+  auto *LastBranch = cast<BranchInst>(LastBB->getTerminator());
+  LastBranch->moveBefore(VectorLatchBB->getTerminator());
----------------
I looked into removing the separate latch block, but unfortunately `widenIntOrFpInduction` still relies on the latch block being created up-front:

```
  // Move the last step to the end of the latch block. This ensures consistent
  // placement of all induction updates.
  auto *LoopVectorLatch = LI->getLoopFor(LoopVectorBody)->getLoopLatch();
  auto *Br = cast<BranchInst>(LoopVectorLatch->getTerminator());
  LastInduction->moveBefore(Br);
  LastInduction->setName("vec.ind.next");

```

Reusing the created vector latch for the exit block of the region is also not straight-forward, because we may need to look through multiple single successors until we reach a the exit VPBB. This is complicated by blocks inside replicate regions, where we would need to check the successor of the region, but *only* for the last iteration in the loop for the region.

So I think it is simpler to keep things as is, until the VPWidenIntOrFpInduction increments are modeled separately.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D116479/new/

https://reviews.llvm.org/D116479