[PATCH] D79175: [ARM][MVE] Tail-Predication: use @llvm.get.active.lane.mask to get the BTC

[Eli Friedman via Phabricator via llvm-commits]

efriedma added a comment.

I'd like to see a few negative testcases, where we can't transform the llvm.get.active.lane.mask.



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Comment at: llvm/lib/Target/ARM/MVETailPredication.cpp:352
+    Value *TripCount, FixedVectorType *VecTy) {
+  int VectorWidth = VecTy->getElementCount().Min;
+  auto *BackedgeTakenCount = ActiveLaneMask->getOperand(1);
----------------
getNumElements() is fine on a FixedVectorType.


================
Comment at: llvm/lib/Target/ARM/MVETailPredication.cpp:384
+  // Evaluate this and bail if it can be negative.
+  if (llvm::isKnownNegativeInLoop(ECMinusTC, L, *SE)) {
+    LLVM_DEBUG(dbgs() << "ARM TP: overflow in element count decrement\n");
----------------
!isKnownNonNegative?


================
Comment at: llvm/lib/Target/ARM/MVETailPredication.cpp:403
+  // If this phi is invariant, it's not a phi in this loop.
+  if (SE->isLoopInvariant(IVExpr, L)) {
+    LLVM_DEBUG(dbgs() << "ARM TP: phi is not incremented in this loop\n");
----------------
I was expecting something more like `IVExpr->getLoop() == L`.  L might not be the innermost loop.


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  https://reviews.llvm.org/D79175/new/

https://reviews.llvm.org/D79175