[llvm] [LoopVectorize] Generate wide active lane masks (PR #147535)

[David Sherwood via llvm-commits]

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@@ -1432,6 +1434,91 @@ static bool isConditionTrueViaVFAndUF(VPValue *Cond, VPlan &Plan,
   return SE.isKnownPredicate(CmpInst::ICMP_EQ, TripCount, C);
 }
 
+static bool useWideActiveLaneMask(VPlan &Plan, ElementCount VF, unsigned UF) {
+  VPRegionBlock *VectorRegion = Plan.getVectorLoopRegion();
+  VPBasicBlock *ExitingVPBB = VectorRegion->getExitingBasicBlock();
+  auto *Term = &ExitingVPBB->back();
+
+  using namespace llvm::VPlanPatternMatch;
+  if (!EnableWideActiveLaneMask || !VF.isVector() || UF == 1 ||
+      !match(Term, m_BranchOnCond(m_Not(m_ActiveLaneMask(
+                       m_VPValue(), m_VPValue(), m_VPValue())))))
+    return false;
+
+  auto *Header = cast<VPBasicBlock>(VectorRegion->getEntry());
+  VPCanonicalIVPHIRecipe *CanonicalIV = Plan.getCanonicalIV();
+  LLVMContext &Ctx = CanonicalIV->getScalarType()->getContext();
+
+  auto extractFromALM = [&](VPInstruction *ALM,
+                            SmallVectorImpl<VPValue *> &Extracts) {
+    DebugLoc DL = ALM->getDebugLoc();
+    for (unsigned Part = 0; Part < UF; ++Part) {
+      SmallVector<VPValue *> Ops;
+      Ops.append({ALM, Plan.getOrAddLiveIn(
+                           ConstantInt::get(IntegerType::getInt64Ty(Ctx),
+                                            VF.getKnownMinValue() * Part))});
+      auto *Ext = new VPWidenIntrinsicRecipe(Intrinsic::vector_extract, Ops,
+                                             IntegerType::getInt1Ty(Ctx), DL);
+      Extracts.push_back(Ext);
+      Ext->insertAfter(ALM);
+    }
+  };
+
+  // Create a list of each active lane mask phi, ordered by unroll part.
+  SmallVector<VPActiveLaneMaskPHIRecipe *> Phis(UF, nullptr);
+  for (VPRecipeBase &R : Header->phis()) {
+    auto *Phi = dyn_cast<VPActiveLaneMaskPHIRecipe>(&R);
+    if (!Phi)
+      continue;
+    VPValue *Index;
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david-arm wrote:

I think for correctness this needs initialising to `nullptr`.

https://github.com/llvm/llvm-project/pull/147535