[llvm] [LV] Vectorize maxnum/minnum w/o fast-math flags. (PR #148239)

[Florian Hahn via llvm-commits]

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@@ -652,3 +652,140 @@ void VPlanTransforms::attachCheckBlock(VPlan &Plan, Value *Cond,
     Term->addMetadata(LLVMContext::MD_prof, BranchWeights);
   }
 }
+
+bool VPlanTransforms::handleMaxMinNumReductionsWithoutFastMath(VPlan &Plan) {
+  VPRegionBlock *LoopRegion = Plan.getVectorLoopRegion();
+  VPReductionPHIRecipe *RedPhiR = nullptr;
+  VPValue *MinMaxOp = nullptr;
+  bool HasUnsupportedPhi = false;
+
+  auto GetMinMaxCompareValue = [](VPSingleDefRecipe *MinMaxOp,
+                                  VPReductionPHIRecipe *RedPhi) -> VPValue * {
+    auto *RepR = dyn_cast<VPReplicateRecipe>(MinMaxOp);
+    if (!isa<VPWidenIntrinsicRecipe>(MinMaxOp) &&
+        !(RepR && (isa<IntrinsicInst>(RepR->getUnderlyingInstr()))))
+      return nullptr;
+
+    if (MinMaxOp->getOperand(0) == RedPhi)
+      return MinMaxOp->getOperand(1);
+    assert(MinMaxOp->getOperand(1) == RedPhi &&
+           "Reduction phi operand expected");
+    return MinMaxOp->getOperand(0);
+  };
+
+  for (auto &R : LoopRegion->getEntryBasicBlock()->phis()) {
+    // TODO: Also support first-order recurrence phis.
+    HasUnsupportedPhi |=
+        !isa<VPCanonicalIVPHIRecipe, VPWidenIntOrFpInductionRecipe,
+             VPReductionPHIRecipe>(&R);
+    auto *Cur = dyn_cast<VPReductionPHIRecipe>(&R);
+    if (!Cur)
+      continue;
+    // For now, only a single reduction is supported.
+    // TODO: Support multiple MaxNum/MinNum reductions and other reductions.
+    if (RedPhiR)
+      return false;
+    if (Cur->getRecurrenceKind() != RecurKind::FMaxNum &&
+        Cur->getRecurrenceKind() != RecurKind::FMinNum)
+      continue;
+
+    RedPhiR = Cur;
+    auto *MinMaxR = dyn_cast<VPRecipeWithIRFlags>(
+        RedPhiR->getBackedgeValue()->getDefiningRecipe());
+    if (!MinMaxR)
+      return false;
+    MinMaxOp = GetMinMaxCompareValue(MinMaxR, RedPhiR);
+    if (!MinMaxOp)
+      return false;
+  }
+
+  if (!RedPhiR)
+    return true;
+
+  if (HasUnsupportedPhi || !Plan.hasScalarTail())
+    return false;
+
----------------
fhahn wrote:

Moved, thanks!

https://github.com/llvm/llvm-project/pull/148239