[VPlan] Construct initial once and pass clones to tryToBuildVPlan (NFC). (#141363)

Update to only build an initial, plain-CFG VPlan once, and then
transform & optimize clones.

This requires changes to ::clone() for VPInstruction and
VPWidenPHIRecipe to allow for proper cloning of the recipes in the
initial VPlan.

PR: #141363

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorizationPlanner.h

@@ -519,8 +519,10 @@ class LoopVectorizationPlanner {
   /// \p Range's largest included VF is restricted to the maximum VF the
   /// returned VPlan is valid for. If no VPlan can be built for the input range,
   /// set the largest included VF to the maximum VF for which no plan could be
-  /// built.
-  VPlanPtr tryToBuildVPlanWithVPRecipes(VFRange &Range, LoopVersioning *LVer);
+  /// built. Each VPlan is built starting from a copy of \p InitialPlan, which
+  /// is a plain CFG VPlan wrapping the original scalar loop.
+  VPlanPtr tryToBuildVPlanWithVPRecipes(VPlanPtr InitialPlan, VFRange &Range,
+                                        LoopVersioning *LVer);
 
   /// Build VPlans for power-of-2 VF's between \p MinVF and \p MaxVF inclusive,
   /// according to the information gathered by Legal when it checked if it is

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -8717,9 +8717,11 @@ void LoopVectorizationPlanner::buildVPlansWithVPRecipes(ElementCount MinVF,
   }
 
   auto MaxVFTimes2 = MaxVF * 2;
+  auto VPlan0 = VPlanTransforms::buildPlainCFG(OrigLoop, *LI);
   for (ElementCount VF = MinVF; ElementCount::isKnownLT(VF, MaxVFTimes2);) {
     VFRange SubRange = {VF, MaxVFTimes2};
-    if (auto Plan = tryToBuildVPlanWithVPRecipes(SubRange, &LVer)) {
+    if (auto Plan = tryToBuildVPlanWithVPRecipes(
+            std::unique_ptr<VPlan>(VPlan0->duplicate()), SubRange, &LVer)) {
       bool HasScalarVF = Plan->hasScalarVFOnly();
       // Now optimize the initial VPlan.
       if (!HasScalarVF)
@@ -8980,9 +8982,8 @@ static void addExitUsersForFirstOrderRecurrences(
   }
 }
 
-VPlanPtr
-LoopVectorizationPlanner::tryToBuildVPlanWithVPRecipes(VFRange &Range,
-                                                       LoopVersioning *LVer) {
+VPlanPtr LoopVectorizationPlanner::tryToBuildVPlanWithVPRecipes(
+    VPlanPtr Plan, VFRange &Range, LoopVersioning *LVer) {
 
   using namespace llvm::VPlanPatternMatch;
   SmallPtrSet<const InterleaveGroup<Instruction> *, 1> InterleaveGroups;
@@ -9004,7 +9005,6 @@ LoopVectorizationPlanner::tryToBuildVPlanWithVPRecipes(VFRange &Range,
             return !CM.requiresScalarEpilogue(VF.isVector());
           },
           Range);
-  auto Plan = VPlanTransforms::buildPlainCFG(OrigLoop, *LI);
   VPlanTransforms::prepareForVectorization(
       *Plan, Legal->getWidestInductionType(), PSE, RequiresScalarEpilogueCheck,
       CM.foldTailByMasking(), OrigLoop,

llvm/lib/Transforms/Vectorize/VPlan.h

@@ -972,7 +972,10 @@ class VPInstruction : public VPRecipeWithIRFlags,
 
   VPInstruction *clone() override {
     SmallVector<VPValue *, 2> Operands(operands());
-    return new VPInstruction(Opcode, Operands, *this, getDebugLoc(), Name);
+    auto *New = new VPInstruction(Opcode, Operands, *this, getDebugLoc(), Name);
+    if (getUnderlyingValue())
+      New->setUnderlyingValue(getUnderlyingInstr());
+    return New;
   }
 
   unsigned getOpcode() const { return Opcode; }
@@ -2090,7 +2093,11 @@ class VPWidenPHIRecipe : public VPSingleDefRecipe, public VPPhiAccessors {
   }
 
   VPWidenPHIRecipe *clone() override {
-    llvm_unreachable("cloning not implemented yet");
+    auto *C = new VPWidenPHIRecipe(cast<PHINode>(getUnderlyingValue()),
+                                   getOperand(0), getDebugLoc(), Name);
+    for (VPValue *Op : make_range(std::next(op_begin()), op_end()))
+      C->addOperand(Op);
+    return C;
   }
 
   ~VPWidenPHIRecipe() override = default;