1 //===-- VPlanTransforms.cpp - Utility VPlan to VPlan transforms -----------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 ///
9 /// \file
10 /// This file implements a set of utility VPlan to VPlan transformations.
11 ///
12 //===----------------------------------------------------------------------===//
13 
14 #include "VPlanTransforms.h"
15 #include "llvm/ADT/PostOrderIterator.h"
16 
17 using namespace llvm;
18 
19 void VPlanTransforms::VPInstructionsToVPRecipes(
20     Loop *OrigLoop, VPlanPtr &Plan,
21     LoopVectorizationLegality::InductionList &Inductions,
22     SmallPtrSetImpl<Instruction *> &DeadInstructions, ScalarEvolution &SE) {
23 
24   auto *TopRegion = cast<VPRegionBlock>(Plan->getEntry());
25   ReversePostOrderTraversal<VPBlockBase *> RPOT(TopRegion->getEntry());
26 
27   for (VPBlockBase *Base : RPOT) {
28     // Do not widen instructions in pre-header and exit blocks.
29     if (Base->getNumPredecessors() == 0 || Base->getNumSuccessors() == 0)
30       continue;
31 
32     VPBasicBlock *VPBB = Base->getEntryBasicBlock();
33     // Introduce each ingredient into VPlan.
34     for (auto I = VPBB->begin(), E = VPBB->end(); I != E;) {
35       VPRecipeBase *Ingredient = &*I++;
36       VPValue *VPV = Ingredient->getVPSingleValue();
37       Instruction *Inst = cast<Instruction>(VPV->getUnderlyingValue());
38       if (DeadInstructions.count(Inst)) {
39         VPValue DummyValue;
40         VPV->replaceAllUsesWith(&DummyValue);
41         Ingredient->eraseFromParent();
42         continue;
43       }
44 
45       VPRecipeBase *NewRecipe = nullptr;
46       if (auto *VPPhi = dyn_cast<VPWidenPHIRecipe>(Ingredient)) {
47         auto *Phi = cast<PHINode>(VPPhi->getUnderlyingValue());
48         InductionDescriptor II = Inductions.lookup(Phi);
49         if (II.getKind() == InductionDescriptor::IK_IntInduction ||
50             II.getKind() == InductionDescriptor::IK_FpInduction) {
51           VPValue *Start = Plan->getOrAddVPValue(II.getStartValue());
52           NewRecipe = new VPWidenIntOrFpInductionRecipe(Phi, Start, nullptr);
53         } else {
54           Plan->addVPValue(Phi, VPPhi);
55           continue;
56         }
57       } else {
58         assert(isa<VPInstruction>(Ingredient) &&
59                "only VPInstructions expected here");
60         assert(!isa<PHINode>(Inst) && "phis should be handled above");
61         // Create VPWidenMemoryInstructionRecipe for loads and stores.
62         if (LoadInst *Load = dyn_cast<LoadInst>(Inst)) {
63           NewRecipe = new VPWidenMemoryInstructionRecipe(
64               *Load, Plan->getOrAddVPValue(getLoadStorePointerOperand(Inst)),
65               nullptr /*Mask*/);
66         } else if (StoreInst *Store = dyn_cast<StoreInst>(Inst)) {
67           NewRecipe = new VPWidenMemoryInstructionRecipe(
68               *Store, Plan->getOrAddVPValue(getLoadStorePointerOperand(Inst)),
69               Plan->getOrAddVPValue(Store->getValueOperand()),
70               nullptr /*Mask*/);
71         } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Inst)) {
72           NewRecipe = new VPWidenGEPRecipe(
73               GEP, Plan->mapToVPValues(GEP->operands()), OrigLoop);
74         } else if (CallInst *CI = dyn_cast<CallInst>(Inst)) {
75           NewRecipe = new VPWidenCallRecipe(
76               *CI, Plan->mapToVPValues(CI->arg_operands()));
77         } else if (SelectInst *SI = dyn_cast<SelectInst>(Inst)) {
78           bool InvariantCond =
79               SE.isLoopInvariant(SE.getSCEV(SI->getOperand(0)), OrigLoop);
80           NewRecipe = new VPWidenSelectRecipe(
81               *SI, Plan->mapToVPValues(SI->operands()), InvariantCond);
82         } else {
83           NewRecipe =
84               new VPWidenRecipe(*Inst, Plan->mapToVPValues(Inst->operands()));
85         }
86       }
87 
88       NewRecipe->insertBefore(Ingredient);
89       if (NewRecipe->getNumDefinedValues() == 1)
90         VPV->replaceAllUsesWith(NewRecipe->getVPSingleValue());
91       else
92         assert(NewRecipe->getNumDefinedValues() == 0 &&
93                "Only recpies with zero or one defined values expected");
94       Ingredient->eraseFromParent();
95       Plan->removeVPValueFor(Inst);
96       for (auto *Def : NewRecipe->definedValues()) {
97         Plan->addVPValue(Inst, Def);
98       }
99     }
100   }
101 }
102 
103 bool VPlanTransforms::sinkScalarOperands(VPlan &Plan) {
104   auto Iter = depth_first(
105       VPBlockRecursiveTraversalWrapper<VPBlockBase *>(Plan.getEntry()));
106   bool Changed = false;
107   // First, collect the operands of all predicated replicate recipes as seeds
108   // for sinking.
109   SetVector<VPValue *> WorkList;
110   for (VPBasicBlock *VPBB : VPBlockUtils::blocksOnly<VPBasicBlock>(Iter)) {
111     for (auto &Recipe : *VPBB) {
112       auto *RepR = dyn_cast<VPReplicateRecipe>(&Recipe);
113       if (!RepR || !RepR->isPredicated())
114         continue;
115       WorkList.insert(RepR->op_begin(), RepR->op_end());
116     }
117   }
118 
119   // Try to sink each replicate recipe in the worklist.
120   while (!WorkList.empty()) {
121     auto *C = WorkList.pop_back_val();
122     auto *SinkCandidate = dyn_cast_or_null<VPReplicateRecipe>(C->Def);
123     if (!SinkCandidate || SinkCandidate->isUniform())
124       continue;
125 
126     // All users of SinkCandidate must be in the same block in order to perform
127     // sinking. Therefore the destination block for sinking must match the block
128     // containing the first user.
129     auto *FirstUser = dyn_cast<VPRecipeBase>(*SinkCandidate->user_begin());
130     if (!FirstUser)
131       continue;
132     VPBasicBlock *SinkTo = FirstUser->getParent();
133     if (SinkCandidate->getParent() == SinkTo ||
134         SinkCandidate->mayHaveSideEffects() ||
135         SinkCandidate->mayReadOrWriteMemory())
136       continue;
137 
138     // All recipe users of the sink candidate must be in the same block SinkTo.
139     if (any_of(SinkCandidate->users(), [SinkTo](VPUser *U) {
140           auto *UI = dyn_cast<VPRecipeBase>(U);
141           return !UI || UI->getParent() != SinkTo;
142         }))
143       continue;
144 
145     SinkCandidate->moveBefore(*SinkTo, SinkTo->getFirstNonPhi());
146     WorkList.insert(SinkCandidate->op_begin(), SinkCandidate->op_end());
147     Changed = true;
148   }
149   return Changed;
150 }
151