1//===- SSAUpdaterBulk.cpp - Unstructured SSA Update Tool ------------------===// 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// This file implements the SSAUpdaterBulk class. 10// 11//===----------------------------------------------------------------------===// 12 13#include "llvm/Transforms/Utils/SSAUpdaterBulk.h" 14#include "llvm/Analysis/IteratedDominanceFrontier.h" 15#include "llvm/IR/BasicBlock.h" 16#include "llvm/IR/Dominators.h" 17#include "llvm/IR/IRBuilder.h" 18#include "llvm/IR/Instructions.h" 19#include "llvm/IR/Use.h" 20#include "llvm/IR/Value.h" 21 22using namespace llvm; 23 24#define DEBUG_TYPE "ssaupdaterbulk" 25 26/// Helper function for finding a block which should have a value for the given 27/// user. For PHI-nodes this block is the corresponding predecessor, for other 28/// instructions it's their parent block. 29static BasicBlock *getUserBB(Use *U) { 30 auto *User = cast<Instruction>(U->getUser()); 31 32 if (auto *UserPN = dyn_cast<PHINode>(User)) 33 return UserPN->getIncomingBlock(*U); 34 else 35 return User->getParent(); 36} 37 38/// Add a new variable to the SSA rewriter. This needs to be called before 39/// AddAvailableValue or AddUse calls. 40unsigned SSAUpdaterBulk::AddVariable(StringRef Name, Type *Ty) { 41 unsigned Var = Rewrites.size(); 42 LLVM_DEBUG(dbgs() << "SSAUpdater: Var=" << Var << ": initialized with Ty = " 43 << *Ty << ", Name = " << Name << "\n"); 44 RewriteInfo RI(Name, Ty); 45 Rewrites.push_back(RI); 46 return Var; 47} 48 49/// Indicate that a rewritten value is available in the specified block with the 50/// specified value. 51void SSAUpdaterBulk::AddAvailableValue(unsigned Var, BasicBlock *BB, Value *V) { 52 assert(Var < Rewrites.size() && "Variable not found!"); 53 LLVM_DEBUG(dbgs() << "SSAUpdater: Var=" << Var 54 << ": added new available value" << *V << " in " 55 << BB->getName() << "\n"); 56 Rewrites[Var].Defines[BB] = V; 57} 58 59/// Record a use of the symbolic value. This use will be updated with a 60/// rewritten value when RewriteAllUses is called. 61void SSAUpdaterBulk::AddUse(unsigned Var, Use *U) { 62 assert(Var < Rewrites.size() && "Variable not found!"); 63 LLVM_DEBUG(dbgs() << "SSAUpdater: Var=" << Var << ": added a use" << *U->get() 64 << " in " << getUserBB(U)->getName() << "\n"); 65 Rewrites[Var].Uses.push_back(U); 66} 67 68/// Return true if the SSAUpdater already has a value for the specified variable 69/// in the specified block. 70bool SSAUpdaterBulk::HasValueForBlock(unsigned Var, BasicBlock *BB) { 71 return (Var < Rewrites.size()) ? Rewrites[Var].Defines.count(BB) : false; 72} 73 74// Compute value at the given block BB. We either should already know it, or we 75// should be able to recursively reach it going up dominator tree. 76Value *SSAUpdaterBulk::computeValueAt(BasicBlock *BB, RewriteInfo &R, 77 DominatorTree *DT) { 78 if (!R.Defines.count(BB)) { 79 if (DT->isReachableFromEntry(BB) && PredCache.get(BB).size()) { 80 BasicBlock *IDom = DT->getNode(BB)->getIDom()->getBlock(); 81 Value *V = computeValueAt(IDom, R, DT); 82 R.Defines[BB] = V; 83 } else 84 R.Defines[BB] = UndefValue::get(R.Ty); 85 } 86 return R.Defines[BB]; 87} 88 89/// Given sets of UsingBlocks and DefBlocks, compute the set of LiveInBlocks. 90/// This is basically a subgraph limited by DefBlocks and UsingBlocks. 91static void 92ComputeLiveInBlocks(const SmallPtrSetImpl<BasicBlock *> &UsingBlocks, 93 const SmallPtrSetImpl<BasicBlock *> &DefBlocks, 94 SmallPtrSetImpl<BasicBlock *> &LiveInBlocks, 95 PredIteratorCache &PredCache) { 96 // To determine liveness, we must iterate through the predecessors of blocks 97 // where the def is live. Blocks are added to the worklist if we need to 98 // check their predecessors. Start with all the using blocks. 99 SmallVector<BasicBlock *, 64> LiveInBlockWorklist(UsingBlocks.begin(), 100 UsingBlocks.end()); 101 102 // Now that we have a set of blocks where the phi is live-in, recursively add 103 // their predecessors until we find the full region the value is live. 104 while (!LiveInBlockWorklist.empty()) { 105 BasicBlock *BB = LiveInBlockWorklist.pop_back_val(); 106 107 // The block really is live in here, insert it into the set. If already in 108 // the set, then it has already been processed. 109 if (!LiveInBlocks.insert(BB).second) 110 continue; 111 112 // Since the value is live into BB, it is either defined in a predecessor or 113 // live into it to. Add the preds to the worklist unless they are a 114 // defining block. 115 for (BasicBlock *P : PredCache.get(BB)) { 116 // The value is not live into a predecessor if it defines the value. 117 if (DefBlocks.count(P)) 118 continue; 119 120 // Otherwise it is, add to the worklist. 121 LiveInBlockWorklist.push_back(P); 122 } 123 } 124} 125 126/// Perform all the necessary updates, including new PHI-nodes insertion and the 127/// requested uses update. 128void SSAUpdaterBulk::RewriteAllUses(DominatorTree *DT, 129 SmallVectorImpl<PHINode *> *InsertedPHIs) { 130 for (auto &R : Rewrites) { 131 // Compute locations for new phi-nodes. 132 // For that we need to initialize DefBlocks from definitions in R.Defines, 133 // UsingBlocks from uses in R.Uses, then compute LiveInBlocks, and then use 134 // this set for computing iterated dominance frontier (IDF). 135 // The IDF blocks are the blocks where we need to insert new phi-nodes. 136 ForwardIDFCalculator IDF(*DT); 137 LLVM_DEBUG(dbgs() << "SSAUpdater: rewriting " << R.Uses.size() 138 << " use(s)\n"); 139 140 SmallPtrSet<BasicBlock *, 2> DefBlocks; 141 for (auto &Def : R.Defines) 142 DefBlocks.insert(Def.first); 143 IDF.setDefiningBlocks(DefBlocks); 144 145 SmallPtrSet<BasicBlock *, 2> UsingBlocks; 146 for (Use *U : R.Uses) 147 UsingBlocks.insert(getUserBB(U)); 148 149 SmallVector<BasicBlock *, 32> IDFBlocks; 150 SmallPtrSet<BasicBlock *, 32> LiveInBlocks; 151 ComputeLiveInBlocks(UsingBlocks, DefBlocks, LiveInBlocks, PredCache); 152 IDF.resetLiveInBlocks(); 153 IDF.setLiveInBlocks(LiveInBlocks); 154 IDF.calculate(IDFBlocks); 155 156 // We've computed IDF, now insert new phi-nodes there. 157 SmallVector<PHINode *, 4> InsertedPHIsForVar; 158 for (auto *FrontierBB : IDFBlocks) { 159 IRBuilder<> B(FrontierBB, FrontierBB->begin()); 160 PHINode *PN = B.CreatePHI(R.Ty, 0, R.Name); 161 R.Defines[FrontierBB] = PN; 162 InsertedPHIsForVar.push_back(PN); 163 if (InsertedPHIs) 164 InsertedPHIs->push_back(PN); 165 } 166 167 // Fill in arguments of the inserted PHIs. 168 for (auto *PN : InsertedPHIsForVar) { 169 BasicBlock *PBB = PN->getParent(); 170 for (BasicBlock *Pred : PredCache.get(PBB)) 171 PN->addIncoming(computeValueAt(Pred, R, DT), Pred); 172 } 173 174 // Rewrite actual uses with the inserted definitions. 175 SmallPtrSet<Use *, 4> ProcessedUses; 176 for (Use *U : R.Uses) { 177 if (!ProcessedUses.insert(U).second) 178 continue; 179 Value *V = computeValueAt(getUserBB(U), R, DT); 180 Value *OldVal = U->get(); 181 assert(OldVal && "Invalid use!"); 182 // Notify that users of the existing value that it is being replaced. 183 if (OldVal != V && OldVal->hasValueHandle()) 184 ValueHandleBase::ValueIsRAUWd(OldVal, V); 185 LLVM_DEBUG(dbgs() << "SSAUpdater: replacing " << *OldVal << " with " << *V 186 << "\n"); 187 U->set(V); 188 } 189 } 190} 191