1 //===- IndVarSimplify.cpp - Induction Variable Elimination ----------------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // Guarantees that all loops with identifiable, linear, induction variables will
11 // be transformed to have a single, canonical, induction variable. After this
12 // pass runs, it guarantees the the first PHI node of the header block in the
13 // loop is the canonical induction variable if there is one.
15 //===----------------------------------------------------------------------===//
17 #include "llvm/Transforms/Scalar.h"
18 #include "llvm/Constants.h"
19 #include "llvm/Type.h"
20 #include "llvm/iPHINode.h"
21 #include "llvm/iOther.h"
22 #include "llvm/Analysis/InductionVariable.h"
23 #include "llvm/Analysis/LoopInfo.h"
24 #include "llvm/Support/CFG.h"
25 #include "llvm/Transforms/Utils/Local.h"
26 #include "Support/Debug.h"
27 #include "Support/Statistic.h"
28 #include "Support/STLExtras.h"
33 Statistic<> NumRemoved ("indvars", "Number of aux indvars removed");
34 Statistic<> NumInserted("indvars", "Number of canonical indvars added");
37 // InsertCast - Cast Val to Ty, setting a useful name on the cast if Val has a
40 static Instruction *InsertCast(Value *Val, const Type *Ty,
41 Instruction *InsertBefore) {
42 return new CastInst(Val, Ty, Val->getName()+"-casted", InsertBefore);
45 static bool TransformLoop(LoopInfo *Loops, Loop *Loop) {
46 // Transform all subloops before this loop...
47 bool Changed = reduce_apply_bool(Loop->getSubLoops().begin(),
48 Loop->getSubLoops().end(),
49 std::bind1st(std::ptr_fun(TransformLoop), Loops));
50 // Get the header node for this loop. All of the phi nodes that could be
51 // induction variables must live in this basic block.
53 BasicBlock *Header = Loop->getHeader();
55 // Loop over all of the PHI nodes in the basic block, calculating the
56 // induction variables that they represent... stuffing the induction variable
57 // info into a vector...
59 std::vector<InductionVariable> IndVars; // Induction variables for block
60 BasicBlock::iterator AfterPHIIt = Header->begin();
61 for (; PHINode *PN = dyn_cast<PHINode>(AfterPHIIt); ++AfterPHIIt)
62 IndVars.push_back(InductionVariable(PN, Loops));
63 // AfterPHIIt now points to first non-phi instruction...
65 // If there are no phi nodes in this basic block, there can't be indvars...
66 if (IndVars.empty()) return Changed;
68 // Loop over the induction variables, looking for a canonical induction
69 // variable, and checking to make sure they are not all unknown induction
72 bool FoundIndVars = false;
73 InductionVariable *Canonical = 0;
74 for (unsigned i = 0; i < IndVars.size(); ++i) {
75 if (IndVars[i].InductionType == InductionVariable::Canonical &&
76 !isa<PointerType>(IndVars[i].Phi->getType()))
77 Canonical = &IndVars[i];
78 if (IndVars[i].InductionType != InductionVariable::Unknown)
82 // No induction variables, bail early... don't add a canonical indvar
83 if (!FoundIndVars) return Changed;
85 // Okay, we want to convert other induction variables to use a canonical
86 // indvar. If we don't have one, add one now...
88 // Create the PHI node for the new induction variable, and insert the phi
89 // node at the start of the PHI nodes...
90 PHINode *PN = new PHINode(Type::UIntTy, "cann-indvar", Header->begin());
92 // Create the increment instruction to add one to the counter...
93 Instruction *Add = BinaryOperator::create(Instruction::Add, PN,
94 ConstantUInt::get(Type::UIntTy,1),
95 "add1-indvar", AfterPHIIt);
97 // Figure out which block is incoming and which is the backedge for the loop
98 BasicBlock *Incoming, *BackEdgeBlock;
99 pred_iterator PI = pred_begin(Header);
100 assert(PI != pred_end(Header) && "Loop headers should have 2 preds!");
101 if (Loop->contains(*PI)) { // First pred is back edge...
102 BackEdgeBlock = *PI++;
106 BackEdgeBlock = *PI++;
108 assert(PI == pred_end(Header) && "Loop headers should have 2 preds!");
110 // Add incoming values for the PHI node...
111 PN->addIncoming(Constant::getNullValue(Type::UIntTy), Incoming);
112 PN->addIncoming(Add, BackEdgeBlock);
114 // Analyze the new induction variable...
115 IndVars.push_back(InductionVariable(PN, Loops));
116 assert(IndVars.back().InductionType == InductionVariable::Canonical &&
117 "Just inserted canonical indvar that is not canonical!");
118 Canonical = &IndVars.back();
122 // If we have a canonical induction variable, make sure that it is the first
123 // one in the basic block.
124 if (&Header->front() != Canonical->Phi)
125 Header->getInstList().splice(Header->begin(), Header->getInstList(),
129 DEBUG(std::cerr << "Induction variables:\n");
131 // Get the current loop iteration count, which is always the value of the
132 // canonical phi node...
134 PHINode *IterCount = Canonical->Phi;
136 // Loop through and replace all of the auxiliary induction variables with
137 // references to the canonical induction variable...
139 for (unsigned i = 0; i < IndVars.size(); ++i) {
140 InductionVariable *IV = &IndVars[i];
142 DEBUG(IV->print(std::cerr));
144 while (isa<PHINode>(AfterPHIIt)) ++AfterPHIIt;
146 // Don't do math with pointers...
147 const Type *IVTy = IV->Phi->getType();
148 if (isa<PointerType>(IVTy)) IVTy = Type::ULongTy;
150 // Don't modify the canonical indvar or unrecognized indvars...
151 if (IV != Canonical && IV->InductionType != InductionVariable::Unknown) {
152 Instruction *Val = IterCount;
153 if (!isa<ConstantInt>(IV->Step) || // If the step != 1
154 !cast<ConstantInt>(IV->Step)->equalsInt(1)) {
156 // If the types are not compatible, insert a cast now...
157 if (Val->getType() != IVTy)
158 Val = InsertCast(Val, IVTy, AfterPHIIt);
159 if (IV->Step->getType() != IVTy)
160 IV->Step = InsertCast(IV->Step, IVTy, AfterPHIIt);
162 Val = BinaryOperator::create(Instruction::Mul, Val, IV->Step,
163 IV->Phi->getName()+"-scale", AfterPHIIt);
167 if (IV->Start != Constant::getNullValue(IV->Start->getType())) {
168 // If the types are not compatible, insert a cast now...
169 if (Val->getType() != IVTy)
170 Val = InsertCast(Val, IVTy, AfterPHIIt);
171 if (IV->Start->getType() != IVTy)
172 IV->Start = InsertCast(IV->Start, IVTy, AfterPHIIt);
174 // Insert the instruction after the phi nodes...
175 Val = BinaryOperator::create(Instruction::Add, Val, IV->Start,
176 IV->Phi->getName()+"-offset", AfterPHIIt);
179 // If the PHI node has a different type than val is, insert a cast now...
180 if (Val->getType() != IV->Phi->getType())
181 Val = InsertCast(Val, IV->Phi->getType(), AfterPHIIt);
183 // Replace all uses of the old PHI node with the new computed value...
184 IV->Phi->replaceAllUsesWith(Val);
186 // Move the PHI name to it's new equivalent value...
187 std::string OldName = IV->Phi->getName();
188 IV->Phi->setName("");
189 Val->setName(OldName);
191 // Get the incoming values used by the PHI node
192 std::vector<Value*> PHIOps;
193 PHIOps.reserve(IV->Phi->getNumIncomingValues());
194 for (unsigned i = 0, e = IV->Phi->getNumIncomingValues(); i != e; ++i)
195 PHIOps.push_back(IV->Phi->getIncomingValue(i));
197 // Delete the old, now unused, phi node...
198 Header->getInstList().erase(IV->Phi);
200 // If the PHI is the last user of any instructions for computing PHI nodes
201 // that are irrelevant now, delete those instructions.
202 while (!PHIOps.empty()) {
203 Instruction *MaybeDead = dyn_cast<Instruction>(PHIOps.back());
206 if (MaybeDead && isInstructionTriviallyDead(MaybeDead)) {
207 PHIOps.insert(PHIOps.end(), MaybeDead->op_begin(),
208 MaybeDead->op_end());
209 MaybeDead->getParent()->getInstList().erase(MaybeDead);
211 // Erase any duplicates entries in the PHIOps list.
212 std::vector<Value*>::iterator It =
213 std::find(PHIOps.begin(), PHIOps.end(), MaybeDead);
214 while (It != PHIOps.end()) {
216 It = std::find(PHIOps.begin(), PHIOps.end(), MaybeDead);
219 // Erasing the instruction could invalidate the AfterPHI iterator!
220 AfterPHIIt = Header->begin();
233 struct InductionVariableSimplify : public FunctionPass {
234 virtual bool runOnFunction(Function &) {
235 LoopInfo &LI = getAnalysis<LoopInfo>();
237 // Induction Variables live in the header nodes of loops
238 return reduce_apply_bool(LI.getTopLevelLoops().begin(),
239 LI.getTopLevelLoops().end(),
240 std::bind1st(std::ptr_fun(TransformLoop), &LI));
243 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
244 AU.addRequired<LoopInfo>();
245 AU.addRequiredID(LoopSimplifyID);
246 AU.setPreservesCFG();
249 RegisterOpt<InductionVariableSimplify> X("indvars",
250 "Canonicalize Induction Variables");
253 Pass *llvm::createIndVarSimplifyPass() {
254 return new InductionVariableSimplify();