1 //===- IndVarSimplify.cpp - Induction Variable Elimination ----------------===//
2 //
3 // InductionVariableSimplify - Transform induction variables in a program
4 //   to all use a single cannonical induction variable per loop.
5 //
6 //===----------------------------------------------------------------------===//
7 
8 #include "llvm/Transforms/Scalar.h"
9 #include "llvm/Analysis/InductionVariable.h"
10 #include "llvm/Analysis/LoopInfo.h"
11 #include "llvm/Analysis/Writer.h"
12 #include "llvm/iPHINode.h"
13 #include "llvm/iOther.h"
14 #include "llvm/Type.h"
15 #include "llvm/Constants.h"
16 #include "llvm/Support/CFG.h"
17 #include "Support/STLExtras.h"
18 #include "Support/StatisticReporter.h"
19 
20 static Statistic<> NumRemoved ("indvars\t\t- Number of aux indvars removed");
21 static Statistic<> NumInserted("indvars\t\t- Number of cannonical indvars added");
22 
23 
24 // InsertCast - Cast Val to Ty, setting a useful name on the cast if Val has a
25 // name...
26 //
27 static Instruction *InsertCast(Instruction *Val, const Type *Ty,
28                                BasicBlock::iterator It) {
29   Instruction *Cast = new CastInst(Val, Ty);
30   if (Val->hasName()) Cast->setName(Val->getName()+"-casted");
31   Val->getParent()->getInstList().insert(It, Cast);
32   return Cast;
33 }
34 
35 static bool TransformLoop(LoopInfo *Loops, Loop *Loop) {
36   // Transform all subloops before this loop...
37   bool Changed = reduce_apply_bool(Loop->getSubLoops().begin(),
38                                    Loop->getSubLoops().end(),
39                               std::bind1st(std::ptr_fun(TransformLoop), Loops));
40   // Get the header node for this loop.  All of the phi nodes that could be
41   // induction variables must live in this basic block.
42   //
43   BasicBlock *Header = Loop->getBlocks().front();
44 
45   // Loop over all of the PHI nodes in the basic block, calculating the
46   // induction variables that they represent... stuffing the induction variable
47   // info into a vector...
48   //
49   std::vector<InductionVariable> IndVars;    // Induction variables for block
50   for (BasicBlock::iterator I = Header->begin();
51        PHINode *PN = dyn_cast<PHINode>(*I); ++I)
52     IndVars.push_back(InductionVariable(PN, Loops));
53 
54   // If there are no phi nodes in this basic block, there can't be indvars...
55   if (IndVars.empty()) return Changed;
56 
57   // Loop over the induction variables, looking for a cannonical induction
58   // variable, and checking to make sure they are not all unknown induction
59   // variables.
60   //
61   bool FoundIndVars = false;
62   InductionVariable *Cannonical = 0;
63   for (unsigned i = 0; i < IndVars.size(); ++i) {
64     if (IndVars[i].InductionType == InductionVariable::Cannonical)
65       Cannonical = &IndVars[i];
66     if (IndVars[i].InductionType != InductionVariable::Unknown)
67       FoundIndVars = true;
68   }
69 
70   // No induction variables, bail early... don't add a cannonnical indvar
71   if (!FoundIndVars) return Changed;
72 
73   // Okay, we want to convert other induction variables to use a cannonical
74   // indvar.  If we don't have one, add one now...
75   if (!Cannonical) {
76     // Create the PHI node for the new induction variable
77     PHINode *PN = new PHINode(Type::UIntTy, "cann-indvar");
78 
79     // Insert the phi node at the end of the other phi nodes...
80     Header->getInstList().insert(Header->begin()+IndVars.size(), PN);
81 
82     // Create the increment instruction to add one to the counter...
83     Instruction *Add = BinaryOperator::create(Instruction::Add, PN,
84                                               ConstantUInt::get(Type::UIntTy,1),
85                                               "add1-indvar");
86 
87     // Insert the add instruction after all of the PHI nodes...
88     Header->getInstList().insert(Header->begin()+(IndVars.size()+1), Add);
89 
90     // Figure out which block is incoming and which is the backedge for the loop
91     BasicBlock *Incoming, *BackEdgeBlock;
92     pred_iterator PI = pred_begin(Header);
93     assert(PI != pred_end(Header) && "Loop headers should have 2 preds!");
94     if (Loop->contains(*PI)) {  // First pred is back edge...
95       BackEdgeBlock = *PI++;
96       Incoming      = *PI++;
97     } else {
98       Incoming      = *PI++;
99       BackEdgeBlock = *PI++;
100     }
101     assert(PI == pred_end(Header) && "Loop headers should have 2 preds!");
102 
103     // Add incoming values for the PHI node...
104     PN->addIncoming(Constant::getNullValue(Type::UIntTy), Incoming);
105     PN->addIncoming(Add, BackEdgeBlock);
106 
107     // Analyze the new induction variable...
108     IndVars.push_back(InductionVariable(PN, Loops));
109     assert(IndVars.back().InductionType == InductionVariable::Cannonical &&
110            "Just inserted cannonical indvar that is not cannonical!");
111     Cannonical = &IndVars.back();
112     ++NumInserted;
113     Changed = true;
114   }
115 
116   DEBUG(cerr << "Induction variables:\n");
117 
118   // Get the current loop iteration count, which is always the value of the
119   // cannonical phi node...
120   //
121   PHINode *IterCount = Cannonical->Phi;
122 
123   // Loop through and replace all of the auxillary induction variables with
124   // references to the primary induction variable...
125   //
126   unsigned InsertPos = IndVars.size();
127   for (unsigned i = 0; i < IndVars.size(); ++i) {
128     InductionVariable *IV = &IndVars[i];
129 
130     DEBUG(cerr << IV);
131 
132     // Don't modify the cannonical indvar or unrecognized indvars...
133     if (IV != Cannonical && IV->InductionType != InductionVariable::Unknown) {
134       Instruction *Val = IterCount;
135       if (!isa<ConstantInt>(IV->Step) ||   // If the step != 1
136           !cast<ConstantInt>(IV->Step)->equalsInt(1)) {
137         std::string Name;   // Create a scale by the step value...
138         if (IV->Phi->hasName()) Name = IV->Phi->getName()+"-scale";
139 
140         // If the types are not compatible, insert a cast now...
141         if (Val->getType() != IV->Step->getType())
142           Val = InsertCast(Val, IV->Step->getType(),
143                            Header->begin()+InsertPos++);
144 
145         Val = BinaryOperator::create(Instruction::Mul, Val, IV->Step, Name);
146         // Insert the phi node at the end of the other phi nodes...
147         Header->getInstList().insert(Header->begin()+InsertPos++, Val);
148       }
149 
150       if (!isa<Constant>(IV->Start) ||   // If the start != 0
151           !cast<Constant>(IV->Start)->isNullValue()) {
152         std::string Name;   // Create a offset by the start value...
153         if (IV->Phi->hasName()) Name = IV->Phi->getName()+"-offset";
154 
155         // If the types are not compatible, insert a cast now...
156         if (Val->getType() != IV->Start->getType())
157           Val = InsertCast(Val, IV->Start->getType(),
158                            Header->begin()+InsertPos++);
159 
160         Val = BinaryOperator::create(Instruction::Add, Val, IV->Start, Name);
161         // Insert the phi node at the end of the other phi nodes...
162         Header->getInstList().insert(Header->begin()+InsertPos++, Val);
163       }
164 
165       // If the PHI node has a different type than val is, insert a cast now...
166       if (Val->getType() != IV->Phi->getType())
167           Val = InsertCast(Val, IV->Phi->getType(),
168                            Header->begin()+InsertPos++);
169 
170       // Replace all uses of the old PHI node with the new computed value...
171       IV->Phi->replaceAllUsesWith(Val);
172 
173       // Move the PHI name to it's new equivalent value...
174       std::string OldName = IV->Phi->getName();
175       IV->Phi->setName("");
176       Val->setName(OldName);
177 
178       // Delete the old, now unused, phi node...
179       Header->getInstList().remove(IV->Phi);
180       delete IV->Phi;
181       InsertPos--;            // Deleted an instr, decrement insert position
182       Changed = true;
183       ++NumRemoved;
184     }
185   }
186 
187   return Changed;
188 }
189 
190 namespace {
191   struct InductionVariableSimplify : public FunctionPass {
192     const char *getPassName() const {
193       return "Induction Variable Cannonicalize";
194     }
195 
196     virtual bool runOnFunction(Function *F) {
197       LoopInfo &LI = getAnalysis<LoopInfo>();
198 
199       // Induction Variables live in the header nodes of loops
200       return reduce_apply_bool(LI.getTopLevelLoops().begin(),
201                                LI.getTopLevelLoops().end(),
202                                std::bind1st(std::ptr_fun(TransformLoop), &LI));
203     }
204 
205     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
206       AU.addRequired(LoopInfo::ID);
207       AU.preservesCFG();
208     }
209   };
210 }
211 
212 Pass *createIndVarSimplifyPass() {
213   return new InductionVariableSimplify();
214 }
215 
216