1 //===- IndVarSimplify.cpp - Induction Variable Elimination ----------------===//
3 // InductionVariableSimplify - Transform induction variables in a program
4 // to all use a single cannonical induction variable per loop.
6 //===----------------------------------------------------------------------===//
8 #include "llvm/Transforms/Scalar/IndVarSimplify.h"
9 #include "llvm/Analysis/InductionVariable.h"
10 #include "llvm/Analysis/LoopInfo.h"
11 #include "llvm/Analysis/Dominators.h"
12 #include "llvm/iPHINode.h"
13 #include "llvm/iOther.h"
14 #include "llvm/Type.h"
15 #include "llvm/ConstantVals.h"
16 #include "Support/STLExtras.h"
20 #include "llvm/Analysis/Writer.h"
23 // InsertCast - Cast Val to Ty, setting a useful name on the cast if Val has a
26 static Instruction *InsertCast(Instruction *Val, const Type *Ty,
27 BasicBlock::iterator It) {
28 Instruction *Cast = new CastInst(Val, Ty);
29 if (Val->hasName()) Cast->setName(Val->getName()+"-casted");
30 Val->getParent()->getInstList().insert(It, Cast);
34 static bool TransformLoop(cfg::LoopInfo *Loops, cfg::Loop *Loop) {
35 // Transform all subloops before this loop...
36 bool Changed = reduce_apply_bool(Loop->getSubLoops().begin(),
37 Loop->getSubLoops().end(),
38 std::bind1st(ptr_fun(TransformLoop), Loops));
39 // Get the header node for this loop. All of the phi nodes that could be
40 // induction variables must live in this basic block.
41 BasicBlock *Header = (BasicBlock*)Loop->getBlocks().front();
43 // Loop over all of the PHI nodes in the basic block, calculating the
44 // induction variables that they represent... stuffing the induction variable
45 // info into a vector...
47 vector<InductionVariable> IndVars; // Induction variables for block
48 for (BasicBlock::iterator I = Header->begin();
49 PHINode *PN = dyn_cast<PHINode>(*I); ++I)
50 IndVars.push_back(InductionVariable(PN, Loops));
52 // If there are no phi nodes in this basic block, there can't be indvars...
53 if (IndVars.empty()) return Changed;
55 // Loop over the induction variables, looking for a cannonical induction
56 // variable, and checking to make sure they are not all unknown induction
59 bool FoundIndVars = false;
60 InductionVariable *Cannonical = 0;
61 for (unsigned i = 0; i < IndVars.size(); ++i) {
62 if (IndVars[i].InductionType == InductionVariable::Cannonical)
63 Cannonical = &IndVars[i];
64 if (IndVars[i].InductionType != InductionVariable::Unknown)
68 // No induction variables, bail early... don't add a cannonnical indvar
69 if (!FoundIndVars) return Changed;
71 // Okay, we want to convert other induction variables to use a cannonical
72 // indvar. If we don't have one, add one now...
74 // Create the PHI node for the new induction variable
75 PHINode *PN = new PHINode(Type::UIntTy, "cann-indvar");
77 // Insert the phi node at the end of the other phi nodes...
78 Header->getInstList().insert(Header->begin()+IndVars.size(), PN);
80 // Create the increment instruction to add one to the counter...
81 Instruction *Add = BinaryOperator::create(Instruction::Add, PN,
82 ConstantUInt::get(Type::UIntTy,1),
85 // Insert the add instruction after all of the PHI nodes...
86 Header->getInstList().insert(Header->begin()+(IndVars.size()+1), Add);
88 // Figure out which block is incoming and which is the backedge for the loop
89 BasicBlock *Incoming, *BackEdgeBlock;
90 BasicBlock::pred_iterator PI = Header->pred_begin();
91 assert(PI != Header->pred_end() && "Loop headers should have 2 preds!");
92 if (Loop->contains(*PI)) { // First pred is back edge...
93 BackEdgeBlock = *PI++;
97 BackEdgeBlock = *PI++;
99 assert(PI == Header->pred_end() && "Loop headers should have 2 preds!");
101 // Add incoming values for the PHI node...
102 PN->addIncoming(Constant::getNullConstant(Type::UIntTy), Incoming);
103 PN->addIncoming(Add, BackEdgeBlock);
105 // Analyze the new induction variable...
106 IndVars.push_back(InductionVariable(PN, Loops));
107 assert(IndVars.back().InductionType == InductionVariable::Cannonical &&
108 "Just inserted cannonical indvar that is not cannonical!");
109 Cannonical = &IndVars.back();
113 cerr << "Induction variables:\n";
116 // Get the current loop iteration count, which is always the value of the
117 // cannonical phi node...
119 PHINode *IterCount = Cannonical->Phi;
121 // Loop through and replace all of the auxillary induction variables with
122 // references to the primary induction variable...
124 unsigned InsertPos = IndVars.size();
125 for (unsigned i = 0; i < IndVars.size(); ++i) {
126 InductionVariable *IV = &IndVars[i];
130 // Don't modify the cannonical indvar or unrecognized indvars...
131 if (IV != Cannonical && IV->InductionType != InductionVariable::Unknown) {
132 Instruction *Val = IterCount;
133 if (!isa<ConstantInt>(IV->Step) || // If the step != 1
134 !cast<ConstantInt>(IV->Step)->equalsInt(1)) {
135 string Name; // Create a scale by the step value...
136 if (IV->Phi->hasName()) Name = IV->Phi->getName()+"-scale";
138 // If the types are not compatible, insert a cast now...
139 if (Val->getType() != IV->Step->getType())
140 Val = InsertCast(Val, IV->Step->getType(),
141 Header->begin()+InsertPos++);
143 Val = BinaryOperator::create(Instruction::Mul, Val, IV->Step, Name);
144 // Insert the phi node at the end of the other phi nodes...
145 Header->getInstList().insert(Header->begin()+InsertPos++, Val);
148 if (!isa<Constant>(IV->Start) || // If the start != 0
149 !cast<Constant>(IV->Start)->isNullValue()) {
150 string Name; // Create a offset by the start value...
151 if (IV->Phi->hasName()) Name = IV->Phi->getName()+"-offset";
153 // If the types are not compatible, insert a cast now...
154 if (Val->getType() != IV->Start->getType())
155 Val = InsertCast(Val, IV->Start->getType(),
156 Header->begin()+InsertPos++);
158 Val = BinaryOperator::create(Instruction::Add, Val, IV->Start, Name);
159 // Insert the phi node at the end of the other phi nodes...
160 Header->getInstList().insert(Header->begin()+InsertPos++, Val);
163 // If the PHI node has a different type than val is, insert a cast now...
164 if (Val->getType() != IV->Phi->getType())
165 Val = InsertCast(Val, IV->Phi->getType(),
166 Header->begin()+InsertPos++);
168 // Replace all uses of the old PHI node with the new computed value...
169 IV->Phi->replaceAllUsesWith(Val);
171 // Move the PHI name to it's new equivalent value...
172 string OldName = IV->Phi->getName();
173 IV->Phi->setName("");
174 Val->setName(OldName);
176 // Delete the old, now unused, phi node...
177 Header->getInstList().remove(IV->Phi);
179 InsertPos--; // Deleted an instr, decrement insert position
186 bool InductionVariableSimplify::doit(Method *M) {
187 if (M->isExternal()) return false;
189 // Figure out the loop structure of the method...
190 cfg::LoopInfo Loops(M);
192 // Induction Variables live in the header nodes of the loops of the method...
193 return reduce_apply_bool(Loops.getTopLevelLoops().begin(),
194 Loops.getTopLevelLoops().end(),
195 std::bind1st(std::ptr_fun(TransformLoop), &Loops));