llvm-6502/lib/Transforms/Scalar/IndVarSimplify.cpp

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//===- IndVarSimplify.cpp - Induction Variable Elimination ----------------===//
//
// InductionVariableSimplify - Transform induction variables in a program
// to all use a single cannonical induction variable per loop.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar/IndVarSimplify.h"
#include "llvm/Analysis/InductionVariable.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/iPHINode.h"
#include "llvm/iOther.h"
#include "llvm/Type.h"
#include "llvm/BasicBlock.h"
#include "llvm/Constants.h"
#include "llvm/Pass.h"
#include "llvm/Support/CFG.h"
#include "Support/STLExtras.h"
#if 0
#define DEBUG
#include "llvm/Analysis/Writer.h"
#endif
// InsertCast - Cast Val to Ty, setting a useful name on the cast if Val has a
// name...
//
static Instruction *InsertCast(Instruction *Val, const Type *Ty,
BasicBlock::iterator It) {
Instruction *Cast = new CastInst(Val, Ty);
if (Val->hasName()) Cast->setName(Val->getName()+"-casted");
Val->getParent()->getInstList().insert(It, Cast);
return Cast;
}
static bool TransformLoop(LoopInfo *Loops, Loop *Loop) {
// Transform all subloops before this loop...
bool Changed = reduce_apply_bool(Loop->getSubLoops().begin(),
Loop->getSubLoops().end(),
std::bind1st(std::ptr_fun(TransformLoop), Loops));
// Get the header node for this loop. All of the phi nodes that could be
// induction variables must live in this basic block.
BasicBlock *Header = (BasicBlock*)Loop->getBlocks().front();
// Loop over all of the PHI nodes in the basic block, calculating the
// induction variables that they represent... stuffing the induction variable
// info into a vector...
//
std::vector<InductionVariable> IndVars; // Induction variables for block
for (BasicBlock::iterator I = Header->begin();
PHINode *PN = dyn_cast<PHINode>(*I); ++I)
IndVars.push_back(InductionVariable(PN, Loops));
// If there are no phi nodes in this basic block, there can't be indvars...
if (IndVars.empty()) return Changed;
// Loop over the induction variables, looking for a cannonical induction
// variable, and checking to make sure they are not all unknown induction
// variables.
//
bool FoundIndVars = false;
InductionVariable *Cannonical = 0;
for (unsigned i = 0; i < IndVars.size(); ++i) {
if (IndVars[i].InductionType == InductionVariable::Cannonical)
Cannonical = &IndVars[i];
if (IndVars[i].InductionType != InductionVariable::Unknown)
FoundIndVars = true;
}
// No induction variables, bail early... don't add a cannonnical indvar
if (!FoundIndVars) return Changed;
// Okay, we want to convert other induction variables to use a cannonical
// indvar. If we don't have one, add one now...
if (!Cannonical) {
// Create the PHI node for the new induction variable
PHINode *PN = new PHINode(Type::UIntTy, "cann-indvar");
// Insert the phi node at the end of the other phi nodes...
Header->getInstList().insert(Header->begin()+IndVars.size(), PN);
// Create the increment instruction to add one to the counter...
Instruction *Add = BinaryOperator::create(Instruction::Add, PN,
ConstantUInt::get(Type::UIntTy,1),
"add1-indvar");
// Insert the add instruction after all of the PHI nodes...
Header->getInstList().insert(Header->begin()+(IndVars.size()+1), Add);
// Figure out which block is incoming and which is the backedge for the loop
BasicBlock *Incoming, *BackEdgeBlock;
pred_iterator PI = pred_begin(Header);
assert(PI != pred_end(Header) && "Loop headers should have 2 preds!");
if (Loop->contains(*PI)) { // First pred is back edge...
BackEdgeBlock = *PI++;
Incoming = *PI++;
} else {
Incoming = *PI++;
BackEdgeBlock = *PI++;
}
assert(PI == pred_end(Header) && "Loop headers should have 2 preds!");
// Add incoming values for the PHI node...
PN->addIncoming(Constant::getNullValue(Type::UIntTy), Incoming);
PN->addIncoming(Add, BackEdgeBlock);
// Analyze the new induction variable...
IndVars.push_back(InductionVariable(PN, Loops));
assert(IndVars.back().InductionType == InductionVariable::Cannonical &&
"Just inserted cannonical indvar that is not cannonical!");
Cannonical = &IndVars.back();
Changed = true;
}
#ifdef DEBUG
cerr << "Induction variables:\n";
#endif
// Get the current loop iteration count, which is always the value of the
// cannonical phi node...
//
PHINode *IterCount = Cannonical->Phi;
// Loop through and replace all of the auxillary induction variables with
// references to the primary induction variable...
//
unsigned InsertPos = IndVars.size();
for (unsigned i = 0; i < IndVars.size(); ++i) {
InductionVariable *IV = &IndVars[i];
#ifdef DEBUG
cerr << IndVars[i];
#endif
// Don't modify the cannonical indvar or unrecognized indvars...
if (IV != Cannonical && IV->InductionType != InductionVariable::Unknown) {
Instruction *Val = IterCount;
if (!isa<ConstantInt>(IV->Step) || // If the step != 1
!cast<ConstantInt>(IV->Step)->equalsInt(1)) {
std::string Name; // Create a scale by the step value...
if (IV->Phi->hasName()) Name = IV->Phi->getName()+"-scale";
// If the types are not compatible, insert a cast now...
if (Val->getType() != IV->Step->getType())
Val = InsertCast(Val, IV->Step->getType(),
Header->begin()+InsertPos++);
Val = BinaryOperator::create(Instruction::Mul, Val, IV->Step, Name);
// Insert the phi node at the end of the other phi nodes...
Header->getInstList().insert(Header->begin()+InsertPos++, Val);
}
if (!isa<Constant>(IV->Start) || // If the start != 0
!cast<Constant>(IV->Start)->isNullValue()) {
std::string Name; // Create a offset by the start value...
if (IV->Phi->hasName()) Name = IV->Phi->getName()+"-offset";
// If the types are not compatible, insert a cast now...
if (Val->getType() != IV->Start->getType())
Val = InsertCast(Val, IV->Start->getType(),
Header->begin()+InsertPos++);
Val = BinaryOperator::create(Instruction::Add, Val, IV->Start, Name);
// Insert the phi node at the end of the other phi nodes...
Header->getInstList().insert(Header->begin()+InsertPos++, Val);
}
// If the PHI node has a different type than val is, insert a cast now...
if (Val->getType() != IV->Phi->getType())
Val = InsertCast(Val, IV->Phi->getType(),
Header->begin()+InsertPos++);
// Replace all uses of the old PHI node with the new computed value...
IV->Phi->replaceAllUsesWith(Val);
// Move the PHI name to it's new equivalent value...
std::string OldName = IV->Phi->getName();
IV->Phi->setName("");
Val->setName(OldName);
// Delete the old, now unused, phi node...
Header->getInstList().remove(IV->Phi);
delete IV->Phi;
InsertPos--; // Deleted an instr, decrement insert position
Changed = true;
}
}
return Changed;
}
static bool doit(Function *M, LoopInfo &Loops) {
// Induction Variables live in the header nodes of the loops of the function
return reduce_apply_bool(Loops.getTopLevelLoops().begin(),
Loops.getTopLevelLoops().end(),
std::bind1st(std::ptr_fun(TransformLoop), &Loops));
}
namespace {
struct InductionVariableSimplify : public FunctionPass {
virtual bool runOnFunction(Function *F) {
return doit(F, getAnalysis<LoopInfo>());
}
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired(LoopInfo::ID);
AU.preservesCFG();
}
};
}
Pass *createIndVarSimplifyPass() {
return new InductionVariableSimplify();
}