llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
Chris Lattner 15cad759fe More minor non-functional changes. This now computes the exit condition, though
it doesn't do anything with it.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@10590 91177308-0d34-0410-b5e6-96231b3b80d8
2003-12-23 07:47:09 +00:00

373 lines
14 KiB
C++

//===- IndVarSimplify.cpp - Induction Variable Elimination ----------------===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// Guarantees that all loops with identifiable, linear, induction variables will
// be transformed to have a single, canonical, induction variable. After this
// pass runs, it guarantees the the first PHI node of the header block in the
// loop is the canonical induction variable if there is one.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "indvar"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Constants.h"
#include "llvm/Type.h"
#include "llvm/Instructions.h"
#include "llvm/Analysis/InductionVariable.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Support/CFG.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Transforms/Utils/Local.h"
#include "Support/Debug.h"
#include "Support/Statistic.h"
using namespace llvm;
namespace {
Statistic<> NumRemoved ("indvars", "Number of aux indvars removed");
Statistic<> NumInserted("indvars", "Number of canonical indvars added");
class IndVarSimplify : public FunctionPass {
LoopInfo *Loops;
TargetData *TD;
bool Changed;
public:
virtual bool runOnFunction(Function &) {
Loops = &getAnalysis<LoopInfo>();
TD = &getAnalysis<TargetData>();
Changed = false;
// Induction Variables live in the header nodes of loops
for (unsigned i = 0, e = Loops->getTopLevelLoops().size(); i != e; ++i)
runOnLoop(Loops->getTopLevelLoops()[i]);
return Changed;
}
unsigned getTypeSize(const Type *Ty) {
if (unsigned Size = Ty->getPrimitiveSize())
return Size;
return TD->getTypeSize(Ty); // Must be a pointer
}
Value *ComputeAuxIndVarValue(InductionVariable &IV, Value *CIV);
void ReplaceIndVar(InductionVariable &IV, Value *Counter);
void runOnLoop(Loop *L);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<TargetData>(); // Need pointer size
AU.addRequired<LoopInfo>();
AU.addRequiredID(LoopSimplifyID);
AU.addPreservedID(LoopSimplifyID);
AU.setPreservesCFG();
}
};
RegisterOpt<IndVarSimplify> X("indvars", "Canonicalize Induction Variables");
}
Pass *llvm::createIndVarSimplifyPass() {
return new IndVarSimplify();
}
void IndVarSimplify::runOnLoop(Loop *Loop) {
// Transform all subloops before this loop...
for (unsigned i = 0, e = Loop->getSubLoops().size(); i != e; ++i)
runOnLoop(Loop->getSubLoops()[i]);
// 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 = Loop->getHeader();
// 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
BasicBlock::iterator AfterPHIIt = Header->begin();
for (; PHINode *PN = dyn_cast<PHINode>(AfterPHIIt); ++AfterPHIIt)
IndVars.push_back(InductionVariable(PN, Loops));
// AfterPHIIt now points to first non-phi instruction...
// If there are no phi nodes in this basic block, there can't be indvars...
if (IndVars.empty()) return;
// Loop over the induction variables, looking for a canonical induction
// variable, and checking to make sure they are not all unknown induction
// variables. Keep track of the largest integer size of the induction
// variable.
//
InductionVariable *Canonical = 0;
unsigned MaxSize = 0;
for (unsigned i = 0; i != IndVars.size(); ++i) {
InductionVariable &IV = IndVars[i];
if (IV.InductionType != InductionVariable::Unknown) {
unsigned IVSize = getTypeSize(IV.Phi->getType());
if (IV.InductionType == InductionVariable::Canonical &&
!isa<PointerType>(IV.Phi->getType()) && IVSize >= MaxSize)
Canonical = &IV;
if (IVSize > MaxSize) MaxSize = IVSize;
// If this variable is larger than the currently identified canonical
// indvar, the canonical indvar is not usable.
if (Canonical && IVSize > getTypeSize(Canonical->Phi->getType()))
Canonical = 0;
}
}
// No induction variables, bail early... don't add a canonical indvar
if (MaxSize == 0) return;
// Figure out what the exit condition of the loop is. We can currently only
// handle loops with a single exit. If we cannot figure out what the
// termination condition is, we leave this variable set to null.
//
SetCondInst *TermCond = 0;
if (Loop->getExitBlocks().size() == 1) {
// Get ExitingBlock - the basic block in the loop which contains the branch
// out of the loop.
BasicBlock *Exit = Loop->getExitBlocks()[0];
pred_iterator PI = pred_begin(Exit);
assert(PI != pred_end(Exit) && "Should have one predecessor in loop!");
BasicBlock *ExitingBlock = *PI;
assert(++PI == pred_end(Exit) && "Exit block should have one pred!");
assert(Loop->isLoopExit(ExitingBlock) && "Exiting block is not loop exit!");
// Since the block is in the loop, yet branches out of it, we know that the
// block must end with multiple destination terminator. Which means it is
// either a conditional branch, a switch instruction, or an invoke.
if (BranchInst *BI = dyn_cast<BranchInst>(ExitingBlock->getTerminator())) {
assert(BI->isConditional() && "Unconditional branch has multiple succs?");
TermCond = dyn_cast<SetCondInst>(BI->getCondition());
} else {
// NOTE: if people actually exit loops with switch instructions, we could
// handle them, but I don't think this is important enough to spend time
// thinking about.
assert(isa<SwitchInst>(ExitingBlock->getTerminator()) ||
isa<InvokeInst>(ExitingBlock->getTerminator()) &&
"Unknown multi-successor terminator!");
}
}
if (TermCond)
DEBUG(std::cerr << "INDVAR: Found termination condition: " << *TermCond);
// Okay, we want to convert other induction variables to use a canonical
// indvar. If we don't have one, add one now...
if (!Canonical) {
// Create the PHI node for the new induction variable, and insert the phi
// node at the start of the PHI nodes...
const Type *IVType;
switch (MaxSize) {
default: assert(0 && "Unknown integer type size!");
case 1: IVType = Type::UByteTy; break;
case 2: IVType = Type::UShortTy; break;
case 4: IVType = Type::UIntTy; break;
case 8: IVType = Type::ULongTy; break;
}
PHINode *PN = new PHINode(IVType, "cann-indvar", Header->begin());
// Create the increment instruction to add one to the counter...
Instruction *Add = BinaryOperator::create(Instruction::Add, PN,
ConstantUInt::get(IVType, 1),
"next-indvar", AfterPHIIt);
// 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(IVType), Incoming);
PN->addIncoming(Add, BackEdgeBlock);
// Analyze the new induction variable...
IndVars.push_back(InductionVariable(PN, Loops));
assert(IndVars.back().InductionType == InductionVariable::Canonical &&
"Just inserted canonical indvar that is not canonical!");
Canonical = &IndVars.back();
++NumInserted;
Changed = true;
DEBUG(std::cerr << "INDVAR: Inserted canonical iv: " << *PN);
} else {
// If we have a canonical induction variable, make sure that it is the first
// one in the basic block.
if (&Header->front() != Canonical->Phi)
Header->getInstList().splice(Header->begin(), Header->getInstList(),
Canonical->Phi);
DEBUG(std::cerr << "IndVar: Existing canonical iv used: "
<< *Canonical->Phi);
}
DEBUG(std::cerr << "INDVAR: Replacing Induction variables:\n");
// Get the current loop iteration count, which is always the value of the
// canonical phi node...
//
PHINode *IterCount = Canonical->Phi;
// Loop through and replace all of the auxiliary induction variables with
// references to the canonical induction variable...
//
for (unsigned i = 0; i != IndVars.size(); ++i) {
InductionVariable *IV = &IndVars[i];
DEBUG(IV->print(std::cerr));
// Don't modify the canonical indvar or unrecognized indvars...
if (IV != Canonical && IV->InductionType != InductionVariable::Unknown) {
ReplaceIndVar(*IV, IterCount);
Changed = true;
++NumRemoved;
}
}
}
/// ComputeAuxIndVarValue - Given an auxillary induction variable, compute and
/// return a value which will always be equal to the induction variable PHI, but
/// is based off of the canonical induction variable CIV.
///
Value *IndVarSimplify::ComputeAuxIndVarValue(InductionVariable &IV, Value *CIV){
Instruction *Phi = IV.Phi;
const Type *IVTy = Phi->getType();
if (isa<PointerType>(IVTy)) // If indexing into a pointer, make the
IVTy = TD->getIntPtrType(); // index the appropriate type.
BasicBlock::iterator AfterPHIIt = Phi;
while (isa<PHINode>(AfterPHIIt)) ++AfterPHIIt;
Value *Val = CIV;
if (Val->getType() != IVTy)
Val = new CastInst(Val, IVTy, Val->getName(), AfterPHIIt);
if (!isa<ConstantInt>(IV.Step) || // If the step != 1
!cast<ConstantInt>(IV.Step)->equalsInt(1)) {
// If the types are not compatible, insert a cast now...
if (IV.Step->getType() != IVTy)
IV.Step = new CastInst(IV.Step, IVTy, IV.Step->getName(), AfterPHIIt);
Val = BinaryOperator::create(Instruction::Mul, Val, IV.Step,
Phi->getName()+"-scale", AfterPHIIt);
}
// If this is a pointer indvar...
if (isa<PointerType>(Phi->getType())) {
std::vector<Value*> Idx;
// FIXME: this should not be needed when we fix PR82!
if (Val->getType() != Type::LongTy)
Val = new CastInst(Val, Type::LongTy, Val->getName(), AfterPHIIt);
Idx.push_back(Val);
Val = new GetElementPtrInst(IV.Start, Idx,
Phi->getName()+"-offset",
AfterPHIIt);
} else if (!isa<Constant>(IV.Start) || // If Start != 0...
!cast<Constant>(IV.Start)->isNullValue()) {
// If the types are not compatible, insert a cast now...
if (IV.Start->getType() != IVTy)
IV.Start = new CastInst(IV.Start, IVTy, IV.Start->getName(),
AfterPHIIt);
// Insert the instruction after the phi nodes...
Val = BinaryOperator::create(Instruction::Add, Val, IV.Start,
Phi->getName()+"-offset", AfterPHIIt);
}
// If the PHI node has a different type than val is, insert a cast now...
if (Val->getType() != Phi->getType())
Val = new CastInst(Val, Phi->getType(), Val->getName(), AfterPHIIt);
// Move the PHI name to it's new equivalent value...
std::string OldName = Phi->getName();
Phi->setName("");
Val->setName(OldName);
return Val;
}
// ReplaceIndVar - Replace all uses of the specified induction variable with
// expressions computed from the specified loop iteration counter variable.
// Return true if instructions were deleted.
void IndVarSimplify::ReplaceIndVar(InductionVariable &IV, Value *CIV) {
Value *IndVarVal = 0;
PHINode *Phi = IV.Phi;
assert(Phi->getNumOperands() == 4 &&
"Only expect induction variables in canonical loops!");
// Remember the incoming values used by the PHI node
std::vector<Value*> PHIOps;
PHIOps.reserve(2);
PHIOps.push_back(Phi->getIncomingValue(0));
PHIOps.push_back(Phi->getIncomingValue(1));
// Delete all of the operands of the PHI node... so that the to-be-deleted PHI
// node does not cause any expressions to be computed that would not otherwise
// be.
Phi->dropAllReferences();
// Now that we are rid of unneeded uses of the PHI node, replace any remaining
// ones with the appropriate code using the canonical induction variable.
while (!Phi->use_empty()) {
Instruction *U = cast<Instruction>(Phi->use_back());
// TODO: Perform LFTR here if possible
if (0) {
} else {
// Replace all uses of the old PHI node with the new computed value...
if (IndVarVal == 0)
IndVarVal = ComputeAuxIndVarValue(IV, CIV);
U->replaceUsesOfWith(Phi, IndVarVal);
}
}
// If the PHI is the last user of any instructions for computing PHI nodes
// that are irrelevant now, delete those instructions.
while (!PHIOps.empty()) {
Instruction *MaybeDead = dyn_cast<Instruction>(PHIOps.back());
PHIOps.pop_back();
if (MaybeDead && isInstructionTriviallyDead(MaybeDead) &&
(!isa<PHINode>(MaybeDead) ||
MaybeDead->getParent() != Phi->getParent())) {
PHIOps.insert(PHIOps.end(), MaybeDead->op_begin(),
MaybeDead->op_end());
MaybeDead->getParent()->getInstList().erase(MaybeDead);
// Erase any duplicates entries in the PHIOps list.
std::vector<Value*>::iterator It =
std::find(PHIOps.begin(), PHIOps.end(), MaybeDead);
while (It != PHIOps.end()) {
PHIOps.erase(It);
It = std::find(PHIOps.begin(), PHIOps.end(), MaybeDead);
}
}
}
// Delete the old, now unused, phi node...
Phi->getParent()->getInstList().erase(Phi);
}