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329c1c6c94
getSubLoops/getTopLevelLoops methods, replacing them with iterator-based accessors. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@10714 91177308-0d34-0410-b5e6-96231b3b80d8
373 lines
14 KiB
C++
373 lines
14 KiB
C++
//===- IndVarSimplify.cpp - Induction Variable Elimination ----------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file was developed by the LLVM research group and is distributed under
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// the University of Illinois Open Source License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// Guarantees that all loops with identifiable, linear, induction variables will
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// be transformed to have a single, canonical, induction variable. After this
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// pass runs, it guarantees the the first PHI node of the header block in the
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// loop is the canonical induction variable if there is one.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "indvar"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Constants.h"
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#include "llvm/Type.h"
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#include "llvm/Instructions.h"
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#include "llvm/Analysis/InductionVariable.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/Support/CFG.h"
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#include "llvm/Target/TargetData.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include "Support/Debug.h"
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#include "Support/Statistic.h"
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using namespace llvm;
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namespace {
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Statistic<> NumRemoved ("indvars", "Number of aux indvars removed");
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Statistic<> NumInserted("indvars", "Number of canonical indvars added");
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class IndVarSimplify : public FunctionPass {
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LoopInfo *Loops;
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TargetData *TD;
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bool Changed;
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public:
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virtual bool runOnFunction(Function &) {
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Loops = &getAnalysis<LoopInfo>();
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TD = &getAnalysis<TargetData>();
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Changed = false;
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// Induction Variables live in the header nodes of loops
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for (LoopInfo::iterator I = Loops->begin(), E = Loops->end(); I != E; ++I)
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runOnLoop(*I);
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return Changed;
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}
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unsigned getTypeSize(const Type *Ty) {
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if (unsigned Size = Ty->getPrimitiveSize())
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return Size;
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return TD->getTypeSize(Ty); // Must be a pointer
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}
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Value *ComputeAuxIndVarValue(InductionVariable &IV, Value *CIV);
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void ReplaceIndVar(InductionVariable &IV, Value *Counter);
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void runOnLoop(Loop *L);
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequired<TargetData>(); // Need pointer size
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AU.addRequired<LoopInfo>();
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AU.addRequiredID(LoopSimplifyID);
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AU.addPreservedID(LoopSimplifyID);
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AU.setPreservesCFG();
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}
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};
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RegisterOpt<IndVarSimplify> X("indvars", "Canonicalize Induction Variables");
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}
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Pass *llvm::createIndVarSimplifyPass() {
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return new IndVarSimplify();
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}
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void IndVarSimplify::runOnLoop(Loop *Loop) {
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// Transform all subloops before this loop...
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for (LoopInfo::iterator I = Loop->begin(), E = Loop->end(); I != E; ++I)
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runOnLoop(*I);
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// Get the header node for this loop. All of the phi nodes that could be
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// induction variables must live in this basic block.
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//
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BasicBlock *Header = Loop->getHeader();
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// Loop over all of the PHI nodes in the basic block, calculating the
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// induction variables that they represent... stuffing the induction variable
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// info into a vector...
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//
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std::vector<InductionVariable> IndVars; // Induction variables for block
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BasicBlock::iterator AfterPHIIt = Header->begin();
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for (; PHINode *PN = dyn_cast<PHINode>(AfterPHIIt); ++AfterPHIIt)
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IndVars.push_back(InductionVariable(PN, Loops));
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// AfterPHIIt now points to first non-phi instruction...
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// If there are no phi nodes in this basic block, there can't be indvars...
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if (IndVars.empty()) return;
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// Loop over the induction variables, looking for a canonical induction
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// variable, and checking to make sure they are not all unknown induction
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// variables. Keep track of the largest integer size of the induction
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// variable.
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//
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InductionVariable *Canonical = 0;
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unsigned MaxSize = 0;
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for (unsigned i = 0; i != IndVars.size(); ++i) {
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InductionVariable &IV = IndVars[i];
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if (IV.InductionType != InductionVariable::Unknown) {
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unsigned IVSize = getTypeSize(IV.Phi->getType());
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if (IV.InductionType == InductionVariable::Canonical &&
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!isa<PointerType>(IV.Phi->getType()) && IVSize >= MaxSize)
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Canonical = &IV;
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if (IVSize > MaxSize) MaxSize = IVSize;
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// If this variable is larger than the currently identified canonical
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// indvar, the canonical indvar is not usable.
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if (Canonical && IVSize > getTypeSize(Canonical->Phi->getType()))
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Canonical = 0;
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}
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}
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// No induction variables, bail early... don't add a canonical indvar
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if (MaxSize == 0) return;
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// Figure out what the exit condition of the loop is. We can currently only
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// handle loops with a single exit. If we cannot figure out what the
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// termination condition is, we leave this variable set to null.
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//
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SetCondInst *TermCond = 0;
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if (Loop->getExitBlocks().size() == 1) {
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// Get ExitingBlock - the basic block in the loop which contains the branch
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// out of the loop.
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BasicBlock *Exit = Loop->getExitBlocks()[0];
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pred_iterator PI = pred_begin(Exit);
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assert(PI != pred_end(Exit) && "Should have one predecessor in loop!");
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BasicBlock *ExitingBlock = *PI;
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assert(++PI == pred_end(Exit) && "Exit block should have one pred!");
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assert(Loop->isLoopExit(ExitingBlock) && "Exiting block is not loop exit!");
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// Since the block is in the loop, yet branches out of it, we know that the
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// block must end with multiple destination terminator. Which means it is
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// either a conditional branch, a switch instruction, or an invoke.
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if (BranchInst *BI = dyn_cast<BranchInst>(ExitingBlock->getTerminator())) {
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assert(BI->isConditional() && "Unconditional branch has multiple succs?");
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TermCond = dyn_cast<SetCondInst>(BI->getCondition());
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} else {
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// NOTE: if people actually exit loops with switch instructions, we could
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// handle them, but I don't think this is important enough to spend time
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// thinking about.
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assert(isa<SwitchInst>(ExitingBlock->getTerminator()) ||
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isa<InvokeInst>(ExitingBlock->getTerminator()) &&
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"Unknown multi-successor terminator!");
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}
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}
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if (TermCond)
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DEBUG(std::cerr << "INDVAR: Found termination condition: " << *TermCond);
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// Okay, we want to convert other induction variables to use a canonical
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// indvar. If we don't have one, add one now...
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if (!Canonical) {
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// Create the PHI node for the new induction variable, and insert the phi
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// node at the start of the PHI nodes...
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const Type *IVType;
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switch (MaxSize) {
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default: assert(0 && "Unknown integer type size!");
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case 1: IVType = Type::UByteTy; break;
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case 2: IVType = Type::UShortTy; break;
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case 4: IVType = Type::UIntTy; break;
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case 8: IVType = Type::ULongTy; break;
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}
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PHINode *PN = new PHINode(IVType, "cann-indvar", Header->begin());
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// Create the increment instruction to add one to the counter...
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Instruction *Add = BinaryOperator::create(Instruction::Add, PN,
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ConstantUInt::get(IVType, 1),
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"next-indvar", AfterPHIIt);
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// Figure out which block is incoming and which is the backedge for the loop
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BasicBlock *Incoming, *BackEdgeBlock;
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pred_iterator PI = pred_begin(Header);
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assert(PI != pred_end(Header) && "Loop headers should have 2 preds!");
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if (Loop->contains(*PI)) { // First pred is back edge...
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BackEdgeBlock = *PI++;
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Incoming = *PI++;
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} else {
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Incoming = *PI++;
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BackEdgeBlock = *PI++;
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}
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assert(PI == pred_end(Header) && "Loop headers should have 2 preds!");
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// Add incoming values for the PHI node...
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PN->addIncoming(Constant::getNullValue(IVType), Incoming);
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PN->addIncoming(Add, BackEdgeBlock);
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// Analyze the new induction variable...
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IndVars.push_back(InductionVariable(PN, Loops));
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assert(IndVars.back().InductionType == InductionVariable::Canonical &&
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"Just inserted canonical indvar that is not canonical!");
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Canonical = &IndVars.back();
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++NumInserted;
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Changed = true;
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DEBUG(std::cerr << "INDVAR: Inserted canonical iv: " << *PN);
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} else {
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// If we have a canonical induction variable, make sure that it is the first
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// one in the basic block.
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if (&Header->front() != Canonical->Phi)
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Header->getInstList().splice(Header->begin(), Header->getInstList(),
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Canonical->Phi);
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DEBUG(std::cerr << "IndVar: Existing canonical iv used: "
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<< *Canonical->Phi);
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}
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DEBUG(std::cerr << "INDVAR: Replacing Induction variables:\n");
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// Get the current loop iteration count, which is always the value of the
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// canonical phi node...
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//
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PHINode *IterCount = Canonical->Phi;
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// Loop through and replace all of the auxiliary induction variables with
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// references to the canonical induction variable...
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//
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for (unsigned i = 0; i != IndVars.size(); ++i) {
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InductionVariable *IV = &IndVars[i];
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DEBUG(IV->print(std::cerr));
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// Don't modify the canonical indvar or unrecognized indvars...
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if (IV != Canonical && IV->InductionType != InductionVariable::Unknown) {
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ReplaceIndVar(*IV, IterCount);
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Changed = true;
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++NumRemoved;
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}
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}
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}
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/// ComputeAuxIndVarValue - Given an auxillary induction variable, compute and
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/// return a value which will always be equal to the induction variable PHI, but
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/// is based off of the canonical induction variable CIV.
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///
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Value *IndVarSimplify::ComputeAuxIndVarValue(InductionVariable &IV, Value *CIV){
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Instruction *Phi = IV.Phi;
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const Type *IVTy = Phi->getType();
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if (isa<PointerType>(IVTy)) // If indexing into a pointer, make the
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IVTy = TD->getIntPtrType(); // index the appropriate type.
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BasicBlock::iterator AfterPHIIt = Phi;
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while (isa<PHINode>(AfterPHIIt)) ++AfterPHIIt;
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Value *Val = CIV;
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if (Val->getType() != IVTy)
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Val = new CastInst(Val, IVTy, Val->getName(), AfterPHIIt);
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if (!isa<ConstantInt>(IV.Step) || // If the step != 1
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!cast<ConstantInt>(IV.Step)->equalsInt(1)) {
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// If the types are not compatible, insert a cast now...
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if (IV.Step->getType() != IVTy)
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IV.Step = new CastInst(IV.Step, IVTy, IV.Step->getName(), AfterPHIIt);
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Val = BinaryOperator::create(Instruction::Mul, Val, IV.Step,
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Phi->getName()+"-scale", AfterPHIIt);
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}
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// If this is a pointer indvar...
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if (isa<PointerType>(Phi->getType())) {
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std::vector<Value*> Idx;
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// FIXME: this should not be needed when we fix PR82!
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if (Val->getType() != Type::LongTy)
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Val = new CastInst(Val, Type::LongTy, Val->getName(), AfterPHIIt);
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Idx.push_back(Val);
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Val = new GetElementPtrInst(IV.Start, Idx,
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Phi->getName()+"-offset",
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AfterPHIIt);
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} else if (!isa<Constant>(IV.Start) || // If Start != 0...
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!cast<Constant>(IV.Start)->isNullValue()) {
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// If the types are not compatible, insert a cast now...
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if (IV.Start->getType() != IVTy)
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IV.Start = new CastInst(IV.Start, IVTy, IV.Start->getName(),
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AfterPHIIt);
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// Insert the instruction after the phi nodes...
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Val = BinaryOperator::create(Instruction::Add, Val, IV.Start,
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Phi->getName()+"-offset", AfterPHIIt);
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}
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// If the PHI node has a different type than val is, insert a cast now...
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if (Val->getType() != Phi->getType())
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Val = new CastInst(Val, Phi->getType(), Val->getName(), AfterPHIIt);
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// Move the PHI name to it's new equivalent value...
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std::string OldName = Phi->getName();
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Phi->setName("");
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Val->setName(OldName);
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return Val;
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}
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// ReplaceIndVar - Replace all uses of the specified induction variable with
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// expressions computed from the specified loop iteration counter variable.
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// Return true if instructions were deleted.
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void IndVarSimplify::ReplaceIndVar(InductionVariable &IV, Value *CIV) {
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Value *IndVarVal = 0;
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PHINode *Phi = IV.Phi;
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assert(Phi->getNumOperands() == 4 &&
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"Only expect induction variables in canonical loops!");
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// Remember the incoming values used by the PHI node
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std::vector<Value*> PHIOps;
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PHIOps.reserve(2);
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PHIOps.push_back(Phi->getIncomingValue(0));
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PHIOps.push_back(Phi->getIncomingValue(1));
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// Delete all of the operands of the PHI node... so that the to-be-deleted PHI
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// node does not cause any expressions to be computed that would not otherwise
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// be.
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Phi->dropAllReferences();
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// Now that we are rid of unneeded uses of the PHI node, replace any remaining
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// ones with the appropriate code using the canonical induction variable.
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while (!Phi->use_empty()) {
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Instruction *U = cast<Instruction>(Phi->use_back());
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// TODO: Perform LFTR here if possible
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if (0) {
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} else {
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// Replace all uses of the old PHI node with the new computed value...
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if (IndVarVal == 0)
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IndVarVal = ComputeAuxIndVarValue(IV, CIV);
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U->replaceUsesOfWith(Phi, IndVarVal);
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}
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}
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// If the PHI is the last user of any instructions for computing PHI nodes
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// that are irrelevant now, delete those instructions.
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while (!PHIOps.empty()) {
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Instruction *MaybeDead = dyn_cast<Instruction>(PHIOps.back());
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PHIOps.pop_back();
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if (MaybeDead && isInstructionTriviallyDead(MaybeDead) &&
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(!isa<PHINode>(MaybeDead) ||
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MaybeDead->getParent() != Phi->getParent())) {
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PHIOps.insert(PHIOps.end(), MaybeDead->op_begin(),
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MaybeDead->op_end());
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MaybeDead->getParent()->getInstList().erase(MaybeDead);
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// Erase any duplicates entries in the PHIOps list.
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std::vector<Value*>::iterator It =
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std::find(PHIOps.begin(), PHIOps.end(), MaybeDead);
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while (It != PHIOps.end()) {
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PHIOps.erase(It);
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It = std::find(PHIOps.begin(), PHIOps.end(), MaybeDead);
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}
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}
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}
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// Delete the old, now unused, phi node...
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Phi->getParent()->getInstList().erase(Phi);
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}
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