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and work better with VC++. Patch contributed by Morten Ofstad! git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@17281 91177308-0d34-0410-b5e6-96231b3b80d8
756 lines
30 KiB
C++
756 lines
30 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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// This transformation analyzes and transforms the induction variables (and
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// computations derived from them) into simpler forms suitable for subsequent
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// analysis and transformation.
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//
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// This transformation make the following changes to each loop with an
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// identifiable induction variable:
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// 1. All loops are transformed to have a SINGLE canonical induction variable
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// which starts at zero and steps by one.
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// 2. The canonical induction variable is guaranteed to be the first PHI node
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// in the loop header block.
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// 3. Any pointer arithmetic recurrences are raised to use array subscripts.
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//
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// If the trip count of a loop is computable, this pass also makes the following
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// changes:
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// 1. The exit condition for the loop is canonicalized to compare the
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// induction value against the exit value. This turns loops like:
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// 'for (i = 7; i*i < 1000; ++i)' into 'for (i = 0; i != 25; ++i)'
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// 2. Any use outside of the loop of an expression derived from the indvar
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// is changed to compute the derived value outside of the loop, eliminating
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// the dependence on the exit value of the induction variable. If the only
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// purpose of the loop is to compute the exit value of some derived
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// expression, this transformation will make the loop dead.
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//
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// This transformation should be followed by strength reduction after all of the
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// desired loop transformations have been performed. Additionally, on targets
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// where it is profitable, the loop could be transformed to count down to zero
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// (the "do loop" optimization).
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/BasicBlock.h"
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#include "llvm/Constants.h"
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#include "llvm/Instructions.h"
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#include "llvm/Type.h"
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#include "llvm/Analysis/ScalarEvolutionExpressions.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/Support/GetElementPtrTypeIterator.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/ADT/Statistic.h"
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using namespace llvm;
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namespace {
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/// SCEVExpander - This class uses information about analyze scalars to
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/// rewrite expressions in canonical form.
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///
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/// Clients should create an instance of this class when rewriting is needed,
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/// and destroying it when finished to allow the release of the associated
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/// memory.
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struct SCEVExpander : public SCEVVisitor<SCEVExpander, Value*> {
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ScalarEvolution &SE;
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LoopInfo &LI;
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std::map<SCEVHandle, Value*> InsertedExpressions;
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std::set<Instruction*> InsertedInstructions;
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Instruction *InsertPt;
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friend struct SCEVVisitor<SCEVExpander, Value*>;
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public:
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SCEVExpander(ScalarEvolution &se, LoopInfo &li) : SE(se), LI(li) {}
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/// isInsertedInstruction - Return true if the specified instruction was
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/// inserted by the code rewriter. If so, the client should not modify the
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/// instruction.
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bool isInsertedInstruction(Instruction *I) const {
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return InsertedInstructions.count(I);
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}
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/// getOrInsertCanonicalInductionVariable - This method returns the
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/// canonical induction variable of the specified type for the specified
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/// loop (inserting one if there is none). A canonical induction variable
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/// starts at zero and steps by one on each iteration.
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Value *getOrInsertCanonicalInductionVariable(const Loop *L, const Type *Ty){
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assert((Ty->isInteger() || Ty->isFloatingPoint()) &&
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"Can only insert integer or floating point induction variables!");
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SCEVHandle H = SCEVAddRecExpr::get(SCEVUnknown::getIntegerSCEV(0, Ty),
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SCEVUnknown::getIntegerSCEV(1, Ty), L);
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return expand(H);
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}
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/// addInsertedValue - Remember the specified instruction as being the
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/// canonical form for the specified SCEV.
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void addInsertedValue(Instruction *I, SCEV *S) {
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InsertedExpressions[S] = (Value*)I;
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InsertedInstructions.insert(I);
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}
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/// expandCodeFor - Insert code to directly compute the specified SCEV
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/// expression into the program. The inserted code is inserted into the
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/// specified block.
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///
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/// If a particular value sign is required, a type may be specified for the
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/// result.
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Value *expandCodeFor(SCEVHandle SH, Instruction *IP, const Type *Ty = 0) {
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// Expand the code for this SCEV.
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this->InsertPt = IP;
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return expandInTy(SH, Ty);
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}
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protected:
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Value *expand(SCEV *S) {
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// Check to see if we already expanded this.
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std::map<SCEVHandle, Value*>::iterator I = InsertedExpressions.find(S);
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if (I != InsertedExpressions.end())
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return I->second;
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Value *V = visit(S);
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InsertedExpressions[S] = V;
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return V;
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}
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Value *expandInTy(SCEV *S, const Type *Ty) {
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Value *V = expand(S);
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if (Ty && V->getType() != Ty) {
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// FIXME: keep track of the cast instruction.
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if (Constant *C = dyn_cast<Constant>(V))
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return ConstantExpr::getCast(C, Ty);
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else if (Instruction *I = dyn_cast<Instruction>(V)) {
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// Check to see if there is already a cast. If there is, use it.
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for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
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UI != E; ++UI) {
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if ((*UI)->getType() == Ty)
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if (CastInst *CI = dyn_cast<CastInst>(cast<Instruction>(*UI))) {
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BasicBlock::iterator It = I; ++It;
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while (isa<PHINode>(It)) ++It;
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if (It != BasicBlock::iterator(CI)) {
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// Splice the cast immediately after the operand in question.
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BasicBlock::InstListType &InstList =
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I->getParent()->getInstList();
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InstList.splice(It, CI->getParent()->getInstList(), CI);
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}
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return CI;
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}
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}
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BasicBlock::iterator IP = I; ++IP;
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if (InvokeInst *II = dyn_cast<InvokeInst>(I))
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IP = II->getNormalDest()->begin();
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while (isa<PHINode>(IP)) ++IP;
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return new CastInst(V, Ty, V->getName(), IP);
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} else {
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// FIXME: check to see if there is already a cast!
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return new CastInst(V, Ty, V->getName(), InsertPt);
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}
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}
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return V;
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}
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Value *visitConstant(SCEVConstant *S) {
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return S->getValue();
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}
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Value *visitTruncateExpr(SCEVTruncateExpr *S) {
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Value *V = expand(S->getOperand());
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return new CastInst(V, S->getType(), "tmp.", InsertPt);
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}
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Value *visitZeroExtendExpr(SCEVZeroExtendExpr *S) {
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Value *V = expandInTy(S->getOperand(),S->getType()->getUnsignedVersion());
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return new CastInst(V, S->getType(), "tmp.", InsertPt);
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}
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Value *visitAddExpr(SCEVAddExpr *S) {
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const Type *Ty = S->getType();
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Value *V = expandInTy(S->getOperand(S->getNumOperands()-1), Ty);
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// Emit a bunch of add instructions
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for (int i = S->getNumOperands()-2; i >= 0; --i)
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V = BinaryOperator::createAdd(V, expandInTy(S->getOperand(i), Ty),
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"tmp.", InsertPt);
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return V;
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}
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Value *visitMulExpr(SCEVMulExpr *S);
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Value *visitUDivExpr(SCEVUDivExpr *S) {
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const Type *Ty = S->getType();
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Value *LHS = expandInTy(S->getLHS(), Ty);
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Value *RHS = expandInTy(S->getRHS(), Ty);
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return BinaryOperator::createDiv(LHS, RHS, "tmp.", InsertPt);
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}
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Value *visitAddRecExpr(SCEVAddRecExpr *S);
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Value *visitUnknown(SCEVUnknown *S) {
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return S->getValue();
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}
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};
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}
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Value *SCEVExpander::visitMulExpr(SCEVMulExpr *S) {
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const Type *Ty = S->getType();
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int FirstOp = 0; // Set if we should emit a subtract.
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if (SCEVConstant *SC = dyn_cast<SCEVConstant>(S->getOperand(0)))
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if (SC->getValue()->isAllOnesValue())
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FirstOp = 1;
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int i = S->getNumOperands()-2;
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Value *V = expandInTy(S->getOperand(i+1), Ty);
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// Emit a bunch of multiply instructions
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for (; i >= FirstOp; --i)
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V = BinaryOperator::createMul(V, expandInTy(S->getOperand(i), Ty),
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"tmp.", InsertPt);
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// -1 * ... ---> 0 - ...
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if (FirstOp == 1)
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V = BinaryOperator::createNeg(V, "tmp.", InsertPt);
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return V;
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}
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Value *SCEVExpander::visitAddRecExpr(SCEVAddRecExpr *S) {
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const Type *Ty = S->getType();
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const Loop *L = S->getLoop();
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// We cannot yet do fp recurrences, e.g. the xform of {X,+,F} --> X+{0,+,F}
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assert(Ty->isIntegral() && "Cannot expand fp recurrences yet!");
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// {X,+,F} --> X + {0,+,F}
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if (!isa<SCEVConstant>(S->getStart()) ||
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!cast<SCEVConstant>(S->getStart())->getValue()->isNullValue()) {
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Value *Start = expandInTy(S->getStart(), Ty);
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std::vector<SCEVHandle> NewOps(S->op_begin(), S->op_end());
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NewOps[0] = SCEVUnknown::getIntegerSCEV(0, Ty);
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Value *Rest = expandInTy(SCEVAddRecExpr::get(NewOps, L), Ty);
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// FIXME: look for an existing add to use.
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return BinaryOperator::createAdd(Rest, Start, "tmp.", InsertPt);
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}
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// {0,+,1} --> Insert a canonical induction variable into the loop!
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if (S->getNumOperands() == 2 &&
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S->getOperand(1) == SCEVUnknown::getIntegerSCEV(1, Ty)) {
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// Create and insert the PHI node for the induction variable in the
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// specified loop.
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BasicBlock *Header = L->getHeader();
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PHINode *PN = new PHINode(Ty, "indvar", Header->begin());
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PN->addIncoming(Constant::getNullValue(Ty), L->getLoopPreheader());
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pred_iterator HPI = pred_begin(Header);
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assert(HPI != pred_end(Header) && "Loop with zero preds???");
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if (!L->contains(*HPI)) ++HPI;
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assert(HPI != pred_end(Header) && L->contains(*HPI) &&
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"No backedge in loop?");
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// Insert a unit add instruction right before the terminator corresponding
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// to the back-edge.
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Constant *One = Ty->isFloatingPoint() ? (Constant*)ConstantFP::get(Ty, 1.0)
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: ConstantInt::get(Ty, 1);
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Instruction *Add = BinaryOperator::createAdd(PN, One, "indvar.next",
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(*HPI)->getTerminator());
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pred_iterator PI = pred_begin(Header);
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if (*PI == L->getLoopPreheader())
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++PI;
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PN->addIncoming(Add, *PI);
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return PN;
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}
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// Get the canonical induction variable I for this loop.
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Value *I = getOrInsertCanonicalInductionVariable(L, Ty);
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if (S->getNumOperands() == 2) { // {0,+,F} --> i*F
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Value *F = expandInTy(S->getOperand(1), Ty);
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return BinaryOperator::createMul(I, F, "tmp.", InsertPt);
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}
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// If this is a chain of recurrences, turn it into a closed form, using the
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// folders, then expandCodeFor the closed form. This allows the folders to
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// simplify the expression without having to build a bunch of special code
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// into this folder.
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SCEVHandle IH = SCEVUnknown::get(I); // Get I as a "symbolic" SCEV.
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SCEVHandle V = S->evaluateAtIteration(IH);
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//std::cerr << "Evaluated: " << *this << "\n to: " << *V << "\n";
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return expandInTy(V, Ty);
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}
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namespace {
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Statistic<> NumRemoved ("indvars", "Number of aux indvars removed");
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Statistic<> NumPointer ("indvars", "Number of pointer indvars promoted");
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Statistic<> NumInserted("indvars", "Number of canonical indvars added");
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Statistic<> NumReplaced("indvars", "Number of exit values replaced");
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Statistic<> NumLFTR ("indvars", "Number of loop exit tests replaced");
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class IndVarSimplify : public FunctionPass {
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LoopInfo *LI;
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ScalarEvolution *SE;
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bool Changed;
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public:
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virtual bool runOnFunction(Function &) {
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LI = &getAnalysis<LoopInfo>();
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SE = &getAnalysis<ScalarEvolution>();
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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 = LI->begin(), E = LI->end(); I != E; ++I)
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runOnLoop(*I);
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return Changed;
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}
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequiredID(LoopSimplifyID);
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AU.addRequired<ScalarEvolution>();
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AU.addRequired<LoopInfo>();
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AU.addPreservedID(LoopSimplifyID);
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AU.setPreservesCFG();
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}
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private:
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void runOnLoop(Loop *L);
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void EliminatePointerRecurrence(PHINode *PN, BasicBlock *Preheader,
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std::set<Instruction*> &DeadInsts);
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void LinearFunctionTestReplace(Loop *L, SCEV *IterationCount,
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SCEVExpander &RW);
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void RewriteLoopExitValues(Loop *L);
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void DeleteTriviallyDeadInstructions(std::set<Instruction*> &Insts);
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};
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RegisterOpt<IndVarSimplify> X("indvars", "Canonicalize Induction Variables");
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}
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FunctionPass *llvm::createIndVarSimplifyPass() {
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return new IndVarSimplify();
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}
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/// DeleteTriviallyDeadInstructions - If any of the instructions is the
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/// specified set are trivially dead, delete them and see if this makes any of
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/// their operands subsequently dead.
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void IndVarSimplify::
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DeleteTriviallyDeadInstructions(std::set<Instruction*> &Insts) {
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while (!Insts.empty()) {
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Instruction *I = *Insts.begin();
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Insts.erase(Insts.begin());
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if (isInstructionTriviallyDead(I)) {
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for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
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if (Instruction *U = dyn_cast<Instruction>(I->getOperand(i)))
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Insts.insert(U);
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SE->deleteInstructionFromRecords(I);
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I->eraseFromParent();
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Changed = true;
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}
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}
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}
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/// EliminatePointerRecurrence - Check to see if this is a trivial GEP pointer
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/// recurrence. If so, change it into an integer recurrence, permitting
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/// analysis by the SCEV routines.
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void IndVarSimplify::EliminatePointerRecurrence(PHINode *PN,
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BasicBlock *Preheader,
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std::set<Instruction*> &DeadInsts) {
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assert(PN->getNumIncomingValues() == 2 && "Noncanonicalized loop!");
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unsigned PreheaderIdx = PN->getBasicBlockIndex(Preheader);
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unsigned BackedgeIdx = PreheaderIdx^1;
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if (GetElementPtrInst *GEPI =
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dyn_cast<GetElementPtrInst>(PN->getIncomingValue(BackedgeIdx)))
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if (GEPI->getOperand(0) == PN) {
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assert(GEPI->getNumOperands() == 2 && "GEP types must mismatch!");
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// Okay, we found a pointer recurrence. Transform this pointer
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// recurrence into an integer recurrence. Compute the value that gets
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// added to the pointer at every iteration.
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Value *AddedVal = GEPI->getOperand(1);
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// Insert a new integer PHI node into the top of the block.
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PHINode *NewPhi = new PHINode(AddedVal->getType(),
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PN->getName()+".rec", PN);
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NewPhi->addIncoming(Constant::getNullValue(NewPhi->getType()), Preheader);
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// Create the new add instruction.
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Value *NewAdd = BinaryOperator::createAdd(NewPhi, AddedVal,
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GEPI->getName()+".rec", GEPI);
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NewPhi->addIncoming(NewAdd, PN->getIncomingBlock(BackedgeIdx));
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// Update the existing GEP to use the recurrence.
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GEPI->setOperand(0, PN->getIncomingValue(PreheaderIdx));
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// Update the GEP to use the new recurrence we just inserted.
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GEPI->setOperand(1, NewAdd);
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// If the incoming value is a constant expr GEP, try peeling out the array
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// 0 index if possible to make things simpler.
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if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GEPI->getOperand(0)))
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if (CE->getOpcode() == Instruction::GetElementPtr) {
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unsigned NumOps = CE->getNumOperands();
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assert(NumOps > 1 && "CE folding didn't work!");
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if (CE->getOperand(NumOps-1)->isNullValue()) {
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// Check to make sure the last index really is an array index.
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gep_type_iterator GTI = gep_type_begin(GEPI);
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for (unsigned i = 1, e = GEPI->getNumOperands()-1;
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i != e; ++i, ++GTI)
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/*empty*/;
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if (isa<SequentialType>(*GTI)) {
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// Pull the last index out of the constant expr GEP.
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std::vector<Value*> CEIdxs(CE->op_begin()+1, CE->op_end()-1);
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Constant *NCE = ConstantExpr::getGetElementPtr(CE->getOperand(0),
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CEIdxs);
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GetElementPtrInst *NGEPI =
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new GetElementPtrInst(NCE, Constant::getNullValue(Type::IntTy),
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NewAdd, GEPI->getName(), GEPI);
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GEPI->replaceAllUsesWith(NGEPI);
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GEPI->eraseFromParent();
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GEPI = NGEPI;
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}
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}
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}
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// Finally, if there are any other users of the PHI node, we must
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// insert a new GEP instruction that uses the pre-incremented version
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// of the induction amount.
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if (!PN->use_empty()) {
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BasicBlock::iterator InsertPos = PN; ++InsertPos;
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while (isa<PHINode>(InsertPos)) ++InsertPos;
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std::string Name = PN->getName(); PN->setName("");
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Value *PreInc =
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new GetElementPtrInst(PN->getIncomingValue(PreheaderIdx),
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std::vector<Value*>(1, NewPhi), Name,
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InsertPos);
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PN->replaceAllUsesWith(PreInc);
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}
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// Delete the old PHI for sure, and the GEP if its otherwise unused.
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DeadInsts.insert(PN);
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++NumPointer;
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Changed = true;
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}
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}
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/// LinearFunctionTestReplace - This method rewrites the exit condition of the
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/// loop to be a canonical != comparison against the incremented loop induction
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/// variable. This pass is able to rewrite the exit tests of any loop where the
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/// SCEV analysis can determine a loop-invariant trip count of the loop, which
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/// is actually a much broader range than just linear tests.
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void IndVarSimplify::LinearFunctionTestReplace(Loop *L, SCEV *IterationCount,
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SCEVExpander &RW) {
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// Find the exit block for the loop. We can currently only handle loops with
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// a single exit.
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std::vector<BasicBlock*> ExitBlocks;
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L->getExitBlocks(ExitBlocks);
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if (ExitBlocks.size() != 1) return;
|
|
BasicBlock *ExitBlock = ExitBlocks[0];
|
|
|
|
// Make sure there is only one predecessor block in the loop.
|
|
BasicBlock *ExitingBlock = 0;
|
|
for (pred_iterator PI = pred_begin(ExitBlock), PE = pred_end(ExitBlock);
|
|
PI != PE; ++PI)
|
|
if (L->contains(*PI)) {
|
|
if (ExitingBlock == 0)
|
|
ExitingBlock = *PI;
|
|
else
|
|
return; // Multiple exits from loop to this block.
|
|
}
|
|
assert(ExitingBlock && "Loop info is broken");
|
|
|
|
if (!isa<BranchInst>(ExitingBlock->getTerminator()))
|
|
return; // Can't rewrite non-branch yet
|
|
BranchInst *BI = cast<BranchInst>(ExitingBlock->getTerminator());
|
|
assert(BI->isConditional() && "Must be conditional to be part of loop!");
|
|
|
|
std::set<Instruction*> InstructionsToDelete;
|
|
if (Instruction *Cond = dyn_cast<Instruction>(BI->getCondition()))
|
|
InstructionsToDelete.insert(Cond);
|
|
|
|
// If the exiting block is not the same as the backedge block, we must compare
|
|
// against the preincremented value, otherwise we prefer to compare against
|
|
// the post-incremented value.
|
|
BasicBlock *Header = L->getHeader();
|
|
pred_iterator HPI = pred_begin(Header);
|
|
assert(HPI != pred_end(Header) && "Loop with zero preds???");
|
|
if (!L->contains(*HPI)) ++HPI;
|
|
assert(HPI != pred_end(Header) && L->contains(*HPI) &&
|
|
"No backedge in loop?");
|
|
|
|
SCEVHandle TripCount = IterationCount;
|
|
Value *IndVar;
|
|
if (*HPI == ExitingBlock) {
|
|
// The IterationCount expression contains the number of times that the
|
|
// backedge actually branches to the loop header. This is one less than the
|
|
// number of times the loop executes, so add one to it.
|
|
Constant *OneC = ConstantInt::get(IterationCount->getType(), 1);
|
|
TripCount = SCEVAddExpr::get(IterationCount, SCEVUnknown::get(OneC));
|
|
IndVar = L->getCanonicalInductionVariableIncrement();
|
|
} else {
|
|
// We have to use the preincremented value...
|
|
IndVar = L->getCanonicalInductionVariable();
|
|
}
|
|
|
|
// Expand the code for the iteration count into the preheader of the loop.
|
|
BasicBlock *Preheader = L->getLoopPreheader();
|
|
Value *ExitCnt = RW.expandCodeFor(TripCount, Preheader->getTerminator(),
|
|
IndVar->getType());
|
|
|
|
// Insert a new setne or seteq instruction before the branch.
|
|
Instruction::BinaryOps Opcode;
|
|
if (L->contains(BI->getSuccessor(0)))
|
|
Opcode = Instruction::SetNE;
|
|
else
|
|
Opcode = Instruction::SetEQ;
|
|
|
|
Value *Cond = new SetCondInst(Opcode, IndVar, ExitCnt, "exitcond", BI);
|
|
BI->setCondition(Cond);
|
|
++NumLFTR;
|
|
Changed = true;
|
|
|
|
DeleteTriviallyDeadInstructions(InstructionsToDelete);
|
|
}
|
|
|
|
|
|
/// RewriteLoopExitValues - Check to see if this loop has a computable
|
|
/// loop-invariant execution count. If so, this means that we can compute the
|
|
/// final value of any expressions that are recurrent in the loop, and
|
|
/// substitute the exit values from the loop into any instructions outside of
|
|
/// the loop that use the final values of the current expressions.
|
|
void IndVarSimplify::RewriteLoopExitValues(Loop *L) {
|
|
BasicBlock *Preheader = L->getLoopPreheader();
|
|
|
|
// Scan all of the instructions in the loop, looking at those that have
|
|
// extra-loop users and which are recurrences.
|
|
SCEVExpander Rewriter(*SE, *LI);
|
|
|
|
// We insert the code into the preheader of the loop if the loop contains
|
|
// multiple exit blocks, or in the exit block if there is exactly one.
|
|
BasicBlock *BlockToInsertInto;
|
|
std::vector<BasicBlock*> ExitBlocks;
|
|
L->getExitBlocks(ExitBlocks);
|
|
if (ExitBlocks.size() == 1)
|
|
BlockToInsertInto = ExitBlocks[0];
|
|
else
|
|
BlockToInsertInto = Preheader;
|
|
BasicBlock::iterator InsertPt = BlockToInsertInto->begin();
|
|
while (isa<PHINode>(InsertPt)) ++InsertPt;
|
|
|
|
bool HasConstantItCount = isa<SCEVConstant>(SE->getIterationCount(L));
|
|
|
|
std::set<Instruction*> InstructionsToDelete;
|
|
|
|
for (unsigned i = 0, e = L->getBlocks().size(); i != e; ++i)
|
|
if (LI->getLoopFor(L->getBlocks()[i]) == L) { // Not in a subloop...
|
|
BasicBlock *BB = L->getBlocks()[i];
|
|
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
|
|
if (I->getType()->isInteger()) { // Is an integer instruction
|
|
SCEVHandle SH = SE->getSCEV(I);
|
|
if (SH->hasComputableLoopEvolution(L) || // Varies predictably
|
|
HasConstantItCount) {
|
|
// Find out if this predictably varying value is actually used
|
|
// outside of the loop. "extra" as opposed to "intra".
|
|
std::vector<User*> ExtraLoopUsers;
|
|
for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
|
|
UI != E; ++UI)
|
|
if (!L->contains(cast<Instruction>(*UI)->getParent()))
|
|
ExtraLoopUsers.push_back(*UI);
|
|
if (!ExtraLoopUsers.empty()) {
|
|
// Okay, this instruction has a user outside of the current loop
|
|
// and varies predictably in this loop. Evaluate the value it
|
|
// contains when the loop exits, and insert code for it.
|
|
SCEVHandle ExitValue = SE->getSCEVAtScope(I, L->getParentLoop());
|
|
if (!isa<SCEVCouldNotCompute>(ExitValue)) {
|
|
Changed = true;
|
|
++NumReplaced;
|
|
Value *NewVal = Rewriter.expandCodeFor(ExitValue, InsertPt,
|
|
I->getType());
|
|
|
|
// Rewrite any users of the computed value outside of the loop
|
|
// with the newly computed value.
|
|
for (unsigned i = 0, e = ExtraLoopUsers.size(); i != e; ++i)
|
|
ExtraLoopUsers[i]->replaceUsesOfWith(I, NewVal);
|
|
|
|
// If this instruction is dead now, schedule it to be removed.
|
|
if (I->use_empty())
|
|
InstructionsToDelete.insert(I);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
DeleteTriviallyDeadInstructions(InstructionsToDelete);
|
|
}
|
|
|
|
|
|
void IndVarSimplify::runOnLoop(Loop *L) {
|
|
// First step. Check to see if there are any trivial GEP pointer recurrences.
|
|
// If there are, change them into integer recurrences, permitting analysis by
|
|
// the SCEV routines.
|
|
//
|
|
BasicBlock *Header = L->getHeader();
|
|
BasicBlock *Preheader = L->getLoopPreheader();
|
|
|
|
std::set<Instruction*> DeadInsts;
|
|
for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
|
|
PHINode *PN = cast<PHINode>(I);
|
|
if (isa<PointerType>(PN->getType()))
|
|
EliminatePointerRecurrence(PN, Preheader, DeadInsts);
|
|
}
|
|
|
|
if (!DeadInsts.empty())
|
|
DeleteTriviallyDeadInstructions(DeadInsts);
|
|
|
|
|
|
// Next, transform all loops nesting inside of this loop.
|
|
for (LoopInfo::iterator I = L->begin(), E = L->end(); I != E; ++I)
|
|
runOnLoop(*I);
|
|
|
|
// Check to see if this loop has a computable loop-invariant execution count.
|
|
// If so, this means that we can compute the final value of any expressions
|
|
// that are recurrent in the loop, and substitute the exit values from the
|
|
// loop into any instructions outside of the loop that use the final values of
|
|
// the current expressions.
|
|
//
|
|
SCEVHandle IterationCount = SE->getIterationCount(L);
|
|
if (!isa<SCEVCouldNotCompute>(IterationCount))
|
|
RewriteLoopExitValues(L);
|
|
|
|
// Next, analyze all of the induction variables in the loop, canonicalizing
|
|
// auxillary induction variables.
|
|
std::vector<std::pair<PHINode*, SCEVHandle> > IndVars;
|
|
|
|
for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
|
|
PHINode *PN = cast<PHINode>(I);
|
|
if (PN->getType()->isInteger()) { // FIXME: when we have fast-math, enable!
|
|
SCEVHandle SCEV = SE->getSCEV(PN);
|
|
if (SCEV->hasComputableLoopEvolution(L))
|
|
// FIXME: Without a strength reduction pass, it is an extremely bad idea
|
|
// to indvar substitute anything more complex than a linear induction
|
|
// variable. Doing so will put expensive multiply instructions inside
|
|
// of the loop. For now just disable indvar subst on anything more
|
|
// complex than a linear addrec.
|
|
if (SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(SCEV))
|
|
if (AR->getNumOperands() == 2 && isa<SCEVConstant>(AR->getOperand(1)))
|
|
IndVars.push_back(std::make_pair(PN, SCEV));
|
|
}
|
|
}
|
|
|
|
// If there are no induction variables in the loop, there is nothing more to
|
|
// do.
|
|
if (IndVars.empty()) {
|
|
// Actually, if we know how many times the loop iterates, lets insert a
|
|
// canonical induction variable to help subsequent passes.
|
|
if (!isa<SCEVCouldNotCompute>(IterationCount)) {
|
|
SCEVExpander Rewriter(*SE, *LI);
|
|
Rewriter.getOrInsertCanonicalInductionVariable(L,
|
|
IterationCount->getType());
|
|
LinearFunctionTestReplace(L, IterationCount, Rewriter);
|
|
}
|
|
return;
|
|
}
|
|
|
|
// Compute the type of the largest recurrence expression.
|
|
//
|
|
const Type *LargestType = IndVars[0].first->getType();
|
|
bool DifferingSizes = false;
|
|
for (unsigned i = 1, e = IndVars.size(); i != e; ++i) {
|
|
const Type *Ty = IndVars[i].first->getType();
|
|
DifferingSizes |= Ty->getPrimitiveSize() != LargestType->getPrimitiveSize();
|
|
if (Ty->getPrimitiveSize() > LargestType->getPrimitiveSize())
|
|
LargestType = Ty;
|
|
}
|
|
|
|
// Create a rewriter object which we'll use to transform the code with.
|
|
SCEVExpander Rewriter(*SE, *LI);
|
|
|
|
// Now that we know the largest of of the induction variables in this loop,
|
|
// insert a canonical induction variable of the largest size.
|
|
LargestType = LargestType->getUnsignedVersion();
|
|
Value *IndVar = Rewriter.getOrInsertCanonicalInductionVariable(L,LargestType);
|
|
++NumInserted;
|
|
Changed = true;
|
|
|
|
if (!isa<SCEVCouldNotCompute>(IterationCount))
|
|
LinearFunctionTestReplace(L, IterationCount, Rewriter);
|
|
|
|
// Now that we have a canonical induction variable, we can rewrite any
|
|
// recurrences in terms of the induction variable. Start with the auxillary
|
|
// induction variables, and recursively rewrite any of their uses.
|
|
BasicBlock::iterator InsertPt = Header->begin();
|
|
while (isa<PHINode>(InsertPt)) ++InsertPt;
|
|
|
|
// If there were induction variables of other sizes, cast the primary
|
|
// induction variable to the right size for them, avoiding the need for the
|
|
// code evaluation methods to insert induction variables of different sizes.
|
|
if (DifferingSizes) {
|
|
bool InsertedSizes[17] = { false };
|
|
InsertedSizes[LargestType->getPrimitiveSize()] = true;
|
|
for (unsigned i = 0, e = IndVars.size(); i != e; ++i)
|
|
if (!InsertedSizes[IndVars[i].first->getType()->getPrimitiveSize()]) {
|
|
PHINode *PN = IndVars[i].first;
|
|
InsertedSizes[PN->getType()->getPrimitiveSize()] = true;
|
|
Instruction *New = new CastInst(IndVar,
|
|
PN->getType()->getUnsignedVersion(),
|
|
"indvar", InsertPt);
|
|
Rewriter.addInsertedValue(New, SE->getSCEV(New));
|
|
}
|
|
}
|
|
|
|
// If there were induction variables of other sizes, cast the primary
|
|
// induction variable to the right size for them, avoiding the need for the
|
|
// code evaluation methods to insert induction variables of different sizes.
|
|
std::map<unsigned, Value*> InsertedSizes;
|
|
while (!IndVars.empty()) {
|
|
PHINode *PN = IndVars.back().first;
|
|
Value *NewVal = Rewriter.expandCodeFor(IndVars.back().second, InsertPt,
|
|
PN->getType());
|
|
std::string Name = PN->getName();
|
|
PN->setName("");
|
|
NewVal->setName(Name);
|
|
|
|
// Replace the old PHI Node with the inserted computation.
|
|
PN->replaceAllUsesWith(NewVal);
|
|
DeadInsts.insert(PN);
|
|
IndVars.pop_back();
|
|
++NumRemoved;
|
|
Changed = true;
|
|
}
|
|
|
|
#if 0
|
|
// Now replace all derived expressions in the loop body with simpler
|
|
// expressions.
|
|
for (unsigned i = 0, e = L->getBlocks().size(); i != e; ++i)
|
|
if (LI->getLoopFor(L->getBlocks()[i]) == L) { // Not in a subloop...
|
|
BasicBlock *BB = L->getBlocks()[i];
|
|
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
|
|
if (I->getType()->isInteger() && // Is an integer instruction
|
|
!I->use_empty() &&
|
|
!Rewriter.isInsertedInstruction(I)) {
|
|
SCEVHandle SH = SE->getSCEV(I);
|
|
Value *V = Rewriter.expandCodeFor(SH, I, I->getType());
|
|
if (V != I) {
|
|
if (isa<Instruction>(V)) {
|
|
std::string Name = I->getName();
|
|
I->setName("");
|
|
V->setName(Name);
|
|
}
|
|
I->replaceAllUsesWith(V);
|
|
DeadInsts.insert(I);
|
|
++NumRemoved;
|
|
Changed = true;
|
|
}
|
|
}
|
|
}
|
|
#endif
|
|
|
|
DeleteTriviallyDeadInstructions(DeadInsts);
|
|
}
|