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to more accurately describe what it does. Expand its doxygen comment to describe what the backedge-taken count is and how it differs from the actual iteration count of the loop. Adjust names and comments in associated code accordingly. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@65382 91177308-0d34-0410-b5e6-96231b3b80d8
947 lines
37 KiB
C++
947 lines
37 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 is distributed under the University of Illinois Open Source
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// 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 makes 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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#define DEBUG_TYPE "indvars"
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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/ScalarEvolutionExpander.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/Analysis/LoopPass.h"
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#include "llvm/Support/CFG.h"
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#include "llvm/Support/Compiler.h"
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#include "llvm/Support/Debug.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/SmallVector.h"
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#include "llvm/ADT/SetVector.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/Statistic.h"
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using namespace llvm;
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STATISTIC(NumRemoved , "Number of aux indvars removed");
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STATISTIC(NumPointer , "Number of pointer indvars promoted");
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STATISTIC(NumInserted, "Number of canonical indvars added");
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STATISTIC(NumReplaced, "Number of exit values replaced");
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STATISTIC(NumLFTR , "Number of loop exit tests replaced");
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namespace {
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class VISIBILITY_HIDDEN IndVarSimplify : public LoopPass {
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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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static char ID; // Pass identification, replacement for typeid
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IndVarSimplify() : LoopPass(&ID) {}
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virtual bool runOnLoop(Loop *L, LPPassManager &LPM);
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequired<ScalarEvolution>();
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AU.addRequiredID(LCSSAID);
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AU.addRequiredID(LoopSimplifyID);
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AU.addRequired<LoopInfo>();
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AU.addPreserved<ScalarEvolution>();
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AU.addPreservedID(LoopSimplifyID);
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AU.addPreservedID(LCSSAID);
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AU.setPreservesCFG();
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}
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private:
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void RewriteNonIntegerIVs(Loop *L);
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void EliminatePointerRecurrence(PHINode *PN, BasicBlock *Preheader,
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SmallPtrSet<Instruction*, 16> &DeadInsts);
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void LinearFunctionTestReplace(Loop *L, SCEVHandle BackedgeTakenCount,
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Value *IndVar,
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BasicBlock *ExitingBlock,
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BranchInst *BI,
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SCEVExpander &Rewriter);
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void RewriteLoopExitValues(Loop *L, SCEV *BackedgeTakenCount);
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void DeleteTriviallyDeadInstructions(SmallPtrSet<Instruction*, 16> &Insts);
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void HandleFloatingPointIV(Loop *L, PHINode *PH,
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SmallPtrSet<Instruction*, 16> &DeadInsts);
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};
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}
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char IndVarSimplify::ID = 0;
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static RegisterPass<IndVarSimplify>
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X("indvars", "Canonicalize Induction Variables");
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Pass *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(SmallPtrSet<Instruction*, 16> &Insts) {
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while (!Insts.empty()) {
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Instruction *I = *Insts.begin();
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Insts.erase(I);
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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->deleteValueFromRecords(I);
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DOUT << "INDVARS: Deleting: " << *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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SmallPtrSet<Instruction*, 16> &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 match!");
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DOUT << "INDVARS: Eliminating pointer recurrence: " << *GEPI;
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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 = PHINode::Create(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(CE);
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for (unsigned i = 1, e = CE->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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SmallVector<Value*, 8> 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[0],
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CEIdxs.size());
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Value *Idx[2];
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Idx[0] = Constant::getNullValue(Type::Int32Ty);
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Idx[1] = NewAdd;
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GetElementPtrInst *NGEPI = GetElementPtrInst::Create(
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NCE, Idx, Idx + 2,
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GEPI->getName(), GEPI);
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SE->deleteValueFromRecords(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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Value *PreInc =
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GetElementPtrInst::Create(PN->getIncomingValue(PreheaderIdx),
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NewPhi, "", InsertPos);
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PreInc->takeName(PN);
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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,
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SCEVHandle BackedgeTakenCount,
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Value *IndVar,
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BasicBlock *ExitingBlock,
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BranchInst *BI,
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SCEVExpander &Rewriter) {
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// If the exiting block is not the same as the backedge block, we must compare
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// against the preincremented value, otherwise we prefer to compare against
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// the post-incremented value.
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Value *CmpIndVar;
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SCEVHandle RHS = BackedgeTakenCount;
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if (ExitingBlock == L->getLoopLatch()) {
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// Add one to the "backedge-taken" count to get the trip count.
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// If this addition may overflow, we have to be more pessimistic and
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// cast the induction variable before doing the add.
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SCEVHandle Zero = SE->getIntegerSCEV(0, BackedgeTakenCount->getType());
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SCEVHandle N =
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SE->getAddExpr(BackedgeTakenCount,
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SE->getIntegerSCEV(1, BackedgeTakenCount->getType()));
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if ((isa<SCEVConstant>(N) && !N->isZero()) ||
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SE->isLoopGuardedByCond(L, ICmpInst::ICMP_NE, N, Zero)) {
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// No overflow. Cast the sum.
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RHS = SE->getTruncateOrZeroExtend(N, IndVar->getType());
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} else {
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// Potential overflow. Cast before doing the add.
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RHS = SE->getTruncateOrZeroExtend(BackedgeTakenCount,
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IndVar->getType());
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RHS = SE->getAddExpr(RHS,
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SE->getIntegerSCEV(1, IndVar->getType()));
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}
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// The BackedgeTaken expression contains the number of times that the
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// backedge branches to the loop header. This is one less than the
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// number of times the loop executes, so use the incremented indvar.
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CmpIndVar = L->getCanonicalInductionVariableIncrement();
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} else {
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// We have to use the preincremented value...
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RHS = SE->getTruncateOrZeroExtend(BackedgeTakenCount,
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IndVar->getType());
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CmpIndVar = IndVar;
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}
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// Expand the code for the iteration count into the preheader of the loop.
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BasicBlock *Preheader = L->getLoopPreheader();
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Value *ExitCnt = Rewriter.expandCodeFor(RHS,
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Preheader->getTerminator());
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// Insert a new icmp_ne or icmp_eq instruction before the branch.
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ICmpInst::Predicate Opcode;
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if (L->contains(BI->getSuccessor(0)))
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Opcode = ICmpInst::ICMP_NE;
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else
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Opcode = ICmpInst::ICMP_EQ;
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DOUT << "INDVARS: Rewriting loop exit condition to:\n"
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<< " LHS:" << *CmpIndVar // includes a newline
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<< " op:\t"
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<< (Opcode == ICmpInst::ICMP_NE ? "!=" : "==") << "\n"
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<< " RHS:\t" << *RHS << "\n";
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Value *Cond = new ICmpInst(Opcode, CmpIndVar, ExitCnt, "exitcond", BI);
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BI->setCondition(Cond);
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++NumLFTR;
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Changed = true;
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}
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/// RewriteLoopExitValues - Check to see if this loop has a computable
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/// loop-invariant execution count. If so, this means that we can compute the
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/// final value of any expressions that are recurrent in the loop, and
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/// substitute the exit values from the loop into any instructions outside of
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/// the loop that use the final values of the current expressions.
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void IndVarSimplify::RewriteLoopExitValues(Loop *L, SCEV *BackedgeTakenCount) {
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BasicBlock *Preheader = L->getLoopPreheader();
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// Scan all of the instructions in the loop, looking at those that have
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// extra-loop users and which are recurrences.
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SCEVExpander Rewriter(*SE, *LI);
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// We insert the code into the preheader of the loop if the loop contains
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// multiple exit blocks, or in the exit block if there is exactly one.
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BasicBlock *BlockToInsertInto;
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SmallVector<BasicBlock*, 8> ExitBlocks;
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L->getUniqueExitBlocks(ExitBlocks);
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if (ExitBlocks.size() == 1)
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BlockToInsertInto = ExitBlocks[0];
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else
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BlockToInsertInto = Preheader;
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BasicBlock::iterator InsertPt = BlockToInsertInto->getFirstNonPHI();
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bool HasConstantItCount = isa<SCEVConstant>(BackedgeTakenCount);
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SmallPtrSet<Instruction*, 16> InstructionsToDelete;
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std::map<Instruction*, Value*> ExitValues;
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// Find all values that are computed inside the loop, but used outside of it.
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// Because of LCSSA, these values will only occur in LCSSA PHI Nodes. Scan
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// the exit blocks of the loop to find them.
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for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
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BasicBlock *ExitBB = ExitBlocks[i];
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// If there are no PHI nodes in this exit block, then no values defined
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// inside the loop are used on this path, skip it.
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PHINode *PN = dyn_cast<PHINode>(ExitBB->begin());
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if (!PN) continue;
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unsigned NumPreds = PN->getNumIncomingValues();
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// Iterate over all of the PHI nodes.
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BasicBlock::iterator BBI = ExitBB->begin();
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while ((PN = dyn_cast<PHINode>(BBI++))) {
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// Iterate over all of the values in all the PHI nodes.
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for (unsigned i = 0; i != NumPreds; ++i) {
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// If the value being merged in is not integer or is not defined
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// in the loop, skip it.
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Value *InVal = PN->getIncomingValue(i);
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if (!isa<Instruction>(InVal) ||
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// SCEV only supports integer expressions for now.
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!isa<IntegerType>(InVal->getType()))
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continue;
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// If this pred is for a subloop, not L itself, skip it.
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if (LI->getLoopFor(PN->getIncomingBlock(i)) != L)
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continue; // The Block is in a subloop, skip it.
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// Check that InVal is defined in the loop.
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Instruction *Inst = cast<Instruction>(InVal);
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if (!L->contains(Inst->getParent()))
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continue;
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// We require that this value either have a computable evolution or that
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// the loop have a constant iteration count. In the case where the loop
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// has a constant iteration count, we can sometimes force evaluation of
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// the exit value through brute force.
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SCEVHandle SH = SE->getSCEV(Inst);
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if (!SH->hasComputableLoopEvolution(L) && !HasConstantItCount)
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continue; // Cannot get exit evolution for the loop value.
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// Okay, this instruction has a user outside of the current loop
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// and varies predictably *inside* the loop. Evaluate the value it
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// contains when the loop exits, if possible.
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SCEVHandle ExitValue = SE->getSCEVAtScope(Inst, L->getParentLoop());
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if (isa<SCEVCouldNotCompute>(ExitValue) ||
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!ExitValue->isLoopInvariant(L))
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continue;
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Changed = true;
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++NumReplaced;
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// See if we already computed the exit value for the instruction, if so,
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// just reuse it.
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Value *&ExitVal = ExitValues[Inst];
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if (!ExitVal)
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ExitVal = Rewriter.expandCodeFor(ExitValue, InsertPt);
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DOUT << "INDVARS: RLEV: AfterLoopVal = " << *ExitVal
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<< " LoopVal = " << *Inst << "\n";
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PN->setIncomingValue(i, ExitVal);
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// If this instruction is dead now, schedule it to be removed.
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if (Inst->use_empty())
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InstructionsToDelete.insert(Inst);
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// See if this is a single-entry LCSSA PHI node. If so, we can (and
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// have to) remove
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// the PHI entirely. This is safe, because the NewVal won't be variant
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// in the loop, so we don't need an LCSSA phi node anymore.
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if (NumPreds == 1) {
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SE->deleteValueFromRecords(PN);
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PN->replaceAllUsesWith(ExitVal);
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PN->eraseFromParent();
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break;
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}
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}
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}
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}
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DeleteTriviallyDeadInstructions(InstructionsToDelete);
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}
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void IndVarSimplify::RewriteNonIntegerIVs(Loop *L) {
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// First step. Check to see if there are any trivial GEP pointer recurrences.
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// If there are, change them into integer recurrences, permitting analysis by
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// the SCEV routines.
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//
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BasicBlock *Header = L->getHeader();
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BasicBlock *Preheader = L->getLoopPreheader();
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SmallPtrSet<Instruction*, 16> DeadInsts;
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for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
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PHINode *PN = cast<PHINode>(I);
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if (isa<PointerType>(PN->getType()))
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EliminatePointerRecurrence(PN, Preheader, DeadInsts);
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else
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HandleFloatingPointIV(L, PN, DeadInsts);
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}
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// If the loop previously had a pointer or floating-point IV, ScalarEvolution
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// may not have been able to compute a trip count. Now that we've done some
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// re-writing, the trip count may be computable.
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if (Changed)
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SE->forgetLoopBackedgeTakenCount(L);
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if (!DeadInsts.empty())
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DeleteTriviallyDeadInstructions(DeadInsts);
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}
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/// getEffectiveIndvarType - Determine the widest type that the
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/// induction-variable PHINode Phi is cast to.
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///
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static const Type *getEffectiveIndvarType(const PHINode *Phi) {
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const Type *Ty = Phi->getType();
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for (Value::use_const_iterator UI = Phi->use_begin(), UE = Phi->use_end();
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UI != UE; ++UI) {
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const Type *CandidateType = NULL;
|
|
if (const ZExtInst *ZI = dyn_cast<ZExtInst>(UI))
|
|
CandidateType = ZI->getDestTy();
|
|
else if (const SExtInst *SI = dyn_cast<SExtInst>(UI))
|
|
CandidateType = SI->getDestTy();
|
|
if (CandidateType &&
|
|
CandidateType->getPrimitiveSizeInBits() >
|
|
Ty->getPrimitiveSizeInBits())
|
|
Ty = CandidateType;
|
|
}
|
|
|
|
return Ty;
|
|
}
|
|
|
|
/// TestOrigIVForWrap - Analyze the original induction variable
|
|
/// that controls the loop's iteration to determine whether it
|
|
/// would ever undergo signed or unsigned overflow. Also, check
|
|
/// whether an induction variable in the same type that starts
|
|
/// at 0 would undergo signed overflow.
|
|
///
|
|
/// In addition to setting the NoSignedWrap, and NoUnsignedWrap,
|
|
/// variables, return the PHI for this induction variable.
|
|
///
|
|
/// TODO: This duplicates a fair amount of ScalarEvolution logic.
|
|
/// Perhaps this can be merged with
|
|
/// ScalarEvolution::getBackedgeTakenCount
|
|
/// and/or ScalarEvolution::get{Sign,Zero}ExtendExpr.
|
|
///
|
|
static const PHINode *TestOrigIVForWrap(const Loop *L,
|
|
const BranchInst *BI,
|
|
const Instruction *OrigCond,
|
|
bool &NoSignedWrap,
|
|
bool &NoUnsignedWrap) {
|
|
// Verify that the loop is sane and find the exit condition.
|
|
const ICmpInst *Cmp = dyn_cast<ICmpInst>(OrigCond);
|
|
if (!Cmp) return 0;
|
|
|
|
const Value *CmpLHS = Cmp->getOperand(0);
|
|
const Value *CmpRHS = Cmp->getOperand(1);
|
|
const BasicBlock *TrueBB = BI->getSuccessor(0);
|
|
const BasicBlock *FalseBB = BI->getSuccessor(1);
|
|
ICmpInst::Predicate Pred = Cmp->getPredicate();
|
|
|
|
// Canonicalize a constant to the RHS.
|
|
if (isa<ConstantInt>(CmpLHS)) {
|
|
Pred = ICmpInst::getSwappedPredicate(Pred);
|
|
std::swap(CmpLHS, CmpRHS);
|
|
}
|
|
// Canonicalize SLE to SLT.
|
|
if (Pred == ICmpInst::ICMP_SLE)
|
|
if (const ConstantInt *CI = dyn_cast<ConstantInt>(CmpRHS))
|
|
if (!CI->getValue().isMaxSignedValue()) {
|
|
CmpRHS = ConstantInt::get(CI->getValue() + 1);
|
|
Pred = ICmpInst::ICMP_SLT;
|
|
}
|
|
// Canonicalize SGT to SGE.
|
|
if (Pred == ICmpInst::ICMP_SGT)
|
|
if (const ConstantInt *CI = dyn_cast<ConstantInt>(CmpRHS))
|
|
if (!CI->getValue().isMaxSignedValue()) {
|
|
CmpRHS = ConstantInt::get(CI->getValue() + 1);
|
|
Pred = ICmpInst::ICMP_SGE;
|
|
}
|
|
// Canonicalize SGE to SLT.
|
|
if (Pred == ICmpInst::ICMP_SGE) {
|
|
std::swap(TrueBB, FalseBB);
|
|
Pred = ICmpInst::ICMP_SLT;
|
|
}
|
|
// Canonicalize ULE to ULT.
|
|
if (Pred == ICmpInst::ICMP_ULE)
|
|
if (const ConstantInt *CI = dyn_cast<ConstantInt>(CmpRHS))
|
|
if (!CI->getValue().isMaxValue()) {
|
|
CmpRHS = ConstantInt::get(CI->getValue() + 1);
|
|
Pred = ICmpInst::ICMP_ULT;
|
|
}
|
|
// Canonicalize UGT to UGE.
|
|
if (Pred == ICmpInst::ICMP_UGT)
|
|
if (const ConstantInt *CI = dyn_cast<ConstantInt>(CmpRHS))
|
|
if (!CI->getValue().isMaxValue()) {
|
|
CmpRHS = ConstantInt::get(CI->getValue() + 1);
|
|
Pred = ICmpInst::ICMP_UGE;
|
|
}
|
|
// Canonicalize UGE to ULT.
|
|
if (Pred == ICmpInst::ICMP_UGE) {
|
|
std::swap(TrueBB, FalseBB);
|
|
Pred = ICmpInst::ICMP_ULT;
|
|
}
|
|
// For now, analyze only LT loops for signed overflow.
|
|
if (Pred != ICmpInst::ICMP_SLT && Pred != ICmpInst::ICMP_ULT)
|
|
return 0;
|
|
|
|
bool isSigned = Pred == ICmpInst::ICMP_SLT;
|
|
|
|
// Get the increment instruction. Look past casts if we will
|
|
// be able to prove that the original induction variable doesn't
|
|
// undergo signed or unsigned overflow, respectively.
|
|
const Value *IncrVal = CmpLHS;
|
|
if (isSigned) {
|
|
if (const SExtInst *SI = dyn_cast<SExtInst>(CmpLHS)) {
|
|
if (!isa<ConstantInt>(CmpRHS) ||
|
|
!cast<ConstantInt>(CmpRHS)->getValue()
|
|
.isSignedIntN(IncrVal->getType()->getPrimitiveSizeInBits()))
|
|
return 0;
|
|
IncrVal = SI->getOperand(0);
|
|
}
|
|
} else {
|
|
if (const ZExtInst *ZI = dyn_cast<ZExtInst>(CmpLHS)) {
|
|
if (!isa<ConstantInt>(CmpRHS) ||
|
|
!cast<ConstantInt>(CmpRHS)->getValue()
|
|
.isIntN(IncrVal->getType()->getPrimitiveSizeInBits()))
|
|
return 0;
|
|
IncrVal = ZI->getOperand(0);
|
|
}
|
|
}
|
|
|
|
// For now, only analyze induction variables that have simple increments.
|
|
const BinaryOperator *IncrOp = dyn_cast<BinaryOperator>(IncrVal);
|
|
if (!IncrOp ||
|
|
IncrOp->getOpcode() != Instruction::Add ||
|
|
!isa<ConstantInt>(IncrOp->getOperand(1)) ||
|
|
!cast<ConstantInt>(IncrOp->getOperand(1))->equalsInt(1))
|
|
return 0;
|
|
|
|
// Make sure the PHI looks like a normal IV.
|
|
const PHINode *PN = dyn_cast<PHINode>(IncrOp->getOperand(0));
|
|
if (!PN || PN->getNumIncomingValues() != 2)
|
|
return 0;
|
|
unsigned IncomingEdge = L->contains(PN->getIncomingBlock(0));
|
|
unsigned BackEdge = !IncomingEdge;
|
|
if (!L->contains(PN->getIncomingBlock(BackEdge)) ||
|
|
PN->getIncomingValue(BackEdge) != IncrOp)
|
|
return 0;
|
|
if (!L->contains(TrueBB))
|
|
return 0;
|
|
|
|
// For now, only analyze loops with a constant start value, so that
|
|
// we can easily determine if the start value is not a maximum value
|
|
// which would wrap on the first iteration.
|
|
const ConstantInt *InitialVal =
|
|
dyn_cast<ConstantInt>(PN->getIncomingValue(IncomingEdge));
|
|
if (!InitialVal)
|
|
return 0;
|
|
|
|
// The original induction variable will start at some non-max value,
|
|
// it counts up by one, and the loop iterates only while it remans
|
|
// less than some value in the same type. As such, it will never wrap.
|
|
if (isSigned && !InitialVal->getValue().isMaxSignedValue()) {
|
|
NoSignedWrap = true;
|
|
} else if (!isSigned && !InitialVal->getValue().isMaxValue())
|
|
NoUnsignedWrap = true;
|
|
return PN;
|
|
}
|
|
|
|
bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
|
|
LI = &getAnalysis<LoopInfo>();
|
|
SE = &getAnalysis<ScalarEvolution>();
|
|
Changed = false;
|
|
|
|
// If there are any floating-point or pointer recurrences, attempt to
|
|
// transform them to use integer recurrences.
|
|
RewriteNonIntegerIVs(L);
|
|
|
|
BasicBlock *Header = L->getHeader();
|
|
BasicBlock *ExitingBlock = L->getExitingBlock();
|
|
SmallPtrSet<Instruction*, 16> DeadInsts;
|
|
|
|
// Verify the input to the pass in already in LCSSA form.
|
|
assert(L->isLCSSAForm());
|
|
|
|
// 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 BackedgeTakenCount = SE->getBackedgeTakenCount(L);
|
|
if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount))
|
|
RewriteLoopExitValues(L, BackedgeTakenCount);
|
|
|
|
// 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);
|
|
// FIXME: It is an extremely bad idea to indvar substitute anything more
|
|
// complex than affine induction variables. Doing so will put expensive
|
|
// polynomial evaluations inside of the loop, and the str reduction pass
|
|
// currently can only reduce affine polynomials. For now just disable
|
|
// indvar subst on anything more complex than an affine addrec.
|
|
if (SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(SCEV))
|
|
if (AR->getLoop() == L && AR->isAffine())
|
|
IndVars.push_back(std::make_pair(PN, SCEV));
|
|
}
|
|
}
|
|
|
|
// Compute the type of the largest recurrence expression, and collect
|
|
// the set of the types of the other recurrence expressions.
|
|
const Type *LargestType = 0;
|
|
SmallSetVector<const Type *, 4> SizesToInsert;
|
|
if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount)) {
|
|
LargestType = BackedgeTakenCount->getType();
|
|
SizesToInsert.insert(BackedgeTakenCount->getType());
|
|
}
|
|
for (unsigned i = 0, e = IndVars.size(); i != e; ++i) {
|
|
const PHINode *PN = IndVars[i].first;
|
|
SizesToInsert.insert(PN->getType());
|
|
const Type *EffTy = getEffectiveIndvarType(PN);
|
|
SizesToInsert.insert(EffTy);
|
|
if (!LargestType ||
|
|
EffTy->getPrimitiveSizeInBits() >
|
|
LargestType->getPrimitiveSizeInBits())
|
|
LargestType = EffTy;
|
|
}
|
|
|
|
// 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.
|
|
Value *IndVar = 0;
|
|
if (!SizesToInsert.empty()) {
|
|
IndVar = Rewriter.getOrInsertCanonicalInductionVariable(L,LargestType);
|
|
++NumInserted;
|
|
Changed = true;
|
|
DOUT << "INDVARS: New CanIV: " << *IndVar;
|
|
}
|
|
|
|
// If we have a trip count expression, rewrite the loop's exit condition
|
|
// using it. We can currently only handle loops with a single exit.
|
|
bool NoSignedWrap = false;
|
|
bool NoUnsignedWrap = false;
|
|
const PHINode *OrigControllingPHI = 0;
|
|
if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount) && ExitingBlock)
|
|
// Can't rewrite non-branch yet.
|
|
if (BranchInst *BI = dyn_cast<BranchInst>(ExitingBlock->getTerminator())) {
|
|
if (Instruction *OrigCond = dyn_cast<Instruction>(BI->getCondition())) {
|
|
// Determine if the OrigIV will ever undergo overflow.
|
|
OrigControllingPHI =
|
|
TestOrigIVForWrap(L, BI, OrigCond,
|
|
NoSignedWrap, NoUnsignedWrap);
|
|
|
|
// We'll be replacing the original condition, so it'll be dead.
|
|
DeadInsts.insert(OrigCond);
|
|
}
|
|
|
|
LinearFunctionTestReplace(L, BackedgeTakenCount, IndVar,
|
|
ExitingBlock, BI, 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->getFirstNonPHI();
|
|
|
|
// 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.
|
|
for (unsigned i = 0, e = SizesToInsert.size(); i != e; ++i) {
|
|
const Type *Ty = SizesToInsert[i];
|
|
if (Ty != LargestType) {
|
|
Instruction *New = new TruncInst(IndVar, Ty, "indvar", InsertPt);
|
|
Rewriter.addInsertedValue(New, SE->getSCEV(New));
|
|
DOUT << "INDVARS: Made trunc IV for type " << *Ty << ": "
|
|
<< *New << "\n";
|
|
}
|
|
}
|
|
|
|
// Rewrite all induction variables in terms of the canonical induction
|
|
// variable.
|
|
while (!IndVars.empty()) {
|
|
PHINode *PN = IndVars.back().first;
|
|
SCEVAddRecExpr *AR = cast<SCEVAddRecExpr>(IndVars.back().second);
|
|
Value *NewVal = Rewriter.expandCodeFor(AR, InsertPt);
|
|
DOUT << "INDVARS: Rewrote IV '" << *AR << "' " << *PN
|
|
<< " into = " << *NewVal << "\n";
|
|
NewVal->takeName(PN);
|
|
|
|
/// If the new canonical induction variable is wider than the original,
|
|
/// and the original has uses that are casts to wider types, see if the
|
|
/// truncate and extend can be omitted.
|
|
if (PN == OrigControllingPHI && PN->getType() != LargestType)
|
|
for (Value::use_iterator UI = PN->use_begin(), UE = PN->use_end();
|
|
UI != UE; ++UI) {
|
|
if (isa<SExtInst>(UI) && NoSignedWrap) {
|
|
SCEVHandle ExtendedStart =
|
|
SE->getSignExtendExpr(AR->getStart(), LargestType);
|
|
SCEVHandle ExtendedStep =
|
|
SE->getSignExtendExpr(AR->getStepRecurrence(*SE), LargestType);
|
|
SCEVHandle ExtendedAddRec =
|
|
SE->getAddRecExpr(ExtendedStart, ExtendedStep, L);
|
|
if (LargestType != UI->getType())
|
|
ExtendedAddRec = SE->getTruncateExpr(ExtendedAddRec, UI->getType());
|
|
Value *TruncIndVar = Rewriter.expandCodeFor(ExtendedAddRec, InsertPt);
|
|
UI->replaceAllUsesWith(TruncIndVar);
|
|
if (Instruction *DeadUse = dyn_cast<Instruction>(*UI))
|
|
DeadInsts.insert(DeadUse);
|
|
}
|
|
if (isa<ZExtInst>(UI) && NoUnsignedWrap) {
|
|
SCEVHandle ExtendedStart =
|
|
SE->getZeroExtendExpr(AR->getStart(), LargestType);
|
|
SCEVHandle ExtendedStep =
|
|
SE->getZeroExtendExpr(AR->getStepRecurrence(*SE), LargestType);
|
|
SCEVHandle ExtendedAddRec =
|
|
SE->getAddRecExpr(ExtendedStart, ExtendedStep, L);
|
|
if (LargestType != UI->getType())
|
|
ExtendedAddRec = SE->getTruncateExpr(ExtendedAddRec, UI->getType());
|
|
Value *TruncIndVar = Rewriter.expandCodeFor(ExtendedAddRec, InsertPt);
|
|
UI->replaceAllUsesWith(TruncIndVar);
|
|
if (Instruction *DeadUse = dyn_cast<Instruction>(*UI))
|
|
DeadInsts.insert(DeadUse);
|
|
}
|
|
}
|
|
|
|
// Replace the old PHI Node with the inserted computation.
|
|
PN->replaceAllUsesWith(NewVal);
|
|
DeadInsts.insert(PN);
|
|
IndVars.pop_back();
|
|
++NumRemoved;
|
|
Changed = true;
|
|
}
|
|
|
|
DeleteTriviallyDeadInstructions(DeadInsts);
|
|
assert(L->isLCSSAForm());
|
|
return Changed;
|
|
}
|
|
|
|
/// Return true if it is OK to use SIToFPInst for an inducation variable
|
|
/// with given inital and exit values.
|
|
static bool useSIToFPInst(ConstantFP &InitV, ConstantFP &ExitV,
|
|
uint64_t intIV, uint64_t intEV) {
|
|
|
|
if (InitV.getValueAPF().isNegative() || ExitV.getValueAPF().isNegative())
|
|
return true;
|
|
|
|
// If the iteration range can be handled by SIToFPInst then use it.
|
|
APInt Max = APInt::getSignedMaxValue(32);
|
|
if (Max.getZExtValue() > static_cast<uint64_t>(abs(intEV - intIV)))
|
|
return true;
|
|
|
|
return false;
|
|
}
|
|
|
|
/// convertToInt - Convert APF to an integer, if possible.
|
|
static bool convertToInt(const APFloat &APF, uint64_t *intVal) {
|
|
|
|
bool isExact = false;
|
|
if (&APF.getSemantics() == &APFloat::PPCDoubleDouble)
|
|
return false;
|
|
if (APF.convertToInteger(intVal, 32, APF.isNegative(),
|
|
APFloat::rmTowardZero, &isExact)
|
|
!= APFloat::opOK)
|
|
return false;
|
|
if (!isExact)
|
|
return false;
|
|
return true;
|
|
|
|
}
|
|
|
|
/// HandleFloatingPointIV - If the loop has floating induction variable
|
|
/// then insert corresponding integer induction variable if possible.
|
|
/// For example,
|
|
/// for(double i = 0; i < 10000; ++i)
|
|
/// bar(i)
|
|
/// is converted into
|
|
/// for(int i = 0; i < 10000; ++i)
|
|
/// bar((double)i);
|
|
///
|
|
void IndVarSimplify::HandleFloatingPointIV(Loop *L, PHINode *PH,
|
|
SmallPtrSet<Instruction*, 16> &DeadInsts) {
|
|
|
|
unsigned IncomingEdge = L->contains(PH->getIncomingBlock(0));
|
|
unsigned BackEdge = IncomingEdge^1;
|
|
|
|
// Check incoming value.
|
|
ConstantFP *InitValue = dyn_cast<ConstantFP>(PH->getIncomingValue(IncomingEdge));
|
|
if (!InitValue) return;
|
|
uint64_t newInitValue = Type::Int32Ty->getPrimitiveSizeInBits();
|
|
if (!convertToInt(InitValue->getValueAPF(), &newInitValue))
|
|
return;
|
|
|
|
// Check IV increment. Reject this PH if increement operation is not
|
|
// an add or increment value can not be represented by an integer.
|
|
BinaryOperator *Incr =
|
|
dyn_cast<BinaryOperator>(PH->getIncomingValue(BackEdge));
|
|
if (!Incr) return;
|
|
if (Incr->getOpcode() != Instruction::Add) return;
|
|
ConstantFP *IncrValue = NULL;
|
|
unsigned IncrVIndex = 1;
|
|
if (Incr->getOperand(1) == PH)
|
|
IncrVIndex = 0;
|
|
IncrValue = dyn_cast<ConstantFP>(Incr->getOperand(IncrVIndex));
|
|
if (!IncrValue) return;
|
|
uint64_t newIncrValue = Type::Int32Ty->getPrimitiveSizeInBits();
|
|
if (!convertToInt(IncrValue->getValueAPF(), &newIncrValue))
|
|
return;
|
|
|
|
// Check Incr uses. One user is PH and the other users is exit condition used
|
|
// by the conditional terminator.
|
|
Value::use_iterator IncrUse = Incr->use_begin();
|
|
Instruction *U1 = cast<Instruction>(IncrUse++);
|
|
if (IncrUse == Incr->use_end()) return;
|
|
Instruction *U2 = cast<Instruction>(IncrUse++);
|
|
if (IncrUse != Incr->use_end()) return;
|
|
|
|
// Find exit condition.
|
|
FCmpInst *EC = dyn_cast<FCmpInst>(U1);
|
|
if (!EC)
|
|
EC = dyn_cast<FCmpInst>(U2);
|
|
if (!EC) return;
|
|
|
|
if (BranchInst *BI = dyn_cast<BranchInst>(EC->getParent()->getTerminator())) {
|
|
if (!BI->isConditional()) return;
|
|
if (BI->getCondition() != EC) return;
|
|
}
|
|
|
|
// Find exit value. If exit value can not be represented as an interger then
|
|
// do not handle this floating point PH.
|
|
ConstantFP *EV = NULL;
|
|
unsigned EVIndex = 1;
|
|
if (EC->getOperand(1) == Incr)
|
|
EVIndex = 0;
|
|
EV = dyn_cast<ConstantFP>(EC->getOperand(EVIndex));
|
|
if (!EV) return;
|
|
uint64_t intEV = Type::Int32Ty->getPrimitiveSizeInBits();
|
|
if (!convertToInt(EV->getValueAPF(), &intEV))
|
|
return;
|
|
|
|
// Find new predicate for integer comparison.
|
|
CmpInst::Predicate NewPred = CmpInst::BAD_ICMP_PREDICATE;
|
|
switch (EC->getPredicate()) {
|
|
case CmpInst::FCMP_OEQ:
|
|
case CmpInst::FCMP_UEQ:
|
|
NewPred = CmpInst::ICMP_EQ;
|
|
break;
|
|
case CmpInst::FCMP_OGT:
|
|
case CmpInst::FCMP_UGT:
|
|
NewPred = CmpInst::ICMP_UGT;
|
|
break;
|
|
case CmpInst::FCMP_OGE:
|
|
case CmpInst::FCMP_UGE:
|
|
NewPred = CmpInst::ICMP_UGE;
|
|
break;
|
|
case CmpInst::FCMP_OLT:
|
|
case CmpInst::FCMP_ULT:
|
|
NewPred = CmpInst::ICMP_ULT;
|
|
break;
|
|
case CmpInst::FCMP_OLE:
|
|
case CmpInst::FCMP_ULE:
|
|
NewPred = CmpInst::ICMP_ULE;
|
|
break;
|
|
default:
|
|
break;
|
|
}
|
|
if (NewPred == CmpInst::BAD_ICMP_PREDICATE) return;
|
|
|
|
// Insert new integer induction variable.
|
|
PHINode *NewPHI = PHINode::Create(Type::Int32Ty,
|
|
PH->getName()+".int", PH);
|
|
NewPHI->addIncoming(ConstantInt::get(Type::Int32Ty, newInitValue),
|
|
PH->getIncomingBlock(IncomingEdge));
|
|
|
|
Value *NewAdd = BinaryOperator::CreateAdd(NewPHI,
|
|
ConstantInt::get(Type::Int32Ty,
|
|
newIncrValue),
|
|
Incr->getName()+".int", Incr);
|
|
NewPHI->addIncoming(NewAdd, PH->getIncomingBlock(BackEdge));
|
|
|
|
ConstantInt *NewEV = ConstantInt::get(Type::Int32Ty, intEV);
|
|
Value *LHS = (EVIndex == 1 ? NewPHI->getIncomingValue(BackEdge) : NewEV);
|
|
Value *RHS = (EVIndex == 1 ? NewEV : NewPHI->getIncomingValue(BackEdge));
|
|
ICmpInst *NewEC = new ICmpInst(NewPred, LHS, RHS, EC->getNameStart(),
|
|
EC->getParent()->getTerminator());
|
|
|
|
// Delete old, floating point, exit comparision instruction.
|
|
EC->replaceAllUsesWith(NewEC);
|
|
DeadInsts.insert(EC);
|
|
|
|
// Delete old, floating point, increment instruction.
|
|
Incr->replaceAllUsesWith(UndefValue::get(Incr->getType()));
|
|
DeadInsts.insert(Incr);
|
|
|
|
// Replace floating induction variable. Give SIToFPInst preference over
|
|
// UIToFPInst because it is faster on platforms that are widely used.
|
|
if (useSIToFPInst(*InitValue, *EV, newInitValue, intEV)) {
|
|
SIToFPInst *Conv = new SIToFPInst(NewPHI, PH->getType(), "indvar.conv",
|
|
PH->getParent()->getFirstNonPHI());
|
|
PH->replaceAllUsesWith(Conv);
|
|
} else {
|
|
UIToFPInst *Conv = new UIToFPInst(NewPHI, PH->getType(), "indvar.conv",
|
|
PH->getParent()->getFirstNonPHI());
|
|
PH->replaceAllUsesWith(Conv);
|
|
}
|
|
DeadInsts.insert(PH);
|
|
}
|
|
|