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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153362 91177308-0d34-0410-b5e6-96231b3b80d8
1737 lines
67 KiB
C++
1737 lines
67 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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// 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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//===----------------------------------------------------------------------===//
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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/IntrinsicInst.h"
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#include "llvm/LLVMContext.h"
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#include "llvm/Type.h"
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#include "llvm/Analysis/Dominators.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/CommandLine.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/Transforms/Utils/BasicBlockUtils.h"
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#include "llvm/Transforms/Utils/SimplifyIndVar.h"
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#include "llvm/Target/TargetData.h"
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/Statistic.h"
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using namespace llvm;
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STATISTIC(NumWidened , "Number of indvars widened");
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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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STATISTIC(NumElimExt , "Number of IV sign/zero extends eliminated");
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STATISTIC(NumElimIV , "Number of congruent IVs eliminated");
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// Trip count verification can be enabled by default under NDEBUG if we
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// implement a strong expression equivalence checker in SCEV. Until then, we
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// use the verify-indvars flag, which may assert in some cases.
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static cl::opt<bool> VerifyIndvars(
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"verify-indvars", cl::Hidden,
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cl::desc("Verify the ScalarEvolution result after running indvars"));
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namespace {
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class IndVarSimplify : public LoopPass {
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LoopInfo *LI;
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ScalarEvolution *SE;
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DominatorTree *DT;
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TargetData *TD;
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SmallVector<WeakVH, 16> DeadInsts;
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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), LI(0), SE(0), DT(0), TD(0),
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Changed(false) {
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initializeIndVarSimplifyPass(*PassRegistry::getPassRegistry());
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}
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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<DominatorTree>();
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AU.addRequired<LoopInfo>();
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AU.addRequired<ScalarEvolution>();
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AU.addRequiredID(LoopSimplifyID);
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AU.addRequiredID(LCSSAID);
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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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virtual void releaseMemory() {
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DeadInsts.clear();
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}
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bool isValidRewrite(Value *FromVal, Value *ToVal);
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void HandleFloatingPointIV(Loop *L, PHINode *PH);
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void RewriteNonIntegerIVs(Loop *L);
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void SimplifyAndExtend(Loop *L, SCEVExpander &Rewriter, LPPassManager &LPM);
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void RewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter);
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Value *LinearFunctionTestReplace(Loop *L, const SCEV *BackedgeTakenCount,
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PHINode *IndVar, SCEVExpander &Rewriter);
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void SinkUnusedInvariants(Loop *L);
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};
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}
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char IndVarSimplify::ID = 0;
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INITIALIZE_PASS_BEGIN(IndVarSimplify, "indvars",
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"Induction Variable Simplification", false, false)
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INITIALIZE_PASS_DEPENDENCY(DominatorTree)
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INITIALIZE_PASS_DEPENDENCY(LoopInfo)
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INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
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INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
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INITIALIZE_PASS_DEPENDENCY(LCSSA)
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INITIALIZE_PASS_END(IndVarSimplify, "indvars",
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"Induction Variable Simplification", false, false)
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Pass *llvm::createIndVarSimplifyPass() {
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return new IndVarSimplify();
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}
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/// isValidRewrite - Return true if the SCEV expansion generated by the
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/// rewriter can replace the original value. SCEV guarantees that it
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/// produces the same value, but the way it is produced may be illegal IR.
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/// Ideally, this function will only be called for verification.
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bool IndVarSimplify::isValidRewrite(Value *FromVal, Value *ToVal) {
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// If an SCEV expression subsumed multiple pointers, its expansion could
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// reassociate the GEP changing the base pointer. This is illegal because the
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// final address produced by a GEP chain must be inbounds relative to its
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// underlying object. Otherwise basic alias analysis, among other things,
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// could fail in a dangerous way. Ultimately, SCEV will be improved to avoid
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// producing an expression involving multiple pointers. Until then, we must
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// bail out here.
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//
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// Retrieve the pointer operand of the GEP. Don't use GetUnderlyingObject
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// because it understands lcssa phis while SCEV does not.
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Value *FromPtr = FromVal;
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Value *ToPtr = ToVal;
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if (GEPOperator *GEP = dyn_cast<GEPOperator>(FromVal)) {
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FromPtr = GEP->getPointerOperand();
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}
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if (GEPOperator *GEP = dyn_cast<GEPOperator>(ToVal)) {
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ToPtr = GEP->getPointerOperand();
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}
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if (FromPtr != FromVal || ToPtr != ToVal) {
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// Quickly check the common case
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if (FromPtr == ToPtr)
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return true;
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// SCEV may have rewritten an expression that produces the GEP's pointer
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// operand. That's ok as long as the pointer operand has the same base
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// pointer. Unlike GetUnderlyingObject(), getPointerBase() will find the
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// base of a recurrence. This handles the case in which SCEV expansion
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// converts a pointer type recurrence into a nonrecurrent pointer base
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// indexed by an integer recurrence.
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// If the GEP base pointer is a vector of pointers, abort.
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if (!FromPtr->getType()->isPointerTy() || !ToPtr->getType()->isPointerTy())
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return false;
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const SCEV *FromBase = SE->getPointerBase(SE->getSCEV(FromPtr));
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const SCEV *ToBase = SE->getPointerBase(SE->getSCEV(ToPtr));
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if (FromBase == ToBase)
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return true;
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DEBUG(dbgs() << "INDVARS: GEP rewrite bail out "
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<< *FromBase << " != " << *ToBase << "\n");
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return false;
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}
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return true;
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}
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/// Determine the insertion point for this user. By default, insert immediately
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/// before the user. SCEVExpander or LICM will hoist loop invariants out of the
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/// loop. For PHI nodes, there may be multiple uses, so compute the nearest
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/// common dominator for the incoming blocks.
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static Instruction *getInsertPointForUses(Instruction *User, Value *Def,
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DominatorTree *DT) {
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PHINode *PHI = dyn_cast<PHINode>(User);
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if (!PHI)
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return User;
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Instruction *InsertPt = 0;
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for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i) {
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if (PHI->getIncomingValue(i) != Def)
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continue;
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BasicBlock *InsertBB = PHI->getIncomingBlock(i);
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if (!InsertPt) {
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InsertPt = InsertBB->getTerminator();
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continue;
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}
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InsertBB = DT->findNearestCommonDominator(InsertPt->getParent(), InsertBB);
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InsertPt = InsertBB->getTerminator();
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}
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assert(InsertPt && "Missing phi operand");
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assert((!isa<Instruction>(Def) ||
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DT->dominates(cast<Instruction>(Def), InsertPt)) &&
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"def does not dominate all uses");
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return InsertPt;
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}
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//===----------------------------------------------------------------------===//
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// RewriteNonIntegerIVs and helpers. Prefer integer IVs.
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//===----------------------------------------------------------------------===//
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/// ConvertToSInt - Convert APF to an integer, if possible.
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static bool ConvertToSInt(const APFloat &APF, int64_t &IntVal) {
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bool isExact = false;
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if (&APF.getSemantics() == &APFloat::PPCDoubleDouble)
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return false;
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// See if we can convert this to an int64_t
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uint64_t UIntVal;
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if (APF.convertToInteger(&UIntVal, 64, true, APFloat::rmTowardZero,
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&isExact) != APFloat::opOK || !isExact)
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return false;
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IntVal = UIntVal;
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return true;
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}
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/// HandleFloatingPointIV - If the loop has floating induction variable
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/// then insert corresponding integer induction variable if possible.
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/// For example,
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/// for(double i = 0; i < 10000; ++i)
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/// bar(i)
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/// is converted into
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/// for(int i = 0; i < 10000; ++i)
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/// bar((double)i);
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///
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void IndVarSimplify::HandleFloatingPointIV(Loop *L, PHINode *PN) {
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unsigned IncomingEdge = L->contains(PN->getIncomingBlock(0));
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unsigned BackEdge = IncomingEdge^1;
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// Check incoming value.
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ConstantFP *InitValueVal =
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dyn_cast<ConstantFP>(PN->getIncomingValue(IncomingEdge));
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int64_t InitValue;
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if (!InitValueVal || !ConvertToSInt(InitValueVal->getValueAPF(), InitValue))
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return;
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// Check IV increment. Reject this PN if increment operation is not
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// an add or increment value can not be represented by an integer.
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BinaryOperator *Incr =
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dyn_cast<BinaryOperator>(PN->getIncomingValue(BackEdge));
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if (Incr == 0 || Incr->getOpcode() != Instruction::FAdd) return;
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// If this is not an add of the PHI with a constantfp, or if the constant fp
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// is not an integer, bail out.
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ConstantFP *IncValueVal = dyn_cast<ConstantFP>(Incr->getOperand(1));
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int64_t IncValue;
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if (IncValueVal == 0 || Incr->getOperand(0) != PN ||
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!ConvertToSInt(IncValueVal->getValueAPF(), IncValue))
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return;
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// Check Incr uses. One user is PN and the other user is an exit condition
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// used by the conditional terminator.
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Value::use_iterator IncrUse = Incr->use_begin();
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Instruction *U1 = cast<Instruction>(*IncrUse++);
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if (IncrUse == Incr->use_end()) return;
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Instruction *U2 = cast<Instruction>(*IncrUse++);
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if (IncrUse != Incr->use_end()) return;
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// Find exit condition, which is an fcmp. If it doesn't exist, or if it isn't
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// only used by a branch, we can't transform it.
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FCmpInst *Compare = dyn_cast<FCmpInst>(U1);
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if (!Compare)
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Compare = dyn_cast<FCmpInst>(U2);
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if (Compare == 0 || !Compare->hasOneUse() ||
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!isa<BranchInst>(Compare->use_back()))
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return;
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BranchInst *TheBr = cast<BranchInst>(Compare->use_back());
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// We need to verify that the branch actually controls the iteration count
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// of the loop. If not, the new IV can overflow and no one will notice.
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// The branch block must be in the loop and one of the successors must be out
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// of the loop.
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assert(TheBr->isConditional() && "Can't use fcmp if not conditional");
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if (!L->contains(TheBr->getParent()) ||
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(L->contains(TheBr->getSuccessor(0)) &&
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L->contains(TheBr->getSuccessor(1))))
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return;
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// If it isn't a comparison with an integer-as-fp (the exit value), we can't
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// transform it.
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ConstantFP *ExitValueVal = dyn_cast<ConstantFP>(Compare->getOperand(1));
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int64_t ExitValue;
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if (ExitValueVal == 0 ||
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!ConvertToSInt(ExitValueVal->getValueAPF(), ExitValue))
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return;
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// Find new predicate for integer comparison.
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CmpInst::Predicate NewPred = CmpInst::BAD_ICMP_PREDICATE;
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switch (Compare->getPredicate()) {
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default: return; // Unknown comparison.
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case CmpInst::FCMP_OEQ:
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case CmpInst::FCMP_UEQ: NewPred = CmpInst::ICMP_EQ; break;
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case CmpInst::FCMP_ONE:
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case CmpInst::FCMP_UNE: NewPred = CmpInst::ICMP_NE; break;
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case CmpInst::FCMP_OGT:
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case CmpInst::FCMP_UGT: NewPred = CmpInst::ICMP_SGT; break;
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case CmpInst::FCMP_OGE:
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case CmpInst::FCMP_UGE: NewPred = CmpInst::ICMP_SGE; break;
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case CmpInst::FCMP_OLT:
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case CmpInst::FCMP_ULT: NewPred = CmpInst::ICMP_SLT; break;
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case CmpInst::FCMP_OLE:
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case CmpInst::FCMP_ULE: NewPred = CmpInst::ICMP_SLE; break;
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}
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// We convert the floating point induction variable to a signed i32 value if
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// we can. This is only safe if the comparison will not overflow in a way
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// that won't be trapped by the integer equivalent operations. Check for this
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// now.
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// TODO: We could use i64 if it is native and the range requires it.
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// The start/stride/exit values must all fit in signed i32.
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if (!isInt<32>(InitValue) || !isInt<32>(IncValue) || !isInt<32>(ExitValue))
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return;
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// If not actually striding (add x, 0.0), avoid touching the code.
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if (IncValue == 0)
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return;
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// Positive and negative strides have different safety conditions.
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if (IncValue > 0) {
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// If we have a positive stride, we require the init to be less than the
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// exit value.
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if (InitValue >= ExitValue)
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return;
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uint32_t Range = uint32_t(ExitValue-InitValue);
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// Check for infinite loop, either:
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// while (i <= Exit) or until (i > Exit)
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if (NewPred == CmpInst::ICMP_SLE || NewPred == CmpInst::ICMP_SGT) {
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if (++Range == 0) return; // Range overflows.
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}
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unsigned Leftover = Range % uint32_t(IncValue);
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// If this is an equality comparison, we require that the strided value
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// exactly land on the exit value, otherwise the IV condition will wrap
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// around and do things the fp IV wouldn't.
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if ((NewPred == CmpInst::ICMP_EQ || NewPred == CmpInst::ICMP_NE) &&
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Leftover != 0)
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return;
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// If the stride would wrap around the i32 before exiting, we can't
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// transform the IV.
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if (Leftover != 0 && int32_t(ExitValue+IncValue) < ExitValue)
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return;
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} else {
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// If we have a negative stride, we require the init to be greater than the
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// exit value.
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if (InitValue <= ExitValue)
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return;
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uint32_t Range = uint32_t(InitValue-ExitValue);
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// Check for infinite loop, either:
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// while (i >= Exit) or until (i < Exit)
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if (NewPred == CmpInst::ICMP_SGE || NewPred == CmpInst::ICMP_SLT) {
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if (++Range == 0) return; // Range overflows.
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}
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unsigned Leftover = Range % uint32_t(-IncValue);
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// If this is an equality comparison, we require that the strided value
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// exactly land on the exit value, otherwise the IV condition will wrap
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// around and do things the fp IV wouldn't.
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if ((NewPred == CmpInst::ICMP_EQ || NewPred == CmpInst::ICMP_NE) &&
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Leftover != 0)
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return;
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// If the stride would wrap around the i32 before exiting, we can't
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// transform the IV.
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if (Leftover != 0 && int32_t(ExitValue+IncValue) > ExitValue)
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return;
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}
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IntegerType *Int32Ty = Type::getInt32Ty(PN->getContext());
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// Insert new integer induction variable.
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PHINode *NewPHI = PHINode::Create(Int32Ty, 2, PN->getName()+".int", PN);
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NewPHI->addIncoming(ConstantInt::get(Int32Ty, InitValue),
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PN->getIncomingBlock(IncomingEdge));
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Value *NewAdd =
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BinaryOperator::CreateAdd(NewPHI, ConstantInt::get(Int32Ty, IncValue),
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Incr->getName()+".int", Incr);
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NewPHI->addIncoming(NewAdd, PN->getIncomingBlock(BackEdge));
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ICmpInst *NewCompare = new ICmpInst(TheBr, NewPred, NewAdd,
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ConstantInt::get(Int32Ty, ExitValue),
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Compare->getName());
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// In the following deletions, PN may become dead and may be deleted.
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// Use a WeakVH to observe whether this happens.
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WeakVH WeakPH = PN;
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// Delete the old floating point exit comparison. The branch starts using the
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// new comparison.
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NewCompare->takeName(Compare);
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Compare->replaceAllUsesWith(NewCompare);
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RecursivelyDeleteTriviallyDeadInstructions(Compare);
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// Delete the old floating point increment.
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Incr->replaceAllUsesWith(UndefValue::get(Incr->getType()));
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RecursivelyDeleteTriviallyDeadInstructions(Incr);
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// If the FP induction variable still has uses, this is because something else
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// in the loop uses its value. In order to canonicalize the induction
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// variable, we chose to eliminate the IV and rewrite it in terms of an
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// int->fp cast.
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//
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// We give preference to sitofp over uitofp because it is faster on most
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// platforms.
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if (WeakPH) {
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Value *Conv = new SIToFPInst(NewPHI, PN->getType(), "indvar.conv",
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PN->getParent()->getFirstInsertionPt());
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PN->replaceAllUsesWith(Conv);
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RecursivelyDeleteTriviallyDeadInstructions(PN);
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}
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Changed = true;
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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 floating-point 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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SmallVector<WeakVH, 8> PHIs;
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for (BasicBlock::iterator I = Header->begin();
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PHINode *PN = dyn_cast<PHINode>(I); ++I)
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PHIs.push_back(PN);
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for (unsigned i = 0, e = PHIs.size(); i != e; ++i)
|
|
if (PHINode *PN = dyn_cast_or_null<PHINode>(&*PHIs[i]))
|
|
HandleFloatingPointIV(L, PN);
|
|
|
|
// If the loop previously had floating-point IV, ScalarEvolution
|
|
// may not have been able to compute a trip count. Now that we've done some
|
|
// re-writing, the trip count may be computable.
|
|
if (Changed)
|
|
SE->forgetLoop(L);
|
|
}
|
|
|
|
//===----------------------------------------------------------------------===//
|
|
// RewriteLoopExitValues - Optimize IV users outside the loop.
|
|
// As a side effect, reduces the amount of IV processing within the loop.
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
/// 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.
|
|
///
|
|
/// This is mostly redundant with the regular IndVarSimplify activities that
|
|
/// happen later, except that it's more powerful in some cases, because it's
|
|
/// able to brute-force evaluate arbitrary instructions as long as they have
|
|
/// constant operands at the beginning of the loop.
|
|
void IndVarSimplify::RewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter) {
|
|
// Verify the input to the pass in already in LCSSA form.
|
|
assert(L->isLCSSAForm(*DT));
|
|
|
|
SmallVector<BasicBlock*, 8> ExitBlocks;
|
|
L->getUniqueExitBlocks(ExitBlocks);
|
|
|
|
// Find all values that are computed inside the loop, but used outside of it.
|
|
// Because of LCSSA, these values will only occur in LCSSA PHI Nodes. Scan
|
|
// the exit blocks of the loop to find them.
|
|
for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
|
|
BasicBlock *ExitBB = ExitBlocks[i];
|
|
|
|
// If there are no PHI nodes in this exit block, then no values defined
|
|
// inside the loop are used on this path, skip it.
|
|
PHINode *PN = dyn_cast<PHINode>(ExitBB->begin());
|
|
if (!PN) continue;
|
|
|
|
unsigned NumPreds = PN->getNumIncomingValues();
|
|
|
|
// Iterate over all of the PHI nodes.
|
|
BasicBlock::iterator BBI = ExitBB->begin();
|
|
while ((PN = dyn_cast<PHINode>(BBI++))) {
|
|
if (PN->use_empty())
|
|
continue; // dead use, don't replace it
|
|
|
|
// SCEV only supports integer expressions for now.
|
|
if (!PN->getType()->isIntegerTy() && !PN->getType()->isPointerTy())
|
|
continue;
|
|
|
|
// It's necessary to tell ScalarEvolution about this explicitly so that
|
|
// it can walk the def-use list and forget all SCEVs, as it may not be
|
|
// watching the PHI itself. Once the new exit value is in place, there
|
|
// may not be a def-use connection between the loop and every instruction
|
|
// which got a SCEVAddRecExpr for that loop.
|
|
SE->forgetValue(PN);
|
|
|
|
// Iterate over all of the values in all the PHI nodes.
|
|
for (unsigned i = 0; i != NumPreds; ++i) {
|
|
// If the value being merged in is not integer or is not defined
|
|
// in the loop, skip it.
|
|
Value *InVal = PN->getIncomingValue(i);
|
|
if (!isa<Instruction>(InVal))
|
|
continue;
|
|
|
|
// If this pred is for a subloop, not L itself, skip it.
|
|
if (LI->getLoopFor(PN->getIncomingBlock(i)) != L)
|
|
continue; // The Block is in a subloop, skip it.
|
|
|
|
// Check that InVal is defined in the loop.
|
|
Instruction *Inst = cast<Instruction>(InVal);
|
|
if (!L->contains(Inst))
|
|
continue;
|
|
|
|
// Okay, this instruction has a user outside of the current loop
|
|
// and varies predictably *inside* the loop. Evaluate the value it
|
|
// contains when the loop exits, if possible.
|
|
const SCEV *ExitValue = SE->getSCEVAtScope(Inst, L->getParentLoop());
|
|
if (!SE->isLoopInvariant(ExitValue, L))
|
|
continue;
|
|
|
|
Value *ExitVal = Rewriter.expandCodeFor(ExitValue, PN->getType(), Inst);
|
|
|
|
DEBUG(dbgs() << "INDVARS: RLEV: AfterLoopVal = " << *ExitVal << '\n'
|
|
<< " LoopVal = " << *Inst << "\n");
|
|
|
|
if (!isValidRewrite(Inst, ExitVal)) {
|
|
DeadInsts.push_back(ExitVal);
|
|
continue;
|
|
}
|
|
Changed = true;
|
|
++NumReplaced;
|
|
|
|
PN->setIncomingValue(i, ExitVal);
|
|
|
|
// If this instruction is dead now, delete it.
|
|
RecursivelyDeleteTriviallyDeadInstructions(Inst);
|
|
|
|
if (NumPreds == 1) {
|
|
// Completely replace a single-pred PHI. This is safe, because the
|
|
// NewVal won't be variant in the loop, so we don't need an LCSSA phi
|
|
// node anymore.
|
|
PN->replaceAllUsesWith(ExitVal);
|
|
RecursivelyDeleteTriviallyDeadInstructions(PN);
|
|
}
|
|
}
|
|
if (NumPreds != 1) {
|
|
// Clone the PHI and delete the original one. This lets IVUsers and
|
|
// any other maps purge the original user from their records.
|
|
PHINode *NewPN = cast<PHINode>(PN->clone());
|
|
NewPN->takeName(PN);
|
|
NewPN->insertBefore(PN);
|
|
PN->replaceAllUsesWith(NewPN);
|
|
PN->eraseFromParent();
|
|
}
|
|
}
|
|
}
|
|
|
|
// The insertion point instruction may have been deleted; clear it out
|
|
// so that the rewriter doesn't trip over it later.
|
|
Rewriter.clearInsertPoint();
|
|
}
|
|
|
|
//===----------------------------------------------------------------------===//
|
|
// IV Widening - Extend the width of an IV to cover its widest uses.
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
namespace {
|
|
// Collect information about induction variables that are used by sign/zero
|
|
// extend operations. This information is recorded by CollectExtend and
|
|
// provides the input to WidenIV.
|
|
struct WideIVInfo {
|
|
PHINode *NarrowIV;
|
|
Type *WidestNativeType; // Widest integer type created [sz]ext
|
|
bool IsSigned; // Was an sext user seen before a zext?
|
|
|
|
WideIVInfo() : NarrowIV(0), WidestNativeType(0), IsSigned(false) {}
|
|
};
|
|
|
|
class WideIVVisitor : public IVVisitor {
|
|
ScalarEvolution *SE;
|
|
const TargetData *TD;
|
|
|
|
public:
|
|
WideIVInfo WI;
|
|
|
|
WideIVVisitor(PHINode *NarrowIV, ScalarEvolution *SCEV,
|
|
const TargetData *TData) :
|
|
SE(SCEV), TD(TData) { WI.NarrowIV = NarrowIV; }
|
|
|
|
// Implement the interface used by simplifyUsersOfIV.
|
|
virtual void visitCast(CastInst *Cast);
|
|
};
|
|
}
|
|
|
|
/// visitCast - Update information about the induction variable that is
|
|
/// extended by this sign or zero extend operation. This is used to determine
|
|
/// the final width of the IV before actually widening it.
|
|
void WideIVVisitor::visitCast(CastInst *Cast) {
|
|
bool IsSigned = Cast->getOpcode() == Instruction::SExt;
|
|
if (!IsSigned && Cast->getOpcode() != Instruction::ZExt)
|
|
return;
|
|
|
|
Type *Ty = Cast->getType();
|
|
uint64_t Width = SE->getTypeSizeInBits(Ty);
|
|
if (TD && !TD->isLegalInteger(Width))
|
|
return;
|
|
|
|
if (!WI.WidestNativeType) {
|
|
WI.WidestNativeType = SE->getEffectiveSCEVType(Ty);
|
|
WI.IsSigned = IsSigned;
|
|
return;
|
|
}
|
|
|
|
// We extend the IV to satisfy the sign of its first user, arbitrarily.
|
|
if (WI.IsSigned != IsSigned)
|
|
return;
|
|
|
|
if (Width > SE->getTypeSizeInBits(WI.WidestNativeType))
|
|
WI.WidestNativeType = SE->getEffectiveSCEVType(Ty);
|
|
}
|
|
|
|
namespace {
|
|
|
|
/// NarrowIVDefUse - Record a link in the Narrow IV def-use chain along with the
|
|
/// WideIV that computes the same value as the Narrow IV def. This avoids
|
|
/// caching Use* pointers.
|
|
struct NarrowIVDefUse {
|
|
Instruction *NarrowDef;
|
|
Instruction *NarrowUse;
|
|
Instruction *WideDef;
|
|
|
|
NarrowIVDefUse(): NarrowDef(0), NarrowUse(0), WideDef(0) {}
|
|
|
|
NarrowIVDefUse(Instruction *ND, Instruction *NU, Instruction *WD):
|
|
NarrowDef(ND), NarrowUse(NU), WideDef(WD) {}
|
|
};
|
|
|
|
/// WidenIV - The goal of this transform is to remove sign and zero extends
|
|
/// without creating any new induction variables. To do this, it creates a new
|
|
/// phi of the wider type and redirects all users, either removing extends or
|
|
/// inserting truncs whenever we stop propagating the type.
|
|
///
|
|
class WidenIV {
|
|
// Parameters
|
|
PHINode *OrigPhi;
|
|
Type *WideType;
|
|
bool IsSigned;
|
|
|
|
// Context
|
|
LoopInfo *LI;
|
|
Loop *L;
|
|
ScalarEvolution *SE;
|
|
DominatorTree *DT;
|
|
|
|
// Result
|
|
PHINode *WidePhi;
|
|
Instruction *WideInc;
|
|
const SCEV *WideIncExpr;
|
|
SmallVectorImpl<WeakVH> &DeadInsts;
|
|
|
|
SmallPtrSet<Instruction*,16> Widened;
|
|
SmallVector<NarrowIVDefUse, 8> NarrowIVUsers;
|
|
|
|
public:
|
|
WidenIV(const WideIVInfo &WI, LoopInfo *LInfo,
|
|
ScalarEvolution *SEv, DominatorTree *DTree,
|
|
SmallVectorImpl<WeakVH> &DI) :
|
|
OrigPhi(WI.NarrowIV),
|
|
WideType(WI.WidestNativeType),
|
|
IsSigned(WI.IsSigned),
|
|
LI(LInfo),
|
|
L(LI->getLoopFor(OrigPhi->getParent())),
|
|
SE(SEv),
|
|
DT(DTree),
|
|
WidePhi(0),
|
|
WideInc(0),
|
|
WideIncExpr(0),
|
|
DeadInsts(DI) {
|
|
assert(L->getHeader() == OrigPhi->getParent() && "Phi must be an IV");
|
|
}
|
|
|
|
PHINode *CreateWideIV(SCEVExpander &Rewriter);
|
|
|
|
protected:
|
|
Value *getExtend(Value *NarrowOper, Type *WideType, bool IsSigned,
|
|
Instruction *Use);
|
|
|
|
Instruction *CloneIVUser(NarrowIVDefUse DU);
|
|
|
|
const SCEVAddRecExpr *GetWideRecurrence(Instruction *NarrowUse);
|
|
|
|
const SCEVAddRecExpr* GetExtendedOperandRecurrence(NarrowIVDefUse DU);
|
|
|
|
Instruction *WidenIVUse(NarrowIVDefUse DU, SCEVExpander &Rewriter);
|
|
|
|
void pushNarrowIVUsers(Instruction *NarrowDef, Instruction *WideDef);
|
|
};
|
|
} // anonymous namespace
|
|
|
|
/// isLoopInvariant - Perform a quick domtree based check for loop invariance
|
|
/// assuming that V is used within the loop. LoopInfo::isLoopInvariant() seems
|
|
/// gratuitous for this purpose.
|
|
static bool isLoopInvariant(Value *V, const Loop *L, const DominatorTree *DT) {
|
|
Instruction *Inst = dyn_cast<Instruction>(V);
|
|
if (!Inst)
|
|
return true;
|
|
|
|
return DT->properlyDominates(Inst->getParent(), L->getHeader());
|
|
}
|
|
|
|
Value *WidenIV::getExtend(Value *NarrowOper, Type *WideType, bool IsSigned,
|
|
Instruction *Use) {
|
|
// Set the debug location and conservative insertion point.
|
|
IRBuilder<> Builder(Use);
|
|
// Hoist the insertion point into loop preheaders as far as possible.
|
|
for (const Loop *L = LI->getLoopFor(Use->getParent());
|
|
L && L->getLoopPreheader() && isLoopInvariant(NarrowOper, L, DT);
|
|
L = L->getParentLoop())
|
|
Builder.SetInsertPoint(L->getLoopPreheader()->getTerminator());
|
|
|
|
return IsSigned ? Builder.CreateSExt(NarrowOper, WideType) :
|
|
Builder.CreateZExt(NarrowOper, WideType);
|
|
}
|
|
|
|
/// CloneIVUser - Instantiate a wide operation to replace a narrow
|
|
/// operation. This only needs to handle operations that can evaluation to
|
|
/// SCEVAddRec. It can safely return 0 for any operation we decide not to clone.
|
|
Instruction *WidenIV::CloneIVUser(NarrowIVDefUse DU) {
|
|
unsigned Opcode = DU.NarrowUse->getOpcode();
|
|
switch (Opcode) {
|
|
default:
|
|
return 0;
|
|
case Instruction::Add:
|
|
case Instruction::Mul:
|
|
case Instruction::UDiv:
|
|
case Instruction::Sub:
|
|
case Instruction::And:
|
|
case Instruction::Or:
|
|
case Instruction::Xor:
|
|
case Instruction::Shl:
|
|
case Instruction::LShr:
|
|
case Instruction::AShr:
|
|
DEBUG(dbgs() << "Cloning IVUser: " << *DU.NarrowUse << "\n");
|
|
|
|
// Replace NarrowDef operands with WideDef. Otherwise, we don't know
|
|
// anything about the narrow operand yet so must insert a [sz]ext. It is
|
|
// probably loop invariant and will be folded or hoisted. If it actually
|
|
// comes from a widened IV, it should be removed during a future call to
|
|
// WidenIVUse.
|
|
Value *LHS = (DU.NarrowUse->getOperand(0) == DU.NarrowDef) ? DU.WideDef :
|
|
getExtend(DU.NarrowUse->getOperand(0), WideType, IsSigned, DU.NarrowUse);
|
|
Value *RHS = (DU.NarrowUse->getOperand(1) == DU.NarrowDef) ? DU.WideDef :
|
|
getExtend(DU.NarrowUse->getOperand(1), WideType, IsSigned, DU.NarrowUse);
|
|
|
|
BinaryOperator *NarrowBO = cast<BinaryOperator>(DU.NarrowUse);
|
|
BinaryOperator *WideBO = BinaryOperator::Create(NarrowBO->getOpcode(),
|
|
LHS, RHS,
|
|
NarrowBO->getName());
|
|
IRBuilder<> Builder(DU.NarrowUse);
|
|
Builder.Insert(WideBO);
|
|
if (const OverflowingBinaryOperator *OBO =
|
|
dyn_cast<OverflowingBinaryOperator>(NarrowBO)) {
|
|
if (OBO->hasNoUnsignedWrap()) WideBO->setHasNoUnsignedWrap();
|
|
if (OBO->hasNoSignedWrap()) WideBO->setHasNoSignedWrap();
|
|
}
|
|
return WideBO;
|
|
}
|
|
}
|
|
|
|
/// No-wrap operations can transfer sign extension of their result to their
|
|
/// operands. Generate the SCEV value for the widened operation without
|
|
/// actually modifying the IR yet. If the expression after extending the
|
|
/// operands is an AddRec for this loop, return it.
|
|
const SCEVAddRecExpr* WidenIV::GetExtendedOperandRecurrence(NarrowIVDefUse DU) {
|
|
// Handle the common case of add<nsw/nuw>
|
|
if (DU.NarrowUse->getOpcode() != Instruction::Add)
|
|
return 0;
|
|
|
|
// One operand (NarrowDef) has already been extended to WideDef. Now determine
|
|
// if extending the other will lead to a recurrence.
|
|
unsigned ExtendOperIdx = DU.NarrowUse->getOperand(0) == DU.NarrowDef ? 1 : 0;
|
|
assert(DU.NarrowUse->getOperand(1-ExtendOperIdx) == DU.NarrowDef && "bad DU");
|
|
|
|
const SCEV *ExtendOperExpr = 0;
|
|
const OverflowingBinaryOperator *OBO =
|
|
cast<OverflowingBinaryOperator>(DU.NarrowUse);
|
|
if (IsSigned && OBO->hasNoSignedWrap())
|
|
ExtendOperExpr = SE->getSignExtendExpr(
|
|
SE->getSCEV(DU.NarrowUse->getOperand(ExtendOperIdx)), WideType);
|
|
else if(!IsSigned && OBO->hasNoUnsignedWrap())
|
|
ExtendOperExpr = SE->getZeroExtendExpr(
|
|
SE->getSCEV(DU.NarrowUse->getOperand(ExtendOperIdx)), WideType);
|
|
else
|
|
return 0;
|
|
|
|
// When creating this AddExpr, don't apply the current operations NSW or NUW
|
|
// flags. This instruction may be guarded by control flow that the no-wrap
|
|
// behavior depends on. Non-control-equivalent instructions can be mapped to
|
|
// the same SCEV expression, and it would be incorrect to transfer NSW/NUW
|
|
// semantics to those operations.
|
|
const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(
|
|
SE->getAddExpr(SE->getSCEV(DU.WideDef), ExtendOperExpr));
|
|
|
|
if (!AddRec || AddRec->getLoop() != L)
|
|
return 0;
|
|
return AddRec;
|
|
}
|
|
|
|
/// GetWideRecurrence - Is this instruction potentially interesting from
|
|
/// IVUsers' perspective after widening it's type? In other words, can the
|
|
/// extend be safely hoisted out of the loop with SCEV reducing the value to a
|
|
/// recurrence on the same loop. If so, return the sign or zero extended
|
|
/// recurrence. Otherwise return NULL.
|
|
const SCEVAddRecExpr *WidenIV::GetWideRecurrence(Instruction *NarrowUse) {
|
|
if (!SE->isSCEVable(NarrowUse->getType()))
|
|
return 0;
|
|
|
|
const SCEV *NarrowExpr = SE->getSCEV(NarrowUse);
|
|
if (SE->getTypeSizeInBits(NarrowExpr->getType())
|
|
>= SE->getTypeSizeInBits(WideType)) {
|
|
// NarrowUse implicitly widens its operand. e.g. a gep with a narrow
|
|
// index. So don't follow this use.
|
|
return 0;
|
|
}
|
|
|
|
const SCEV *WideExpr = IsSigned ?
|
|
SE->getSignExtendExpr(NarrowExpr, WideType) :
|
|
SE->getZeroExtendExpr(NarrowExpr, WideType);
|
|
const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(WideExpr);
|
|
if (!AddRec || AddRec->getLoop() != L)
|
|
return 0;
|
|
return AddRec;
|
|
}
|
|
|
|
/// WidenIVUse - Determine whether an individual user of the narrow IV can be
|
|
/// widened. If so, return the wide clone of the user.
|
|
Instruction *WidenIV::WidenIVUse(NarrowIVDefUse DU, SCEVExpander &Rewriter) {
|
|
|
|
// Stop traversing the def-use chain at inner-loop phis or post-loop phis.
|
|
if (isa<PHINode>(DU.NarrowUse) &&
|
|
LI->getLoopFor(DU.NarrowUse->getParent()) != L)
|
|
return 0;
|
|
|
|
// Our raison d'etre! Eliminate sign and zero extension.
|
|
if (IsSigned ? isa<SExtInst>(DU.NarrowUse) : isa<ZExtInst>(DU.NarrowUse)) {
|
|
Value *NewDef = DU.WideDef;
|
|
if (DU.NarrowUse->getType() != WideType) {
|
|
unsigned CastWidth = SE->getTypeSizeInBits(DU.NarrowUse->getType());
|
|
unsigned IVWidth = SE->getTypeSizeInBits(WideType);
|
|
if (CastWidth < IVWidth) {
|
|
// The cast isn't as wide as the IV, so insert a Trunc.
|
|
IRBuilder<> Builder(DU.NarrowUse);
|
|
NewDef = Builder.CreateTrunc(DU.WideDef, DU.NarrowUse->getType());
|
|
}
|
|
else {
|
|
// A wider extend was hidden behind a narrower one. This may induce
|
|
// another round of IV widening in which the intermediate IV becomes
|
|
// dead. It should be very rare.
|
|
DEBUG(dbgs() << "INDVARS: New IV " << *WidePhi
|
|
<< " not wide enough to subsume " << *DU.NarrowUse << "\n");
|
|
DU.NarrowUse->replaceUsesOfWith(DU.NarrowDef, DU.WideDef);
|
|
NewDef = DU.NarrowUse;
|
|
}
|
|
}
|
|
if (NewDef != DU.NarrowUse) {
|
|
DEBUG(dbgs() << "INDVARS: eliminating " << *DU.NarrowUse
|
|
<< " replaced by " << *DU.WideDef << "\n");
|
|
++NumElimExt;
|
|
DU.NarrowUse->replaceAllUsesWith(NewDef);
|
|
DeadInsts.push_back(DU.NarrowUse);
|
|
}
|
|
// Now that the extend is gone, we want to expose it's uses for potential
|
|
// further simplification. We don't need to directly inform SimplifyIVUsers
|
|
// of the new users, because their parent IV will be processed later as a
|
|
// new loop phi. If we preserved IVUsers analysis, we would also want to
|
|
// push the uses of WideDef here.
|
|
|
|
// No further widening is needed. The deceased [sz]ext had done it for us.
|
|
return 0;
|
|
}
|
|
|
|
// Does this user itself evaluate to a recurrence after widening?
|
|
const SCEVAddRecExpr *WideAddRec = GetWideRecurrence(DU.NarrowUse);
|
|
if (!WideAddRec) {
|
|
WideAddRec = GetExtendedOperandRecurrence(DU);
|
|
}
|
|
if (!WideAddRec) {
|
|
// This user does not evaluate to a recurence after widening, so don't
|
|
// follow it. Instead insert a Trunc to kill off the original use,
|
|
// eventually isolating the original narrow IV so it can be removed.
|
|
IRBuilder<> Builder(getInsertPointForUses(DU.NarrowUse, DU.NarrowDef, DT));
|
|
Value *Trunc = Builder.CreateTrunc(DU.WideDef, DU.NarrowDef->getType());
|
|
DU.NarrowUse->replaceUsesOfWith(DU.NarrowDef, Trunc);
|
|
return 0;
|
|
}
|
|
// Assume block terminators cannot evaluate to a recurrence. We can't to
|
|
// insert a Trunc after a terminator if there happens to be a critical edge.
|
|
assert(DU.NarrowUse != DU.NarrowUse->getParent()->getTerminator() &&
|
|
"SCEV is not expected to evaluate a block terminator");
|
|
|
|
// Reuse the IV increment that SCEVExpander created as long as it dominates
|
|
// NarrowUse.
|
|
Instruction *WideUse = 0;
|
|
if (WideAddRec == WideIncExpr
|
|
&& Rewriter.hoistIVInc(WideInc, DU.NarrowUse))
|
|
WideUse = WideInc;
|
|
else {
|
|
WideUse = CloneIVUser(DU);
|
|
if (!WideUse)
|
|
return 0;
|
|
}
|
|
// Evaluation of WideAddRec ensured that the narrow expression could be
|
|
// extended outside the loop without overflow. This suggests that the wide use
|
|
// evaluates to the same expression as the extended narrow use, but doesn't
|
|
// absolutely guarantee it. Hence the following failsafe check. In rare cases
|
|
// where it fails, we simply throw away the newly created wide use.
|
|
if (WideAddRec != SE->getSCEV(WideUse)) {
|
|
DEBUG(dbgs() << "Wide use expression mismatch: " << *WideUse
|
|
<< ": " << *SE->getSCEV(WideUse) << " != " << *WideAddRec << "\n");
|
|
DeadInsts.push_back(WideUse);
|
|
return 0;
|
|
}
|
|
|
|
// Returning WideUse pushes it on the worklist.
|
|
return WideUse;
|
|
}
|
|
|
|
/// pushNarrowIVUsers - Add eligible users of NarrowDef to NarrowIVUsers.
|
|
///
|
|
void WidenIV::pushNarrowIVUsers(Instruction *NarrowDef, Instruction *WideDef) {
|
|
for (Value::use_iterator UI = NarrowDef->use_begin(),
|
|
UE = NarrowDef->use_end(); UI != UE; ++UI) {
|
|
Instruction *NarrowUse = cast<Instruction>(*UI);
|
|
|
|
// Handle data flow merges and bizarre phi cycles.
|
|
if (!Widened.insert(NarrowUse))
|
|
continue;
|
|
|
|
NarrowIVUsers.push_back(NarrowIVDefUse(NarrowDef, NarrowUse, WideDef));
|
|
}
|
|
}
|
|
|
|
/// CreateWideIV - Process a single induction variable. First use the
|
|
/// SCEVExpander to create a wide induction variable that evaluates to the same
|
|
/// recurrence as the original narrow IV. Then use a worklist to forward
|
|
/// traverse the narrow IV's def-use chain. After WidenIVUse has processed all
|
|
/// interesting IV users, the narrow IV will be isolated for removal by
|
|
/// DeleteDeadPHIs.
|
|
///
|
|
/// It would be simpler to delete uses as they are processed, but we must avoid
|
|
/// invalidating SCEV expressions.
|
|
///
|
|
PHINode *WidenIV::CreateWideIV(SCEVExpander &Rewriter) {
|
|
// Is this phi an induction variable?
|
|
const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(OrigPhi));
|
|
if (!AddRec)
|
|
return NULL;
|
|
|
|
// Widen the induction variable expression.
|
|
const SCEV *WideIVExpr = IsSigned ?
|
|
SE->getSignExtendExpr(AddRec, WideType) :
|
|
SE->getZeroExtendExpr(AddRec, WideType);
|
|
|
|
assert(SE->getEffectiveSCEVType(WideIVExpr->getType()) == WideType &&
|
|
"Expect the new IV expression to preserve its type");
|
|
|
|
// Can the IV be extended outside the loop without overflow?
|
|
AddRec = dyn_cast<SCEVAddRecExpr>(WideIVExpr);
|
|
if (!AddRec || AddRec->getLoop() != L)
|
|
return NULL;
|
|
|
|
// An AddRec must have loop-invariant operands. Since this AddRec is
|
|
// materialized by a loop header phi, the expression cannot have any post-loop
|
|
// operands, so they must dominate the loop header.
|
|
assert(SE->properlyDominates(AddRec->getStart(), L->getHeader()) &&
|
|
SE->properlyDominates(AddRec->getStepRecurrence(*SE), L->getHeader())
|
|
&& "Loop header phi recurrence inputs do not dominate the loop");
|
|
|
|
// The rewriter provides a value for the desired IV expression. This may
|
|
// either find an existing phi or materialize a new one. Either way, we
|
|
// expect a well-formed cyclic phi-with-increments. i.e. any operand not part
|
|
// of the phi-SCC dominates the loop entry.
|
|
Instruction *InsertPt = L->getHeader()->begin();
|
|
WidePhi = cast<PHINode>(Rewriter.expandCodeFor(AddRec, WideType, InsertPt));
|
|
|
|
// Remembering the WideIV increment generated by SCEVExpander allows
|
|
// WidenIVUse to reuse it when widening the narrow IV's increment. We don't
|
|
// employ a general reuse mechanism because the call above is the only call to
|
|
// SCEVExpander. Henceforth, we produce 1-to-1 narrow to wide uses.
|
|
if (BasicBlock *LatchBlock = L->getLoopLatch()) {
|
|
WideInc =
|
|
cast<Instruction>(WidePhi->getIncomingValueForBlock(LatchBlock));
|
|
WideIncExpr = SE->getSCEV(WideInc);
|
|
}
|
|
|
|
DEBUG(dbgs() << "Wide IV: " << *WidePhi << "\n");
|
|
++NumWidened;
|
|
|
|
// Traverse the def-use chain using a worklist starting at the original IV.
|
|
assert(Widened.empty() && NarrowIVUsers.empty() && "expect initial state" );
|
|
|
|
Widened.insert(OrigPhi);
|
|
pushNarrowIVUsers(OrigPhi, WidePhi);
|
|
|
|
while (!NarrowIVUsers.empty()) {
|
|
NarrowIVDefUse DU = NarrowIVUsers.pop_back_val();
|
|
|
|
// Process a def-use edge. This may replace the use, so don't hold a
|
|
// use_iterator across it.
|
|
Instruction *WideUse = WidenIVUse(DU, Rewriter);
|
|
|
|
// Follow all def-use edges from the previous narrow use.
|
|
if (WideUse)
|
|
pushNarrowIVUsers(DU.NarrowUse, WideUse);
|
|
|
|
// WidenIVUse may have removed the def-use edge.
|
|
if (DU.NarrowDef->use_empty())
|
|
DeadInsts.push_back(DU.NarrowDef);
|
|
}
|
|
return WidePhi;
|
|
}
|
|
|
|
//===----------------------------------------------------------------------===//
|
|
// Simplification of IV users based on SCEV evaluation.
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
|
|
/// SimplifyAndExtend - Iteratively perform simplification on a worklist of IV
|
|
/// users. Each successive simplification may push more users which may
|
|
/// themselves be candidates for simplification.
|
|
///
|
|
/// Sign/Zero extend elimination is interleaved with IV simplification.
|
|
///
|
|
void IndVarSimplify::SimplifyAndExtend(Loop *L,
|
|
SCEVExpander &Rewriter,
|
|
LPPassManager &LPM) {
|
|
SmallVector<WideIVInfo, 8> WideIVs;
|
|
|
|
SmallVector<PHINode*, 8> LoopPhis;
|
|
for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I) {
|
|
LoopPhis.push_back(cast<PHINode>(I));
|
|
}
|
|
// Each round of simplification iterates through the SimplifyIVUsers worklist
|
|
// for all current phis, then determines whether any IVs can be
|
|
// widened. Widening adds new phis to LoopPhis, inducing another round of
|
|
// simplification on the wide IVs.
|
|
while (!LoopPhis.empty()) {
|
|
// Evaluate as many IV expressions as possible before widening any IVs. This
|
|
// forces SCEV to set no-wrap flags before evaluating sign/zero
|
|
// extension. The first time SCEV attempts to normalize sign/zero extension,
|
|
// the result becomes final. So for the most predictable results, we delay
|
|
// evaluation of sign/zero extend evaluation until needed, and avoid running
|
|
// other SCEV based analysis prior to SimplifyAndExtend.
|
|
do {
|
|
PHINode *CurrIV = LoopPhis.pop_back_val();
|
|
|
|
// Information about sign/zero extensions of CurrIV.
|
|
WideIVVisitor WIV(CurrIV, SE, TD);
|
|
|
|
Changed |= simplifyUsersOfIV(CurrIV, SE, &LPM, DeadInsts, &WIV);
|
|
|
|
if (WIV.WI.WidestNativeType) {
|
|
WideIVs.push_back(WIV.WI);
|
|
}
|
|
} while(!LoopPhis.empty());
|
|
|
|
for (; !WideIVs.empty(); WideIVs.pop_back()) {
|
|
WidenIV Widener(WideIVs.back(), LI, SE, DT, DeadInsts);
|
|
if (PHINode *WidePhi = Widener.CreateWideIV(Rewriter)) {
|
|
Changed = true;
|
|
LoopPhis.push_back(WidePhi);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
//===----------------------------------------------------------------------===//
|
|
// LinearFunctionTestReplace and its kin. Rewrite the loop exit condition.
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
/// Check for expressions that ScalarEvolution generates to compute
|
|
/// BackedgeTakenInfo. If these expressions have not been reduced, then
|
|
/// expanding them may incur additional cost (albeit in the loop preheader).
|
|
static bool isHighCostExpansion(const SCEV *S, BranchInst *BI,
|
|
SmallPtrSet<const SCEV*, 8> &Processed,
|
|
ScalarEvolution *SE) {
|
|
if (!Processed.insert(S))
|
|
return false;
|
|
|
|
// If the backedge-taken count is a UDiv, it's very likely a UDiv that
|
|
// ScalarEvolution's HowFarToZero or HowManyLessThans produced to compute a
|
|
// precise expression, rather than a UDiv from the user's code. If we can't
|
|
// find a UDiv in the code with some simple searching, assume the former and
|
|
// forego rewriting the loop.
|
|
if (isa<SCEVUDivExpr>(S)) {
|
|
ICmpInst *OrigCond = dyn_cast<ICmpInst>(BI->getCondition());
|
|
if (!OrigCond) return true;
|
|
const SCEV *R = SE->getSCEV(OrigCond->getOperand(1));
|
|
R = SE->getMinusSCEV(R, SE->getConstant(R->getType(), 1));
|
|
if (R != S) {
|
|
const SCEV *L = SE->getSCEV(OrigCond->getOperand(0));
|
|
L = SE->getMinusSCEV(L, SE->getConstant(L->getType(), 1));
|
|
if (L != S)
|
|
return true;
|
|
}
|
|
}
|
|
|
|
// Recurse past add expressions, which commonly occur in the
|
|
// BackedgeTakenCount. They may already exist in program code, and if not,
|
|
// they are not too expensive rematerialize.
|
|
if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
|
|
for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end();
|
|
I != E; ++I) {
|
|
if (isHighCostExpansion(*I, BI, Processed, SE))
|
|
return true;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
// HowManyLessThans uses a Max expression whenever the loop is not guarded by
|
|
// the exit condition.
|
|
if (isa<SCEVSMaxExpr>(S) || isa<SCEVUMaxExpr>(S))
|
|
return true;
|
|
|
|
// If we haven't recognized an expensive SCEV pattern, assume it's an
|
|
// expression produced by program code.
|
|
return false;
|
|
}
|
|
|
|
/// canExpandBackedgeTakenCount - Return true if this loop's backedge taken
|
|
/// count expression can be safely and cheaply expanded into an instruction
|
|
/// sequence that can be used by LinearFunctionTestReplace.
|
|
///
|
|
/// TODO: This fails for pointer-type loop counters with greater than one byte
|
|
/// strides, consequently preventing LFTR from running. For the purpose of LFTR
|
|
/// we could skip this check in the case that the LFTR loop counter (chosen by
|
|
/// FindLoopCounter) is also pointer type. Instead, we could directly convert
|
|
/// the loop test to an inequality test by checking the target data's alignment
|
|
/// of element types (given that the initial pointer value originates from or is
|
|
/// used by ABI constrained operation, as opposed to inttoptr/ptrtoint).
|
|
/// However, we don't yet have a strong motivation for converting loop tests
|
|
/// into inequality tests.
|
|
static bool canExpandBackedgeTakenCount(Loop *L, ScalarEvolution *SE) {
|
|
const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L);
|
|
if (isa<SCEVCouldNotCompute>(BackedgeTakenCount) ||
|
|
BackedgeTakenCount->isZero())
|
|
return false;
|
|
|
|
if (!L->getExitingBlock())
|
|
return false;
|
|
|
|
// Can't rewrite non-branch yet.
|
|
BranchInst *BI = dyn_cast<BranchInst>(L->getExitingBlock()->getTerminator());
|
|
if (!BI)
|
|
return false;
|
|
|
|
SmallPtrSet<const SCEV*, 8> Processed;
|
|
if (isHighCostExpansion(BackedgeTakenCount, BI, Processed, SE))
|
|
return false;
|
|
|
|
return true;
|
|
}
|
|
|
|
/// getLoopPhiForCounter - Return the loop header phi IFF IncV adds a loop
|
|
/// invariant value to the phi.
|
|
static PHINode *getLoopPhiForCounter(Value *IncV, Loop *L, DominatorTree *DT) {
|
|
Instruction *IncI = dyn_cast<Instruction>(IncV);
|
|
if (!IncI)
|
|
return 0;
|
|
|
|
switch (IncI->getOpcode()) {
|
|
case Instruction::Add:
|
|
case Instruction::Sub:
|
|
break;
|
|
case Instruction::GetElementPtr:
|
|
// An IV counter must preserve its type.
|
|
if (IncI->getNumOperands() == 2)
|
|
break;
|
|
default:
|
|
return 0;
|
|
}
|
|
|
|
PHINode *Phi = dyn_cast<PHINode>(IncI->getOperand(0));
|
|
if (Phi && Phi->getParent() == L->getHeader()) {
|
|
if (isLoopInvariant(IncI->getOperand(1), L, DT))
|
|
return Phi;
|
|
return 0;
|
|
}
|
|
if (IncI->getOpcode() == Instruction::GetElementPtr)
|
|
return 0;
|
|
|
|
// Allow add/sub to be commuted.
|
|
Phi = dyn_cast<PHINode>(IncI->getOperand(1));
|
|
if (Phi && Phi->getParent() == L->getHeader()) {
|
|
if (isLoopInvariant(IncI->getOperand(0), L, DT))
|
|
return Phi;
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
/// needsLFTR - LinearFunctionTestReplace policy. Return true unless we can show
|
|
/// that the current exit test is already sufficiently canonical.
|
|
static bool needsLFTR(Loop *L, DominatorTree *DT) {
|
|
assert(L->getExitingBlock() && "expected loop exit");
|
|
|
|
BasicBlock *LatchBlock = L->getLoopLatch();
|
|
// Don't bother with LFTR if the loop is not properly simplified.
|
|
if (!LatchBlock)
|
|
return false;
|
|
|
|
BranchInst *BI = dyn_cast<BranchInst>(L->getExitingBlock()->getTerminator());
|
|
assert(BI && "expected exit branch");
|
|
|
|
// Do LFTR to simplify the exit condition to an ICMP.
|
|
ICmpInst *Cond = dyn_cast<ICmpInst>(BI->getCondition());
|
|
if (!Cond)
|
|
return true;
|
|
|
|
// Do LFTR to simplify the exit ICMP to EQ/NE
|
|
ICmpInst::Predicate Pred = Cond->getPredicate();
|
|
if (Pred != ICmpInst::ICMP_NE && Pred != ICmpInst::ICMP_EQ)
|
|
return true;
|
|
|
|
// Look for a loop invariant RHS
|
|
Value *LHS = Cond->getOperand(0);
|
|
Value *RHS = Cond->getOperand(1);
|
|
if (!isLoopInvariant(RHS, L, DT)) {
|
|
if (!isLoopInvariant(LHS, L, DT))
|
|
return true;
|
|
std::swap(LHS, RHS);
|
|
}
|
|
// Look for a simple IV counter LHS
|
|
PHINode *Phi = dyn_cast<PHINode>(LHS);
|
|
if (!Phi)
|
|
Phi = getLoopPhiForCounter(LHS, L, DT);
|
|
|
|
if (!Phi)
|
|
return true;
|
|
|
|
// Do LFTR if the exit condition's IV is *not* a simple counter.
|
|
Value *IncV = Phi->getIncomingValueForBlock(L->getLoopLatch());
|
|
return Phi != getLoopPhiForCounter(IncV, L, DT);
|
|
}
|
|
|
|
/// AlmostDeadIV - Return true if this IV has any uses other than the (soon to
|
|
/// be rewritten) loop exit test.
|
|
static bool AlmostDeadIV(PHINode *Phi, BasicBlock *LatchBlock, Value *Cond) {
|
|
int LatchIdx = Phi->getBasicBlockIndex(LatchBlock);
|
|
Value *IncV = Phi->getIncomingValue(LatchIdx);
|
|
|
|
for (Value::use_iterator UI = Phi->use_begin(), UE = Phi->use_end();
|
|
UI != UE; ++UI) {
|
|
if (*UI != Cond && *UI != IncV) return false;
|
|
}
|
|
|
|
for (Value::use_iterator UI = IncV->use_begin(), UE = IncV->use_end();
|
|
UI != UE; ++UI) {
|
|
if (*UI != Cond && *UI != Phi) return false;
|
|
}
|
|
return true;
|
|
}
|
|
|
|
/// FindLoopCounter - Find an affine IV in canonical form.
|
|
///
|
|
/// BECount may be an i8* pointer type. The pointer difference is already
|
|
/// valid count without scaling the address stride, so it remains a pointer
|
|
/// expression as far as SCEV is concerned.
|
|
///
|
|
/// FIXME: Accept -1 stride and set IVLimit = IVInit - BECount
|
|
///
|
|
/// FIXME: Accept non-unit stride as long as SCEV can reduce BECount * Stride.
|
|
/// This is difficult in general for SCEV because of potential overflow. But we
|
|
/// could at least handle constant BECounts.
|
|
static PHINode *
|
|
FindLoopCounter(Loop *L, const SCEV *BECount,
|
|
ScalarEvolution *SE, DominatorTree *DT, const TargetData *TD) {
|
|
uint64_t BCWidth = SE->getTypeSizeInBits(BECount->getType());
|
|
|
|
Value *Cond =
|
|
cast<BranchInst>(L->getExitingBlock()->getTerminator())->getCondition();
|
|
|
|
// Loop over all of the PHI nodes, looking for a simple counter.
|
|
PHINode *BestPhi = 0;
|
|
const SCEV *BestInit = 0;
|
|
BasicBlock *LatchBlock = L->getLoopLatch();
|
|
assert(LatchBlock && "needsLFTR should guarantee a loop latch");
|
|
|
|
for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I) {
|
|
PHINode *Phi = cast<PHINode>(I);
|
|
if (!SE->isSCEVable(Phi->getType()))
|
|
continue;
|
|
|
|
// Avoid comparing an integer IV against a pointer Limit.
|
|
if (BECount->getType()->isPointerTy() && !Phi->getType()->isPointerTy())
|
|
continue;
|
|
|
|
const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(Phi));
|
|
if (!AR || AR->getLoop() != L || !AR->isAffine())
|
|
continue;
|
|
|
|
// AR may be a pointer type, while BECount is an integer type.
|
|
// AR may be wider than BECount. With eq/ne tests overflow is immaterial.
|
|
// AR may not be a narrower type, or we may never exit.
|
|
uint64_t PhiWidth = SE->getTypeSizeInBits(AR->getType());
|
|
if (PhiWidth < BCWidth || (TD && !TD->isLegalInteger(PhiWidth)))
|
|
continue;
|
|
|
|
const SCEV *Step = dyn_cast<SCEVConstant>(AR->getStepRecurrence(*SE));
|
|
if (!Step || !Step->isOne())
|
|
continue;
|
|
|
|
int LatchIdx = Phi->getBasicBlockIndex(LatchBlock);
|
|
Value *IncV = Phi->getIncomingValue(LatchIdx);
|
|
if (getLoopPhiForCounter(IncV, L, DT) != Phi)
|
|
continue;
|
|
|
|
const SCEV *Init = AR->getStart();
|
|
|
|
if (BestPhi && !AlmostDeadIV(BestPhi, LatchBlock, Cond)) {
|
|
// Don't force a live loop counter if another IV can be used.
|
|
if (AlmostDeadIV(Phi, LatchBlock, Cond))
|
|
continue;
|
|
|
|
// Prefer to count-from-zero. This is a more "canonical" counter form. It
|
|
// also prefers integer to pointer IVs.
|
|
if (BestInit->isZero() != Init->isZero()) {
|
|
if (BestInit->isZero())
|
|
continue;
|
|
}
|
|
// If two IVs both count from zero or both count from nonzero then the
|
|
// narrower is likely a dead phi that has been widened. Use the wider phi
|
|
// to allow the other to be eliminated.
|
|
if (PhiWidth <= SE->getTypeSizeInBits(BestPhi->getType()))
|
|
continue;
|
|
}
|
|
BestPhi = Phi;
|
|
BestInit = Init;
|
|
}
|
|
return BestPhi;
|
|
}
|
|
|
|
/// genLoopLimit - Help LinearFunctionTestReplace by generating a value that
|
|
/// holds the RHS of the new loop test.
|
|
static Value *genLoopLimit(PHINode *IndVar, const SCEV *IVCount, Loop *L,
|
|
SCEVExpander &Rewriter, ScalarEvolution *SE) {
|
|
const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(IndVar));
|
|
assert(AR && AR->getLoop() == L && AR->isAffine() && "bad loop counter");
|
|
const SCEV *IVInit = AR->getStart();
|
|
|
|
// IVInit may be a pointer while IVCount is an integer when FindLoopCounter
|
|
// finds a valid pointer IV. Sign extend BECount in order to materialize a
|
|
// GEP. Avoid running SCEVExpander on a new pointer value, instead reusing
|
|
// the existing GEPs whenever possible.
|
|
if (IndVar->getType()->isPointerTy()
|
|
&& !IVCount->getType()->isPointerTy()) {
|
|
|
|
Type *OfsTy = SE->getEffectiveSCEVType(IVInit->getType());
|
|
const SCEV *IVOffset = SE->getTruncateOrSignExtend(IVCount, OfsTy);
|
|
|
|
// Expand the code for the iteration count.
|
|
assert(SE->isLoopInvariant(IVOffset, L) &&
|
|
"Computed iteration count is not loop invariant!");
|
|
BranchInst *BI = cast<BranchInst>(L->getExitingBlock()->getTerminator());
|
|
Value *GEPOffset = Rewriter.expandCodeFor(IVOffset, OfsTy, BI);
|
|
|
|
Value *GEPBase = IndVar->getIncomingValueForBlock(L->getLoopPreheader());
|
|
assert(AR->getStart() == SE->getSCEV(GEPBase) && "bad loop counter");
|
|
// We could handle pointer IVs other than i8*, but we need to compensate for
|
|
// gep index scaling. See canExpandBackedgeTakenCount comments.
|
|
assert(SE->getSizeOfExpr(
|
|
cast<PointerType>(GEPBase->getType())->getElementType())->isOne()
|
|
&& "unit stride pointer IV must be i8*");
|
|
|
|
IRBuilder<> Builder(L->getLoopPreheader()->getTerminator());
|
|
return Builder.CreateGEP(GEPBase, GEPOffset, "lftr.limit");
|
|
}
|
|
else {
|
|
// In any other case, convert both IVInit and IVCount to integers before
|
|
// comparing. This may result in SCEV expension of pointers, but in practice
|
|
// SCEV will fold the pointer arithmetic away as such:
|
|
// BECount = (IVEnd - IVInit - 1) => IVLimit = IVInit (postinc).
|
|
//
|
|
// Valid Cases: (1) both integers is most common; (2) both may be pointers
|
|
// for simple memset-style loops; (3) IVInit is an integer and IVCount is a
|
|
// pointer may occur when enable-iv-rewrite generates a canonical IV on top
|
|
// of case #2.
|
|
|
|
const SCEV *IVLimit = 0;
|
|
// For unit stride, IVCount = Start + BECount with 2's complement overflow.
|
|
// For non-zero Start, compute IVCount here.
|
|
if (AR->getStart()->isZero())
|
|
IVLimit = IVCount;
|
|
else {
|
|
assert(AR->getStepRecurrence(*SE)->isOne() && "only handles unit stride");
|
|
const SCEV *IVInit = AR->getStart();
|
|
|
|
// For integer IVs, truncate the IV before computing IVInit + BECount.
|
|
if (SE->getTypeSizeInBits(IVInit->getType())
|
|
> SE->getTypeSizeInBits(IVCount->getType()))
|
|
IVInit = SE->getTruncateExpr(IVInit, IVCount->getType());
|
|
|
|
IVLimit = SE->getAddExpr(IVInit, IVCount);
|
|
}
|
|
// Expand the code for the iteration count.
|
|
BranchInst *BI = cast<BranchInst>(L->getExitingBlock()->getTerminator());
|
|
IRBuilder<> Builder(BI);
|
|
assert(SE->isLoopInvariant(IVLimit, L) &&
|
|
"Computed iteration count is not loop invariant!");
|
|
// Ensure that we generate the same type as IndVar, or a smaller integer
|
|
// type. In the presence of null pointer values, we have an integer type
|
|
// SCEV expression (IVInit) for a pointer type IV value (IndVar).
|
|
Type *LimitTy = IVCount->getType()->isPointerTy() ?
|
|
IndVar->getType() : IVCount->getType();
|
|
return Rewriter.expandCodeFor(IVLimit, LimitTy, BI);
|
|
}
|
|
}
|
|
|
|
/// LinearFunctionTestReplace - This method rewrites the exit condition of the
|
|
/// loop to be a canonical != comparison against the incremented loop induction
|
|
/// variable. This pass is able to rewrite the exit tests of any loop where the
|
|
/// SCEV analysis can determine a loop-invariant trip count of the loop, which
|
|
/// is actually a much broader range than just linear tests.
|
|
Value *IndVarSimplify::
|
|
LinearFunctionTestReplace(Loop *L,
|
|
const SCEV *BackedgeTakenCount,
|
|
PHINode *IndVar,
|
|
SCEVExpander &Rewriter) {
|
|
assert(canExpandBackedgeTakenCount(L, SE) && "precondition");
|
|
|
|
// LFTR can ignore IV overflow and truncate to the width of
|
|
// BECount. This avoids materializing the add(zext(add)) expression.
|
|
Type *CntTy = BackedgeTakenCount->getType();
|
|
|
|
const SCEV *IVCount = BackedgeTakenCount;
|
|
|
|
// If the exiting block is the same as the backedge block, we prefer to
|
|
// compare against the post-incremented value, otherwise we must compare
|
|
// against the preincremented value.
|
|
Value *CmpIndVar;
|
|
if (L->getExitingBlock() == L->getLoopLatch()) {
|
|
// Add one to the "backedge-taken" count to get the trip count.
|
|
// If this addition may overflow, we have to be more pessimistic and
|
|
// cast the induction variable before doing the add.
|
|
const SCEV *N =
|
|
SE->getAddExpr(IVCount, SE->getConstant(IVCount->getType(), 1));
|
|
if (CntTy == IVCount->getType())
|
|
IVCount = N;
|
|
else {
|
|
const SCEV *Zero = SE->getConstant(IVCount->getType(), 0);
|
|
if ((isa<SCEVConstant>(N) && !N->isZero()) ||
|
|
SE->isLoopEntryGuardedByCond(L, ICmpInst::ICMP_NE, N, Zero)) {
|
|
// No overflow. Cast the sum.
|
|
IVCount = SE->getTruncateOrZeroExtend(N, CntTy);
|
|
} else {
|
|
// Potential overflow. Cast before doing the add.
|
|
IVCount = SE->getTruncateOrZeroExtend(IVCount, CntTy);
|
|
IVCount = SE->getAddExpr(IVCount, SE->getConstant(CntTy, 1));
|
|
}
|
|
}
|
|
// The BackedgeTaken expression contains the number of times that the
|
|
// backedge branches to the loop header. This is one less than the
|
|
// number of times the loop executes, so use the incremented indvar.
|
|
CmpIndVar = IndVar->getIncomingValueForBlock(L->getExitingBlock());
|
|
} else {
|
|
// We must use the preincremented value...
|
|
IVCount = SE->getTruncateOrZeroExtend(IVCount, CntTy);
|
|
CmpIndVar = IndVar;
|
|
}
|
|
|
|
Value *ExitCnt = genLoopLimit(IndVar, IVCount, L, Rewriter, SE);
|
|
assert(ExitCnt->getType()->isPointerTy() == IndVar->getType()->isPointerTy()
|
|
&& "genLoopLimit missed a cast");
|
|
|
|
// Insert a new icmp_ne or icmp_eq instruction before the branch.
|
|
BranchInst *BI = cast<BranchInst>(L->getExitingBlock()->getTerminator());
|
|
ICmpInst::Predicate P;
|
|
if (L->contains(BI->getSuccessor(0)))
|
|
P = ICmpInst::ICMP_NE;
|
|
else
|
|
P = ICmpInst::ICMP_EQ;
|
|
|
|
DEBUG(dbgs() << "INDVARS: Rewriting loop exit condition to:\n"
|
|
<< " LHS:" << *CmpIndVar << '\n'
|
|
<< " op:\t"
|
|
<< (P == ICmpInst::ICMP_NE ? "!=" : "==") << "\n"
|
|
<< " RHS:\t" << *ExitCnt << "\n"
|
|
<< " IVCount:\t" << *IVCount << "\n");
|
|
|
|
IRBuilder<> Builder(BI);
|
|
if (SE->getTypeSizeInBits(CmpIndVar->getType())
|
|
> SE->getTypeSizeInBits(ExitCnt->getType())) {
|
|
CmpIndVar = Builder.CreateTrunc(CmpIndVar, ExitCnt->getType(),
|
|
"lftr.wideiv");
|
|
}
|
|
|
|
Value *Cond = Builder.CreateICmp(P, CmpIndVar, ExitCnt, "exitcond");
|
|
Value *OrigCond = BI->getCondition();
|
|
// It's tempting to use replaceAllUsesWith here to fully replace the old
|
|
// comparison, but that's not immediately safe, since users of the old
|
|
// comparison may not be dominated by the new comparison. Instead, just
|
|
// update the branch to use the new comparison; in the common case this
|
|
// will make old comparison dead.
|
|
BI->setCondition(Cond);
|
|
DeadInsts.push_back(OrigCond);
|
|
|
|
++NumLFTR;
|
|
Changed = true;
|
|
return Cond;
|
|
}
|
|
|
|
//===----------------------------------------------------------------------===//
|
|
// SinkUnusedInvariants. A late subpass to cleanup loop preheaders.
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
/// If there's a single exit block, sink any loop-invariant values that
|
|
/// were defined in the preheader but not used inside the loop into the
|
|
/// exit block to reduce register pressure in the loop.
|
|
void IndVarSimplify::SinkUnusedInvariants(Loop *L) {
|
|
BasicBlock *ExitBlock = L->getExitBlock();
|
|
if (!ExitBlock) return;
|
|
|
|
BasicBlock *Preheader = L->getLoopPreheader();
|
|
if (!Preheader) return;
|
|
|
|
Instruction *InsertPt = ExitBlock->getFirstInsertionPt();
|
|
BasicBlock::iterator I = Preheader->getTerminator();
|
|
while (I != Preheader->begin()) {
|
|
--I;
|
|
// New instructions were inserted at the end of the preheader.
|
|
if (isa<PHINode>(I))
|
|
break;
|
|
|
|
// Don't move instructions which might have side effects, since the side
|
|
// effects need to complete before instructions inside the loop. Also don't
|
|
// move instructions which might read memory, since the loop may modify
|
|
// memory. Note that it's okay if the instruction might have undefined
|
|
// behavior: LoopSimplify guarantees that the preheader dominates the exit
|
|
// block.
|
|
if (I->mayHaveSideEffects() || I->mayReadFromMemory())
|
|
continue;
|
|
|
|
// Skip debug info intrinsics.
|
|
if (isa<DbgInfoIntrinsic>(I))
|
|
continue;
|
|
|
|
// Skip landingpad instructions.
|
|
if (isa<LandingPadInst>(I))
|
|
continue;
|
|
|
|
// Don't sink alloca: we never want to sink static alloca's out of the
|
|
// entry block, and correctly sinking dynamic alloca's requires
|
|
// checks for stacksave/stackrestore intrinsics.
|
|
// FIXME: Refactor this check somehow?
|
|
if (isa<AllocaInst>(I))
|
|
continue;
|
|
|
|
// Determine if there is a use in or before the loop (direct or
|
|
// otherwise).
|
|
bool UsedInLoop = false;
|
|
for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
|
|
UI != UE; ++UI) {
|
|
User *U = *UI;
|
|
BasicBlock *UseBB = cast<Instruction>(U)->getParent();
|
|
if (PHINode *P = dyn_cast<PHINode>(U)) {
|
|
unsigned i =
|
|
PHINode::getIncomingValueNumForOperand(UI.getOperandNo());
|
|
UseBB = P->getIncomingBlock(i);
|
|
}
|
|
if (UseBB == Preheader || L->contains(UseBB)) {
|
|
UsedInLoop = true;
|
|
break;
|
|
}
|
|
}
|
|
|
|
// If there is, the def must remain in the preheader.
|
|
if (UsedInLoop)
|
|
continue;
|
|
|
|
// Otherwise, sink it to the exit block.
|
|
Instruction *ToMove = I;
|
|
bool Done = false;
|
|
|
|
if (I != Preheader->begin()) {
|
|
// Skip debug info intrinsics.
|
|
do {
|
|
--I;
|
|
} while (isa<DbgInfoIntrinsic>(I) && I != Preheader->begin());
|
|
|
|
if (isa<DbgInfoIntrinsic>(I) && I == Preheader->begin())
|
|
Done = true;
|
|
} else {
|
|
Done = true;
|
|
}
|
|
|
|
ToMove->moveBefore(InsertPt);
|
|
if (Done) break;
|
|
InsertPt = ToMove;
|
|
}
|
|
}
|
|
|
|
//===----------------------------------------------------------------------===//
|
|
// IndVarSimplify driver. Manage several subpasses of IV simplification.
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
|
|
// If LoopSimplify form is not available, stay out of trouble. Some notes:
|
|
// - LSR currently only supports LoopSimplify-form loops. Indvars'
|
|
// canonicalization can be a pessimization without LSR to "clean up"
|
|
// afterwards.
|
|
// - We depend on having a preheader; in particular,
|
|
// Loop::getCanonicalInductionVariable only supports loops with preheaders,
|
|
// and we're in trouble if we can't find the induction variable even when
|
|
// we've manually inserted one.
|
|
if (!L->isLoopSimplifyForm())
|
|
return false;
|
|
|
|
LI = &getAnalysis<LoopInfo>();
|
|
SE = &getAnalysis<ScalarEvolution>();
|
|
DT = &getAnalysis<DominatorTree>();
|
|
TD = getAnalysisIfAvailable<TargetData>();
|
|
|
|
DeadInsts.clear();
|
|
Changed = false;
|
|
|
|
// If there are any floating-point recurrences, attempt to
|
|
// transform them to use integer recurrences.
|
|
RewriteNonIntegerIVs(L);
|
|
|
|
const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L);
|
|
|
|
// Create a rewriter object which we'll use to transform the code with.
|
|
SCEVExpander Rewriter(*SE, "indvars");
|
|
#ifndef NDEBUG
|
|
Rewriter.setDebugType(DEBUG_TYPE);
|
|
#endif
|
|
|
|
// Eliminate redundant IV users.
|
|
//
|
|
// Simplification works best when run before other consumers of SCEV. We
|
|
// attempt to avoid evaluating SCEVs for sign/zero extend operations until
|
|
// other expressions involving loop IVs have been evaluated. This helps SCEV
|
|
// set no-wrap flags before normalizing sign/zero extension.
|
|
Rewriter.disableCanonicalMode();
|
|
SimplifyAndExtend(L, Rewriter, LPM);
|
|
|
|
// 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.
|
|
//
|
|
if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount))
|
|
RewriteLoopExitValues(L, Rewriter);
|
|
|
|
// Eliminate redundant IV cycles.
|
|
NumElimIV += Rewriter.replaceCongruentIVs(L, DT, DeadInsts);
|
|
|
|
// 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.
|
|
if (canExpandBackedgeTakenCount(L, SE) && needsLFTR(L, DT)) {
|
|
PHINode *IndVar = FindLoopCounter(L, BackedgeTakenCount, SE, DT, TD);
|
|
if (IndVar) {
|
|
// Check preconditions for proper SCEVExpander operation. SCEV does not
|
|
// express SCEVExpander's dependencies, such as LoopSimplify. Instead any
|
|
// pass that uses the SCEVExpander must do it. This does not work well for
|
|
// loop passes because SCEVExpander makes assumptions about all loops, while
|
|
// LoopPassManager only forces the current loop to be simplified.
|
|
//
|
|
// FIXME: SCEV expansion has no way to bail out, so the caller must
|
|
// explicitly check any assumptions made by SCEV. Brittle.
|
|
const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(BackedgeTakenCount);
|
|
if (!AR || AR->getLoop()->getLoopPreheader())
|
|
(void)LinearFunctionTestReplace(L, BackedgeTakenCount, IndVar,
|
|
Rewriter);
|
|
}
|
|
}
|
|
// Clear the rewriter cache, because values that are in the rewriter's cache
|
|
// can be deleted in the loop below, causing the AssertingVH in the cache to
|
|
// trigger.
|
|
Rewriter.clear();
|
|
|
|
// Now that we're done iterating through lists, clean up any instructions
|
|
// which are now dead.
|
|
while (!DeadInsts.empty())
|
|
if (Instruction *Inst =
|
|
dyn_cast_or_null<Instruction>(&*DeadInsts.pop_back_val()))
|
|
RecursivelyDeleteTriviallyDeadInstructions(Inst);
|
|
|
|
// The Rewriter may not be used from this point on.
|
|
|
|
// Loop-invariant instructions in the preheader that aren't used in the
|
|
// loop may be sunk below the loop to reduce register pressure.
|
|
SinkUnusedInvariants(L);
|
|
|
|
// Clean up dead instructions.
|
|
Changed |= DeleteDeadPHIs(L->getHeader());
|
|
// Check a post-condition.
|
|
assert(L->isLCSSAForm(*DT) &&
|
|
"Indvars did not leave the loop in lcssa form!");
|
|
|
|
// Verify that LFTR, and any other change have not interfered with SCEV's
|
|
// ability to compute trip count.
|
|
#ifndef NDEBUG
|
|
if (VerifyIndvars && !isa<SCEVCouldNotCompute>(BackedgeTakenCount)) {
|
|
SE->forgetLoop(L);
|
|
const SCEV *NewBECount = SE->getBackedgeTakenCount(L);
|
|
if (SE->getTypeSizeInBits(BackedgeTakenCount->getType()) <
|
|
SE->getTypeSizeInBits(NewBECount->getType()))
|
|
NewBECount = SE->getTruncateOrNoop(NewBECount,
|
|
BackedgeTakenCount->getType());
|
|
else
|
|
BackedgeTakenCount = SE->getTruncateOrNoop(BackedgeTakenCount,
|
|
NewBECount->getType());
|
|
assert(BackedgeTakenCount == NewBECount && "indvars must preserve SCEV");
|
|
}
|
|
#endif
|
|
|
|
return Changed;
|
|
}
|