IndVarSimplify.cpp revision 4dfdf242c1917e98f407818eb5b68ae0b4678f26
1c91307af2622f6625525f3c1f9c954376df950adChia-chi Yeh//===- IndVarSimplify.cpp - Induction Variable Elimination ----------------===// 20a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang// 30a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang// The LLVM Compiler Infrastructure 40a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang// 50a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang// This file is distributed under the University of Illinois Open Source 60a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang// License. See LICENSE.TXT for details. 70a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang// 80a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang//===----------------------------------------------------------------------===// 90a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang// 100a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang// This transformation analyzes and transforms the induction variables (and 110a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang// computations derived from them) into simpler forms suitable for subsequent 120a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang// analysis and transformation. 130a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang// 140a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang// This transformation makes the following changes to each loop with an 150a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang// identifiable induction variable: 160a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang// 1. All loops are transformed to have a SINGLE canonical induction variable 170a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang// which starts at zero and steps by one. 180a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang// 2. The canonical induction variable is guaranteed to be the first PHI node 190a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang// in the loop header block. 200a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang// 3. The canonical induction variable is guaranteed to be in a wide enough 210a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang// type so that IV expressions need not be (directly) zero-extended or 220a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang// sign-extended. 230a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang// 4. Any pointer arithmetic recurrences are raised to use array subscripts. 240a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang// 250a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang// If the trip count of a loop is computable, this pass also makes the following 260a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang// changes: 270a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang// 1. The exit condition for the loop is canonicalized to compare the 280a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang// induction value against the exit value. This turns loops like: 290a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang// 'for (i = 7; i*i < 1000; ++i)' into 'for (i = 0; i != 25; ++i)' 300a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang// 2. Any use outside of the loop of an expression derived from the indvar 310a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang// is changed to compute the derived value outside of the loop, eliminating 320a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang// the dependence on the exit value of the induction variable. If the only 330a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang// purpose of the loop is to compute the exit value of some derived 340a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang// expression, this transformation will make the loop dead. 350a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang// 360a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang// This transformation should be followed by strength reduction after all of the 370a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang// desired loop transformations have been performed. 380a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang// 390a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang//===----------------------------------------------------------------------===// 400a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang 410a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang#define DEBUG_TYPE "indvars" 420a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang#include "llvm/Transforms/Scalar.h" 430a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang#include "llvm/BasicBlock.h" 440a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang#include "llvm/Constants.h" 450a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang#include "llvm/Instructions.h" 460a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang#include "llvm/IntrinsicInst.h" 470a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang#include "llvm/LLVMContext.h" 480a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang#include "llvm/Type.h" 490a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang#include "llvm/Analysis/Dominators.h" 500a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang#include "llvm/Analysis/IVUsers.h" 510a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang#include "llvm/Analysis/ScalarEvolutionExpander.h" 520a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang#include "llvm/Analysis/LoopInfo.h" 530a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang#include "llvm/Analysis/LoopPass.h" 540a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang#include "llvm/Support/CFG.h" 550a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang#include "llvm/Support/CommandLine.h" 560a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang#include "llvm/Support/Debug.h" 570a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang#include "llvm/Support/raw_ostream.h" 580a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang#include "llvm/Transforms/Utils/Local.h" 590a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang#include "llvm/Transforms/Utils/BasicBlockUtils.h" 600a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang#include "llvm/ADT/SmallVector.h" 610a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang#include "llvm/ADT/Statistic.h" 620a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang#include "llvm/ADT/STLExtras.h" 630a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wangusing namespace llvm; 640a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang 650a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih WangSTATISTIC(NumRemoved , "Number of aux indvars removed"); 660a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih WangSTATISTIC(NumInserted, "Number of canonical indvars added"); 670a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih WangSTATISTIC(NumReplaced, "Number of exit values replaced"); 680a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih WangSTATISTIC(NumLFTR , "Number of loop exit tests replaced"); 690a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang 700a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wangnamespace { 710a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang class IndVarSimplify : public LoopPass { 720a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang IVUsers *IU; 730a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang LoopInfo *LI; 740a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang ScalarEvolution *SE; 750a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang DominatorTree *DT; 760a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang SmallVector<WeakVH, 16> DeadInsts; 770a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang bool Changed; 780a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang public: 790a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang 800a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang static char ID; // Pass identification, replacement for typeid 810a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang IndVarSimplify() : LoopPass(ID) { 820a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang initializeIndVarSimplifyPass(*PassRegistry::getPassRegistry()); 830a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang } 840a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang 850a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang virtual bool runOnLoop(Loop *L, LPPassManager &LPM); 860a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang 870a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang virtual void getAnalysisUsage(AnalysisUsage &AU) const { 880a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang AU.addRequired<DominatorTree>(); 890a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang AU.addRequired<LoopInfo>(); 900a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang AU.addRequired<ScalarEvolution>(); 91c91307af2622f6625525f3c1f9c954376df950adChia-chi Yeh AU.addRequiredID(LoopSimplifyID); 920a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang AU.addRequiredID(LCSSAID); 930a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang AU.addRequired<IVUsers>(); 940a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang AU.addPreserved<ScalarEvolution>(); 950a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang AU.addPreservedID(LoopSimplifyID); 960a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang AU.addPreservedID(LCSSAID); 970a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang AU.addPreserved<IVUsers>(); 980a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang AU.setPreservesCFG(); 990a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang } 1000a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang 1010a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang private: 1020a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang bool isValidRewrite(Value *FromVal, Value *ToVal); 1030a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang 1040a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang void EliminateIVComparisons(); 1050a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang void EliminateIVRemainders(); 1060a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang void RewriteNonIntegerIVs(Loop *L); 1070a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang 1080a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang bool canExpandBackedgeTakenCount(Loop *L, 1090a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang const SCEV *BackedgeTakenCount); 1100a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang 1110a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang ICmpInst *LinearFunctionTestReplace(Loop *L, const SCEV *BackedgeTakenCount, 1120a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang PHINode *IndVar, 1130a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang SCEVExpander &Rewriter); 1140a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang void RewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter); 1150a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang 1160a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang void RewriteIVExpressions(Loop *L, SCEVExpander &Rewriter); 1170a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang 1180a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang void SinkUnusedInvariants(Loop *L); 1190a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang 1200a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang void HandleFloatingPointIV(Loop *L, PHINode *PH); 1210a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang }; 1220a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang} 1230a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang 1240a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wangchar IndVarSimplify::ID = 0; 1250a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih WangINITIALIZE_PASS_BEGIN(IndVarSimplify, "indvars", 1260a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang "Canonicalize Induction Variables", false, false) 1270a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih WangINITIALIZE_PASS_DEPENDENCY(DominatorTree) 1280a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih WangINITIALIZE_PASS_DEPENDENCY(LoopInfo) 1290a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih WangINITIALIZE_PASS_DEPENDENCY(ScalarEvolution) 1300a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih WangINITIALIZE_PASS_DEPENDENCY(LoopSimplify) 1310a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih WangINITIALIZE_PASS_DEPENDENCY(LCSSA) 1320a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih WangINITIALIZE_PASS_DEPENDENCY(IVUsers) 1330a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih WangINITIALIZE_PASS_END(IndVarSimplify, "indvars", 1340a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang "Canonicalize Induction Variables", false, false) 1350a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang 1360a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih WangPass *llvm::createIndVarSimplifyPass() { 1370a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang return new IndVarSimplify(); 1380a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang} 1390a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang 1400a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang/// isValidRewrite - Return true if the SCEV expansion generated by the 1410a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang/// rewriter can replace the original value. SCEV guarantees that it 1420a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang/// produces the same value, but the way it is produced may be illegal IR. 1430a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang/// Ideally, this function will only be called for verification. 1440a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wangbool IndVarSimplify::isValidRewrite(Value *FromVal, Value *ToVal) { 1450a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang // If an SCEV expression subsumed multiple pointers, its expansion could 1460a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang // reassociate the GEP changing the base pointer. This is illegal because the 1470a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang // final address produced by a GEP chain must be inbounds relative to its 1480a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang // underlying object. Otherwise basic alias analysis, among other things, 1490a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang // could fail in a dangerous way. Ultimately, SCEV will be improved to avoid 1500a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang // producing an expression involving multiple pointers. Until then, we must 1510a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang // bail out here. 1520a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang // 1530a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang // Retrieve the pointer operand of the GEP. Don't use GetUnderlyingObject 1540a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang // because it understands lcssa phis while SCEV does not. 1550a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang Value *FromPtr = FromVal; 1560a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang Value *ToPtr = ToVal; 1570a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang if (GEPOperator *GEP = dyn_cast<GEPOperator>(FromVal)) { 1580a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang FromPtr = GEP->getPointerOperand(); 1590a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang } 1600a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang if (GEPOperator *GEP = dyn_cast<GEPOperator>(ToVal)) { 1610a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang ToPtr = GEP->getPointerOperand(); 1620a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang } 1630a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang if (FromPtr != FromVal || ToPtr != ToVal) { 1640a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang // Quickly check the common case 1650a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang if (FromPtr == ToPtr) 1660a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang return true; 1670a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang 1680a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang // SCEV may have rewritten an expression that produces the GEP's pointer 1690a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang // operand. That's ok as long as the pointer operand has the same base 1700a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang // pointer. Unlike GetUnderlyingObject(), getPointerBase() will find the 1710a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang // base of a recurrence. This handles the case in which SCEV expansion 1720a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang // converts a pointer type recurrence into a nonrecurrent pointer base 1730a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang // indexed by an integer recurrence. 1740a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang const SCEV *FromBase = SE->getPointerBase(SE->getSCEV(FromPtr)); 1750a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang const SCEV *ToBase = SE->getPointerBase(SE->getSCEV(ToPtr)); 1760a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang if (FromBase == ToBase) 1770a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang return true; 1780a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang 1790a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang DEBUG(dbgs() << "INDVARS: GEP rewrite bail out " 1800a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang << *FromBase << " != " << *ToBase << "\n"); 1810a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang 1820a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang return false; 1830a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang } 1840a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang return true; 1850a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang} 1860a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang 1870a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang/// canExpandBackedgeTakenCount - Return true if this loop's backedge taken 1880a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang/// count expression can be safely and cheaply expanded into an instruction 1890a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang/// sequence that can be used by LinearFunctionTestReplace. 1900a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wangbool IndVarSimplify:: 1910a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih WangcanExpandBackedgeTakenCount(Loop *L, 1920a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang const SCEV *BackedgeTakenCount) { 1930a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang if (isa<SCEVCouldNotCompute>(BackedgeTakenCount) || 1940a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang BackedgeTakenCount->isZero()) 1950a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang return false; 1960a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang 1970a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang if (!L->getExitingBlock()) 1980a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang return false; 1990a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang 2000a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang // Can't rewrite non-branch yet. 2010a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang BranchInst *BI = dyn_cast<BranchInst>(L->getExitingBlock()->getTerminator()); 2020a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang if (!BI) 2030a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang return false; 2040a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang 2050a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang // Special case: If the backedge-taken count is a UDiv, it's very likely a 2060a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang // UDiv that ScalarEvolution produced in order to compute a precise 2070a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang // expression, rather than a UDiv from the user's code. If we can't find a 2080a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang // UDiv in the code with some simple searching, assume the former and forego 2090a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang // rewriting the loop. 2100a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang if (isa<SCEVUDivExpr>(BackedgeTakenCount)) { 2110a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang ICmpInst *OrigCond = dyn_cast<ICmpInst>(BI->getCondition()); 2120a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang if (!OrigCond) return 0; 2130a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang const SCEV *R = SE->getSCEV(OrigCond->getOperand(1)); 2140a1907d434839af6a9cb6329bbde60b237bf53dcChung-yih Wang R = SE->getMinusSCEV(R, SE->getConstant(R->getType(), 1)); 215 if (R != BackedgeTakenCount) { 216 const SCEV *L = SE->getSCEV(OrigCond->getOperand(0)); 217 L = SE->getMinusSCEV(L, SE->getConstant(L->getType(), 1)); 218 if (L != BackedgeTakenCount) 219 return false; 220 } 221 } 222 return true; 223} 224 225/// LinearFunctionTestReplace - This method rewrites the exit condition of the 226/// loop to be a canonical != comparison against the incremented loop induction 227/// variable. This pass is able to rewrite the exit tests of any loop where the 228/// SCEV analysis can determine a loop-invariant trip count of the loop, which 229/// is actually a much broader range than just linear tests. 230ICmpInst *IndVarSimplify:: 231LinearFunctionTestReplace(Loop *L, 232 const SCEV *BackedgeTakenCount, 233 PHINode *IndVar, 234 SCEVExpander &Rewriter) { 235 assert(canExpandBackedgeTakenCount(L, BackedgeTakenCount) && "precondition"); 236 BranchInst *BI = cast<BranchInst>(L->getExitingBlock()->getTerminator()); 237 238 // If the exiting block is not the same as the backedge block, we must compare 239 // against the preincremented value, otherwise we prefer to compare against 240 // the post-incremented value. 241 Value *CmpIndVar; 242 const SCEV *RHS = BackedgeTakenCount; 243 if (L->getExitingBlock() == L->getLoopLatch()) { 244 // Add one to the "backedge-taken" count to get the trip count. 245 // If this addition may overflow, we have to be more pessimistic and 246 // cast the induction variable before doing the add. 247 const SCEV *Zero = SE->getConstant(BackedgeTakenCount->getType(), 0); 248 const SCEV *N = 249 SE->getAddExpr(BackedgeTakenCount, 250 SE->getConstant(BackedgeTakenCount->getType(), 1)); 251 if ((isa<SCEVConstant>(N) && !N->isZero()) || 252 SE->isLoopEntryGuardedByCond(L, ICmpInst::ICMP_NE, N, Zero)) { 253 // No overflow. Cast the sum. 254 RHS = SE->getTruncateOrZeroExtend(N, IndVar->getType()); 255 } else { 256 // Potential overflow. Cast before doing the add. 257 RHS = SE->getTruncateOrZeroExtend(BackedgeTakenCount, 258 IndVar->getType()); 259 RHS = SE->getAddExpr(RHS, 260 SE->getConstant(IndVar->getType(), 1)); 261 } 262 263 // The BackedgeTaken expression contains the number of times that the 264 // backedge branches to the loop header. This is one less than the 265 // number of times the loop executes, so use the incremented indvar. 266 CmpIndVar = IndVar->getIncomingValueForBlock(L->getExitingBlock()); 267 } else { 268 // We have to use the preincremented value... 269 RHS = SE->getTruncateOrZeroExtend(BackedgeTakenCount, 270 IndVar->getType()); 271 CmpIndVar = IndVar; 272 } 273 274 // Expand the code for the iteration count. 275 assert(SE->isLoopInvariant(RHS, L) && 276 "Computed iteration count is not loop invariant!"); 277 Value *ExitCnt = Rewriter.expandCodeFor(RHS, IndVar->getType(), BI); 278 279 // Insert a new icmp_ne or icmp_eq instruction before the branch. 280 ICmpInst::Predicate Opcode; 281 if (L->contains(BI->getSuccessor(0))) 282 Opcode = ICmpInst::ICMP_NE; 283 else 284 Opcode = ICmpInst::ICMP_EQ; 285 286 DEBUG(dbgs() << "INDVARS: Rewriting loop exit condition to:\n" 287 << " LHS:" << *CmpIndVar << '\n' 288 << " op:\t" 289 << (Opcode == ICmpInst::ICMP_NE ? "!=" : "==") << "\n" 290 << " RHS:\t" << *RHS << "\n"); 291 292 ICmpInst *Cond = new ICmpInst(BI, Opcode, CmpIndVar, ExitCnt, "exitcond"); 293 294 Value *OrigCond = BI->getCondition(); 295 // It's tempting to use replaceAllUsesWith here to fully replace the old 296 // comparison, but that's not immediately safe, since users of the old 297 // comparison may not be dominated by the new comparison. Instead, just 298 // update the branch to use the new comparison; in the common case this 299 // will make old comparison dead. 300 BI->setCondition(Cond); 301 DeadInsts.push_back(OrigCond); 302 303 ++NumLFTR; 304 Changed = true; 305 return Cond; 306} 307 308/// RewriteLoopExitValues - Check to see if this loop has a computable 309/// loop-invariant execution count. If so, this means that we can compute the 310/// final value of any expressions that are recurrent in the loop, and 311/// substitute the exit values from the loop into any instructions outside of 312/// the loop that use the final values of the current expressions. 313/// 314/// This is mostly redundant with the regular IndVarSimplify activities that 315/// happen later, except that it's more powerful in some cases, because it's 316/// able to brute-force evaluate arbitrary instructions as long as they have 317/// constant operands at the beginning of the loop. 318void IndVarSimplify::RewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter) { 319 // Verify the input to the pass in already in LCSSA form. 320 assert(L->isLCSSAForm(*DT)); 321 322 SmallVector<BasicBlock*, 8> ExitBlocks; 323 L->getUniqueExitBlocks(ExitBlocks); 324 325 // Find all values that are computed inside the loop, but used outside of it. 326 // Because of LCSSA, these values will only occur in LCSSA PHI Nodes. Scan 327 // the exit blocks of the loop to find them. 328 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) { 329 BasicBlock *ExitBB = ExitBlocks[i]; 330 331 // If there are no PHI nodes in this exit block, then no values defined 332 // inside the loop are used on this path, skip it. 333 PHINode *PN = dyn_cast<PHINode>(ExitBB->begin()); 334 if (!PN) continue; 335 336 unsigned NumPreds = PN->getNumIncomingValues(); 337 338 // Iterate over all of the PHI nodes. 339 BasicBlock::iterator BBI = ExitBB->begin(); 340 while ((PN = dyn_cast<PHINode>(BBI++))) { 341 if (PN->use_empty()) 342 continue; // dead use, don't replace it 343 344 // SCEV only supports integer expressions for now. 345 if (!PN->getType()->isIntegerTy() && !PN->getType()->isPointerTy()) 346 continue; 347 348 // It's necessary to tell ScalarEvolution about this explicitly so that 349 // it can walk the def-use list and forget all SCEVs, as it may not be 350 // watching the PHI itself. Once the new exit value is in place, there 351 // may not be a def-use connection between the loop and every instruction 352 // which got a SCEVAddRecExpr for that loop. 353 SE->forgetValue(PN); 354 355 // Iterate over all of the values in all the PHI nodes. 356 for (unsigned i = 0; i != NumPreds; ++i) { 357 // If the value being merged in is not integer or is not defined 358 // in the loop, skip it. 359 Value *InVal = PN->getIncomingValue(i); 360 if (!isa<Instruction>(InVal)) 361 continue; 362 363 // If this pred is for a subloop, not L itself, skip it. 364 if (LI->getLoopFor(PN->getIncomingBlock(i)) != L) 365 continue; // The Block is in a subloop, skip it. 366 367 // Check that InVal is defined in the loop. 368 Instruction *Inst = cast<Instruction>(InVal); 369 if (!L->contains(Inst)) 370 continue; 371 372 // Okay, this instruction has a user outside of the current loop 373 // and varies predictably *inside* the loop. Evaluate the value it 374 // contains when the loop exits, if possible. 375 const SCEV *ExitValue = SE->getSCEVAtScope(Inst, L->getParentLoop()); 376 if (!SE->isLoopInvariant(ExitValue, L)) 377 continue; 378 379 Value *ExitVal = Rewriter.expandCodeFor(ExitValue, PN->getType(), Inst); 380 381 DEBUG(dbgs() << "INDVARS: RLEV: AfterLoopVal = " << *ExitVal << '\n' 382 << " LoopVal = " << *Inst << "\n"); 383 384 if (!isValidRewrite(Inst, ExitVal)) { 385 DeadInsts.push_back(ExitVal); 386 continue; 387 } 388 Changed = true; 389 ++NumReplaced; 390 391 PN->setIncomingValue(i, ExitVal); 392 393 // If this instruction is dead now, delete it. 394 RecursivelyDeleteTriviallyDeadInstructions(Inst); 395 396 if (NumPreds == 1) { 397 // Completely replace a single-pred PHI. This is safe, because the 398 // NewVal won't be variant in the loop, so we don't need an LCSSA phi 399 // node anymore. 400 PN->replaceAllUsesWith(ExitVal); 401 RecursivelyDeleteTriviallyDeadInstructions(PN); 402 } 403 } 404 if (NumPreds != 1) { 405 // Clone the PHI and delete the original one. This lets IVUsers and 406 // any other maps purge the original user from their records. 407 PHINode *NewPN = cast<PHINode>(PN->clone()); 408 NewPN->takeName(PN); 409 NewPN->insertBefore(PN); 410 PN->replaceAllUsesWith(NewPN); 411 PN->eraseFromParent(); 412 } 413 } 414 } 415 416 // The insertion point instruction may have been deleted; clear it out 417 // so that the rewriter doesn't trip over it later. 418 Rewriter.clearInsertPoint(); 419} 420 421void IndVarSimplify::RewriteNonIntegerIVs(Loop *L) { 422 // First step. Check to see if there are any floating-point recurrences. 423 // If there are, change them into integer recurrences, permitting analysis by 424 // the SCEV routines. 425 // 426 BasicBlock *Header = L->getHeader(); 427 428 SmallVector<WeakVH, 8> PHIs; 429 for (BasicBlock::iterator I = Header->begin(); 430 PHINode *PN = dyn_cast<PHINode>(I); ++I) 431 PHIs.push_back(PN); 432 433 for (unsigned i = 0, e = PHIs.size(); i != e; ++i) 434 if (PHINode *PN = dyn_cast_or_null<PHINode>(&*PHIs[i])) 435 HandleFloatingPointIV(L, PN); 436 437 // If the loop previously had floating-point IV, ScalarEvolution 438 // may not have been able to compute a trip count. Now that we've done some 439 // re-writing, the trip count may be computable. 440 if (Changed) 441 SE->forgetLoop(L); 442} 443 444void IndVarSimplify::EliminateIVComparisons() { 445 // Look for ICmp users. 446 for (IVUsers::iterator I = IU->begin(), E = IU->end(); I != E; ++I) { 447 IVStrideUse &UI = *I; 448 ICmpInst *ICmp = dyn_cast<ICmpInst>(UI.getUser()); 449 if (!ICmp) continue; 450 451 bool Swapped = UI.getOperandValToReplace() == ICmp->getOperand(1); 452 ICmpInst::Predicate Pred = ICmp->getPredicate(); 453 if (Swapped) Pred = ICmpInst::getSwappedPredicate(Pred); 454 455 // Get the SCEVs for the ICmp operands. 456 const SCEV *S = IU->getReplacementExpr(UI); 457 const SCEV *X = SE->getSCEV(ICmp->getOperand(!Swapped)); 458 459 // Simplify unnecessary loops away. 460 const Loop *ICmpLoop = LI->getLoopFor(ICmp->getParent()); 461 S = SE->getSCEVAtScope(S, ICmpLoop); 462 X = SE->getSCEVAtScope(X, ICmpLoop); 463 464 // If the condition is always true or always false, replace it with 465 // a constant value. 466 if (SE->isKnownPredicate(Pred, S, X)) 467 ICmp->replaceAllUsesWith(ConstantInt::getTrue(ICmp->getContext())); 468 else if (SE->isKnownPredicate(ICmpInst::getInversePredicate(Pred), S, X)) 469 ICmp->replaceAllUsesWith(ConstantInt::getFalse(ICmp->getContext())); 470 else 471 continue; 472 473 DEBUG(dbgs() << "INDVARS: Eliminated comparison: " << *ICmp << '\n'); 474 DeadInsts.push_back(ICmp); 475 } 476} 477 478void IndVarSimplify::EliminateIVRemainders() { 479 // Look for SRem and URem users. 480 for (IVUsers::iterator I = IU->begin(), E = IU->end(); I != E; ++I) { 481 IVStrideUse &UI = *I; 482 BinaryOperator *Rem = dyn_cast<BinaryOperator>(UI.getUser()); 483 if (!Rem) continue; 484 485 bool isSigned = Rem->getOpcode() == Instruction::SRem; 486 if (!isSigned && Rem->getOpcode() != Instruction::URem) 487 continue; 488 489 // We're only interested in the case where we know something about 490 // the numerator. 491 if (UI.getOperandValToReplace() != Rem->getOperand(0)) 492 continue; 493 494 // Get the SCEVs for the ICmp operands. 495 const SCEV *S = SE->getSCEV(Rem->getOperand(0)); 496 const SCEV *X = SE->getSCEV(Rem->getOperand(1)); 497 498 // Simplify unnecessary loops away. 499 const Loop *ICmpLoop = LI->getLoopFor(Rem->getParent()); 500 S = SE->getSCEVAtScope(S, ICmpLoop); 501 X = SE->getSCEVAtScope(X, ICmpLoop); 502 503 // i % n --> i if i is in [0,n). 504 if ((!isSigned || SE->isKnownNonNegative(S)) && 505 SE->isKnownPredicate(isSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT, 506 S, X)) 507 Rem->replaceAllUsesWith(Rem->getOperand(0)); 508 else { 509 // (i+1) % n --> (i+1)==n?0:(i+1) if i is in [0,n). 510 const SCEV *LessOne = 511 SE->getMinusSCEV(S, SE->getConstant(S->getType(), 1)); 512 if ((!isSigned || SE->isKnownNonNegative(LessOne)) && 513 SE->isKnownPredicate(isSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT, 514 LessOne, X)) { 515 ICmpInst *ICmp = new ICmpInst(Rem, ICmpInst::ICMP_EQ, 516 Rem->getOperand(0), Rem->getOperand(1), 517 "tmp"); 518 SelectInst *Sel = 519 SelectInst::Create(ICmp, 520 ConstantInt::get(Rem->getType(), 0), 521 Rem->getOperand(0), "tmp", Rem); 522 Rem->replaceAllUsesWith(Sel); 523 } else 524 continue; 525 } 526 527 // Inform IVUsers about the new users. 528 if (Instruction *I = dyn_cast<Instruction>(Rem->getOperand(0))) 529 IU->AddUsersIfInteresting(I); 530 531 DEBUG(dbgs() << "INDVARS: Simplified rem: " << *Rem << '\n'); 532 DeadInsts.push_back(Rem); 533 } 534} 535 536bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) { 537 // If LoopSimplify form is not available, stay out of trouble. Some notes: 538 // - LSR currently only supports LoopSimplify-form loops. Indvars' 539 // canonicalization can be a pessimization without LSR to "clean up" 540 // afterwards. 541 // - We depend on having a preheader; in particular, 542 // Loop::getCanonicalInductionVariable only supports loops with preheaders, 543 // and we're in trouble if we can't find the induction variable even when 544 // we've manually inserted one. 545 if (!L->isLoopSimplifyForm()) 546 return false; 547 548 IU = &getAnalysis<IVUsers>(); 549 LI = &getAnalysis<LoopInfo>(); 550 SE = &getAnalysis<ScalarEvolution>(); 551 DT = &getAnalysis<DominatorTree>(); 552 DeadInsts.clear(); 553 Changed = false; 554 555 // If there are any floating-point recurrences, attempt to 556 // transform them to use integer recurrences. 557 RewriteNonIntegerIVs(L); 558 559 const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L); 560 561 // Create a rewriter object which we'll use to transform the code with. 562 SCEVExpander Rewriter(*SE); 563 564 // Check to see if this loop has a computable loop-invariant execution count. 565 // If so, this means that we can compute the final value of any expressions 566 // that are recurrent in the loop, and substitute the exit values from the 567 // loop into any instructions outside of the loop that use the final values of 568 // the current expressions. 569 // 570 if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount)) 571 RewriteLoopExitValues(L, Rewriter); 572 573 // Simplify ICmp IV users. 574 EliminateIVComparisons(); 575 576 // Simplify SRem and URem IV users. 577 EliminateIVRemainders(); 578 579 // Compute the type of the largest recurrence expression, and decide whether 580 // a canonical induction variable should be inserted. 581 const Type *LargestType = 0; 582 bool NeedCannIV = false; 583 bool ExpandBECount = canExpandBackedgeTakenCount(L, BackedgeTakenCount); 584 if (ExpandBECount) { 585 // If we have a known trip count and a single exit block, we'll be 586 // rewriting the loop exit test condition below, which requires a 587 // canonical induction variable. 588 NeedCannIV = true; 589 const Type *Ty = BackedgeTakenCount->getType(); 590 if (!LargestType || 591 SE->getTypeSizeInBits(Ty) > 592 SE->getTypeSizeInBits(LargestType)) 593 LargestType = SE->getEffectiveSCEVType(Ty); 594 } 595 for (IVUsers::const_iterator I = IU->begin(), E = IU->end(); I != E; ++I) { 596 NeedCannIV = true; 597 const Type *Ty = 598 SE->getEffectiveSCEVType(I->getOperandValToReplace()->getType()); 599 if (!LargestType || 600 SE->getTypeSizeInBits(Ty) > 601 SE->getTypeSizeInBits(LargestType)) 602 LargestType = Ty; 603 } 604 605 // Now that we know the largest of the induction variable expressions 606 // in this loop, insert a canonical induction variable of the largest size. 607 PHINode *IndVar = 0; 608 if (NeedCannIV) { 609 // Check to see if the loop already has any canonical-looking induction 610 // variables. If any are present and wider than the planned canonical 611 // induction variable, temporarily remove them, so that the Rewriter 612 // doesn't attempt to reuse them. 613 SmallVector<PHINode *, 2> OldCannIVs; 614 while (PHINode *OldCannIV = L->getCanonicalInductionVariable()) { 615 if (SE->getTypeSizeInBits(OldCannIV->getType()) > 616 SE->getTypeSizeInBits(LargestType)) 617 OldCannIV->removeFromParent(); 618 else 619 break; 620 OldCannIVs.push_back(OldCannIV); 621 } 622 623 IndVar = Rewriter.getOrInsertCanonicalInductionVariable(L, LargestType); 624 625 ++NumInserted; 626 Changed = true; 627 DEBUG(dbgs() << "INDVARS: New CanIV: " << *IndVar << '\n'); 628 629 // Now that the official induction variable is established, reinsert 630 // any old canonical-looking variables after it so that the IR remains 631 // consistent. They will be deleted as part of the dead-PHI deletion at 632 // the end of the pass. 633 while (!OldCannIVs.empty()) { 634 PHINode *OldCannIV = OldCannIVs.pop_back_val(); 635 OldCannIV->insertBefore(L->getHeader()->getFirstNonPHI()); 636 } 637 } 638 639 // If we have a trip count expression, rewrite the loop's exit condition 640 // using it. We can currently only handle loops with a single exit. 641 ICmpInst *NewICmp = 0; 642 if (ExpandBECount) { 643 assert(canExpandBackedgeTakenCount(L, BackedgeTakenCount) && 644 "canonical IV disrupted BackedgeTaken expansion"); 645 assert(NeedCannIV && 646 "LinearFunctionTestReplace requires a canonical induction variable"); 647 NewICmp = LinearFunctionTestReplace(L, BackedgeTakenCount, IndVar, 648 Rewriter); 649 } 650 651 // Rewrite IV-derived expressions. 652 RewriteIVExpressions(L, Rewriter); 653 654 // Clear the rewriter cache, because values that are in the rewriter's cache 655 // can be deleted in the loop below, causing the AssertingVH in the cache to 656 // trigger. 657 Rewriter.clear(); 658 659 // Now that we're done iterating through lists, clean up any instructions 660 // which are now dead. 661 while (!DeadInsts.empty()) 662 if (Instruction *Inst = 663 dyn_cast_or_null<Instruction>(&*DeadInsts.pop_back_val())) 664 RecursivelyDeleteTriviallyDeadInstructions(Inst); 665 666 // The Rewriter may not be used from this point on. 667 668 // Loop-invariant instructions in the preheader that aren't used in the 669 // loop may be sunk below the loop to reduce register pressure. 670 SinkUnusedInvariants(L); 671 672 // For completeness, inform IVUsers of the IV use in the newly-created 673 // loop exit test instruction. 674 if (NewICmp) 675 IU->AddUsersIfInteresting(cast<Instruction>(NewICmp->getOperand(0))); 676 677 // Clean up dead instructions. 678 Changed |= DeleteDeadPHIs(L->getHeader()); 679 // Check a post-condition. 680 assert(L->isLCSSAForm(*DT) && "Indvars did not leave the loop in lcssa form!"); 681 return Changed; 682} 683 684// FIXME: It is an extremely bad idea to indvar substitute anything more 685// complex than affine induction variables. Doing so will put expensive 686// polynomial evaluations inside of the loop, and the str reduction pass 687// currently can only reduce affine polynomials. For now just disable 688// indvar subst on anything more complex than an affine addrec, unless 689// it can be expanded to a trivial value. 690static bool isSafe(const SCEV *S, const Loop *L, ScalarEvolution *SE) { 691 // Loop-invariant values are safe. 692 if (SE->isLoopInvariant(S, L)) return true; 693 694 // Affine addrecs are safe. Non-affine are not, because LSR doesn't know how 695 // to transform them into efficient code. 696 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) 697 return AR->isAffine(); 698 699 // An add is safe it all its operands are safe. 700 if (const SCEVCommutativeExpr *Commutative = dyn_cast<SCEVCommutativeExpr>(S)) { 701 for (SCEVCommutativeExpr::op_iterator I = Commutative->op_begin(), 702 E = Commutative->op_end(); I != E; ++I) 703 if (!isSafe(*I, L, SE)) return false; 704 return true; 705 } 706 707 // A cast is safe if its operand is. 708 if (const SCEVCastExpr *C = dyn_cast<SCEVCastExpr>(S)) 709 return isSafe(C->getOperand(), L, SE); 710 711 // A udiv is safe if its operands are. 712 if (const SCEVUDivExpr *UD = dyn_cast<SCEVUDivExpr>(S)) 713 return isSafe(UD->getLHS(), L, SE) && 714 isSafe(UD->getRHS(), L, SE); 715 716 // SCEVUnknown is always safe. 717 if (isa<SCEVUnknown>(S)) 718 return true; 719 720 // Nothing else is safe. 721 return false; 722} 723 724void IndVarSimplify::RewriteIVExpressions(Loop *L, SCEVExpander &Rewriter) { 725 // Rewrite all induction variable expressions in terms of the canonical 726 // induction variable. 727 // 728 // If there were induction variables of other sizes or offsets, manually 729 // add the offsets to the primary induction variable and cast, avoiding 730 // the need for the code evaluation methods to insert induction variables 731 // of different sizes. 732 for (IVUsers::iterator UI = IU->begin(), E = IU->end(); UI != E; ++UI) { 733 Value *Op = UI->getOperandValToReplace(); 734 const Type *UseTy = Op->getType(); 735 Instruction *User = UI->getUser(); 736 737 // Compute the final addrec to expand into code. 738 const SCEV *AR = IU->getReplacementExpr(*UI); 739 740 // Evaluate the expression out of the loop, if possible. 741 if (!L->contains(UI->getUser())) { 742 const SCEV *ExitVal = SE->getSCEVAtScope(AR, L->getParentLoop()); 743 if (SE->isLoopInvariant(ExitVal, L)) 744 AR = ExitVal; 745 } 746 747 // FIXME: It is an extremely bad idea to indvar substitute anything more 748 // complex than affine induction variables. Doing so will put expensive 749 // polynomial evaluations inside of the loop, and the str reduction pass 750 // currently can only reduce affine polynomials. For now just disable 751 // indvar subst on anything more complex than an affine addrec, unless 752 // it can be expanded to a trivial value. 753 if (!isSafe(AR, L, SE)) 754 continue; 755 756 // Determine the insertion point for this user. By default, insert 757 // immediately before the user. The SCEVExpander class will automatically 758 // hoist loop invariants out of the loop. For PHI nodes, there may be 759 // multiple uses, so compute the nearest common dominator for the 760 // incoming blocks. 761 Instruction *InsertPt = User; 762 if (PHINode *PHI = dyn_cast<PHINode>(InsertPt)) 763 for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i) 764 if (PHI->getIncomingValue(i) == Op) { 765 if (InsertPt == User) 766 InsertPt = PHI->getIncomingBlock(i)->getTerminator(); 767 else 768 InsertPt = 769 DT->findNearestCommonDominator(InsertPt->getParent(), 770 PHI->getIncomingBlock(i)) 771 ->getTerminator(); 772 } 773 774 // Now expand it into actual Instructions and patch it into place. 775 Value *NewVal = Rewriter.expandCodeFor(AR, UseTy, InsertPt); 776 777 DEBUG(dbgs() << "INDVARS: Rewrote IV '" << *AR << "' " << *Op << '\n' 778 << " into = " << *NewVal << "\n"); 779 780 if (!isValidRewrite(Op, NewVal)) { 781 DeadInsts.push_back(NewVal); 782 continue; 783 } 784 // Inform ScalarEvolution that this value is changing. The change doesn't 785 // affect its value, but it does potentially affect which use lists the 786 // value will be on after the replacement, which affects ScalarEvolution's 787 // ability to walk use lists and drop dangling pointers when a value is 788 // deleted. 789 SE->forgetValue(User); 790 791 // Patch the new value into place. 792 if (Op->hasName()) 793 NewVal->takeName(Op); 794 User->replaceUsesOfWith(Op, NewVal); 795 UI->setOperandValToReplace(NewVal); 796 797 ++NumRemoved; 798 Changed = true; 799 800 // The old value may be dead now. 801 DeadInsts.push_back(Op); 802 } 803} 804 805/// If there's a single exit block, sink any loop-invariant values that 806/// were defined in the preheader but not used inside the loop into the 807/// exit block to reduce register pressure in the loop. 808void IndVarSimplify::SinkUnusedInvariants(Loop *L) { 809 BasicBlock *ExitBlock = L->getExitBlock(); 810 if (!ExitBlock) return; 811 812 BasicBlock *Preheader = L->getLoopPreheader(); 813 if (!Preheader) return; 814 815 Instruction *InsertPt = ExitBlock->getFirstNonPHI(); 816 BasicBlock::iterator I = Preheader->getTerminator(); 817 while (I != Preheader->begin()) { 818 --I; 819 // New instructions were inserted at the end of the preheader. 820 if (isa<PHINode>(I)) 821 break; 822 823 // Don't move instructions which might have side effects, since the side 824 // effects need to complete before instructions inside the loop. Also don't 825 // move instructions which might read memory, since the loop may modify 826 // memory. Note that it's okay if the instruction might have undefined 827 // behavior: LoopSimplify guarantees that the preheader dominates the exit 828 // block. 829 if (I->mayHaveSideEffects() || I->mayReadFromMemory()) 830 continue; 831 832 // Skip debug info intrinsics. 833 if (isa<DbgInfoIntrinsic>(I)) 834 continue; 835 836 // Don't sink static AllocaInsts out of the entry block, which would 837 // turn them into dynamic allocas! 838 if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) 839 if (AI->isStaticAlloca()) 840 continue; 841 842 // Determine if there is a use in or before the loop (direct or 843 // otherwise). 844 bool UsedInLoop = false; 845 for (Value::use_iterator UI = I->use_begin(), UE = I->use_end(); 846 UI != UE; ++UI) { 847 User *U = *UI; 848 BasicBlock *UseBB = cast<Instruction>(U)->getParent(); 849 if (PHINode *P = dyn_cast<PHINode>(U)) { 850 unsigned i = 851 PHINode::getIncomingValueNumForOperand(UI.getOperandNo()); 852 UseBB = P->getIncomingBlock(i); 853 } 854 if (UseBB == Preheader || L->contains(UseBB)) { 855 UsedInLoop = true; 856 break; 857 } 858 } 859 860 // If there is, the def must remain in the preheader. 861 if (UsedInLoop) 862 continue; 863 864 // Otherwise, sink it to the exit block. 865 Instruction *ToMove = I; 866 bool Done = false; 867 868 if (I != Preheader->begin()) { 869 // Skip debug info intrinsics. 870 do { 871 --I; 872 } while (isa<DbgInfoIntrinsic>(I) && I != Preheader->begin()); 873 874 if (isa<DbgInfoIntrinsic>(I) && I == Preheader->begin()) 875 Done = true; 876 } else { 877 Done = true; 878 } 879 880 ToMove->moveBefore(InsertPt); 881 if (Done) break; 882 InsertPt = ToMove; 883 } 884} 885 886/// ConvertToSInt - Convert APF to an integer, if possible. 887static bool ConvertToSInt(const APFloat &APF, int64_t &IntVal) { 888 bool isExact = false; 889 if (&APF.getSemantics() == &APFloat::PPCDoubleDouble) 890 return false; 891 // See if we can convert this to an int64_t 892 uint64_t UIntVal; 893 if (APF.convertToInteger(&UIntVal, 64, true, APFloat::rmTowardZero, 894 &isExact) != APFloat::opOK || !isExact) 895 return false; 896 IntVal = UIntVal; 897 return true; 898} 899 900/// HandleFloatingPointIV - If the loop has floating induction variable 901/// then insert corresponding integer induction variable if possible. 902/// For example, 903/// for(double i = 0; i < 10000; ++i) 904/// bar(i) 905/// is converted into 906/// for(int i = 0; i < 10000; ++i) 907/// bar((double)i); 908/// 909void IndVarSimplify::HandleFloatingPointIV(Loop *L, PHINode *PN) { 910 unsigned IncomingEdge = L->contains(PN->getIncomingBlock(0)); 911 unsigned BackEdge = IncomingEdge^1; 912 913 // Check incoming value. 914 ConstantFP *InitValueVal = 915 dyn_cast<ConstantFP>(PN->getIncomingValue(IncomingEdge)); 916 917 int64_t InitValue; 918 if (!InitValueVal || !ConvertToSInt(InitValueVal->getValueAPF(), InitValue)) 919 return; 920 921 // Check IV increment. Reject this PN if increment operation is not 922 // an add or increment value can not be represented by an integer. 923 BinaryOperator *Incr = 924 dyn_cast<BinaryOperator>(PN->getIncomingValue(BackEdge)); 925 if (Incr == 0 || Incr->getOpcode() != Instruction::FAdd) return; 926 927 // If this is not an add of the PHI with a constantfp, or if the constant fp 928 // is not an integer, bail out. 929 ConstantFP *IncValueVal = dyn_cast<ConstantFP>(Incr->getOperand(1)); 930 int64_t IncValue; 931 if (IncValueVal == 0 || Incr->getOperand(0) != PN || 932 !ConvertToSInt(IncValueVal->getValueAPF(), IncValue)) 933 return; 934 935 // Check Incr uses. One user is PN and the other user is an exit condition 936 // used by the conditional terminator. 937 Value::use_iterator IncrUse = Incr->use_begin(); 938 Instruction *U1 = cast<Instruction>(*IncrUse++); 939 if (IncrUse == Incr->use_end()) return; 940 Instruction *U2 = cast<Instruction>(*IncrUse++); 941 if (IncrUse != Incr->use_end()) return; 942 943 // Find exit condition, which is an fcmp. If it doesn't exist, or if it isn't 944 // only used by a branch, we can't transform it. 945 FCmpInst *Compare = dyn_cast<FCmpInst>(U1); 946 if (!Compare) 947 Compare = dyn_cast<FCmpInst>(U2); 948 if (Compare == 0 || !Compare->hasOneUse() || 949 !isa<BranchInst>(Compare->use_back())) 950 return; 951 952 BranchInst *TheBr = cast<BranchInst>(Compare->use_back()); 953 954 // We need to verify that the branch actually controls the iteration count 955 // of the loop. If not, the new IV can overflow and no one will notice. 956 // The branch block must be in the loop and one of the successors must be out 957 // of the loop. 958 assert(TheBr->isConditional() && "Can't use fcmp if not conditional"); 959 if (!L->contains(TheBr->getParent()) || 960 (L->contains(TheBr->getSuccessor(0)) && 961 L->contains(TheBr->getSuccessor(1)))) 962 return; 963 964 965 // If it isn't a comparison with an integer-as-fp (the exit value), we can't 966 // transform it. 967 ConstantFP *ExitValueVal = dyn_cast<ConstantFP>(Compare->getOperand(1)); 968 int64_t ExitValue; 969 if (ExitValueVal == 0 || 970 !ConvertToSInt(ExitValueVal->getValueAPF(), ExitValue)) 971 return; 972 973 // Find new predicate for integer comparison. 974 CmpInst::Predicate NewPred = CmpInst::BAD_ICMP_PREDICATE; 975 switch (Compare->getPredicate()) { 976 default: return; // Unknown comparison. 977 case CmpInst::FCMP_OEQ: 978 case CmpInst::FCMP_UEQ: NewPred = CmpInst::ICMP_EQ; break; 979 case CmpInst::FCMP_ONE: 980 case CmpInst::FCMP_UNE: NewPred = CmpInst::ICMP_NE; break; 981 case CmpInst::FCMP_OGT: 982 case CmpInst::FCMP_UGT: NewPred = CmpInst::ICMP_SGT; break; 983 case CmpInst::FCMP_OGE: 984 case CmpInst::FCMP_UGE: NewPred = CmpInst::ICMP_SGE; break; 985 case CmpInst::FCMP_OLT: 986 case CmpInst::FCMP_ULT: NewPred = CmpInst::ICMP_SLT; break; 987 case CmpInst::FCMP_OLE: 988 case CmpInst::FCMP_ULE: NewPred = CmpInst::ICMP_SLE; break; 989 } 990 991 // We convert the floating point induction variable to a signed i32 value if 992 // we can. This is only safe if the comparison will not overflow in a way 993 // that won't be trapped by the integer equivalent operations. Check for this 994 // now. 995 // TODO: We could use i64 if it is native and the range requires it. 996 997 // The start/stride/exit values must all fit in signed i32. 998 if (!isInt<32>(InitValue) || !isInt<32>(IncValue) || !isInt<32>(ExitValue)) 999 return; 1000 1001 // If not actually striding (add x, 0.0), avoid touching the code. 1002 if (IncValue == 0) 1003 return; 1004 1005 // Positive and negative strides have different safety conditions. 1006 if (IncValue > 0) { 1007 // If we have a positive stride, we require the init to be less than the 1008 // exit value and an equality or less than comparison. 1009 if (InitValue >= ExitValue || 1010 NewPred == CmpInst::ICMP_SGT || NewPred == CmpInst::ICMP_SGE) 1011 return; 1012 1013 uint32_t Range = uint32_t(ExitValue-InitValue); 1014 if (NewPred == CmpInst::ICMP_SLE) { 1015 // Normalize SLE -> SLT, check for infinite loop. 1016 if (++Range == 0) return; // Range overflows. 1017 } 1018 1019 unsigned Leftover = Range % uint32_t(IncValue); 1020 1021 // If this is an equality comparison, we require that the strided value 1022 // exactly land on the exit value, otherwise the IV condition will wrap 1023 // around and do things the fp IV wouldn't. 1024 if ((NewPred == CmpInst::ICMP_EQ || NewPred == CmpInst::ICMP_NE) && 1025 Leftover != 0) 1026 return; 1027 1028 // If the stride would wrap around the i32 before exiting, we can't 1029 // transform the IV. 1030 if (Leftover != 0 && int32_t(ExitValue+IncValue) < ExitValue) 1031 return; 1032 1033 } else { 1034 // If we have a negative stride, we require the init to be greater than the 1035 // exit value and an equality or greater than comparison. 1036 if (InitValue >= ExitValue || 1037 NewPred == CmpInst::ICMP_SLT || NewPred == CmpInst::ICMP_SLE) 1038 return; 1039 1040 uint32_t Range = uint32_t(InitValue-ExitValue); 1041 if (NewPred == CmpInst::ICMP_SGE) { 1042 // Normalize SGE -> SGT, check for infinite loop. 1043 if (++Range == 0) return; // Range overflows. 1044 } 1045 1046 unsigned Leftover = Range % uint32_t(-IncValue); 1047 1048 // If this is an equality comparison, we require that the strided value 1049 // exactly land on the exit value, otherwise the IV condition will wrap 1050 // around and do things the fp IV wouldn't. 1051 if ((NewPred == CmpInst::ICMP_EQ || NewPred == CmpInst::ICMP_NE) && 1052 Leftover != 0) 1053 return; 1054 1055 // If the stride would wrap around the i32 before exiting, we can't 1056 // transform the IV. 1057 if (Leftover != 0 && int32_t(ExitValue+IncValue) > ExitValue) 1058 return; 1059 } 1060 1061 const IntegerType *Int32Ty = Type::getInt32Ty(PN->getContext()); 1062 1063 // Insert new integer induction variable. 1064 PHINode *NewPHI = PHINode::Create(Int32Ty, 2, PN->getName()+".int", PN); 1065 NewPHI->addIncoming(ConstantInt::get(Int32Ty, InitValue), 1066 PN->getIncomingBlock(IncomingEdge)); 1067 1068 Value *NewAdd = 1069 BinaryOperator::CreateAdd(NewPHI, ConstantInt::get(Int32Ty, IncValue), 1070 Incr->getName()+".int", Incr); 1071 NewPHI->addIncoming(NewAdd, PN->getIncomingBlock(BackEdge)); 1072 1073 ICmpInst *NewCompare = new ICmpInst(TheBr, NewPred, NewAdd, 1074 ConstantInt::get(Int32Ty, ExitValue), 1075 Compare->getName()); 1076 1077 // In the following deletions, PN may become dead and may be deleted. 1078 // Use a WeakVH to observe whether this happens. 1079 WeakVH WeakPH = PN; 1080 1081 // Delete the old floating point exit comparison. The branch starts using the 1082 // new comparison. 1083 NewCompare->takeName(Compare); 1084 Compare->replaceAllUsesWith(NewCompare); 1085 RecursivelyDeleteTriviallyDeadInstructions(Compare); 1086 1087 // Delete the old floating point increment. 1088 Incr->replaceAllUsesWith(UndefValue::get(Incr->getType())); 1089 RecursivelyDeleteTriviallyDeadInstructions(Incr); 1090 1091 // If the FP induction variable still has uses, this is because something else 1092 // in the loop uses its value. In order to canonicalize the induction 1093 // variable, we chose to eliminate the IV and rewrite it in terms of an 1094 // int->fp cast. 1095 // 1096 // We give preference to sitofp over uitofp because it is faster on most 1097 // platforms. 1098 if (WeakPH) { 1099 Value *Conv = new SIToFPInst(NewPHI, PN->getType(), "indvar.conv", 1100 PN->getParent()->getFirstNonPHI()); 1101 PN->replaceAllUsesWith(Conv); 1102 RecursivelyDeleteTriviallyDeadInstructions(PN); 1103 } 1104 1105 // Add a new IVUsers entry for the newly-created integer PHI. 1106 IU->AddUsersIfInteresting(NewPHI); 1107} 1108