InstCombinePHI.cpp revision 218893
1202375Srdivacky//===- InstCombinePHI.cpp -------------------------------------------------===// 2202375Srdivacky// 3202375Srdivacky// The LLVM Compiler Infrastructure 4202375Srdivacky// 5202375Srdivacky// This file is distributed under the University of Illinois Open Source 6202375Srdivacky// License. See LICENSE.TXT for details. 7202375Srdivacky// 8202375Srdivacky//===----------------------------------------------------------------------===// 9202375Srdivacky// 10202375Srdivacky// This file implements the visitPHINode function. 11202375Srdivacky// 12202375Srdivacky//===----------------------------------------------------------------------===// 13202375Srdivacky 14202375Srdivacky#include "InstCombine.h" 15218893Sdim#include "llvm/Analysis/InstructionSimplify.h" 16202375Srdivacky#include "llvm/Target/TargetData.h" 17202375Srdivacky#include "llvm/ADT/SmallPtrSet.h" 18202375Srdivacky#include "llvm/ADT/STLExtras.h" 19202375Srdivackyusing namespace llvm; 20202375Srdivacky 21202375Srdivacky/// FoldPHIArgBinOpIntoPHI - If we have something like phi [add (a,b), add(a,c)] 22202375Srdivacky/// and if a/b/c and the add's all have a single use, turn this into a phi 23202375Srdivacky/// and a single binop. 24202375SrdivackyInstruction *InstCombiner::FoldPHIArgBinOpIntoPHI(PHINode &PN) { 25202375Srdivacky Instruction *FirstInst = cast<Instruction>(PN.getIncomingValue(0)); 26202375Srdivacky assert(isa<BinaryOperator>(FirstInst) || isa<CmpInst>(FirstInst)); 27202375Srdivacky unsigned Opc = FirstInst->getOpcode(); 28202375Srdivacky Value *LHSVal = FirstInst->getOperand(0); 29202375Srdivacky Value *RHSVal = FirstInst->getOperand(1); 30202375Srdivacky 31202375Srdivacky const Type *LHSType = LHSVal->getType(); 32202375Srdivacky const Type *RHSType = RHSVal->getType(); 33202375Srdivacky 34218893Sdim bool isNUW = false, isNSW = false, isExact = false; 35218893Sdim if (OverflowingBinaryOperator *BO = 36218893Sdim dyn_cast<OverflowingBinaryOperator>(FirstInst)) { 37218893Sdim isNUW = BO->hasNoUnsignedWrap(); 38218893Sdim isNSW = BO->hasNoSignedWrap(); 39218893Sdim } else if (PossiblyExactOperator *PEO = 40218893Sdim dyn_cast<PossiblyExactOperator>(FirstInst)) 41218893Sdim isExact = PEO->isExact(); 42218893Sdim 43202375Srdivacky // Scan to see if all operands are the same opcode, and all have one use. 44202375Srdivacky for (unsigned i = 1; i != PN.getNumIncomingValues(); ++i) { 45202375Srdivacky Instruction *I = dyn_cast<Instruction>(PN.getIncomingValue(i)); 46202375Srdivacky if (!I || I->getOpcode() != Opc || !I->hasOneUse() || 47202375Srdivacky // Verify type of the LHS matches so we don't fold cmp's of different 48218893Sdim // types. 49202375Srdivacky I->getOperand(0)->getType() != LHSType || 50202375Srdivacky I->getOperand(1)->getType() != RHSType) 51202375Srdivacky return 0; 52202375Srdivacky 53202375Srdivacky // If they are CmpInst instructions, check their predicates 54218893Sdim if (CmpInst *CI = dyn_cast<CmpInst>(I)) 55218893Sdim if (CI->getPredicate() != cast<CmpInst>(FirstInst)->getPredicate()) 56202375Srdivacky return 0; 57202375Srdivacky 58218893Sdim if (isNUW) 59218893Sdim isNUW = cast<OverflowingBinaryOperator>(I)->hasNoUnsignedWrap(); 60218893Sdim if (isNSW) 61218893Sdim isNSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap(); 62218893Sdim if (isExact) 63218893Sdim isExact = cast<PossiblyExactOperator>(I)->isExact(); 64218893Sdim 65202375Srdivacky // Keep track of which operand needs a phi node. 66202375Srdivacky if (I->getOperand(0) != LHSVal) LHSVal = 0; 67202375Srdivacky if (I->getOperand(1) != RHSVal) RHSVal = 0; 68202375Srdivacky } 69202375Srdivacky 70202375Srdivacky // If both LHS and RHS would need a PHI, don't do this transformation, 71202375Srdivacky // because it would increase the number of PHIs entering the block, 72202375Srdivacky // which leads to higher register pressure. This is especially 73202375Srdivacky // bad when the PHIs are in the header of a loop. 74202375Srdivacky if (!LHSVal && !RHSVal) 75202375Srdivacky return 0; 76202375Srdivacky 77202375Srdivacky // Otherwise, this is safe to transform! 78202375Srdivacky 79202375Srdivacky Value *InLHS = FirstInst->getOperand(0); 80202375Srdivacky Value *InRHS = FirstInst->getOperand(1); 81202375Srdivacky PHINode *NewLHS = 0, *NewRHS = 0; 82202375Srdivacky if (LHSVal == 0) { 83202375Srdivacky NewLHS = PHINode::Create(LHSType, 84202375Srdivacky FirstInst->getOperand(0)->getName() + ".pn"); 85202375Srdivacky NewLHS->reserveOperandSpace(PN.getNumOperands()/2); 86202375Srdivacky NewLHS->addIncoming(InLHS, PN.getIncomingBlock(0)); 87202375Srdivacky InsertNewInstBefore(NewLHS, PN); 88202375Srdivacky LHSVal = NewLHS; 89202375Srdivacky } 90202375Srdivacky 91202375Srdivacky if (RHSVal == 0) { 92202375Srdivacky NewRHS = PHINode::Create(RHSType, 93202375Srdivacky FirstInst->getOperand(1)->getName() + ".pn"); 94202375Srdivacky NewRHS->reserveOperandSpace(PN.getNumOperands()/2); 95202375Srdivacky NewRHS->addIncoming(InRHS, PN.getIncomingBlock(0)); 96202375Srdivacky InsertNewInstBefore(NewRHS, PN); 97202375Srdivacky RHSVal = NewRHS; 98202375Srdivacky } 99202375Srdivacky 100202375Srdivacky // Add all operands to the new PHIs. 101202375Srdivacky if (NewLHS || NewRHS) { 102202375Srdivacky for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) { 103202375Srdivacky Instruction *InInst = cast<Instruction>(PN.getIncomingValue(i)); 104202375Srdivacky if (NewLHS) { 105202375Srdivacky Value *NewInLHS = InInst->getOperand(0); 106202375Srdivacky NewLHS->addIncoming(NewInLHS, PN.getIncomingBlock(i)); 107202375Srdivacky } 108202375Srdivacky if (NewRHS) { 109202375Srdivacky Value *NewInRHS = InInst->getOperand(1); 110202375Srdivacky NewRHS->addIncoming(NewInRHS, PN.getIncomingBlock(i)); 111202375Srdivacky } 112202375Srdivacky } 113202375Srdivacky } 114202375Srdivacky 115218893Sdim if (CmpInst *CIOp = dyn_cast<CmpInst>(FirstInst)) 116218893Sdim return CmpInst::Create(CIOp->getOpcode(), CIOp->getPredicate(), 117218893Sdim LHSVal, RHSVal); 118218893Sdim 119218893Sdim BinaryOperator *BinOp = cast<BinaryOperator>(FirstInst); 120218893Sdim BinaryOperator *NewBinOp = 121218893Sdim BinaryOperator::Create(BinOp->getOpcode(), LHSVal, RHSVal); 122218893Sdim if (isNUW) NewBinOp->setHasNoUnsignedWrap(); 123218893Sdim if (isNSW) NewBinOp->setHasNoSignedWrap(); 124218893Sdim if (isExact) NewBinOp->setIsExact(); 125218893Sdim return NewBinOp; 126202375Srdivacky} 127202375Srdivacky 128202375SrdivackyInstruction *InstCombiner::FoldPHIArgGEPIntoPHI(PHINode &PN) { 129202375Srdivacky GetElementPtrInst *FirstInst =cast<GetElementPtrInst>(PN.getIncomingValue(0)); 130202375Srdivacky 131202375Srdivacky SmallVector<Value*, 16> FixedOperands(FirstInst->op_begin(), 132202375Srdivacky FirstInst->op_end()); 133202375Srdivacky // This is true if all GEP bases are allocas and if all indices into them are 134202375Srdivacky // constants. 135202375Srdivacky bool AllBasePointersAreAllocas = true; 136202375Srdivacky 137202375Srdivacky // We don't want to replace this phi if the replacement would require 138202375Srdivacky // more than one phi, which leads to higher register pressure. This is 139202375Srdivacky // especially bad when the PHIs are in the header of a loop. 140202375Srdivacky bool NeededPhi = false; 141202375Srdivacky 142218893Sdim bool AllInBounds = true; 143218893Sdim 144202375Srdivacky // Scan to see if all operands are the same opcode, and all have one use. 145202375Srdivacky for (unsigned i = 1; i != PN.getNumIncomingValues(); ++i) { 146202375Srdivacky GetElementPtrInst *GEP= dyn_cast<GetElementPtrInst>(PN.getIncomingValue(i)); 147202375Srdivacky if (!GEP || !GEP->hasOneUse() || GEP->getType() != FirstInst->getType() || 148202375Srdivacky GEP->getNumOperands() != FirstInst->getNumOperands()) 149202375Srdivacky return 0; 150202375Srdivacky 151218893Sdim AllInBounds &= GEP->isInBounds(); 152218893Sdim 153202375Srdivacky // Keep track of whether or not all GEPs are of alloca pointers. 154202375Srdivacky if (AllBasePointersAreAllocas && 155202375Srdivacky (!isa<AllocaInst>(GEP->getOperand(0)) || 156202375Srdivacky !GEP->hasAllConstantIndices())) 157202375Srdivacky AllBasePointersAreAllocas = false; 158202375Srdivacky 159202375Srdivacky // Compare the operand lists. 160202375Srdivacky for (unsigned op = 0, e = FirstInst->getNumOperands(); op != e; ++op) { 161202375Srdivacky if (FirstInst->getOperand(op) == GEP->getOperand(op)) 162202375Srdivacky continue; 163202375Srdivacky 164202375Srdivacky // Don't merge two GEPs when two operands differ (introducing phi nodes) 165202375Srdivacky // if one of the PHIs has a constant for the index. The index may be 166202375Srdivacky // substantially cheaper to compute for the constants, so making it a 167202375Srdivacky // variable index could pessimize the path. This also handles the case 168202375Srdivacky // for struct indices, which must always be constant. 169202375Srdivacky if (isa<ConstantInt>(FirstInst->getOperand(op)) || 170202375Srdivacky isa<ConstantInt>(GEP->getOperand(op))) 171202375Srdivacky return 0; 172202375Srdivacky 173202375Srdivacky if (FirstInst->getOperand(op)->getType() !=GEP->getOperand(op)->getType()) 174202375Srdivacky return 0; 175202375Srdivacky 176202375Srdivacky // If we already needed a PHI for an earlier operand, and another operand 177202375Srdivacky // also requires a PHI, we'd be introducing more PHIs than we're 178202375Srdivacky // eliminating, which increases register pressure on entry to the PHI's 179202375Srdivacky // block. 180202375Srdivacky if (NeededPhi) 181202375Srdivacky return 0; 182202375Srdivacky 183202375Srdivacky FixedOperands[op] = 0; // Needs a PHI. 184202375Srdivacky NeededPhi = true; 185202375Srdivacky } 186202375Srdivacky } 187202375Srdivacky 188202375Srdivacky // If all of the base pointers of the PHI'd GEPs are from allocas, don't 189202375Srdivacky // bother doing this transformation. At best, this will just save a bit of 190202375Srdivacky // offset calculation, but all the predecessors will have to materialize the 191202375Srdivacky // stack address into a register anyway. We'd actually rather *clone* the 192202375Srdivacky // load up into the predecessors so that we have a load of a gep of an alloca, 193202375Srdivacky // which can usually all be folded into the load. 194202375Srdivacky if (AllBasePointersAreAllocas) 195202375Srdivacky return 0; 196202375Srdivacky 197202375Srdivacky // Otherwise, this is safe to transform. Insert PHI nodes for each operand 198202375Srdivacky // that is variable. 199202375Srdivacky SmallVector<PHINode*, 16> OperandPhis(FixedOperands.size()); 200202375Srdivacky 201202375Srdivacky bool HasAnyPHIs = false; 202202375Srdivacky for (unsigned i = 0, e = FixedOperands.size(); i != e; ++i) { 203202375Srdivacky if (FixedOperands[i]) continue; // operand doesn't need a phi. 204202375Srdivacky Value *FirstOp = FirstInst->getOperand(i); 205202375Srdivacky PHINode *NewPN = PHINode::Create(FirstOp->getType(), 206202375Srdivacky FirstOp->getName()+".pn"); 207202375Srdivacky InsertNewInstBefore(NewPN, PN); 208202375Srdivacky 209202375Srdivacky NewPN->reserveOperandSpace(e); 210202375Srdivacky NewPN->addIncoming(FirstOp, PN.getIncomingBlock(0)); 211202375Srdivacky OperandPhis[i] = NewPN; 212202375Srdivacky FixedOperands[i] = NewPN; 213202375Srdivacky HasAnyPHIs = true; 214202375Srdivacky } 215202375Srdivacky 216202375Srdivacky 217202375Srdivacky // Add all operands to the new PHIs. 218202375Srdivacky if (HasAnyPHIs) { 219202375Srdivacky for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) { 220202375Srdivacky GetElementPtrInst *InGEP =cast<GetElementPtrInst>(PN.getIncomingValue(i)); 221202375Srdivacky BasicBlock *InBB = PN.getIncomingBlock(i); 222202375Srdivacky 223202375Srdivacky for (unsigned op = 0, e = OperandPhis.size(); op != e; ++op) 224202375Srdivacky if (PHINode *OpPhi = OperandPhis[op]) 225202375Srdivacky OpPhi->addIncoming(InGEP->getOperand(op), InBB); 226202375Srdivacky } 227202375Srdivacky } 228202375Srdivacky 229202375Srdivacky Value *Base = FixedOperands[0]; 230218893Sdim GetElementPtrInst *NewGEP = 231202375Srdivacky GetElementPtrInst::Create(Base, FixedOperands.begin()+1, 232202375Srdivacky FixedOperands.end()); 233218893Sdim if (AllInBounds) NewGEP->setIsInBounds(); 234218893Sdim return NewGEP; 235202375Srdivacky} 236202375Srdivacky 237202375Srdivacky 238202375Srdivacky/// isSafeAndProfitableToSinkLoad - Return true if we know that it is safe to 239202375Srdivacky/// sink the load out of the block that defines it. This means that it must be 240202375Srdivacky/// obvious the value of the load is not changed from the point of the load to 241202375Srdivacky/// the end of the block it is in. 242202375Srdivacky/// 243202375Srdivacky/// Finally, it is safe, but not profitable, to sink a load targetting a 244202375Srdivacky/// non-address-taken alloca. Doing so will cause us to not promote the alloca 245202375Srdivacky/// to a register. 246202375Srdivackystatic bool isSafeAndProfitableToSinkLoad(LoadInst *L) { 247202375Srdivacky BasicBlock::iterator BBI = L, E = L->getParent()->end(); 248202375Srdivacky 249202375Srdivacky for (++BBI; BBI != E; ++BBI) 250202375Srdivacky if (BBI->mayWriteToMemory()) 251202375Srdivacky return false; 252202375Srdivacky 253202375Srdivacky // Check for non-address taken alloca. If not address-taken already, it isn't 254202375Srdivacky // profitable to do this xform. 255202375Srdivacky if (AllocaInst *AI = dyn_cast<AllocaInst>(L->getOperand(0))) { 256202375Srdivacky bool isAddressTaken = false; 257202375Srdivacky for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); 258202375Srdivacky UI != E; ++UI) { 259210299Sed User *U = *UI; 260210299Sed if (isa<LoadInst>(U)) continue; 261210299Sed if (StoreInst *SI = dyn_cast<StoreInst>(U)) { 262202375Srdivacky // If storing TO the alloca, then the address isn't taken. 263202375Srdivacky if (SI->getOperand(1) == AI) continue; 264202375Srdivacky } 265202375Srdivacky isAddressTaken = true; 266202375Srdivacky break; 267202375Srdivacky } 268202375Srdivacky 269202375Srdivacky if (!isAddressTaken && AI->isStaticAlloca()) 270202375Srdivacky return false; 271202375Srdivacky } 272202375Srdivacky 273202375Srdivacky // If this load is a load from a GEP with a constant offset from an alloca, 274202375Srdivacky // then we don't want to sink it. In its present form, it will be 275202375Srdivacky // load [constant stack offset]. Sinking it will cause us to have to 276202375Srdivacky // materialize the stack addresses in each predecessor in a register only to 277202375Srdivacky // do a shared load from register in the successor. 278202375Srdivacky if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(L->getOperand(0))) 279202375Srdivacky if (AllocaInst *AI = dyn_cast<AllocaInst>(GEP->getOperand(0))) 280202375Srdivacky if (AI->isStaticAlloca() && GEP->hasAllConstantIndices()) 281202375Srdivacky return false; 282202375Srdivacky 283202375Srdivacky return true; 284202375Srdivacky} 285202375Srdivacky 286202375SrdivackyInstruction *InstCombiner::FoldPHIArgLoadIntoPHI(PHINode &PN) { 287202375Srdivacky LoadInst *FirstLI = cast<LoadInst>(PN.getIncomingValue(0)); 288202375Srdivacky 289202375Srdivacky // When processing loads, we need to propagate two bits of information to the 290202375Srdivacky // sunk load: whether it is volatile, and what its alignment is. We currently 291202375Srdivacky // don't sink loads when some have their alignment specified and some don't. 292202375Srdivacky // visitLoadInst will propagate an alignment onto the load when TD is around, 293202375Srdivacky // and if TD isn't around, we can't handle the mixed case. 294202375Srdivacky bool isVolatile = FirstLI->isVolatile(); 295202375Srdivacky unsigned LoadAlignment = FirstLI->getAlignment(); 296204792Srdivacky unsigned LoadAddrSpace = FirstLI->getPointerAddressSpace(); 297202375Srdivacky 298202375Srdivacky // We can't sink the load if the loaded value could be modified between the 299202375Srdivacky // load and the PHI. 300202375Srdivacky if (FirstLI->getParent() != PN.getIncomingBlock(0) || 301202375Srdivacky !isSafeAndProfitableToSinkLoad(FirstLI)) 302202375Srdivacky return 0; 303202375Srdivacky 304202375Srdivacky // If the PHI is of volatile loads and the load block has multiple 305202375Srdivacky // successors, sinking it would remove a load of the volatile value from 306202375Srdivacky // the path through the other successor. 307202375Srdivacky if (isVolatile && 308202375Srdivacky FirstLI->getParent()->getTerminator()->getNumSuccessors() != 1) 309202375Srdivacky return 0; 310202375Srdivacky 311202375Srdivacky // Check to see if all arguments are the same operation. 312202375Srdivacky for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) { 313202375Srdivacky LoadInst *LI = dyn_cast<LoadInst>(PN.getIncomingValue(i)); 314202375Srdivacky if (!LI || !LI->hasOneUse()) 315202375Srdivacky return 0; 316202375Srdivacky 317202375Srdivacky // We can't sink the load if the loaded value could be modified between 318202375Srdivacky // the load and the PHI. 319202375Srdivacky if (LI->isVolatile() != isVolatile || 320202375Srdivacky LI->getParent() != PN.getIncomingBlock(i) || 321204792Srdivacky LI->getPointerAddressSpace() != LoadAddrSpace || 322202375Srdivacky !isSafeAndProfitableToSinkLoad(LI)) 323202375Srdivacky return 0; 324202375Srdivacky 325202375Srdivacky // If some of the loads have an alignment specified but not all of them, 326202375Srdivacky // we can't do the transformation. 327202375Srdivacky if ((LoadAlignment != 0) != (LI->getAlignment() != 0)) 328202375Srdivacky return 0; 329202375Srdivacky 330202375Srdivacky LoadAlignment = std::min(LoadAlignment, LI->getAlignment()); 331202375Srdivacky 332202375Srdivacky // If the PHI is of volatile loads and the load block has multiple 333202375Srdivacky // successors, sinking it would remove a load of the volatile value from 334202375Srdivacky // the path through the other successor. 335202375Srdivacky if (isVolatile && 336202375Srdivacky LI->getParent()->getTerminator()->getNumSuccessors() != 1) 337202375Srdivacky return 0; 338202375Srdivacky } 339202375Srdivacky 340202375Srdivacky // Okay, they are all the same operation. Create a new PHI node of the 341202375Srdivacky // correct type, and PHI together all of the LHS's of the instructions. 342202375Srdivacky PHINode *NewPN = PHINode::Create(FirstLI->getOperand(0)->getType(), 343202375Srdivacky PN.getName()+".in"); 344202375Srdivacky NewPN->reserveOperandSpace(PN.getNumOperands()/2); 345202375Srdivacky 346202375Srdivacky Value *InVal = FirstLI->getOperand(0); 347202375Srdivacky NewPN->addIncoming(InVal, PN.getIncomingBlock(0)); 348202375Srdivacky 349202375Srdivacky // Add all operands to the new PHI. 350202375Srdivacky for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) { 351202375Srdivacky Value *NewInVal = cast<LoadInst>(PN.getIncomingValue(i))->getOperand(0); 352202375Srdivacky if (NewInVal != InVal) 353202375Srdivacky InVal = 0; 354202375Srdivacky NewPN->addIncoming(NewInVal, PN.getIncomingBlock(i)); 355202375Srdivacky } 356202375Srdivacky 357202375Srdivacky Value *PhiVal; 358202375Srdivacky if (InVal) { 359202375Srdivacky // The new PHI unions all of the same values together. This is really 360202375Srdivacky // common, so we handle it intelligently here for compile-time speed. 361202375Srdivacky PhiVal = InVal; 362202375Srdivacky delete NewPN; 363202375Srdivacky } else { 364202375Srdivacky InsertNewInstBefore(NewPN, PN); 365202375Srdivacky PhiVal = NewPN; 366202375Srdivacky } 367202375Srdivacky 368202375Srdivacky // If this was a volatile load that we are merging, make sure to loop through 369202375Srdivacky // and mark all the input loads as non-volatile. If we don't do this, we will 370202375Srdivacky // insert a new volatile load and the old ones will not be deletable. 371202375Srdivacky if (isVolatile) 372202375Srdivacky for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) 373202375Srdivacky cast<LoadInst>(PN.getIncomingValue(i))->setVolatile(false); 374202375Srdivacky 375202375Srdivacky return new LoadInst(PhiVal, "", isVolatile, LoadAlignment); 376202375Srdivacky} 377202375Srdivacky 378202375Srdivacky 379202375Srdivacky 380202375Srdivacky/// FoldPHIArgOpIntoPHI - If all operands to a PHI node are the same "unary" 381202375Srdivacky/// operator and they all are only used by the PHI, PHI together their 382202375Srdivacky/// inputs, and do the operation once, to the result of the PHI. 383202375SrdivackyInstruction *InstCombiner::FoldPHIArgOpIntoPHI(PHINode &PN) { 384202375Srdivacky Instruction *FirstInst = cast<Instruction>(PN.getIncomingValue(0)); 385202375Srdivacky 386202375Srdivacky if (isa<GetElementPtrInst>(FirstInst)) 387202375Srdivacky return FoldPHIArgGEPIntoPHI(PN); 388202375Srdivacky if (isa<LoadInst>(FirstInst)) 389202375Srdivacky return FoldPHIArgLoadIntoPHI(PN); 390202375Srdivacky 391202375Srdivacky // Scan the instruction, looking for input operations that can be folded away. 392202375Srdivacky // If all input operands to the phi are the same instruction (e.g. a cast from 393202375Srdivacky // the same type or "+42") we can pull the operation through the PHI, reducing 394202375Srdivacky // code size and simplifying code. 395202375Srdivacky Constant *ConstantOp = 0; 396202375Srdivacky const Type *CastSrcTy = 0; 397218893Sdim bool isNUW = false, isNSW = false, isExact = false; 398202375Srdivacky 399202375Srdivacky if (isa<CastInst>(FirstInst)) { 400202375Srdivacky CastSrcTy = FirstInst->getOperand(0)->getType(); 401202375Srdivacky 402202375Srdivacky // Be careful about transforming integer PHIs. We don't want to pessimize 403202375Srdivacky // the code by turning an i32 into an i1293. 404204642Srdivacky if (PN.getType()->isIntegerTy() && CastSrcTy->isIntegerTy()) { 405202375Srdivacky if (!ShouldChangeType(PN.getType(), CastSrcTy)) 406202375Srdivacky return 0; 407202375Srdivacky } 408202375Srdivacky } else if (isa<BinaryOperator>(FirstInst) || isa<CmpInst>(FirstInst)) { 409202375Srdivacky // Can fold binop, compare or shift here if the RHS is a constant, 410202375Srdivacky // otherwise call FoldPHIArgBinOpIntoPHI. 411202375Srdivacky ConstantOp = dyn_cast<Constant>(FirstInst->getOperand(1)); 412202375Srdivacky if (ConstantOp == 0) 413202375Srdivacky return FoldPHIArgBinOpIntoPHI(PN); 414218893Sdim 415218893Sdim if (OverflowingBinaryOperator *BO = 416218893Sdim dyn_cast<OverflowingBinaryOperator>(FirstInst)) { 417218893Sdim isNUW = BO->hasNoUnsignedWrap(); 418218893Sdim isNSW = BO->hasNoSignedWrap(); 419218893Sdim } else if (PossiblyExactOperator *PEO = 420218893Sdim dyn_cast<PossiblyExactOperator>(FirstInst)) 421218893Sdim isExact = PEO->isExact(); 422202375Srdivacky } else { 423202375Srdivacky return 0; // Cannot fold this operation. 424202375Srdivacky } 425202375Srdivacky 426202375Srdivacky // Check to see if all arguments are the same operation. 427202375Srdivacky for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) { 428202375Srdivacky Instruction *I = dyn_cast<Instruction>(PN.getIncomingValue(i)); 429202375Srdivacky if (I == 0 || !I->hasOneUse() || !I->isSameOperationAs(FirstInst)) 430202375Srdivacky return 0; 431202375Srdivacky if (CastSrcTy) { 432202375Srdivacky if (I->getOperand(0)->getType() != CastSrcTy) 433202375Srdivacky return 0; // Cast operation must match. 434202375Srdivacky } else if (I->getOperand(1) != ConstantOp) { 435202375Srdivacky return 0; 436202375Srdivacky } 437218893Sdim 438218893Sdim if (isNUW) 439218893Sdim isNUW = cast<OverflowingBinaryOperator>(I)->hasNoUnsignedWrap(); 440218893Sdim if (isNSW) 441218893Sdim isNSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap(); 442218893Sdim if (isExact) 443218893Sdim isExact = cast<PossiblyExactOperator>(I)->isExact(); 444202375Srdivacky } 445202375Srdivacky 446202375Srdivacky // Okay, they are all the same operation. Create a new PHI node of the 447202375Srdivacky // correct type, and PHI together all of the LHS's of the instructions. 448202375Srdivacky PHINode *NewPN = PHINode::Create(FirstInst->getOperand(0)->getType(), 449202375Srdivacky PN.getName()+".in"); 450202375Srdivacky NewPN->reserveOperandSpace(PN.getNumOperands()/2); 451202375Srdivacky 452202375Srdivacky Value *InVal = FirstInst->getOperand(0); 453202375Srdivacky NewPN->addIncoming(InVal, PN.getIncomingBlock(0)); 454202375Srdivacky 455202375Srdivacky // Add all operands to the new PHI. 456202375Srdivacky for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) { 457202375Srdivacky Value *NewInVal = cast<Instruction>(PN.getIncomingValue(i))->getOperand(0); 458202375Srdivacky if (NewInVal != InVal) 459202375Srdivacky InVal = 0; 460202375Srdivacky NewPN->addIncoming(NewInVal, PN.getIncomingBlock(i)); 461202375Srdivacky } 462202375Srdivacky 463202375Srdivacky Value *PhiVal; 464202375Srdivacky if (InVal) { 465202375Srdivacky // The new PHI unions all of the same values together. This is really 466202375Srdivacky // common, so we handle it intelligently here for compile-time speed. 467202375Srdivacky PhiVal = InVal; 468202375Srdivacky delete NewPN; 469202375Srdivacky } else { 470202375Srdivacky InsertNewInstBefore(NewPN, PN); 471202375Srdivacky PhiVal = NewPN; 472202375Srdivacky } 473202375Srdivacky 474202375Srdivacky // Insert and return the new operation. 475202375Srdivacky if (CastInst *FirstCI = dyn_cast<CastInst>(FirstInst)) 476202375Srdivacky return CastInst::Create(FirstCI->getOpcode(), PhiVal, PN.getType()); 477202375Srdivacky 478218893Sdim if (BinaryOperator *BinOp = dyn_cast<BinaryOperator>(FirstInst)) { 479218893Sdim BinOp = BinaryOperator::Create(BinOp->getOpcode(), PhiVal, ConstantOp); 480218893Sdim if (isNUW) BinOp->setHasNoUnsignedWrap(); 481218893Sdim if (isNSW) BinOp->setHasNoSignedWrap(); 482218893Sdim if (isExact) BinOp->setIsExact(); 483218893Sdim return BinOp; 484218893Sdim } 485202375Srdivacky 486202375Srdivacky CmpInst *CIOp = cast<CmpInst>(FirstInst); 487202375Srdivacky return CmpInst::Create(CIOp->getOpcode(), CIOp->getPredicate(), 488202375Srdivacky PhiVal, ConstantOp); 489202375Srdivacky} 490202375Srdivacky 491202375Srdivacky/// DeadPHICycle - Return true if this PHI node is only used by a PHI node cycle 492202375Srdivacky/// that is dead. 493202375Srdivackystatic bool DeadPHICycle(PHINode *PN, 494202375Srdivacky SmallPtrSet<PHINode*, 16> &PotentiallyDeadPHIs) { 495202375Srdivacky if (PN->use_empty()) return true; 496202375Srdivacky if (!PN->hasOneUse()) return false; 497202375Srdivacky 498202375Srdivacky // Remember this node, and if we find the cycle, return. 499202375Srdivacky if (!PotentiallyDeadPHIs.insert(PN)) 500202375Srdivacky return true; 501202375Srdivacky 502202375Srdivacky // Don't scan crazily complex things. 503202375Srdivacky if (PotentiallyDeadPHIs.size() == 16) 504202375Srdivacky return false; 505202375Srdivacky 506202375Srdivacky if (PHINode *PU = dyn_cast<PHINode>(PN->use_back())) 507202375Srdivacky return DeadPHICycle(PU, PotentiallyDeadPHIs); 508202375Srdivacky 509202375Srdivacky return false; 510202375Srdivacky} 511202375Srdivacky 512202375Srdivacky/// PHIsEqualValue - Return true if this phi node is always equal to 513202375Srdivacky/// NonPhiInVal. This happens with mutually cyclic phi nodes like: 514202375Srdivacky/// z = some value; x = phi (y, z); y = phi (x, z) 515202375Srdivackystatic bool PHIsEqualValue(PHINode *PN, Value *NonPhiInVal, 516202375Srdivacky SmallPtrSet<PHINode*, 16> &ValueEqualPHIs) { 517202375Srdivacky // See if we already saw this PHI node. 518202375Srdivacky if (!ValueEqualPHIs.insert(PN)) 519202375Srdivacky return true; 520202375Srdivacky 521202375Srdivacky // Don't scan crazily complex things. 522202375Srdivacky if (ValueEqualPHIs.size() == 16) 523202375Srdivacky return false; 524202375Srdivacky 525202375Srdivacky // Scan the operands to see if they are either phi nodes or are equal to 526202375Srdivacky // the value. 527202375Srdivacky for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 528202375Srdivacky Value *Op = PN->getIncomingValue(i); 529202375Srdivacky if (PHINode *OpPN = dyn_cast<PHINode>(Op)) { 530202375Srdivacky if (!PHIsEqualValue(OpPN, NonPhiInVal, ValueEqualPHIs)) 531202375Srdivacky return false; 532202375Srdivacky } else if (Op != NonPhiInVal) 533202375Srdivacky return false; 534202375Srdivacky } 535202375Srdivacky 536202375Srdivacky return true; 537202375Srdivacky} 538202375Srdivacky 539202375Srdivacky 540202375Srdivackynamespace { 541202375Srdivackystruct PHIUsageRecord { 542202375Srdivacky unsigned PHIId; // The ID # of the PHI (something determinstic to sort on) 543202375Srdivacky unsigned Shift; // The amount shifted. 544202375Srdivacky Instruction *Inst; // The trunc instruction. 545202375Srdivacky 546202375Srdivacky PHIUsageRecord(unsigned pn, unsigned Sh, Instruction *User) 547202375Srdivacky : PHIId(pn), Shift(Sh), Inst(User) {} 548202375Srdivacky 549202375Srdivacky bool operator<(const PHIUsageRecord &RHS) const { 550202375Srdivacky if (PHIId < RHS.PHIId) return true; 551202375Srdivacky if (PHIId > RHS.PHIId) return false; 552202375Srdivacky if (Shift < RHS.Shift) return true; 553202375Srdivacky if (Shift > RHS.Shift) return false; 554202375Srdivacky return Inst->getType()->getPrimitiveSizeInBits() < 555202375Srdivacky RHS.Inst->getType()->getPrimitiveSizeInBits(); 556202375Srdivacky } 557202375Srdivacky}; 558202375Srdivacky 559202375Srdivackystruct LoweredPHIRecord { 560202375Srdivacky PHINode *PN; // The PHI that was lowered. 561202375Srdivacky unsigned Shift; // The amount shifted. 562202375Srdivacky unsigned Width; // The width extracted. 563202375Srdivacky 564202375Srdivacky LoweredPHIRecord(PHINode *pn, unsigned Sh, const Type *Ty) 565202375Srdivacky : PN(pn), Shift(Sh), Width(Ty->getPrimitiveSizeInBits()) {} 566202375Srdivacky 567202375Srdivacky // Ctor form used by DenseMap. 568202375Srdivacky LoweredPHIRecord(PHINode *pn, unsigned Sh) 569202375Srdivacky : PN(pn), Shift(Sh), Width(0) {} 570202375Srdivacky}; 571202375Srdivacky} 572202375Srdivacky 573202375Srdivackynamespace llvm { 574202375Srdivacky template<> 575202375Srdivacky struct DenseMapInfo<LoweredPHIRecord> { 576202375Srdivacky static inline LoweredPHIRecord getEmptyKey() { 577202375Srdivacky return LoweredPHIRecord(0, 0); 578202375Srdivacky } 579202375Srdivacky static inline LoweredPHIRecord getTombstoneKey() { 580202375Srdivacky return LoweredPHIRecord(0, 1); 581202375Srdivacky } 582202375Srdivacky static unsigned getHashValue(const LoweredPHIRecord &Val) { 583202375Srdivacky return DenseMapInfo<PHINode*>::getHashValue(Val.PN) ^ (Val.Shift>>3) ^ 584202375Srdivacky (Val.Width>>3); 585202375Srdivacky } 586202375Srdivacky static bool isEqual(const LoweredPHIRecord &LHS, 587202375Srdivacky const LoweredPHIRecord &RHS) { 588202375Srdivacky return LHS.PN == RHS.PN && LHS.Shift == RHS.Shift && 589202375Srdivacky LHS.Width == RHS.Width; 590202375Srdivacky } 591202375Srdivacky }; 592202375Srdivacky template <> 593202375Srdivacky struct isPodLike<LoweredPHIRecord> { static const bool value = true; }; 594202375Srdivacky} 595202375Srdivacky 596202375Srdivacky 597202375Srdivacky/// SliceUpIllegalIntegerPHI - This is an integer PHI and we know that it has an 598202375Srdivacky/// illegal type: see if it is only used by trunc or trunc(lshr) operations. If 599202375Srdivacky/// so, we split the PHI into the various pieces being extracted. This sort of 600202375Srdivacky/// thing is introduced when SROA promotes an aggregate to large integer values. 601202375Srdivacky/// 602202375Srdivacky/// TODO: The user of the trunc may be an bitcast to float/double/vector or an 603202375Srdivacky/// inttoptr. We should produce new PHIs in the right type. 604202375Srdivacky/// 605202375SrdivackyInstruction *InstCombiner::SliceUpIllegalIntegerPHI(PHINode &FirstPhi) { 606202375Srdivacky // PHIUsers - Keep track of all of the truncated values extracted from a set 607202375Srdivacky // of PHIs, along with their offset. These are the things we want to rewrite. 608202375Srdivacky SmallVector<PHIUsageRecord, 16> PHIUsers; 609202375Srdivacky 610202375Srdivacky // PHIs are often mutually cyclic, so we keep track of a whole set of PHI 611202375Srdivacky // nodes which are extracted from. PHIsToSlice is a set we use to avoid 612202375Srdivacky // revisiting PHIs, PHIsInspected is a ordered list of PHIs that we need to 613202375Srdivacky // check the uses of (to ensure they are all extracts). 614202375Srdivacky SmallVector<PHINode*, 8> PHIsToSlice; 615202375Srdivacky SmallPtrSet<PHINode*, 8> PHIsInspected; 616202375Srdivacky 617202375Srdivacky PHIsToSlice.push_back(&FirstPhi); 618202375Srdivacky PHIsInspected.insert(&FirstPhi); 619202375Srdivacky 620202375Srdivacky for (unsigned PHIId = 0; PHIId != PHIsToSlice.size(); ++PHIId) { 621202375Srdivacky PHINode *PN = PHIsToSlice[PHIId]; 622202375Srdivacky 623202375Srdivacky // Scan the input list of the PHI. If any input is an invoke, and if the 624202375Srdivacky // input is defined in the predecessor, then we won't be split the critical 625202375Srdivacky // edge which is required to insert a truncate. Because of this, we have to 626202375Srdivacky // bail out. 627202375Srdivacky for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 628202375Srdivacky InvokeInst *II = dyn_cast<InvokeInst>(PN->getIncomingValue(i)); 629202375Srdivacky if (II == 0) continue; 630202375Srdivacky if (II->getParent() != PN->getIncomingBlock(i)) 631202375Srdivacky continue; 632202375Srdivacky 633202375Srdivacky // If we have a phi, and if it's directly in the predecessor, then we have 634202375Srdivacky // a critical edge where we need to put the truncate. Since we can't 635202375Srdivacky // split the edge in instcombine, we have to bail out. 636202375Srdivacky return 0; 637202375Srdivacky } 638202375Srdivacky 639202375Srdivacky 640202375Srdivacky for (Value::use_iterator UI = PN->use_begin(), E = PN->use_end(); 641202375Srdivacky UI != E; ++UI) { 642202375Srdivacky Instruction *User = cast<Instruction>(*UI); 643202375Srdivacky 644202375Srdivacky // If the user is a PHI, inspect its uses recursively. 645202375Srdivacky if (PHINode *UserPN = dyn_cast<PHINode>(User)) { 646202375Srdivacky if (PHIsInspected.insert(UserPN)) 647202375Srdivacky PHIsToSlice.push_back(UserPN); 648202375Srdivacky continue; 649202375Srdivacky } 650202375Srdivacky 651202375Srdivacky // Truncates are always ok. 652202375Srdivacky if (isa<TruncInst>(User)) { 653202375Srdivacky PHIUsers.push_back(PHIUsageRecord(PHIId, 0, User)); 654202375Srdivacky continue; 655202375Srdivacky } 656202375Srdivacky 657202375Srdivacky // Otherwise it must be a lshr which can only be used by one trunc. 658202375Srdivacky if (User->getOpcode() != Instruction::LShr || 659202375Srdivacky !User->hasOneUse() || !isa<TruncInst>(User->use_back()) || 660202375Srdivacky !isa<ConstantInt>(User->getOperand(1))) 661202375Srdivacky return 0; 662202375Srdivacky 663202375Srdivacky unsigned Shift = cast<ConstantInt>(User->getOperand(1))->getZExtValue(); 664202375Srdivacky PHIUsers.push_back(PHIUsageRecord(PHIId, Shift, User->use_back())); 665202375Srdivacky } 666202375Srdivacky } 667202375Srdivacky 668202375Srdivacky // If we have no users, they must be all self uses, just nuke the PHI. 669202375Srdivacky if (PHIUsers.empty()) 670202375Srdivacky return ReplaceInstUsesWith(FirstPhi, UndefValue::get(FirstPhi.getType())); 671202375Srdivacky 672202375Srdivacky // If this phi node is transformable, create new PHIs for all the pieces 673202375Srdivacky // extracted out of it. First, sort the users by their offset and size. 674202375Srdivacky array_pod_sort(PHIUsers.begin(), PHIUsers.end()); 675202375Srdivacky 676202375Srdivacky DEBUG(errs() << "SLICING UP PHI: " << FirstPhi << '\n'; 677202375Srdivacky for (unsigned i = 1, e = PHIsToSlice.size(); i != e; ++i) 678202375Srdivacky errs() << "AND USER PHI #" << i << ": " << *PHIsToSlice[i] <<'\n'; 679202375Srdivacky ); 680202375Srdivacky 681202375Srdivacky // PredValues - This is a temporary used when rewriting PHI nodes. It is 682202375Srdivacky // hoisted out here to avoid construction/destruction thrashing. 683202375Srdivacky DenseMap<BasicBlock*, Value*> PredValues; 684202375Srdivacky 685202375Srdivacky // ExtractedVals - Each new PHI we introduce is saved here so we don't 686202375Srdivacky // introduce redundant PHIs. 687202375Srdivacky DenseMap<LoweredPHIRecord, PHINode*> ExtractedVals; 688202375Srdivacky 689202375Srdivacky for (unsigned UserI = 0, UserE = PHIUsers.size(); UserI != UserE; ++UserI) { 690202375Srdivacky unsigned PHIId = PHIUsers[UserI].PHIId; 691202375Srdivacky PHINode *PN = PHIsToSlice[PHIId]; 692202375Srdivacky unsigned Offset = PHIUsers[UserI].Shift; 693202375Srdivacky const Type *Ty = PHIUsers[UserI].Inst->getType(); 694202375Srdivacky 695202375Srdivacky PHINode *EltPHI; 696202375Srdivacky 697202375Srdivacky // If we've already lowered a user like this, reuse the previously lowered 698202375Srdivacky // value. 699202375Srdivacky if ((EltPHI = ExtractedVals[LoweredPHIRecord(PN, Offset, Ty)]) == 0) { 700202375Srdivacky 701202375Srdivacky // Otherwise, Create the new PHI node for this user. 702202375Srdivacky EltPHI = PHINode::Create(Ty, PN->getName()+".off"+Twine(Offset), PN); 703202375Srdivacky assert(EltPHI->getType() != PN->getType() && 704202375Srdivacky "Truncate didn't shrink phi?"); 705202375Srdivacky 706202375Srdivacky for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 707202375Srdivacky BasicBlock *Pred = PN->getIncomingBlock(i); 708202375Srdivacky Value *&PredVal = PredValues[Pred]; 709202375Srdivacky 710202375Srdivacky // If we already have a value for this predecessor, reuse it. 711202375Srdivacky if (PredVal) { 712202375Srdivacky EltPHI->addIncoming(PredVal, Pred); 713202375Srdivacky continue; 714202375Srdivacky } 715202375Srdivacky 716202375Srdivacky // Handle the PHI self-reuse case. 717202375Srdivacky Value *InVal = PN->getIncomingValue(i); 718202375Srdivacky if (InVal == PN) { 719202375Srdivacky PredVal = EltPHI; 720202375Srdivacky EltPHI->addIncoming(PredVal, Pred); 721202375Srdivacky continue; 722202375Srdivacky } 723202375Srdivacky 724202375Srdivacky if (PHINode *InPHI = dyn_cast<PHINode>(PN)) { 725202375Srdivacky // If the incoming value was a PHI, and if it was one of the PHIs we 726202375Srdivacky // already rewrote it, just use the lowered value. 727202375Srdivacky if (Value *Res = ExtractedVals[LoweredPHIRecord(InPHI, Offset, Ty)]) { 728202375Srdivacky PredVal = Res; 729202375Srdivacky EltPHI->addIncoming(PredVal, Pred); 730202375Srdivacky continue; 731202375Srdivacky } 732202375Srdivacky } 733202375Srdivacky 734202375Srdivacky // Otherwise, do an extract in the predecessor. 735202375Srdivacky Builder->SetInsertPoint(Pred, Pred->getTerminator()); 736202375Srdivacky Value *Res = InVal; 737202375Srdivacky if (Offset) 738202375Srdivacky Res = Builder->CreateLShr(Res, ConstantInt::get(InVal->getType(), 739202375Srdivacky Offset), "extract"); 740202375Srdivacky Res = Builder->CreateTrunc(Res, Ty, "extract.t"); 741202375Srdivacky PredVal = Res; 742202375Srdivacky EltPHI->addIncoming(Res, Pred); 743202375Srdivacky 744202375Srdivacky // If the incoming value was a PHI, and if it was one of the PHIs we are 745202375Srdivacky // rewriting, we will ultimately delete the code we inserted. This 746202375Srdivacky // means we need to revisit that PHI to make sure we extract out the 747202375Srdivacky // needed piece. 748202375Srdivacky if (PHINode *OldInVal = dyn_cast<PHINode>(PN->getIncomingValue(i))) 749202375Srdivacky if (PHIsInspected.count(OldInVal)) { 750202375Srdivacky unsigned RefPHIId = std::find(PHIsToSlice.begin(),PHIsToSlice.end(), 751202375Srdivacky OldInVal)-PHIsToSlice.begin(); 752202375Srdivacky PHIUsers.push_back(PHIUsageRecord(RefPHIId, Offset, 753202375Srdivacky cast<Instruction>(Res))); 754202375Srdivacky ++UserE; 755202375Srdivacky } 756202375Srdivacky } 757202375Srdivacky PredValues.clear(); 758202375Srdivacky 759202375Srdivacky DEBUG(errs() << " Made element PHI for offset " << Offset << ": " 760202375Srdivacky << *EltPHI << '\n'); 761202375Srdivacky ExtractedVals[LoweredPHIRecord(PN, Offset, Ty)] = EltPHI; 762202375Srdivacky } 763202375Srdivacky 764202375Srdivacky // Replace the use of this piece with the PHI node. 765202375Srdivacky ReplaceInstUsesWith(*PHIUsers[UserI].Inst, EltPHI); 766202375Srdivacky } 767202375Srdivacky 768202375Srdivacky // Replace all the remaining uses of the PHI nodes (self uses and the lshrs) 769202375Srdivacky // with undefs. 770202375Srdivacky Value *Undef = UndefValue::get(FirstPhi.getType()); 771202375Srdivacky for (unsigned i = 1, e = PHIsToSlice.size(); i != e; ++i) 772202375Srdivacky ReplaceInstUsesWith(*PHIsToSlice[i], Undef); 773202375Srdivacky return ReplaceInstUsesWith(FirstPhi, Undef); 774202375Srdivacky} 775202375Srdivacky 776202375Srdivacky// PHINode simplification 777202375Srdivacky// 778202375SrdivackyInstruction *InstCombiner::visitPHINode(PHINode &PN) { 779202375Srdivacky // If LCSSA is around, don't mess with Phi nodes 780202375Srdivacky if (MustPreserveLCSSA) return 0; 781218893Sdim 782218893Sdim if (Value *V = SimplifyInstruction(&PN, TD)) 783202375Srdivacky return ReplaceInstUsesWith(PN, V); 784202375Srdivacky 785202375Srdivacky // If all PHI operands are the same operation, pull them through the PHI, 786202375Srdivacky // reducing code size. 787202375Srdivacky if (isa<Instruction>(PN.getIncomingValue(0)) && 788202375Srdivacky isa<Instruction>(PN.getIncomingValue(1)) && 789202375Srdivacky cast<Instruction>(PN.getIncomingValue(0))->getOpcode() == 790202375Srdivacky cast<Instruction>(PN.getIncomingValue(1))->getOpcode() && 791202375Srdivacky // FIXME: The hasOneUse check will fail for PHIs that use the value more 792202375Srdivacky // than themselves more than once. 793202375Srdivacky PN.getIncomingValue(0)->hasOneUse()) 794202375Srdivacky if (Instruction *Result = FoldPHIArgOpIntoPHI(PN)) 795202375Srdivacky return Result; 796202375Srdivacky 797202375Srdivacky // If this is a trivial cycle in the PHI node graph, remove it. Basically, if 798202375Srdivacky // this PHI only has a single use (a PHI), and if that PHI only has one use (a 799202375Srdivacky // PHI)... break the cycle. 800202375Srdivacky if (PN.hasOneUse()) { 801202375Srdivacky Instruction *PHIUser = cast<Instruction>(PN.use_back()); 802202375Srdivacky if (PHINode *PU = dyn_cast<PHINode>(PHIUser)) { 803202375Srdivacky SmallPtrSet<PHINode*, 16> PotentiallyDeadPHIs; 804202375Srdivacky PotentiallyDeadPHIs.insert(&PN); 805202375Srdivacky if (DeadPHICycle(PU, PotentiallyDeadPHIs)) 806202375Srdivacky return ReplaceInstUsesWith(PN, UndefValue::get(PN.getType())); 807202375Srdivacky } 808202375Srdivacky 809202375Srdivacky // If this phi has a single use, and if that use just computes a value for 810202375Srdivacky // the next iteration of a loop, delete the phi. This occurs with unused 811202375Srdivacky // induction variables, e.g. "for (int j = 0; ; ++j);". Detecting this 812202375Srdivacky // common case here is good because the only other things that catch this 813202375Srdivacky // are induction variable analysis (sometimes) and ADCE, which is only run 814202375Srdivacky // late. 815202375Srdivacky if (PHIUser->hasOneUse() && 816202375Srdivacky (isa<BinaryOperator>(PHIUser) || isa<GetElementPtrInst>(PHIUser)) && 817202375Srdivacky PHIUser->use_back() == &PN) { 818202375Srdivacky return ReplaceInstUsesWith(PN, UndefValue::get(PN.getType())); 819202375Srdivacky } 820202375Srdivacky } 821202375Srdivacky 822202375Srdivacky // We sometimes end up with phi cycles that non-obviously end up being the 823202375Srdivacky // same value, for example: 824202375Srdivacky // z = some value; x = phi (y, z); y = phi (x, z) 825202375Srdivacky // where the phi nodes don't necessarily need to be in the same block. Do a 826202375Srdivacky // quick check to see if the PHI node only contains a single non-phi value, if 827202375Srdivacky // so, scan to see if the phi cycle is actually equal to that value. 828202375Srdivacky { 829202375Srdivacky unsigned InValNo = 0, NumOperandVals = PN.getNumIncomingValues(); 830202375Srdivacky // Scan for the first non-phi operand. 831202375Srdivacky while (InValNo != NumOperandVals && 832202375Srdivacky isa<PHINode>(PN.getIncomingValue(InValNo))) 833202375Srdivacky ++InValNo; 834202375Srdivacky 835202375Srdivacky if (InValNo != NumOperandVals) { 836202375Srdivacky Value *NonPhiInVal = PN.getOperand(InValNo); 837202375Srdivacky 838202375Srdivacky // Scan the rest of the operands to see if there are any conflicts, if so 839202375Srdivacky // there is no need to recursively scan other phis. 840202375Srdivacky for (++InValNo; InValNo != NumOperandVals; ++InValNo) { 841202375Srdivacky Value *OpVal = PN.getIncomingValue(InValNo); 842202375Srdivacky if (OpVal != NonPhiInVal && !isa<PHINode>(OpVal)) 843202375Srdivacky break; 844202375Srdivacky } 845202375Srdivacky 846202375Srdivacky // If we scanned over all operands, then we have one unique value plus 847202375Srdivacky // phi values. Scan PHI nodes to see if they all merge in each other or 848202375Srdivacky // the value. 849202375Srdivacky if (InValNo == NumOperandVals) { 850202375Srdivacky SmallPtrSet<PHINode*, 16> ValueEqualPHIs; 851202375Srdivacky if (PHIsEqualValue(&PN, NonPhiInVal, ValueEqualPHIs)) 852202375Srdivacky return ReplaceInstUsesWith(PN, NonPhiInVal); 853202375Srdivacky } 854202375Srdivacky } 855202375Srdivacky } 856202375Srdivacky 857202375Srdivacky // If there are multiple PHIs, sort their operands so that they all list 858202375Srdivacky // the blocks in the same order. This will help identical PHIs be eliminated 859202375Srdivacky // by other passes. Other passes shouldn't depend on this for correctness 860202375Srdivacky // however. 861202375Srdivacky PHINode *FirstPN = cast<PHINode>(PN.getParent()->begin()); 862202375Srdivacky if (&PN != FirstPN) 863202375Srdivacky for (unsigned i = 0, e = FirstPN->getNumIncomingValues(); i != e; ++i) { 864202375Srdivacky BasicBlock *BBA = PN.getIncomingBlock(i); 865202375Srdivacky BasicBlock *BBB = FirstPN->getIncomingBlock(i); 866202375Srdivacky if (BBA != BBB) { 867202375Srdivacky Value *VA = PN.getIncomingValue(i); 868202375Srdivacky unsigned j = PN.getBasicBlockIndex(BBB); 869202375Srdivacky Value *VB = PN.getIncomingValue(j); 870202375Srdivacky PN.setIncomingBlock(i, BBB); 871202375Srdivacky PN.setIncomingValue(i, VB); 872202375Srdivacky PN.setIncomingBlock(j, BBA); 873202375Srdivacky PN.setIncomingValue(j, VA); 874202375Srdivacky // NOTE: Instcombine normally would want us to "return &PN" if we 875202375Srdivacky // modified any of the operands of an instruction. However, since we 876202375Srdivacky // aren't adding or removing uses (just rearranging them) we don't do 877202375Srdivacky // this in this case. 878202375Srdivacky } 879202375Srdivacky } 880202375Srdivacky 881202375Srdivacky // If this is an integer PHI and we know that it has an illegal type, see if 882202375Srdivacky // it is only used by trunc or trunc(lshr) operations. If so, we split the 883202375Srdivacky // PHI into the various pieces being extracted. This sort of thing is 884202375Srdivacky // introduced when SROA promotes an aggregate to a single large integer type. 885204642Srdivacky if (PN.getType()->isIntegerTy() && TD && 886202375Srdivacky !TD->isLegalInteger(PN.getType()->getPrimitiveSizeInBits())) 887202375Srdivacky if (Instruction *Res = SliceUpIllegalIntegerPHI(PN)) 888202375Srdivacky return Res; 889202375Srdivacky 890202375Srdivacky return 0; 891202375Srdivacky} 892