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" 15249423Sdim#include "llvm/ADT/STLExtras.h" 16249423Sdim#include "llvm/ADT/SmallPtrSet.h" 17218893Sdim#include "llvm/Analysis/InstructionSimplify.h" 18249423Sdim#include "llvm/IR/DataLayout.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); 30251662Sdim 31226633Sdim Type *LHSType = LHSVal->getType(); 32226633Sdim Type *RHSType = RHSVal->getType(); 33251662Sdim 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(); 42251662Sdim 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; 57251662Sdim 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(); 64251662Sdim 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; 76251662Sdim 77202375Srdivacky // Otherwise, this is safe to transform! 78251662Sdim 79202375Srdivacky Value *InLHS = FirstInst->getOperand(0); 80202375Srdivacky Value *InRHS = FirstInst->getOperand(1); 81202375Srdivacky PHINode *NewLHS = 0, *NewRHS = 0; 82202375Srdivacky if (LHSVal == 0) { 83221345Sdim NewLHS = PHINode::Create(LHSType, PN.getNumIncomingValues(), 84202375Srdivacky FirstInst->getOperand(0)->getName() + ".pn"); 85202375Srdivacky NewLHS->addIncoming(InLHS, PN.getIncomingBlock(0)); 86202375Srdivacky InsertNewInstBefore(NewLHS, PN); 87202375Srdivacky LHSVal = NewLHS; 88202375Srdivacky } 89251662Sdim 90202375Srdivacky if (RHSVal == 0) { 91221345Sdim NewRHS = PHINode::Create(RHSType, PN.getNumIncomingValues(), 92202375Srdivacky FirstInst->getOperand(1)->getName() + ".pn"); 93202375Srdivacky NewRHS->addIncoming(InRHS, PN.getIncomingBlock(0)); 94202375Srdivacky InsertNewInstBefore(NewRHS, PN); 95202375Srdivacky RHSVal = NewRHS; 96202375Srdivacky } 97251662Sdim 98202375Srdivacky // Add all operands to the new PHIs. 99202375Srdivacky if (NewLHS || NewRHS) { 100202375Srdivacky for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) { 101202375Srdivacky Instruction *InInst = cast<Instruction>(PN.getIncomingValue(i)); 102202375Srdivacky if (NewLHS) { 103202375Srdivacky Value *NewInLHS = InInst->getOperand(0); 104202375Srdivacky NewLHS->addIncoming(NewInLHS, PN.getIncomingBlock(i)); 105202375Srdivacky } 106202375Srdivacky if (NewRHS) { 107202375Srdivacky Value *NewInRHS = InInst->getOperand(1); 108202375Srdivacky NewRHS->addIncoming(NewInRHS, PN.getIncomingBlock(i)); 109202375Srdivacky } 110202375Srdivacky } 111202375Srdivacky } 112251662Sdim 113223017Sdim if (CmpInst *CIOp = dyn_cast<CmpInst>(FirstInst)) { 114223017Sdim CmpInst *NewCI = CmpInst::Create(CIOp->getOpcode(), CIOp->getPredicate(), 115223017Sdim LHSVal, RHSVal); 116223017Sdim NewCI->setDebugLoc(FirstInst->getDebugLoc()); 117223017Sdim return NewCI; 118223017Sdim } 119223017Sdim 120218893Sdim BinaryOperator *BinOp = cast<BinaryOperator>(FirstInst); 121218893Sdim BinaryOperator *NewBinOp = 122218893Sdim BinaryOperator::Create(BinOp->getOpcode(), LHSVal, RHSVal); 123218893Sdim if (isNUW) NewBinOp->setHasNoUnsignedWrap(); 124218893Sdim if (isNSW) NewBinOp->setHasNoSignedWrap(); 125218893Sdim if (isExact) NewBinOp->setIsExact(); 126223017Sdim NewBinOp->setDebugLoc(FirstInst->getDebugLoc()); 127218893Sdim return NewBinOp; 128202375Srdivacky} 129202375Srdivacky 130202375SrdivackyInstruction *InstCombiner::FoldPHIArgGEPIntoPHI(PHINode &PN) { 131202375Srdivacky GetElementPtrInst *FirstInst =cast<GetElementPtrInst>(PN.getIncomingValue(0)); 132251662Sdim 133251662Sdim SmallVector<Value*, 16> FixedOperands(FirstInst->op_begin(), 134202375Srdivacky FirstInst->op_end()); 135202375Srdivacky // This is true if all GEP bases are allocas and if all indices into them are 136202375Srdivacky // constants. 137202375Srdivacky bool AllBasePointersAreAllocas = true; 138202375Srdivacky 139202375Srdivacky // We don't want to replace this phi if the replacement would require 140202375Srdivacky // more than one phi, which leads to higher register pressure. This is 141202375Srdivacky // especially bad when the PHIs are in the header of a loop. 142202375Srdivacky bool NeededPhi = false; 143251662Sdim 144218893Sdim bool AllInBounds = true; 145251662Sdim 146202375Srdivacky // Scan to see if all operands are the same opcode, and all have one use. 147202375Srdivacky for (unsigned i = 1; i != PN.getNumIncomingValues(); ++i) { 148202375Srdivacky GetElementPtrInst *GEP= dyn_cast<GetElementPtrInst>(PN.getIncomingValue(i)); 149202375Srdivacky if (!GEP || !GEP->hasOneUse() || GEP->getType() != FirstInst->getType() || 150202375Srdivacky GEP->getNumOperands() != FirstInst->getNumOperands()) 151202375Srdivacky return 0; 152202375Srdivacky 153218893Sdim AllInBounds &= GEP->isInBounds(); 154251662Sdim 155202375Srdivacky // Keep track of whether or not all GEPs are of alloca pointers. 156202375Srdivacky if (AllBasePointersAreAllocas && 157202375Srdivacky (!isa<AllocaInst>(GEP->getOperand(0)) || 158202375Srdivacky !GEP->hasAllConstantIndices())) 159202375Srdivacky AllBasePointersAreAllocas = false; 160251662Sdim 161202375Srdivacky // Compare the operand lists. 162202375Srdivacky for (unsigned op = 0, e = FirstInst->getNumOperands(); op != e; ++op) { 163202375Srdivacky if (FirstInst->getOperand(op) == GEP->getOperand(op)) 164202375Srdivacky continue; 165251662Sdim 166202375Srdivacky // Don't merge two GEPs when two operands differ (introducing phi nodes) 167202375Srdivacky // if one of the PHIs has a constant for the index. The index may be 168202375Srdivacky // substantially cheaper to compute for the constants, so making it a 169202375Srdivacky // variable index could pessimize the path. This also handles the case 170202375Srdivacky // for struct indices, which must always be constant. 171202375Srdivacky if (isa<ConstantInt>(FirstInst->getOperand(op)) || 172202375Srdivacky isa<ConstantInt>(GEP->getOperand(op))) 173202375Srdivacky return 0; 174251662Sdim 175202375Srdivacky if (FirstInst->getOperand(op)->getType() !=GEP->getOperand(op)->getType()) 176202375Srdivacky return 0; 177202375Srdivacky 178202375Srdivacky // If we already needed a PHI for an earlier operand, and another operand 179202375Srdivacky // also requires a PHI, we'd be introducing more PHIs than we're 180202375Srdivacky // eliminating, which increases register pressure on entry to the PHI's 181202375Srdivacky // block. 182202375Srdivacky if (NeededPhi) 183202375Srdivacky return 0; 184202375Srdivacky 185202375Srdivacky FixedOperands[op] = 0; // Needs a PHI. 186202375Srdivacky NeededPhi = true; 187202375Srdivacky } 188202375Srdivacky } 189251662Sdim 190202375Srdivacky // If all of the base pointers of the PHI'd GEPs are from allocas, don't 191202375Srdivacky // bother doing this transformation. At best, this will just save a bit of 192202375Srdivacky // offset calculation, but all the predecessors will have to materialize the 193202375Srdivacky // stack address into a register anyway. We'd actually rather *clone* the 194202375Srdivacky // load up into the predecessors so that we have a load of a gep of an alloca, 195202375Srdivacky // which can usually all be folded into the load. 196202375Srdivacky if (AllBasePointersAreAllocas) 197202375Srdivacky return 0; 198251662Sdim 199202375Srdivacky // Otherwise, this is safe to transform. Insert PHI nodes for each operand 200202375Srdivacky // that is variable. 201202375Srdivacky SmallVector<PHINode*, 16> OperandPhis(FixedOperands.size()); 202251662Sdim 203202375Srdivacky bool HasAnyPHIs = false; 204202375Srdivacky for (unsigned i = 0, e = FixedOperands.size(); i != e; ++i) { 205202375Srdivacky if (FixedOperands[i]) continue; // operand doesn't need a phi. 206202375Srdivacky Value *FirstOp = FirstInst->getOperand(i); 207221345Sdim PHINode *NewPN = PHINode::Create(FirstOp->getType(), e, 208202375Srdivacky FirstOp->getName()+".pn"); 209202375Srdivacky InsertNewInstBefore(NewPN, PN); 210251662Sdim 211202375Srdivacky NewPN->addIncoming(FirstOp, PN.getIncomingBlock(0)); 212202375Srdivacky OperandPhis[i] = NewPN; 213202375Srdivacky FixedOperands[i] = NewPN; 214202375Srdivacky HasAnyPHIs = true; 215202375Srdivacky } 216202375Srdivacky 217251662Sdim 218202375Srdivacky // Add all operands to the new PHIs. 219202375Srdivacky if (HasAnyPHIs) { 220202375Srdivacky for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) { 221202375Srdivacky GetElementPtrInst *InGEP =cast<GetElementPtrInst>(PN.getIncomingValue(i)); 222202375Srdivacky BasicBlock *InBB = PN.getIncomingBlock(i); 223251662Sdim 224202375Srdivacky for (unsigned op = 0, e = OperandPhis.size(); op != e; ++op) 225202375Srdivacky if (PHINode *OpPhi = OperandPhis[op]) 226202375Srdivacky OpPhi->addIncoming(InGEP->getOperand(op), InBB); 227202375Srdivacky } 228202375Srdivacky } 229251662Sdim 230202375Srdivacky Value *Base = FixedOperands[0]; 231251662Sdim GetElementPtrInst *NewGEP = 232226633Sdim GetElementPtrInst::Create(Base, makeArrayRef(FixedOperands).slice(1)); 233218893Sdim if (AllInBounds) NewGEP->setIsInBounds(); 234223017Sdim NewGEP->setDebugLoc(FirstInst->getDebugLoc()); 235218893Sdim return NewGEP; 236202375Srdivacky} 237202375Srdivacky 238202375Srdivacky 239202375Srdivacky/// isSafeAndProfitableToSinkLoad - Return true if we know that it is safe to 240202375Srdivacky/// sink the load out of the block that defines it. This means that it must be 241202375Srdivacky/// obvious the value of the load is not changed from the point of the load to 242202375Srdivacky/// the end of the block it is in. 243202375Srdivacky/// 244221345Sdim/// Finally, it is safe, but not profitable, to sink a load targeting a 245202375Srdivacky/// non-address-taken alloca. Doing so will cause us to not promote the alloca 246202375Srdivacky/// to a register. 247202375Srdivackystatic bool isSafeAndProfitableToSinkLoad(LoadInst *L) { 248202375Srdivacky BasicBlock::iterator BBI = L, E = L->getParent()->end(); 249251662Sdim 250202375Srdivacky for (++BBI; BBI != E; ++BBI) 251202375Srdivacky if (BBI->mayWriteToMemory()) 252202375Srdivacky return false; 253251662Sdim 254202375Srdivacky // Check for non-address taken alloca. If not address-taken already, it isn't 255202375Srdivacky // profitable to do this xform. 256202375Srdivacky if (AllocaInst *AI = dyn_cast<AllocaInst>(L->getOperand(0))) { 257202375Srdivacky bool isAddressTaken = false; 258202375Srdivacky for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); 259202375Srdivacky UI != E; ++UI) { 260210299Sed User *U = *UI; 261210299Sed if (isa<LoadInst>(U)) continue; 262210299Sed if (StoreInst *SI = dyn_cast<StoreInst>(U)) { 263202375Srdivacky // If storing TO the alloca, then the address isn't taken. 264202375Srdivacky if (SI->getOperand(1) == AI) continue; 265202375Srdivacky } 266202375Srdivacky isAddressTaken = true; 267202375Srdivacky break; 268202375Srdivacky } 269251662Sdim 270202375Srdivacky if (!isAddressTaken && AI->isStaticAlloca()) 271202375Srdivacky return false; 272202375Srdivacky } 273251662Sdim 274202375Srdivacky // If this load is a load from a GEP with a constant offset from an alloca, 275202375Srdivacky // then we don't want to sink it. In its present form, it will be 276202375Srdivacky // load [constant stack offset]. Sinking it will cause us to have to 277202375Srdivacky // materialize the stack addresses in each predecessor in a register only to 278202375Srdivacky // do a shared load from register in the successor. 279202375Srdivacky if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(L->getOperand(0))) 280202375Srdivacky if (AllocaInst *AI = dyn_cast<AllocaInst>(GEP->getOperand(0))) 281202375Srdivacky if (AI->isStaticAlloca() && GEP->hasAllConstantIndices()) 282202375Srdivacky return false; 283251662Sdim 284202375Srdivacky return true; 285202375Srdivacky} 286202375Srdivacky 287202375SrdivackyInstruction *InstCombiner::FoldPHIArgLoadIntoPHI(PHINode &PN) { 288202375Srdivacky LoadInst *FirstLI = cast<LoadInst>(PN.getIncomingValue(0)); 289226633Sdim 290226633Sdim // FIXME: This is overconservative; this transform is allowed in some cases 291226633Sdim // for atomic operations. 292226633Sdim if (FirstLI->isAtomic()) 293226633Sdim return 0; 294226633Sdim 295202375Srdivacky // When processing loads, we need to propagate two bits of information to the 296202375Srdivacky // sunk load: whether it is volatile, and what its alignment is. We currently 297202375Srdivacky // don't sink loads when some have their alignment specified and some don't. 298202375Srdivacky // visitLoadInst will propagate an alignment onto the load when TD is around, 299202375Srdivacky // and if TD isn't around, we can't handle the mixed case. 300202375Srdivacky bool isVolatile = FirstLI->isVolatile(); 301202375Srdivacky unsigned LoadAlignment = FirstLI->getAlignment(); 302204792Srdivacky unsigned LoadAddrSpace = FirstLI->getPointerAddressSpace(); 303251662Sdim 304202375Srdivacky // We can't sink the load if the loaded value could be modified between the 305202375Srdivacky // load and the PHI. 306202375Srdivacky if (FirstLI->getParent() != PN.getIncomingBlock(0) || 307202375Srdivacky !isSafeAndProfitableToSinkLoad(FirstLI)) 308202375Srdivacky return 0; 309251662Sdim 310202375Srdivacky // If the PHI is of volatile loads and the load block has multiple 311202375Srdivacky // successors, sinking it would remove a load of the volatile value from 312202375Srdivacky // the path through the other successor. 313251662Sdim if (isVolatile && 314202375Srdivacky FirstLI->getParent()->getTerminator()->getNumSuccessors() != 1) 315202375Srdivacky return 0; 316251662Sdim 317202375Srdivacky // Check to see if all arguments are the same operation. 318202375Srdivacky for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) { 319202375Srdivacky LoadInst *LI = dyn_cast<LoadInst>(PN.getIncomingValue(i)); 320202375Srdivacky if (!LI || !LI->hasOneUse()) 321202375Srdivacky return 0; 322251662Sdim 323251662Sdim // We can't sink the load if the loaded value could be modified between 324202375Srdivacky // the load and the PHI. 325202375Srdivacky if (LI->isVolatile() != isVolatile || 326202375Srdivacky LI->getParent() != PN.getIncomingBlock(i) || 327204792Srdivacky LI->getPointerAddressSpace() != LoadAddrSpace || 328202375Srdivacky !isSafeAndProfitableToSinkLoad(LI)) 329202375Srdivacky return 0; 330251662Sdim 331202375Srdivacky // If some of the loads have an alignment specified but not all of them, 332202375Srdivacky // we can't do the transformation. 333202375Srdivacky if ((LoadAlignment != 0) != (LI->getAlignment() != 0)) 334202375Srdivacky return 0; 335251662Sdim 336202375Srdivacky LoadAlignment = std::min(LoadAlignment, LI->getAlignment()); 337251662Sdim 338202375Srdivacky // If the PHI is of volatile loads and the load block has multiple 339202375Srdivacky // successors, sinking it would remove a load of the volatile value from 340202375Srdivacky // the path through the other successor. 341202375Srdivacky if (isVolatile && 342202375Srdivacky LI->getParent()->getTerminator()->getNumSuccessors() != 1) 343202375Srdivacky return 0; 344202375Srdivacky } 345251662Sdim 346202375Srdivacky // Okay, they are all the same operation. Create a new PHI node of the 347202375Srdivacky // correct type, and PHI together all of the LHS's of the instructions. 348202375Srdivacky PHINode *NewPN = PHINode::Create(FirstLI->getOperand(0)->getType(), 349221345Sdim PN.getNumIncomingValues(), 350202375Srdivacky PN.getName()+".in"); 351251662Sdim 352202375Srdivacky Value *InVal = FirstLI->getOperand(0); 353202375Srdivacky NewPN->addIncoming(InVal, PN.getIncomingBlock(0)); 354251662Sdim 355202375Srdivacky // Add all operands to the new PHI. 356202375Srdivacky for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) { 357202375Srdivacky Value *NewInVal = cast<LoadInst>(PN.getIncomingValue(i))->getOperand(0); 358202375Srdivacky if (NewInVal != InVal) 359202375Srdivacky InVal = 0; 360202375Srdivacky NewPN->addIncoming(NewInVal, PN.getIncomingBlock(i)); 361202375Srdivacky } 362251662Sdim 363202375Srdivacky Value *PhiVal; 364202375Srdivacky if (InVal) { 365202375Srdivacky // The new PHI unions all of the same values together. This is really 366202375Srdivacky // common, so we handle it intelligently here for compile-time speed. 367202375Srdivacky PhiVal = InVal; 368202375Srdivacky delete NewPN; 369202375Srdivacky } else { 370202375Srdivacky InsertNewInstBefore(NewPN, PN); 371202375Srdivacky PhiVal = NewPN; 372202375Srdivacky } 373251662Sdim 374202375Srdivacky // If this was a volatile load that we are merging, make sure to loop through 375202375Srdivacky // and mark all the input loads as non-volatile. If we don't do this, we will 376202375Srdivacky // insert a new volatile load and the old ones will not be deletable. 377202375Srdivacky if (isVolatile) 378202375Srdivacky for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) 379202375Srdivacky cast<LoadInst>(PN.getIncomingValue(i))->setVolatile(false); 380251662Sdim 381223017Sdim LoadInst *NewLI = new LoadInst(PhiVal, "", isVolatile, LoadAlignment); 382223017Sdim NewLI->setDebugLoc(FirstLI->getDebugLoc()); 383223017Sdim return NewLI; 384202375Srdivacky} 385202375Srdivacky 386202375Srdivacky 387202375Srdivacky 388202375Srdivacky/// FoldPHIArgOpIntoPHI - If all operands to a PHI node are the same "unary" 389202375Srdivacky/// operator and they all are only used by the PHI, PHI together their 390202375Srdivacky/// inputs, and do the operation once, to the result of the PHI. 391202375SrdivackyInstruction *InstCombiner::FoldPHIArgOpIntoPHI(PHINode &PN) { 392202375Srdivacky Instruction *FirstInst = cast<Instruction>(PN.getIncomingValue(0)); 393202375Srdivacky 394202375Srdivacky if (isa<GetElementPtrInst>(FirstInst)) 395202375Srdivacky return FoldPHIArgGEPIntoPHI(PN); 396202375Srdivacky if (isa<LoadInst>(FirstInst)) 397202375Srdivacky return FoldPHIArgLoadIntoPHI(PN); 398251662Sdim 399202375Srdivacky // Scan the instruction, looking for input operations that can be folded away. 400202375Srdivacky // If all input operands to the phi are the same instruction (e.g. a cast from 401202375Srdivacky // the same type or "+42") we can pull the operation through the PHI, reducing 402202375Srdivacky // code size and simplifying code. 403202375Srdivacky Constant *ConstantOp = 0; 404226633Sdim Type *CastSrcTy = 0; 405218893Sdim bool isNUW = false, isNSW = false, isExact = false; 406251662Sdim 407202375Srdivacky if (isa<CastInst>(FirstInst)) { 408202375Srdivacky CastSrcTy = FirstInst->getOperand(0)->getType(); 409202375Srdivacky 410202375Srdivacky // Be careful about transforming integer PHIs. We don't want to pessimize 411202375Srdivacky // the code by turning an i32 into an i1293. 412204642Srdivacky if (PN.getType()->isIntegerTy() && CastSrcTy->isIntegerTy()) { 413202375Srdivacky if (!ShouldChangeType(PN.getType(), CastSrcTy)) 414202375Srdivacky return 0; 415202375Srdivacky } 416202375Srdivacky } else if (isa<BinaryOperator>(FirstInst) || isa<CmpInst>(FirstInst)) { 417251662Sdim // Can fold binop, compare or shift here if the RHS is a constant, 418202375Srdivacky // otherwise call FoldPHIArgBinOpIntoPHI. 419202375Srdivacky ConstantOp = dyn_cast<Constant>(FirstInst->getOperand(1)); 420202375Srdivacky if (ConstantOp == 0) 421202375Srdivacky return FoldPHIArgBinOpIntoPHI(PN); 422251662Sdim 423218893Sdim if (OverflowingBinaryOperator *BO = 424218893Sdim dyn_cast<OverflowingBinaryOperator>(FirstInst)) { 425218893Sdim isNUW = BO->hasNoUnsignedWrap(); 426218893Sdim isNSW = BO->hasNoSignedWrap(); 427218893Sdim } else if (PossiblyExactOperator *PEO = 428218893Sdim dyn_cast<PossiblyExactOperator>(FirstInst)) 429218893Sdim isExact = PEO->isExact(); 430202375Srdivacky } else { 431202375Srdivacky return 0; // Cannot fold this operation. 432202375Srdivacky } 433202375Srdivacky 434202375Srdivacky // Check to see if all arguments are the same operation. 435202375Srdivacky for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) { 436202375Srdivacky Instruction *I = dyn_cast<Instruction>(PN.getIncomingValue(i)); 437202375Srdivacky if (I == 0 || !I->hasOneUse() || !I->isSameOperationAs(FirstInst)) 438202375Srdivacky return 0; 439202375Srdivacky if (CastSrcTy) { 440202375Srdivacky if (I->getOperand(0)->getType() != CastSrcTy) 441202375Srdivacky return 0; // Cast operation must match. 442202375Srdivacky } else if (I->getOperand(1) != ConstantOp) { 443202375Srdivacky return 0; 444202375Srdivacky } 445251662Sdim 446218893Sdim if (isNUW) 447218893Sdim isNUW = cast<OverflowingBinaryOperator>(I)->hasNoUnsignedWrap(); 448218893Sdim if (isNSW) 449218893Sdim isNSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap(); 450218893Sdim if (isExact) 451218893Sdim isExact = cast<PossiblyExactOperator>(I)->isExact(); 452202375Srdivacky } 453202375Srdivacky 454202375Srdivacky // Okay, they are all the same operation. Create a new PHI node of the 455202375Srdivacky // correct type, and PHI together all of the LHS's of the instructions. 456202375Srdivacky PHINode *NewPN = PHINode::Create(FirstInst->getOperand(0)->getType(), 457221345Sdim PN.getNumIncomingValues(), 458202375Srdivacky PN.getName()+".in"); 459202375Srdivacky 460202375Srdivacky Value *InVal = FirstInst->getOperand(0); 461202375Srdivacky NewPN->addIncoming(InVal, PN.getIncomingBlock(0)); 462202375Srdivacky 463202375Srdivacky // Add all operands to the new PHI. 464202375Srdivacky for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) { 465202375Srdivacky Value *NewInVal = cast<Instruction>(PN.getIncomingValue(i))->getOperand(0); 466202375Srdivacky if (NewInVal != InVal) 467202375Srdivacky InVal = 0; 468202375Srdivacky NewPN->addIncoming(NewInVal, PN.getIncomingBlock(i)); 469202375Srdivacky } 470202375Srdivacky 471202375Srdivacky Value *PhiVal; 472202375Srdivacky if (InVal) { 473202375Srdivacky // The new PHI unions all of the same values together. This is really 474202375Srdivacky // common, so we handle it intelligently here for compile-time speed. 475202375Srdivacky PhiVal = InVal; 476202375Srdivacky delete NewPN; 477202375Srdivacky } else { 478202375Srdivacky InsertNewInstBefore(NewPN, PN); 479202375Srdivacky PhiVal = NewPN; 480202375Srdivacky } 481202375Srdivacky 482202375Srdivacky // Insert and return the new operation. 483223017Sdim if (CastInst *FirstCI = dyn_cast<CastInst>(FirstInst)) { 484223017Sdim CastInst *NewCI = CastInst::Create(FirstCI->getOpcode(), PhiVal, 485223017Sdim PN.getType()); 486223017Sdim NewCI->setDebugLoc(FirstInst->getDebugLoc()); 487223017Sdim return NewCI; 488223017Sdim } 489251662Sdim 490218893Sdim if (BinaryOperator *BinOp = dyn_cast<BinaryOperator>(FirstInst)) { 491218893Sdim BinOp = BinaryOperator::Create(BinOp->getOpcode(), PhiVal, ConstantOp); 492218893Sdim if (isNUW) BinOp->setHasNoUnsignedWrap(); 493218893Sdim if (isNSW) BinOp->setHasNoSignedWrap(); 494218893Sdim if (isExact) BinOp->setIsExact(); 495223017Sdim BinOp->setDebugLoc(FirstInst->getDebugLoc()); 496218893Sdim return BinOp; 497218893Sdim } 498251662Sdim 499202375Srdivacky CmpInst *CIOp = cast<CmpInst>(FirstInst); 500223017Sdim CmpInst *NewCI = CmpInst::Create(CIOp->getOpcode(), CIOp->getPredicate(), 501223017Sdim PhiVal, ConstantOp); 502223017Sdim NewCI->setDebugLoc(FirstInst->getDebugLoc()); 503223017Sdim return NewCI; 504202375Srdivacky} 505202375Srdivacky 506202375Srdivacky/// DeadPHICycle - Return true if this PHI node is only used by a PHI node cycle 507202375Srdivacky/// that is dead. 508202375Srdivackystatic bool DeadPHICycle(PHINode *PN, 509202375Srdivacky SmallPtrSet<PHINode*, 16> &PotentiallyDeadPHIs) { 510202375Srdivacky if (PN->use_empty()) return true; 511202375Srdivacky if (!PN->hasOneUse()) return false; 512202375Srdivacky 513202375Srdivacky // Remember this node, and if we find the cycle, return. 514202375Srdivacky if (!PotentiallyDeadPHIs.insert(PN)) 515202375Srdivacky return true; 516251662Sdim 517202375Srdivacky // Don't scan crazily complex things. 518202375Srdivacky if (PotentiallyDeadPHIs.size() == 16) 519202375Srdivacky return false; 520202375Srdivacky 521202375Srdivacky if (PHINode *PU = dyn_cast<PHINode>(PN->use_back())) 522202375Srdivacky return DeadPHICycle(PU, PotentiallyDeadPHIs); 523202375Srdivacky 524202375Srdivacky return false; 525202375Srdivacky} 526202375Srdivacky 527202375Srdivacky/// PHIsEqualValue - Return true if this phi node is always equal to 528202375Srdivacky/// NonPhiInVal. This happens with mutually cyclic phi nodes like: 529202375Srdivacky/// z = some value; x = phi (y, z); y = phi (x, z) 530251662Sdimstatic bool PHIsEqualValue(PHINode *PN, Value *NonPhiInVal, 531202375Srdivacky SmallPtrSet<PHINode*, 16> &ValueEqualPHIs) { 532202375Srdivacky // See if we already saw this PHI node. 533202375Srdivacky if (!ValueEqualPHIs.insert(PN)) 534202375Srdivacky return true; 535251662Sdim 536202375Srdivacky // Don't scan crazily complex things. 537202375Srdivacky if (ValueEqualPHIs.size() == 16) 538202375Srdivacky return false; 539251662Sdim 540202375Srdivacky // Scan the operands to see if they are either phi nodes or are equal to 541202375Srdivacky // the value. 542202375Srdivacky for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 543202375Srdivacky Value *Op = PN->getIncomingValue(i); 544202375Srdivacky if (PHINode *OpPN = dyn_cast<PHINode>(Op)) { 545202375Srdivacky if (!PHIsEqualValue(OpPN, NonPhiInVal, ValueEqualPHIs)) 546202375Srdivacky return false; 547202375Srdivacky } else if (Op != NonPhiInVal) 548202375Srdivacky return false; 549202375Srdivacky } 550251662Sdim 551202375Srdivacky return true; 552202375Srdivacky} 553202375Srdivacky 554202375Srdivacky 555202375Srdivackynamespace { 556202375Srdivackystruct PHIUsageRecord { 557202375Srdivacky unsigned PHIId; // The ID # of the PHI (something determinstic to sort on) 558202375Srdivacky unsigned Shift; // The amount shifted. 559202375Srdivacky Instruction *Inst; // The trunc instruction. 560251662Sdim 561202375Srdivacky PHIUsageRecord(unsigned pn, unsigned Sh, Instruction *User) 562202375Srdivacky : PHIId(pn), Shift(Sh), Inst(User) {} 563251662Sdim 564202375Srdivacky bool operator<(const PHIUsageRecord &RHS) const { 565202375Srdivacky if (PHIId < RHS.PHIId) return true; 566202375Srdivacky if (PHIId > RHS.PHIId) return false; 567202375Srdivacky if (Shift < RHS.Shift) return true; 568202375Srdivacky if (Shift > RHS.Shift) return false; 569202375Srdivacky return Inst->getType()->getPrimitiveSizeInBits() < 570202375Srdivacky RHS.Inst->getType()->getPrimitiveSizeInBits(); 571202375Srdivacky } 572202375Srdivacky}; 573251662Sdim 574202375Srdivackystruct LoweredPHIRecord { 575202375Srdivacky PHINode *PN; // The PHI that was lowered. 576202375Srdivacky unsigned Shift; // The amount shifted. 577202375Srdivacky unsigned Width; // The width extracted. 578251662Sdim 579226633Sdim LoweredPHIRecord(PHINode *pn, unsigned Sh, Type *Ty) 580202375Srdivacky : PN(pn), Shift(Sh), Width(Ty->getPrimitiveSizeInBits()) {} 581251662Sdim 582202375Srdivacky // Ctor form used by DenseMap. 583202375Srdivacky LoweredPHIRecord(PHINode *pn, unsigned Sh) 584202375Srdivacky : PN(pn), Shift(Sh), Width(0) {} 585202375Srdivacky}; 586202375Srdivacky} 587202375Srdivacky 588202375Srdivackynamespace llvm { 589202375Srdivacky template<> 590202375Srdivacky struct DenseMapInfo<LoweredPHIRecord> { 591202375Srdivacky static inline LoweredPHIRecord getEmptyKey() { 592202375Srdivacky return LoweredPHIRecord(0, 0); 593202375Srdivacky } 594202375Srdivacky static inline LoweredPHIRecord getTombstoneKey() { 595202375Srdivacky return LoweredPHIRecord(0, 1); 596202375Srdivacky } 597202375Srdivacky static unsigned getHashValue(const LoweredPHIRecord &Val) { 598202375Srdivacky return DenseMapInfo<PHINode*>::getHashValue(Val.PN) ^ (Val.Shift>>3) ^ 599202375Srdivacky (Val.Width>>3); 600202375Srdivacky } 601202375Srdivacky static bool isEqual(const LoweredPHIRecord &LHS, 602202375Srdivacky const LoweredPHIRecord &RHS) { 603202375Srdivacky return LHS.PN == RHS.PN && LHS.Shift == RHS.Shift && 604202375Srdivacky LHS.Width == RHS.Width; 605202375Srdivacky } 606202375Srdivacky }; 607202375Srdivacky} 608202375Srdivacky 609202375Srdivacky 610202375Srdivacky/// SliceUpIllegalIntegerPHI - This is an integer PHI and we know that it has an 611202375Srdivacky/// illegal type: see if it is only used by trunc or trunc(lshr) operations. If 612202375Srdivacky/// so, we split the PHI into the various pieces being extracted. This sort of 613202375Srdivacky/// thing is introduced when SROA promotes an aggregate to large integer values. 614202375Srdivacky/// 615202375Srdivacky/// TODO: The user of the trunc may be an bitcast to float/double/vector or an 616202375Srdivacky/// inttoptr. We should produce new PHIs in the right type. 617202375Srdivacky/// 618202375SrdivackyInstruction *InstCombiner::SliceUpIllegalIntegerPHI(PHINode &FirstPhi) { 619202375Srdivacky // PHIUsers - Keep track of all of the truncated values extracted from a set 620202375Srdivacky // of PHIs, along with their offset. These are the things we want to rewrite. 621202375Srdivacky SmallVector<PHIUsageRecord, 16> PHIUsers; 622251662Sdim 623202375Srdivacky // PHIs are often mutually cyclic, so we keep track of a whole set of PHI 624202375Srdivacky // nodes which are extracted from. PHIsToSlice is a set we use to avoid 625202375Srdivacky // revisiting PHIs, PHIsInspected is a ordered list of PHIs that we need to 626202375Srdivacky // check the uses of (to ensure they are all extracts). 627202375Srdivacky SmallVector<PHINode*, 8> PHIsToSlice; 628202375Srdivacky SmallPtrSet<PHINode*, 8> PHIsInspected; 629251662Sdim 630202375Srdivacky PHIsToSlice.push_back(&FirstPhi); 631202375Srdivacky PHIsInspected.insert(&FirstPhi); 632251662Sdim 633202375Srdivacky for (unsigned PHIId = 0; PHIId != PHIsToSlice.size(); ++PHIId) { 634202375Srdivacky PHINode *PN = PHIsToSlice[PHIId]; 635251662Sdim 636202375Srdivacky // Scan the input list of the PHI. If any input is an invoke, and if the 637202375Srdivacky // input is defined in the predecessor, then we won't be split the critical 638202375Srdivacky // edge which is required to insert a truncate. Because of this, we have to 639202375Srdivacky // bail out. 640202375Srdivacky for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 641202375Srdivacky InvokeInst *II = dyn_cast<InvokeInst>(PN->getIncomingValue(i)); 642202375Srdivacky if (II == 0) continue; 643202375Srdivacky if (II->getParent() != PN->getIncomingBlock(i)) 644202375Srdivacky continue; 645251662Sdim 646202375Srdivacky // If we have a phi, and if it's directly in the predecessor, then we have 647202375Srdivacky // a critical edge where we need to put the truncate. Since we can't 648202375Srdivacky // split the edge in instcombine, we have to bail out. 649202375Srdivacky return 0; 650202375Srdivacky } 651251662Sdim 652251662Sdim 653202375Srdivacky for (Value::use_iterator UI = PN->use_begin(), E = PN->use_end(); 654202375Srdivacky UI != E; ++UI) { 655202375Srdivacky Instruction *User = cast<Instruction>(*UI); 656251662Sdim 657202375Srdivacky // If the user is a PHI, inspect its uses recursively. 658202375Srdivacky if (PHINode *UserPN = dyn_cast<PHINode>(User)) { 659202375Srdivacky if (PHIsInspected.insert(UserPN)) 660202375Srdivacky PHIsToSlice.push_back(UserPN); 661202375Srdivacky continue; 662202375Srdivacky } 663251662Sdim 664202375Srdivacky // Truncates are always ok. 665202375Srdivacky if (isa<TruncInst>(User)) { 666202375Srdivacky PHIUsers.push_back(PHIUsageRecord(PHIId, 0, User)); 667202375Srdivacky continue; 668202375Srdivacky } 669251662Sdim 670202375Srdivacky // Otherwise it must be a lshr which can only be used by one trunc. 671202375Srdivacky if (User->getOpcode() != Instruction::LShr || 672202375Srdivacky !User->hasOneUse() || !isa<TruncInst>(User->use_back()) || 673202375Srdivacky !isa<ConstantInt>(User->getOperand(1))) 674202375Srdivacky return 0; 675251662Sdim 676202375Srdivacky unsigned Shift = cast<ConstantInt>(User->getOperand(1))->getZExtValue(); 677202375Srdivacky PHIUsers.push_back(PHIUsageRecord(PHIId, Shift, User->use_back())); 678202375Srdivacky } 679202375Srdivacky } 680251662Sdim 681202375Srdivacky // If we have no users, they must be all self uses, just nuke the PHI. 682202375Srdivacky if (PHIUsers.empty()) 683202375Srdivacky return ReplaceInstUsesWith(FirstPhi, UndefValue::get(FirstPhi.getType())); 684251662Sdim 685202375Srdivacky // If this phi node is transformable, create new PHIs for all the pieces 686202375Srdivacky // extracted out of it. First, sort the users by their offset and size. 687202375Srdivacky array_pod_sort(PHIUsers.begin(), PHIUsers.end()); 688251662Sdim 689263508Sdim DEBUG(dbgs() << "SLICING UP PHI: " << FirstPhi << '\n'; 690263508Sdim for (unsigned i = 1, e = PHIsToSlice.size(); i != e; ++i) 691263508Sdim dbgs() << "AND USER PHI #" << i << ": " << *PHIsToSlice[i] << '\n'; 692263508Sdim ); 693251662Sdim 694202375Srdivacky // PredValues - This is a temporary used when rewriting PHI nodes. It is 695202375Srdivacky // hoisted out here to avoid construction/destruction thrashing. 696202375Srdivacky DenseMap<BasicBlock*, Value*> PredValues; 697251662Sdim 698202375Srdivacky // ExtractedVals - Each new PHI we introduce is saved here so we don't 699202375Srdivacky // introduce redundant PHIs. 700202375Srdivacky DenseMap<LoweredPHIRecord, PHINode*> ExtractedVals; 701251662Sdim 702202375Srdivacky for (unsigned UserI = 0, UserE = PHIUsers.size(); UserI != UserE; ++UserI) { 703202375Srdivacky unsigned PHIId = PHIUsers[UserI].PHIId; 704202375Srdivacky PHINode *PN = PHIsToSlice[PHIId]; 705202375Srdivacky unsigned Offset = PHIUsers[UserI].Shift; 706226633Sdim Type *Ty = PHIUsers[UserI].Inst->getType(); 707251662Sdim 708202375Srdivacky PHINode *EltPHI; 709251662Sdim 710202375Srdivacky // If we've already lowered a user like this, reuse the previously lowered 711202375Srdivacky // value. 712202375Srdivacky if ((EltPHI = ExtractedVals[LoweredPHIRecord(PN, Offset, Ty)]) == 0) { 713251662Sdim 714202375Srdivacky // Otherwise, Create the new PHI node for this user. 715221345Sdim EltPHI = PHINode::Create(Ty, PN->getNumIncomingValues(), 716221345Sdim PN->getName()+".off"+Twine(Offset), PN); 717202375Srdivacky assert(EltPHI->getType() != PN->getType() && 718202375Srdivacky "Truncate didn't shrink phi?"); 719251662Sdim 720202375Srdivacky for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 721202375Srdivacky BasicBlock *Pred = PN->getIncomingBlock(i); 722202375Srdivacky Value *&PredVal = PredValues[Pred]; 723251662Sdim 724202375Srdivacky // If we already have a value for this predecessor, reuse it. 725202375Srdivacky if (PredVal) { 726202375Srdivacky EltPHI->addIncoming(PredVal, Pred); 727202375Srdivacky continue; 728202375Srdivacky } 729202375Srdivacky 730202375Srdivacky // Handle the PHI self-reuse case. 731202375Srdivacky Value *InVal = PN->getIncomingValue(i); 732202375Srdivacky if (InVal == PN) { 733202375Srdivacky PredVal = EltPHI; 734202375Srdivacky EltPHI->addIncoming(PredVal, Pred); 735202375Srdivacky continue; 736202375Srdivacky } 737251662Sdim 738202375Srdivacky if (PHINode *InPHI = dyn_cast<PHINode>(PN)) { 739202375Srdivacky // If the incoming value was a PHI, and if it was one of the PHIs we 740202375Srdivacky // already rewrote it, just use the lowered value. 741202375Srdivacky if (Value *Res = ExtractedVals[LoweredPHIRecord(InPHI, Offset, Ty)]) { 742202375Srdivacky PredVal = Res; 743202375Srdivacky EltPHI->addIncoming(PredVal, Pred); 744202375Srdivacky continue; 745202375Srdivacky } 746202375Srdivacky } 747251662Sdim 748202375Srdivacky // Otherwise, do an extract in the predecessor. 749202375Srdivacky Builder->SetInsertPoint(Pred, Pred->getTerminator()); 750202375Srdivacky Value *Res = InVal; 751202375Srdivacky if (Offset) 752202375Srdivacky Res = Builder->CreateLShr(Res, ConstantInt::get(InVal->getType(), 753202375Srdivacky Offset), "extract"); 754202375Srdivacky Res = Builder->CreateTrunc(Res, Ty, "extract.t"); 755202375Srdivacky PredVal = Res; 756202375Srdivacky EltPHI->addIncoming(Res, Pred); 757251662Sdim 758202375Srdivacky // If the incoming value was a PHI, and if it was one of the PHIs we are 759202375Srdivacky // rewriting, we will ultimately delete the code we inserted. This 760202375Srdivacky // means we need to revisit that PHI to make sure we extract out the 761202375Srdivacky // needed piece. 762202375Srdivacky if (PHINode *OldInVal = dyn_cast<PHINode>(PN->getIncomingValue(i))) 763202375Srdivacky if (PHIsInspected.count(OldInVal)) { 764202375Srdivacky unsigned RefPHIId = std::find(PHIsToSlice.begin(),PHIsToSlice.end(), 765202375Srdivacky OldInVal)-PHIsToSlice.begin(); 766251662Sdim PHIUsers.push_back(PHIUsageRecord(RefPHIId, Offset, 767202375Srdivacky cast<Instruction>(Res))); 768202375Srdivacky ++UserE; 769202375Srdivacky } 770202375Srdivacky } 771202375Srdivacky PredValues.clear(); 772251662Sdim 773263508Sdim DEBUG(dbgs() << " Made element PHI for offset " << Offset << ": " 774202375Srdivacky << *EltPHI << '\n'); 775202375Srdivacky ExtractedVals[LoweredPHIRecord(PN, Offset, Ty)] = EltPHI; 776202375Srdivacky } 777251662Sdim 778202375Srdivacky // Replace the use of this piece with the PHI node. 779202375Srdivacky ReplaceInstUsesWith(*PHIUsers[UserI].Inst, EltPHI); 780202375Srdivacky } 781251662Sdim 782202375Srdivacky // Replace all the remaining uses of the PHI nodes (self uses and the lshrs) 783202375Srdivacky // with undefs. 784202375Srdivacky Value *Undef = UndefValue::get(FirstPhi.getType()); 785202375Srdivacky for (unsigned i = 1, e = PHIsToSlice.size(); i != e; ++i) 786202375Srdivacky ReplaceInstUsesWith(*PHIsToSlice[i], Undef); 787202375Srdivacky return ReplaceInstUsesWith(FirstPhi, Undef); 788202375Srdivacky} 789202375Srdivacky 790202375Srdivacky// PHINode simplification 791202375Srdivacky// 792202375SrdivackyInstruction *InstCombiner::visitPHINode(PHINode &PN) { 793263508Sdim if (Value *V = SimplifyInstruction(&PN, TD, TLI)) 794202375Srdivacky return ReplaceInstUsesWith(PN, V); 795202375Srdivacky 796202375Srdivacky // If all PHI operands are the same operation, pull them through the PHI, 797202375Srdivacky // reducing code size. 798202375Srdivacky if (isa<Instruction>(PN.getIncomingValue(0)) && 799202375Srdivacky isa<Instruction>(PN.getIncomingValue(1)) && 800202375Srdivacky cast<Instruction>(PN.getIncomingValue(0))->getOpcode() == 801202375Srdivacky cast<Instruction>(PN.getIncomingValue(1))->getOpcode() && 802202375Srdivacky // FIXME: The hasOneUse check will fail for PHIs that use the value more 803202375Srdivacky // than themselves more than once. 804202375Srdivacky PN.getIncomingValue(0)->hasOneUse()) 805202375Srdivacky if (Instruction *Result = FoldPHIArgOpIntoPHI(PN)) 806202375Srdivacky return Result; 807202375Srdivacky 808202375Srdivacky // If this is a trivial cycle in the PHI node graph, remove it. Basically, if 809202375Srdivacky // this PHI only has a single use (a PHI), and if that PHI only has one use (a 810202375Srdivacky // PHI)... break the cycle. 811202375Srdivacky if (PN.hasOneUse()) { 812202375Srdivacky Instruction *PHIUser = cast<Instruction>(PN.use_back()); 813202375Srdivacky if (PHINode *PU = dyn_cast<PHINode>(PHIUser)) { 814202375Srdivacky SmallPtrSet<PHINode*, 16> PotentiallyDeadPHIs; 815202375Srdivacky PotentiallyDeadPHIs.insert(&PN); 816202375Srdivacky if (DeadPHICycle(PU, PotentiallyDeadPHIs)) 817202375Srdivacky return ReplaceInstUsesWith(PN, UndefValue::get(PN.getType())); 818202375Srdivacky } 819251662Sdim 820202375Srdivacky // If this phi has a single use, and if that use just computes a value for 821202375Srdivacky // the next iteration of a loop, delete the phi. This occurs with unused 822202375Srdivacky // induction variables, e.g. "for (int j = 0; ; ++j);". Detecting this 823202375Srdivacky // common case here is good because the only other things that catch this 824202375Srdivacky // are induction variable analysis (sometimes) and ADCE, which is only run 825202375Srdivacky // late. 826202375Srdivacky if (PHIUser->hasOneUse() && 827202375Srdivacky (isa<BinaryOperator>(PHIUser) || isa<GetElementPtrInst>(PHIUser)) && 828202375Srdivacky PHIUser->use_back() == &PN) { 829202375Srdivacky return ReplaceInstUsesWith(PN, UndefValue::get(PN.getType())); 830202375Srdivacky } 831202375Srdivacky } 832202375Srdivacky 833202375Srdivacky // We sometimes end up with phi cycles that non-obviously end up being the 834202375Srdivacky // same value, for example: 835202375Srdivacky // z = some value; x = phi (y, z); y = phi (x, z) 836202375Srdivacky // where the phi nodes don't necessarily need to be in the same block. Do a 837202375Srdivacky // quick check to see if the PHI node only contains a single non-phi value, if 838202375Srdivacky // so, scan to see if the phi cycle is actually equal to that value. 839202375Srdivacky { 840221345Sdim unsigned InValNo = 0, NumIncomingVals = PN.getNumIncomingValues(); 841202375Srdivacky // Scan for the first non-phi operand. 842221345Sdim while (InValNo != NumIncomingVals && 843202375Srdivacky isa<PHINode>(PN.getIncomingValue(InValNo))) 844202375Srdivacky ++InValNo; 845202375Srdivacky 846221345Sdim if (InValNo != NumIncomingVals) { 847221345Sdim Value *NonPhiInVal = PN.getIncomingValue(InValNo); 848251662Sdim 849202375Srdivacky // Scan the rest of the operands to see if there are any conflicts, if so 850202375Srdivacky // there is no need to recursively scan other phis. 851221345Sdim for (++InValNo; InValNo != NumIncomingVals; ++InValNo) { 852202375Srdivacky Value *OpVal = PN.getIncomingValue(InValNo); 853202375Srdivacky if (OpVal != NonPhiInVal && !isa<PHINode>(OpVal)) 854202375Srdivacky break; 855202375Srdivacky } 856251662Sdim 857202375Srdivacky // If we scanned over all operands, then we have one unique value plus 858202375Srdivacky // phi values. Scan PHI nodes to see if they all merge in each other or 859202375Srdivacky // the value. 860221345Sdim if (InValNo == NumIncomingVals) { 861202375Srdivacky SmallPtrSet<PHINode*, 16> ValueEqualPHIs; 862202375Srdivacky if (PHIsEqualValue(&PN, NonPhiInVal, ValueEqualPHIs)) 863202375Srdivacky return ReplaceInstUsesWith(PN, NonPhiInVal); 864202375Srdivacky } 865202375Srdivacky } 866202375Srdivacky } 867202375Srdivacky 868202375Srdivacky // If there are multiple PHIs, sort their operands so that they all list 869202375Srdivacky // the blocks in the same order. This will help identical PHIs be eliminated 870202375Srdivacky // by other passes. Other passes shouldn't depend on this for correctness 871202375Srdivacky // however. 872202375Srdivacky PHINode *FirstPN = cast<PHINode>(PN.getParent()->begin()); 873202375Srdivacky if (&PN != FirstPN) 874202375Srdivacky for (unsigned i = 0, e = FirstPN->getNumIncomingValues(); i != e; ++i) { 875202375Srdivacky BasicBlock *BBA = PN.getIncomingBlock(i); 876202375Srdivacky BasicBlock *BBB = FirstPN->getIncomingBlock(i); 877202375Srdivacky if (BBA != BBB) { 878202375Srdivacky Value *VA = PN.getIncomingValue(i); 879202375Srdivacky unsigned j = PN.getBasicBlockIndex(BBB); 880202375Srdivacky Value *VB = PN.getIncomingValue(j); 881202375Srdivacky PN.setIncomingBlock(i, BBB); 882202375Srdivacky PN.setIncomingValue(i, VB); 883202375Srdivacky PN.setIncomingBlock(j, BBA); 884202375Srdivacky PN.setIncomingValue(j, VA); 885202375Srdivacky // NOTE: Instcombine normally would want us to "return &PN" if we 886202375Srdivacky // modified any of the operands of an instruction. However, since we 887202375Srdivacky // aren't adding or removing uses (just rearranging them) we don't do 888202375Srdivacky // this in this case. 889202375Srdivacky } 890202375Srdivacky } 891202375Srdivacky 892202375Srdivacky // If this is an integer PHI and we know that it has an illegal type, see if 893202375Srdivacky // it is only used by trunc or trunc(lshr) operations. If so, we split the 894202375Srdivacky // PHI into the various pieces being extracted. This sort of thing is 895202375Srdivacky // introduced when SROA promotes an aggregate to a single large integer type. 896204642Srdivacky if (PN.getType()->isIntegerTy() && TD && 897202375Srdivacky !TD->isLegalInteger(PN.getType()->getPrimitiveSizeInBits())) 898202375Srdivacky if (Instruction *Res = SliceUpIllegalIntegerPHI(PN)) 899202375Srdivacky return Res; 900251662Sdim 901202375Srdivacky return 0; 902202375Srdivacky} 903