//===- CodeGenPrepare.cpp - Prepare a function for code generation --------===// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // This pass munges the code in the input function to better prepare it for // SelectionDAG-based code generation. This works around limitations in it's // basic-block-at-a-time approach. It should eventually be removed. // //===----------------------------------------------------------------------===// #define DEBUG_TYPE "codegenprepare" #include "llvm/Transforms/Scalar.h" #include "llvm/Constants.h" #include "llvm/DerivedTypes.h" #include "llvm/Function.h" #include "llvm/InlineAsm.h" #include "llvm/Instructions.h" #include "llvm/Pass.h" #include "llvm/Target/TargetAsmInfo.h" #include "llvm/Target/TargetData.h" #include "llvm/Target/TargetLowering.h" #include "llvm/Target/TargetMachine.h" #include "llvm/Transforms/Utils/BasicBlockUtils.h" #include "llvm/Transforms/Utils/Local.h" #include "llvm/ADT/DenseMap.h" #include "llvm/ADT/SmallSet.h" #include "llvm/Support/CallSite.h" #include "llvm/Support/CommandLine.h" #include "llvm/Support/Compiler.h" #include "llvm/Support/Debug.h" #include "llvm/Support/GetElementPtrTypeIterator.h" #include "llvm/Support/PatternMatch.h" using namespace llvm; using namespace llvm::PatternMatch; static cl::opt FactorCommonPreds("split-critical-paths-tweak", cl::init(false), cl::Hidden); namespace { class VISIBILITY_HIDDEN CodeGenPrepare : public FunctionPass { /// TLI - Keep a pointer of a TargetLowering to consult for determining /// transformation profitability. const TargetLowering *TLI; /// BackEdges - Keep a set of all the loop back edges. /// SmallSet, 8> BackEdges; public: static char ID; // Pass identification, replacement for typeid explicit CodeGenPrepare(const TargetLowering *tli = 0) : FunctionPass(&ID), TLI(tli) {} bool runOnFunction(Function &F); private: bool EliminateMostlyEmptyBlocks(Function &F); bool CanMergeBlocks(const BasicBlock *BB, const BasicBlock *DestBB) const; void EliminateMostlyEmptyBlock(BasicBlock *BB); bool OptimizeBlock(BasicBlock &BB); bool OptimizeMemoryInst(Instruction *I, Value *Addr, const Type *AccessTy, DenseMap &SunkAddrs); bool OptimizeInlineAsmInst(Instruction *I, CallSite CS, DenseMap &SunkAddrs); bool OptimizeExtUses(Instruction *I); void findLoopBackEdges(Function &F); }; } char CodeGenPrepare::ID = 0; static RegisterPass X("codegenprepare", "Optimize for code generation"); FunctionPass *llvm::createCodeGenPreparePass(const TargetLowering *TLI) { return new CodeGenPrepare(TLI); } /// findLoopBackEdges - Do a DFS walk to find loop back edges. /// void CodeGenPrepare::findLoopBackEdges(Function &F) { SmallPtrSet Visited; SmallVector, 8> VisitStack; SmallPtrSet InStack; BasicBlock *BB = &F.getEntryBlock(); if (succ_begin(BB) == succ_end(BB)) return; Visited.insert(BB); VisitStack.push_back(std::make_pair(BB, succ_begin(BB))); InStack.insert(BB); do { std::pair &Top = VisitStack.back(); BasicBlock *ParentBB = Top.first; succ_iterator &I = Top.second; bool FoundNew = false; while (I != succ_end(ParentBB)) { BB = *I++; if (Visited.insert(BB)) { FoundNew = true; break; } // Successor is in VisitStack, it's a back edge. if (InStack.count(BB)) BackEdges.insert(std::make_pair(ParentBB, BB)); } if (FoundNew) { // Go down one level if there is a unvisited successor. InStack.insert(BB); VisitStack.push_back(std::make_pair(BB, succ_begin(BB))); } else { // Go up one level. std::pair &Pop = VisitStack.back(); InStack.erase(Pop.first); VisitStack.pop_back(); } } while (!VisitStack.empty()); } bool CodeGenPrepare::runOnFunction(Function &F) { bool EverMadeChange = false; // First pass, eliminate blocks that contain only PHI nodes and an // unconditional branch. EverMadeChange |= EliminateMostlyEmptyBlocks(F); // Now find loop back edges. findLoopBackEdges(F); bool MadeChange = true; while (MadeChange) { MadeChange = false; for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) MadeChange |= OptimizeBlock(*BB); EverMadeChange |= MadeChange; } return EverMadeChange; } /// EliminateMostlyEmptyBlocks - eliminate blocks that contain only PHI nodes /// and an unconditional branch. Passes before isel (e.g. LSR/loopsimplify) /// often split edges in ways that are non-optimal for isel. Start by /// eliminating these blocks so we can split them the way we want them. bool CodeGenPrepare::EliminateMostlyEmptyBlocks(Function &F) { bool MadeChange = false; // Note that this intentionally skips the entry block. for (Function::iterator I = ++F.begin(), E = F.end(); I != E; ) { BasicBlock *BB = I++; // If this block doesn't end with an uncond branch, ignore it. BranchInst *BI = dyn_cast(BB->getTerminator()); if (!BI || !BI->isUnconditional()) continue; // If the instruction before the branch isn't a phi node, then other stuff // is happening here. BasicBlock::iterator BBI = BI; if (BBI != BB->begin()) { --BBI; if (!isa(BBI)) continue; } // Do not break infinite loops. BasicBlock *DestBB = BI->getSuccessor(0); if (DestBB == BB) continue; if (!CanMergeBlocks(BB, DestBB)) continue; EliminateMostlyEmptyBlock(BB); MadeChange = true; } return MadeChange; } /// CanMergeBlocks - Return true if we can merge BB into DestBB if there is a /// single uncond branch between them, and BB contains no other non-phi /// instructions. bool CodeGenPrepare::CanMergeBlocks(const BasicBlock *BB, const BasicBlock *DestBB) const { // We only want to eliminate blocks whose phi nodes are used by phi nodes in // the successor. If there are more complex condition (e.g. preheaders), // don't mess around with them. BasicBlock::const_iterator BBI = BB->begin(); while (const PHINode *PN = dyn_cast(BBI++)) { for (Value::use_const_iterator UI = PN->use_begin(), E = PN->use_end(); UI != E; ++UI) { const Instruction *User = cast(*UI); if (User->getParent() != DestBB || !isa(User)) return false; // If User is inside DestBB block and it is a PHINode then check // incoming value. If incoming value is not from BB then this is // a complex condition (e.g. preheaders) we want to avoid here. if (User->getParent() == DestBB) { if (const PHINode *UPN = dyn_cast(User)) for (unsigned I = 0, E = UPN->getNumIncomingValues(); I != E; ++I) { Instruction *Insn = dyn_cast(UPN->getIncomingValue(I)); if (Insn && Insn->getParent() == BB && Insn->getParent() != UPN->getIncomingBlock(I)) return false; } } } } // If BB and DestBB contain any common predecessors, then the phi nodes in BB // and DestBB may have conflicting incoming values for the block. If so, we // can't merge the block. const PHINode *DestBBPN = dyn_cast(DestBB->begin()); if (!DestBBPN) return true; // no conflict. // Collect the preds of BB. SmallPtrSet BBPreds; if (const PHINode *BBPN = dyn_cast(BB->begin())) { // It is faster to get preds from a PHI than with pred_iterator. for (unsigned i = 0, e = BBPN->getNumIncomingValues(); i != e; ++i) BBPreds.insert(BBPN->getIncomingBlock(i)); } else { BBPreds.insert(pred_begin(BB), pred_end(BB)); } // Walk the preds of DestBB. for (unsigned i = 0, e = DestBBPN->getNumIncomingValues(); i != e; ++i) { BasicBlock *Pred = DestBBPN->getIncomingBlock(i); if (BBPreds.count(Pred)) { // Common predecessor? BBI = DestBB->begin(); while (const PHINode *PN = dyn_cast(BBI++)) { const Value *V1 = PN->getIncomingValueForBlock(Pred); const Value *V2 = PN->getIncomingValueForBlock(BB); // If V2 is a phi node in BB, look up what the mapped value will be. if (const PHINode *V2PN = dyn_cast(V2)) if (V2PN->getParent() == BB) V2 = V2PN->getIncomingValueForBlock(Pred); // If there is a conflict, bail out. if (V1 != V2) return false; } } } return true; } /// EliminateMostlyEmptyBlock - Eliminate a basic block that have only phi's and /// an unconditional branch in it. void CodeGenPrepare::EliminateMostlyEmptyBlock(BasicBlock *BB) { BranchInst *BI = cast(BB->getTerminator()); BasicBlock *DestBB = BI->getSuccessor(0); DOUT << "MERGING MOSTLY EMPTY BLOCKS - BEFORE:\n" << *BB << *DestBB; // If the destination block has a single pred, then this is a trivial edge, // just collapse it. if (BasicBlock *SinglePred = DestBB->getSinglePredecessor()) { if (SinglePred != DestBB) { // Remember if SinglePred was the entry block of the function. If so, we // will need to move BB back to the entry position. bool isEntry = SinglePred == &SinglePred->getParent()->getEntryBlock(); MergeBasicBlockIntoOnlyPred(DestBB); if (isEntry && BB != &BB->getParent()->getEntryBlock()) BB->moveBefore(&BB->getParent()->getEntryBlock()); DOUT << "AFTER:\n" << *DestBB << "\n\n\n"; return; } } // Otherwise, we have multiple predecessors of BB. Update the PHIs in DestBB // to handle the new incoming edges it is about to have. PHINode *PN; for (BasicBlock::iterator BBI = DestBB->begin(); (PN = dyn_cast(BBI)); ++BBI) { // Remove the incoming value for BB, and remember it. Value *InVal = PN->removeIncomingValue(BB, false); // Two options: either the InVal is a phi node defined in BB or it is some // value that dominates BB. PHINode *InValPhi = dyn_cast(InVal); if (InValPhi && InValPhi->getParent() == BB) { // Add all of the input values of the input PHI as inputs of this phi. for (unsigned i = 0, e = InValPhi->getNumIncomingValues(); i != e; ++i) PN->addIncoming(InValPhi->getIncomingValue(i), InValPhi->getIncomingBlock(i)); } else { // Otherwise, add one instance of the dominating value for each edge that // we will be adding. if (PHINode *BBPN = dyn_cast(BB->begin())) { for (unsigned i = 0, e = BBPN->getNumIncomingValues(); i != e; ++i) PN->addIncoming(InVal, BBPN->getIncomingBlock(i)); } else { for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) PN->addIncoming(InVal, *PI); } } } // The PHIs are now updated, change everything that refers to BB to use // DestBB and remove BB. BB->replaceAllUsesWith(DestBB); BB->eraseFromParent(); DOUT << "AFTER:\n" << *DestBB << "\n\n\n"; } /// SplitEdgeNicely - Split the critical edge from TI to its specified /// successor if it will improve codegen. We only do this if the successor has /// phi nodes (otherwise critical edges are ok). If there is already another /// predecessor of the succ that is empty (and thus has no phi nodes), use it /// instead of introducing a new block. static void SplitEdgeNicely(TerminatorInst *TI, unsigned SuccNum, SmallSet, 8> &BackEdges, Pass *P) { BasicBlock *TIBB = TI->getParent(); BasicBlock *Dest = TI->getSuccessor(SuccNum); assert(isa(Dest->begin()) && "This should only be called if Dest has a PHI!"); // As a hack, never split backedges of loops. Even though the copy for any // PHIs inserted on the backedge would be dead for exits from the loop, we // assume that the cost of *splitting* the backedge would be too high. if (BackEdges.count(std::make_pair(TIBB, Dest))) return; if (!FactorCommonPreds) { /// TIPHIValues - This array is lazily computed to determine the values of /// PHIs in Dest that TI would provide. SmallVector TIPHIValues; // Check to see if Dest has any blocks that can be used as a split edge for // this terminator. for (pred_iterator PI = pred_begin(Dest), E = pred_end(Dest); PI != E; ++PI) { BasicBlock *Pred = *PI; // To be usable, the pred has to end with an uncond branch to the dest. BranchInst *PredBr = dyn_cast(Pred->getTerminator()); if (!PredBr || !PredBr->isUnconditional() || // Must be empty other than the branch. &Pred->front() != PredBr || // Cannot be the entry block; its label does not get emitted. Pred == &(Dest->getParent()->getEntryBlock())) continue; // Finally, since we know that Dest has phi nodes in it, we have to make // sure that jumping to Pred will have the same affect as going to Dest in // terms of PHI values. PHINode *PN; unsigned PHINo = 0; bool FoundMatch = true; for (BasicBlock::iterator I = Dest->begin(); (PN = dyn_cast(I)); ++I, ++PHINo) { if (PHINo == TIPHIValues.size()) TIPHIValues.push_back(PN->getIncomingValueForBlock(TIBB)); // If the PHI entry doesn't work, we can't use this pred. if (TIPHIValues[PHINo] != PN->getIncomingValueForBlock(Pred)) { FoundMatch = false; break; } } // If we found a workable predecessor, change TI to branch to Succ. if (FoundMatch) { Dest->removePredecessor(TIBB); TI->setSuccessor(SuccNum, Pred); return; } } SplitCriticalEdge(TI, SuccNum, P, true); return; } PHINode *PN; SmallVector TIPHIValues; for (BasicBlock::iterator I = Dest->begin(); (PN = dyn_cast(I)); ++I) TIPHIValues.push_back(PN->getIncomingValueForBlock(TIBB)); SmallVector IdenticalPreds; for (pred_iterator PI = pred_begin(Dest), E = pred_end(Dest); PI != E; ++PI) { BasicBlock *Pred = *PI; if (BackEdges.count(std::make_pair(Pred, Dest))) continue; if (PI == TIBB) IdenticalPreds.push_back(Pred); else { bool Identical = true; unsigned PHINo = 0; for (BasicBlock::iterator I = Dest->begin(); (PN = dyn_cast(I)); ++I, ++PHINo) if (TIPHIValues[PHINo] != PN->getIncomingValueForBlock(Pred)) { Identical = false; break; } if (Identical) IdenticalPreds.push_back(Pred); } } assert(!IdenticalPreds.empty()); SplitBlockPredecessors(Dest, &IdenticalPreds[0], IdenticalPreds.size(), ".critedge", P); } /// OptimizeNoopCopyExpression - If the specified cast instruction is a noop /// copy (e.g. it's casting from one pointer type to another, int->uint, or /// int->sbyte on PPC), sink it into user blocks to reduce the number of virtual /// registers that must be created and coalesced. /// /// Return true if any changes are made. /// static bool OptimizeNoopCopyExpression(CastInst *CI, const TargetLowering &TLI){ // If this is a noop copy, MVT SrcVT = TLI.getValueType(CI->getOperand(0)->getType()); MVT DstVT = TLI.getValueType(CI->getType()); // This is an fp<->int conversion? if (SrcVT.isInteger() != DstVT.isInteger()) return false; // If this is an extension, it will be a zero or sign extension, which // isn't a noop. if (SrcVT.bitsLT(DstVT)) return false; // If these values will be promoted, find out what they will be promoted // to. This helps us consider truncates on PPC as noop copies when they // are. if (TLI.getTypeAction(SrcVT) == TargetLowering::Promote) SrcVT = TLI.getTypeToTransformTo(SrcVT); if (TLI.getTypeAction(DstVT) == TargetLowering::Promote) DstVT = TLI.getTypeToTransformTo(DstVT); // If, after promotion, these are the same types, this is a noop copy. if (SrcVT != DstVT) return false; BasicBlock *DefBB = CI->getParent(); /// InsertedCasts - Only insert a cast in each block once. DenseMap InsertedCasts; bool MadeChange = false; for (Value::use_iterator UI = CI->use_begin(), E = CI->use_end(); UI != E; ) { Use &TheUse = UI.getUse(); Instruction *User = cast(*UI); // Figure out which BB this cast is used in. For PHI's this is the // appropriate predecessor block. BasicBlock *UserBB = User->getParent(); if (PHINode *PN = dyn_cast(User)) { UserBB = PN->getIncomingBlock(UI); } // Preincrement use iterator so we don't invalidate it. ++UI; // If this user is in the same block as the cast, don't change the cast. if (UserBB == DefBB) continue; // If we have already inserted a cast into this block, use it. CastInst *&InsertedCast = InsertedCasts[UserBB]; if (!InsertedCast) { BasicBlock::iterator InsertPt = UserBB->getFirstNonPHI(); InsertedCast = CastInst::Create(CI->getOpcode(), CI->getOperand(0), CI->getType(), "", InsertPt); MadeChange = true; } // Replace a use of the cast with a use of the new cast. TheUse = InsertedCast; } // If we removed all uses, nuke the cast. if (CI->use_empty()) { CI->eraseFromParent(); MadeChange = true; } return MadeChange; } /// OptimizeCmpExpression - sink the given CmpInst into user blocks to reduce /// the number of virtual registers that must be created and coalesced. This is /// a clear win except on targets with multiple condition code registers /// (PowerPC), where it might lose; some adjustment may be wanted there. /// /// Return true if any changes are made. static bool OptimizeCmpExpression(CmpInst *CI) { BasicBlock *DefBB = CI->getParent(); /// InsertedCmp - Only insert a cmp in each block once. DenseMap InsertedCmps; bool MadeChange = false; for (Value::use_iterator UI = CI->use_begin(), E = CI->use_end(); UI != E; ) { Use &TheUse = UI.getUse(); Instruction *User = cast(*UI); // Preincrement use iterator so we don't invalidate it. ++UI; // Don't bother for PHI nodes. if (isa(User)) continue; // Figure out which BB this cmp is used in. BasicBlock *UserBB = User->getParent(); // If this user is in the same block as the cmp, don't change the cmp. if (UserBB == DefBB) continue; // If we have already inserted a cmp into this block, use it. CmpInst *&InsertedCmp = InsertedCmps[UserBB]; if (!InsertedCmp) { BasicBlock::iterator InsertPt = UserBB->getFirstNonPHI(); InsertedCmp = CmpInst::Create(CI->getOpcode(), CI->getPredicate(), CI->getOperand(0), CI->getOperand(1), "", InsertPt); MadeChange = true; } // Replace a use of the cmp with a use of the new cmp. TheUse = InsertedCmp; } // If we removed all uses, nuke the cmp. if (CI->use_empty()) CI->eraseFromParent(); return MadeChange; } //===----------------------------------------------------------------------===// // Addressing Mode Analysis and Optimization //===----------------------------------------------------------------------===// namespace { /// ExtAddrMode - This is an extended version of TargetLowering::AddrMode /// which holds actual Value*'s for register values. struct ExtAddrMode : public TargetLowering::AddrMode { Value *BaseReg; Value *ScaledReg; ExtAddrMode() : BaseReg(0), ScaledReg(0) {} void print(OStream &OS) const; void dump() const { print(cerr); cerr << '\n'; } }; } // end anonymous namespace static inline OStream &operator<<(OStream &OS, const ExtAddrMode &AM) { AM.print(OS); return OS; } void ExtAddrMode::print(OStream &OS) const { bool NeedPlus = false; OS << "["; if (BaseGV) OS << (NeedPlus ? " + " : "") << "GV:%" << BaseGV->getName(), NeedPlus = true; if (BaseOffs) OS << (NeedPlus ? " + " : "") << BaseOffs, NeedPlus = true; if (BaseReg) OS << (NeedPlus ? " + " : "") << "Base:%" << BaseReg->getName(), NeedPlus = true; if (Scale) OS << (NeedPlus ? " + " : "") << Scale << "*%" << ScaledReg->getName(), NeedPlus = true; OS << ']'; } namespace { /// AddressingModeMatcher - This class exposes a single public method, which is /// used to construct a "maximal munch" of the addressing mode for the target /// specified by TLI for an access to "V" with an access type of AccessTy. This /// returns the addressing mode that is actually matched by value, but also /// returns the list of instructions involved in that addressing computation in /// AddrModeInsts. class AddressingModeMatcher { SmallVectorImpl &AddrModeInsts; const TargetLowering &TLI; /// AccessTy/MemoryInst - This is the type for the access (e.g. double) and /// the memory instruction that we're computing this address for. const Type *AccessTy; Instruction *MemoryInst; /// AddrMode - This is the addressing mode that we're building up. This is /// part of the return value of this addressing mode matching stuff. ExtAddrMode &AddrMode; /// IgnoreProfitability - This is set to true when we should not do /// profitability checks. When true, IsProfitableToFoldIntoAddressingMode /// always returns true. bool IgnoreProfitability; AddressingModeMatcher(SmallVectorImpl &AMI, const TargetLowering &T, const Type *AT, Instruction *MI, ExtAddrMode &AM) : AddrModeInsts(AMI), TLI(T), AccessTy(AT), MemoryInst(MI), AddrMode(AM) { IgnoreProfitability = false; } public: /// Match - Find the maximal addressing mode that a load/store of V can fold, /// give an access type of AccessTy. This returns a list of involved /// instructions in AddrModeInsts. static ExtAddrMode Match(Value *V, const Type *AccessTy, Instruction *MemoryInst, SmallVectorImpl &AddrModeInsts, const TargetLowering &TLI) { ExtAddrMode Result; bool Success = AddressingModeMatcher(AddrModeInsts, TLI, AccessTy, MemoryInst, Result).MatchAddr(V, 0); Success = Success; assert(Success && "Couldn't select *anything*?"); return Result; } private: bool MatchScaledValue(Value *ScaleReg, int64_t Scale, unsigned Depth); bool MatchAddr(Value *V, unsigned Depth); bool MatchOperationAddr(User *Operation, unsigned Opcode, unsigned Depth); bool IsProfitableToFoldIntoAddressingMode(Instruction *I, ExtAddrMode &AMBefore, ExtAddrMode &AMAfter); bool ValueAlreadyLiveAtInst(Value *Val, Value *KnownLive1, Value *KnownLive2); }; } // end anonymous namespace /// MatchScaledValue - Try adding ScaleReg*Scale to the current addressing mode. /// Return true and update AddrMode if this addr mode is legal for the target, /// false if not. bool AddressingModeMatcher::MatchScaledValue(Value *ScaleReg, int64_t Scale, unsigned Depth) { // If Scale is 1, then this is the same as adding ScaleReg to the addressing // mode. Just process that directly. if (Scale == 1) return MatchAddr(ScaleReg, Depth); // If the scale is 0, it takes nothing to add this. if (Scale == 0) return true; // If we already have a scale of this value, we can add to it, otherwise, we // need an available scale field. if (AddrMode.Scale != 0 && AddrMode.ScaledReg != ScaleReg) return false; ExtAddrMode TestAddrMode = AddrMode; // Add scale to turn X*4+X*3 -> X*7. This could also do things like // [A+B + A*7] -> [B+A*8]. TestAddrMode.Scale += Scale; TestAddrMode.ScaledReg = ScaleReg; // If the new address isn't legal, bail out. if (!TLI.isLegalAddressingMode(TestAddrMode, AccessTy)) return false; // It was legal, so commit it. AddrMode = TestAddrMode; // Okay, we decided that we can add ScaleReg+Scale to AddrMode. Check now // to see if ScaleReg is actually X+C. If so, we can turn this into adding // X*Scale + C*Scale to addr mode. ConstantInt *CI; Value *AddLHS; if (isa(ScaleReg) && // not a constant expr. match(ScaleReg, m_Add(m_Value(AddLHS), m_ConstantInt(CI)))) { TestAddrMode.ScaledReg = AddLHS; TestAddrMode.BaseOffs += CI->getSExtValue()*TestAddrMode.Scale; // If this addressing mode is legal, commit it and remember that we folded // this instruction. if (TLI.isLegalAddressingMode(TestAddrMode, AccessTy)) { AddrModeInsts.push_back(cast(ScaleReg)); AddrMode = TestAddrMode; return true; } } // Otherwise, not (x+c)*scale, just return what we have. return true; } /// MightBeFoldableInst - This is a little filter, which returns true if an /// addressing computation involving I might be folded into a load/store /// accessing it. This doesn't need to be perfect, but needs to accept at least /// the set of instructions that MatchOperationAddr can. static bool MightBeFoldableInst(Instruction *I) { switch (I->getOpcode()) { case Instruction::BitCast: // Don't touch identity bitcasts. if (I->getType() == I->getOperand(0)->getType()) return false; return isa(I->getType()) || isa(I->getType()); case Instruction::PtrToInt: // PtrToInt is always a noop, as we know that the int type is pointer sized. return true; case Instruction::IntToPtr: // We know the input is intptr_t, so this is foldable. return true; case Instruction::Add: return true; case Instruction::Mul: case Instruction::Shl: // Can only handle X*C and X << C. return isa(I->getOperand(1)); case Instruction::GetElementPtr: return true; default: return false; } } /// MatchOperationAddr - Given an instruction or constant expr, see if we can /// fold the operation into the addressing mode. If so, update the addressing /// mode and return true, otherwise return false without modifying AddrMode. bool AddressingModeMatcher::MatchOperationAddr(User *AddrInst, unsigned Opcode, unsigned Depth) { // Avoid exponential behavior on extremely deep expression trees. if (Depth >= 5) return false; switch (Opcode) { case Instruction::PtrToInt: // PtrToInt is always a noop, as we know that the int type is pointer sized. return MatchAddr(AddrInst->getOperand(0), Depth); case Instruction::IntToPtr: // This inttoptr is a no-op if the integer type is pointer sized. if (TLI.getValueType(AddrInst->getOperand(0)->getType()) == TLI.getPointerTy()) return MatchAddr(AddrInst->getOperand(0), Depth); return false; case Instruction::BitCast: // BitCast is always a noop, and we can handle it as long as it is // int->int or pointer->pointer (we don't want int<->fp or something). if ((isa(AddrInst->getOperand(0)->getType()) || isa(AddrInst->getOperand(0)->getType())) && // Don't touch identity bitcasts. These were probably put here by LSR, // and we don't want to mess around with them. Assume it knows what it // is doing. AddrInst->getOperand(0)->getType() != AddrInst->getType()) return MatchAddr(AddrInst->getOperand(0), Depth); return false; case Instruction::Add: { // Check to see if we can merge in the RHS then the LHS. If so, we win. ExtAddrMode BackupAddrMode = AddrMode; unsigned OldSize = AddrModeInsts.size(); if (MatchAddr(AddrInst->getOperand(1), Depth+1) && MatchAddr(AddrInst->getOperand(0), Depth+1)) return true; // Restore the old addr mode info. AddrMode = BackupAddrMode; AddrModeInsts.resize(OldSize); // Otherwise this was over-aggressive. Try merging in the LHS then the RHS. if (MatchAddr(AddrInst->getOperand(0), Depth+1) && MatchAddr(AddrInst->getOperand(1), Depth+1)) return true; // Otherwise we definitely can't merge the ADD in. AddrMode = BackupAddrMode; AddrModeInsts.resize(OldSize); break; } //case Instruction::Or: // TODO: We can handle "Or Val, Imm" iff this OR is equivalent to an ADD. //break; case Instruction::Mul: case Instruction::Shl: { // Can only handle X*C and X << C. ConstantInt *RHS = dyn_cast(AddrInst->getOperand(1)); if (!RHS) return false; int64_t Scale = RHS->getSExtValue(); if (Opcode == Instruction::Shl) Scale = 1 << Scale; return MatchScaledValue(AddrInst->getOperand(0), Scale, Depth); } case Instruction::GetElementPtr: { // Scan the GEP. We check it if it contains constant offsets and at most // one variable offset. int VariableOperand = -1; unsigned VariableScale = 0; int64_t ConstantOffset = 0; const TargetData *TD = TLI.getTargetData(); gep_type_iterator GTI = gep_type_begin(AddrInst); for (unsigned i = 1, e = AddrInst->getNumOperands(); i != e; ++i, ++GTI) { if (const StructType *STy = dyn_cast(*GTI)) { const StructLayout *SL = TD->getStructLayout(STy); unsigned Idx = cast(AddrInst->getOperand(i))->getZExtValue(); ConstantOffset += SL->getElementOffset(Idx); } else { uint64_t TypeSize = TD->getTypePaddedSize(GTI.getIndexedType()); if (ConstantInt *CI = dyn_cast(AddrInst->getOperand(i))) { ConstantOffset += CI->getSExtValue()*TypeSize; } else if (TypeSize) { // Scales of zero don't do anything. // We only allow one variable index at the moment. if (VariableOperand != -1) return false; // Remember the variable index. VariableOperand = i; VariableScale = TypeSize; } } } // A common case is for the GEP to only do a constant offset. In this case, // just add it to the disp field and check validity. if (VariableOperand == -1) { AddrMode.BaseOffs += ConstantOffset; if (ConstantOffset == 0 || TLI.isLegalAddressingMode(AddrMode, AccessTy)){ // Check to see if we can fold the base pointer in too. if (MatchAddr(AddrInst->getOperand(0), Depth+1)) return true; } AddrMode.BaseOffs -= ConstantOffset; return false; } // Save the valid addressing mode in case we can't match. ExtAddrMode BackupAddrMode = AddrMode; // Check that this has no base reg yet. If so, we won't have a place to // put the base of the GEP (assuming it is not a null ptr). bool SetBaseReg = true; if (isa(AddrInst->getOperand(0))) SetBaseReg = false; // null pointer base doesn't need representation. else if (AddrMode.HasBaseReg) return false; // Base register already specified, can't match GEP. else { // Otherwise, we'll use the GEP base as the BaseReg. AddrMode.HasBaseReg = true; AddrMode.BaseReg = AddrInst->getOperand(0); } // See if the scale and offset amount is valid for this target. AddrMode.BaseOffs += ConstantOffset; if (!MatchScaledValue(AddrInst->getOperand(VariableOperand), VariableScale, Depth)) { AddrMode = BackupAddrMode; return false; } // If we have a null as the base of the GEP, folding in the constant offset // plus variable scale is all we can do. if (!SetBaseReg) return true; // If this match succeeded, we know that we can form an address with the // GepBase as the basereg. Match the base pointer of the GEP more // aggressively by zeroing out BaseReg and rematching. If the base is // (for example) another GEP, this allows merging in that other GEP into // the addressing mode we're forming. AddrMode.HasBaseReg = false; AddrMode.BaseReg = 0; bool Success = MatchAddr(AddrInst->getOperand(0), Depth+1); assert(Success && "MatchAddr should be able to fill in BaseReg!"); Success=Success; return true; } } return false; } /// MatchAddr - If we can, try to add the value of 'Addr' into the current /// addressing mode. If Addr can't be added to AddrMode this returns false and /// leaves AddrMode unmodified. This assumes that Addr is either a pointer type /// or intptr_t for the target. /// bool AddressingModeMatcher::MatchAddr(Value *Addr, unsigned Depth) { if (ConstantInt *CI = dyn_cast(Addr)) { // Fold in immediates if legal for the target. AddrMode.BaseOffs += CI->getSExtValue(); if (TLI.isLegalAddressingMode(AddrMode, AccessTy)) return true; AddrMode.BaseOffs -= CI->getSExtValue(); } else if (GlobalValue *GV = dyn_cast(Addr)) { // If this is a global variable, try to fold it into the addressing mode. if (AddrMode.BaseGV == 0) { AddrMode.BaseGV = GV; if (TLI.isLegalAddressingMode(AddrMode, AccessTy)) return true; AddrMode.BaseGV = 0; } } else if (Instruction *I = dyn_cast(Addr)) { ExtAddrMode BackupAddrMode = AddrMode; unsigned OldSize = AddrModeInsts.size(); // Check to see if it is possible to fold this operation. if (MatchOperationAddr(I, I->getOpcode(), Depth)) { // Okay, it's possible to fold this. Check to see if it is actually // *profitable* to do so. We use a simple cost model to avoid increasing // register pressure too much. if (I->hasOneUse() || IsProfitableToFoldIntoAddressingMode(I, BackupAddrMode, AddrMode)) { AddrModeInsts.push_back(I); return true; } // It isn't profitable to do this, roll back. //cerr << "NOT FOLDING: " << *I; AddrMode = BackupAddrMode; AddrModeInsts.resize(OldSize); } } else if (ConstantExpr *CE = dyn_cast(Addr)) { if (MatchOperationAddr(CE, CE->getOpcode(), Depth)) return true; } else if (isa(Addr)) { // Null pointer gets folded without affecting the addressing mode. return true; } // Worse case, the target should support [reg] addressing modes. :) if (!AddrMode.HasBaseReg) { AddrMode.HasBaseReg = true; AddrMode.BaseReg = Addr; // Still check for legality in case the target supports [imm] but not [i+r]. if (TLI.isLegalAddressingMode(AddrMode, AccessTy)) return true; AddrMode.HasBaseReg = false; AddrMode.BaseReg = 0; } // If the base register is already taken, see if we can do [r+r]. if (AddrMode.Scale == 0) { AddrMode.Scale = 1; AddrMode.ScaledReg = Addr; if (TLI.isLegalAddressingMode(AddrMode, AccessTy)) return true; AddrMode.Scale = 0; AddrMode.ScaledReg = 0; } // Couldn't match. return false; } /// IsOperandAMemoryOperand - Check to see if all uses of OpVal by the specified /// inline asm call are due to memory operands. If so, return true, otherwise /// return false. static bool IsOperandAMemoryOperand(CallInst *CI, InlineAsm *IA, Value *OpVal, const TargetLowering &TLI) { std::vector Constraints = IA->ParseConstraints(); unsigned ArgNo = 1; // ArgNo - The operand of the CallInst. for (unsigned i = 0, e = Constraints.size(); i != e; ++i) { TargetLowering::AsmOperandInfo OpInfo(Constraints[i]); // Compute the value type for each operand. switch (OpInfo.Type) { case InlineAsm::isOutput: if (OpInfo.isIndirect) OpInfo.CallOperandVal = CI->getOperand(ArgNo++); break; case InlineAsm::isInput: OpInfo.CallOperandVal = CI->getOperand(ArgNo++); break; case InlineAsm::isClobber: // Nothing to do. break; } // Compute the constraint code and ConstraintType to use. TLI.ComputeConstraintToUse(OpInfo, SDValue(), OpInfo.ConstraintType == TargetLowering::C_Memory); // If this asm operand is our Value*, and if it isn't an indirect memory // operand, we can't fold it! if (OpInfo.CallOperandVal == OpVal && (OpInfo.ConstraintType != TargetLowering::C_Memory || !OpInfo.isIndirect)) return false; } return true; } /// FindAllMemoryUses - Recursively walk all the uses of I until we find a /// memory use. If we find an obviously non-foldable instruction, return true. /// Add the ultimately found memory instructions to MemoryUses. static bool FindAllMemoryUses(Instruction *I, SmallVectorImpl > &MemoryUses, SmallPtrSet &ConsideredInsts, const TargetLowering &TLI) { // If we already considered this instruction, we're done. if (!ConsideredInsts.insert(I)) return false; // If this is an obviously unfoldable instruction, bail out. if (!MightBeFoldableInst(I)) return true; // Loop over all the uses, recursively processing them. for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E; ++UI) { if (LoadInst *LI = dyn_cast(*UI)) { MemoryUses.push_back(std::make_pair(LI, UI.getOperandNo())); continue; } if (StoreInst *SI = dyn_cast(*UI)) { if (UI.getOperandNo() == 0) return true; // Storing addr, not into addr. MemoryUses.push_back(std::make_pair(SI, UI.getOperandNo())); continue; } if (CallInst *CI = dyn_cast(*UI)) { InlineAsm *IA = dyn_cast(CI->getCalledValue()); if (IA == 0) return true; // If this is a memory operand, we're cool, otherwise bail out. if (!IsOperandAMemoryOperand(CI, IA, I, TLI)) return true; continue; } if (FindAllMemoryUses(cast(*UI), MemoryUses, ConsideredInsts, TLI)) return true; } return false; } /// ValueAlreadyLiveAtInst - Retrn true if Val is already known to be live at /// the use site that we're folding it into. If so, there is no cost to /// include it in the addressing mode. KnownLive1 and KnownLive2 are two values /// that we know are live at the instruction already. bool AddressingModeMatcher::ValueAlreadyLiveAtInst(Value *Val,Value *KnownLive1, Value *KnownLive2) { // If Val is either of the known-live values, we know it is live! if (Val == 0 || Val == KnownLive1 || Val == KnownLive2) return true; // All values other than instructions and arguments (e.g. constants) are live. if (!isa(Val) && !isa(Val)) return true; // If Val is a constant sized alloca in the entry block, it is live, this is // true because it is just a reference to the stack/frame pointer, which is // live for the whole function. if (AllocaInst *AI = dyn_cast(Val)) if (AI->isStaticAlloca()) return true; // Check to see if this value is already used in the memory instruction's // block. If so, it's already live into the block at the very least, so we // can reasonably fold it. BasicBlock *MemBB = MemoryInst->getParent(); for (Value::use_iterator UI = Val->use_begin(), E = Val->use_end(); UI != E; ++UI) // We know that uses of arguments and instructions have to be instructions. if (cast(*UI)->getParent() == MemBB) return true; return false; } /// IsProfitableToFoldIntoAddressingMode - It is possible for the addressing /// mode of the machine to fold the specified instruction into a load or store /// that ultimately uses it. However, the specified instruction has multiple /// uses. Given this, it may actually increase register pressure to fold it /// into the load. For example, consider this code: /// /// X = ... /// Y = X+1 /// use(Y) -> nonload/store /// Z = Y+1 /// load Z /// /// In this case, Y has multiple uses, and can be folded into the load of Z /// (yielding load [X+2]). However, doing this will cause both "X" and "X+1" to /// be live at the use(Y) line. If we don't fold Y into load Z, we use one /// fewer register. Since Y can't be folded into "use(Y)" we don't increase the /// number of computations either. /// /// Note that this (like most of CodeGenPrepare) is just a rough heuristic. If /// X was live across 'load Z' for other reasons, we actually *would* want to /// fold the addressing mode in the Z case. This would make Y die earlier. bool AddressingModeMatcher:: IsProfitableToFoldIntoAddressingMode(Instruction *I, ExtAddrMode &AMBefore, ExtAddrMode &AMAfter) { if (IgnoreProfitability) return true; // AMBefore is the addressing mode before this instruction was folded into it, // and AMAfter is the addressing mode after the instruction was folded. Get // the set of registers referenced by AMAfter and subtract out those // referenced by AMBefore: this is the set of values which folding in this // address extends the lifetime of. // // Note that there are only two potential values being referenced here, // BaseReg and ScaleReg (global addresses are always available, as are any // folded immediates). Value *BaseReg = AMAfter.BaseReg, *ScaledReg = AMAfter.ScaledReg; // If the BaseReg or ScaledReg was referenced by the previous addrmode, their // lifetime wasn't extended by adding this instruction. if (ValueAlreadyLiveAtInst(BaseReg, AMBefore.BaseReg, AMBefore.ScaledReg)) BaseReg = 0; if (ValueAlreadyLiveAtInst(ScaledReg, AMBefore.BaseReg, AMBefore.ScaledReg)) ScaledReg = 0; // If folding this instruction (and it's subexprs) didn't extend any live // ranges, we're ok with it. if (BaseReg == 0 && ScaledReg == 0) return true; // If all uses of this instruction are ultimately load/store/inlineasm's, // check to see if their addressing modes will include this instruction. If // so, we can fold it into all uses, so it doesn't matter if it has multiple // uses. SmallVector, 16> MemoryUses; SmallPtrSet ConsideredInsts; if (FindAllMemoryUses(I, MemoryUses, ConsideredInsts, TLI)) return false; // Has a non-memory, non-foldable use! // Now that we know that all uses of this instruction are part of a chain of // computation involving only operations that could theoretically be folded // into a memory use, loop over each of these uses and see if they could // *actually* fold the instruction. SmallVector MatchedAddrModeInsts; for (unsigned i = 0, e = MemoryUses.size(); i != e; ++i) { Instruction *User = MemoryUses[i].first; unsigned OpNo = MemoryUses[i].second; // Get the access type of this use. If the use isn't a pointer, we don't // know what it accesses. Value *Address = User->getOperand(OpNo); if (!isa(Address->getType())) return false; const Type *AddressAccessTy = cast(Address->getType())->getElementType(); // Do a match against the root of this address, ignoring profitability. This // will tell us if the addressing mode for the memory operation will // *actually* cover the shared instruction. ExtAddrMode Result; AddressingModeMatcher Matcher(MatchedAddrModeInsts, TLI, AddressAccessTy, MemoryInst, Result); Matcher.IgnoreProfitability = true; bool Success = Matcher.MatchAddr(Address, 0); Success = Success; assert(Success && "Couldn't select *anything*?"); // If the match didn't cover I, then it won't be shared by it. if (std::find(MatchedAddrModeInsts.begin(), MatchedAddrModeInsts.end(), I) == MatchedAddrModeInsts.end()) return false; MatchedAddrModeInsts.clear(); } return true; } //===----------------------------------------------------------------------===// // Memory Optimization //===----------------------------------------------------------------------===// /// IsNonLocalValue - Return true if the specified values are defined in a /// different basic block than BB. static bool IsNonLocalValue(Value *V, BasicBlock *BB) { if (Instruction *I = dyn_cast(V)) return I->getParent() != BB; return false; } /// OptimizeMemoryInst - Load and Store Instructions have often have /// addressing modes that can do significant amounts of computation. As such, /// instruction selection will try to get the load or store to do as much /// computation as possible for the program. The problem is that isel can only /// see within a single block. As such, we sink as much legal addressing mode /// stuff into the block as possible. /// /// This method is used to optimize both load/store and inline asms with memory /// operands. bool CodeGenPrepare::OptimizeMemoryInst(Instruction *MemoryInst, Value *Addr, const Type *AccessTy, DenseMap &SunkAddrs) { // Figure out what addressing mode will be built up for this operation. SmallVector AddrModeInsts; ExtAddrMode AddrMode = AddressingModeMatcher::Match(Addr, AccessTy,MemoryInst, AddrModeInsts, *TLI); // Check to see if any of the instructions supersumed by this addr mode are // non-local to I's BB. bool AnyNonLocal = false; for (unsigned i = 0, e = AddrModeInsts.size(); i != e; ++i) { if (IsNonLocalValue(AddrModeInsts[i], MemoryInst->getParent())) { AnyNonLocal = true; break; } } // If all the instructions matched are already in this BB, don't do anything. if (!AnyNonLocal) { DEBUG(cerr << "CGP: Found local addrmode: " << AddrMode << "\n"); return false; } // Insert this computation right after this user. Since our caller is // scanning from the top of the BB to the bottom, reuse of the expr are // guaranteed to happen later. BasicBlock::iterator InsertPt = MemoryInst; // Now that we determined the addressing expression we want to use and know // that we have to sink it into this block. Check to see if we have already // done this for some other load/store instr in this block. If so, reuse the // computation. Value *&SunkAddr = SunkAddrs[Addr]; if (SunkAddr) { DEBUG(cerr << "CGP: Reusing nonlocal addrmode: " << AddrMode << "\n"); if (SunkAddr->getType() != Addr->getType()) SunkAddr = new BitCastInst(SunkAddr, Addr->getType(), "tmp", InsertPt); } else { DEBUG(cerr << "CGP: SINKING nonlocal addrmode: " << AddrMode << "\n"); const Type *IntPtrTy = TLI->getTargetData()->getIntPtrType(); Value *Result = 0; // Start with the scale value. if (AddrMode.Scale) { Value *V = AddrMode.ScaledReg; if (V->getType() == IntPtrTy) { // done. } else if (isa(V->getType())) { V = new PtrToIntInst(V, IntPtrTy, "sunkaddr", InsertPt); } else if (cast(IntPtrTy)->getBitWidth() < cast(V->getType())->getBitWidth()) { V = new TruncInst(V, IntPtrTy, "sunkaddr", InsertPt); } else { V = new SExtInst(V, IntPtrTy, "sunkaddr", InsertPt); } if (AddrMode.Scale != 1) V = BinaryOperator::CreateMul(V, ConstantInt::get(IntPtrTy, AddrMode.Scale), "sunkaddr", InsertPt); Result = V; } // Add in the base register. if (AddrMode.BaseReg) { Value *V = AddrMode.BaseReg; if (V->getType() != IntPtrTy) V = new PtrToIntInst(V, IntPtrTy, "sunkaddr", InsertPt); if (Result) Result = BinaryOperator::CreateAdd(Result, V, "sunkaddr", InsertPt); else Result = V; } // Add in the BaseGV if present. if (AddrMode.BaseGV) { Value *V = new PtrToIntInst(AddrMode.BaseGV, IntPtrTy, "sunkaddr", InsertPt); if (Result) Result = BinaryOperator::CreateAdd(Result, V, "sunkaddr", InsertPt); else Result = V; } // Add in the Base Offset if present. if (AddrMode.BaseOffs) { Value *V = ConstantInt::get(IntPtrTy, AddrMode.BaseOffs); if (Result) Result = BinaryOperator::CreateAdd(Result, V, "sunkaddr", InsertPt); else Result = V; } if (Result == 0) SunkAddr = Constant::getNullValue(Addr->getType()); else SunkAddr = new IntToPtrInst(Result, Addr->getType(), "sunkaddr",InsertPt); } MemoryInst->replaceUsesOfWith(Addr, SunkAddr); if (Addr->use_empty()) RecursivelyDeleteTriviallyDeadInstructions(Addr); return true; } /// OptimizeInlineAsmInst - If there are any memory operands, use /// OptimizeMemoryInst to sink their address computing into the block when /// possible / profitable. bool CodeGenPrepare::OptimizeInlineAsmInst(Instruction *I, CallSite CS, DenseMap &SunkAddrs) { bool MadeChange = false; InlineAsm *IA = cast(CS.getCalledValue()); // Do a prepass over the constraints, canonicalizing them, and building up the // ConstraintOperands list. std::vector ConstraintInfos = IA->ParseConstraints(); /// ConstraintOperands - Information about all of the constraints. std::vector ConstraintOperands; unsigned ArgNo = 0; // ArgNo - The argument of the CallInst. for (unsigned i = 0, e = ConstraintInfos.size(); i != e; ++i) { ConstraintOperands. push_back(TargetLowering::AsmOperandInfo(ConstraintInfos[i])); TargetLowering::AsmOperandInfo &OpInfo = ConstraintOperands.back(); // Compute the value type for each operand. switch (OpInfo.Type) { case InlineAsm::isOutput: if (OpInfo.isIndirect) OpInfo.CallOperandVal = CS.getArgument(ArgNo++); break; case InlineAsm::isInput: OpInfo.CallOperandVal = CS.getArgument(ArgNo++); break; case InlineAsm::isClobber: // Nothing to do. break; } // Compute the constraint code and ConstraintType to use. TLI->ComputeConstraintToUse(OpInfo, SDValue(), OpInfo.ConstraintType == TargetLowering::C_Memory); if (OpInfo.ConstraintType == TargetLowering::C_Memory && OpInfo.isIndirect) { Value *OpVal = OpInfo.CallOperandVal; MadeChange |= OptimizeMemoryInst(I, OpVal, OpVal->getType(), SunkAddrs); } } return MadeChange; } bool CodeGenPrepare::OptimizeExtUses(Instruction *I) { BasicBlock *DefBB = I->getParent(); // If both result of the {s|z}xt and its source are live out, rewrite all // other uses of the source with result of extension. Value *Src = I->getOperand(0); if (Src->hasOneUse()) return false; // Only do this xform if truncating is free. if (TLI && !TLI->isTruncateFree(I->getType(), Src->getType())) return false; // Only safe to perform the optimization if the source is also defined in // this block. if (!isa(Src) || DefBB != cast(Src)->getParent()) return false; bool DefIsLiveOut = false; for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E; ++UI) { Instruction *User = cast(*UI); // Figure out which BB this ext is used in. BasicBlock *UserBB = User->getParent(); if (UserBB == DefBB) continue; DefIsLiveOut = true; break; } if (!DefIsLiveOut) return false; // Make sure non of the uses are PHI nodes. for (Value::use_iterator UI = Src->use_begin(), E = Src->use_end(); UI != E; ++UI) { Instruction *User = cast(*UI); BasicBlock *UserBB = User->getParent(); if (UserBB == DefBB) continue; // Be conservative. We don't want this xform to end up introducing // reloads just before load / store instructions. if (isa(User) || isa(User) || isa(User)) return false; } // InsertedTruncs - Only insert one trunc in each block once. DenseMap InsertedTruncs; bool MadeChange = false; for (Value::use_iterator UI = Src->use_begin(), E = Src->use_end(); UI != E; ++UI) { Use &TheUse = UI.getUse(); Instruction *User = cast(*UI); // Figure out which BB this ext is used in. BasicBlock *UserBB = User->getParent(); if (UserBB == DefBB) continue; // Both src and def are live in this block. Rewrite the use. Instruction *&InsertedTrunc = InsertedTruncs[UserBB]; if (!InsertedTrunc) { BasicBlock::iterator InsertPt = UserBB->getFirstNonPHI(); InsertedTrunc = new TruncInst(I, Src->getType(), "", InsertPt); } // Replace a use of the {s|z}ext source with a use of the result. TheUse = InsertedTrunc; MadeChange = true; } return MadeChange; } // In this pass we look for GEP and cast instructions that are used // across basic blocks and rewrite them to improve basic-block-at-a-time // selection. bool CodeGenPrepare::OptimizeBlock(BasicBlock &BB) { bool MadeChange = false; // Split all critical edges where the dest block has a PHI. TerminatorInst *BBTI = BB.getTerminator(); if (BBTI->getNumSuccessors() > 1) { for (unsigned i = 0, e = BBTI->getNumSuccessors(); i != e; ++i) { BasicBlock *SuccBB = BBTI->getSuccessor(i); if (isa(SuccBB->begin()) && isCriticalEdge(BBTI, i, true)) SplitEdgeNicely(BBTI, i, BackEdges, this); } } // Keep track of non-local addresses that have been sunk into this block. // This allows us to avoid inserting duplicate code for blocks with multiple // load/stores of the same address. DenseMap SunkAddrs; for (BasicBlock::iterator BBI = BB.begin(), E = BB.end(); BBI != E; ) { Instruction *I = BBI++; if (CastInst *CI = dyn_cast(I)) { // If the source of the cast is a constant, then this should have // already been constant folded. The only reason NOT to constant fold // it is if something (e.g. LSR) was careful to place the constant // evaluation in a block other than then one that uses it (e.g. to hoist // the address of globals out of a loop). If this is the case, we don't // want to forward-subst the cast. if (isa(CI->getOperand(0))) continue; bool Change = false; if (TLI) { Change = OptimizeNoopCopyExpression(CI, *TLI); MadeChange |= Change; } if (!Change && (isa(I) || isa(I))) MadeChange |= OptimizeExtUses(I); } else if (CmpInst *CI = dyn_cast(I)) { MadeChange |= OptimizeCmpExpression(CI); } else if (LoadInst *LI = dyn_cast(I)) { if (TLI) MadeChange |= OptimizeMemoryInst(I, I->getOperand(0), LI->getType(), SunkAddrs); } else if (StoreInst *SI = dyn_cast(I)) { if (TLI) MadeChange |= OptimizeMemoryInst(I, SI->getOperand(1), SI->getOperand(0)->getType(), SunkAddrs); } else if (GetElementPtrInst *GEPI = dyn_cast(I)) { if (GEPI->hasAllZeroIndices()) { /// The GEP operand must be a pointer, so must its result -> BitCast Instruction *NC = new BitCastInst(GEPI->getOperand(0), GEPI->getType(), GEPI->getName(), GEPI); GEPI->replaceAllUsesWith(NC); GEPI->eraseFromParent(); MadeChange = true; BBI = NC; } } else if (CallInst *CI = dyn_cast(I)) { // If we found an inline asm expession, and if the target knows how to // lower it to normal LLVM code, do so now. if (TLI && isa(CI->getCalledValue())) if (const TargetAsmInfo *TAI = TLI->getTargetMachine().getTargetAsmInfo()) { if (TAI->ExpandInlineAsm(CI)) BBI = BB.begin(); else // Sink address computing for memory operands into the block. MadeChange |= OptimizeInlineAsmInst(I, &(*CI), SunkAddrs); } } } return MadeChange; }