1 //===-- Local.h - Functions to perform local transformations ----*- C++ -*-===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // This family of functions perform various local transformations to the 11 // program. 12 // 13 //===----------------------------------------------------------------------===// 14 15 #ifndef LLVM_TRANSFORMS_UTILS_LOCAL_H 16 #define LLVM_TRANSFORMS_UTILS_LOCAL_H 17 18 #include "llvm/IR/DataLayout.h" 19 #include "llvm/IR/GetElementPtrTypeIterator.h" 20 #include "llvm/IR/IRBuilder.h" 21 #include "llvm/IR/Operator.h" 22 23 namespace llvm { 24 25 class User; 26 class BasicBlock; 27 class Function; 28 class BranchInst; 29 class Instruction; 30 class DbgDeclareInst; 31 class StoreInst; 32 class LoadInst; 33 class Value; 34 class Pass; 35 class PHINode; 36 class AllocaInst; 37 class AssumptionCache; 38 class ConstantExpr; 39 class DataLayout; 40 class TargetLibraryInfo; 41 class TargetTransformInfo; 42 class DIBuilder; 43 class AliasAnalysis; 44 class DominatorTree; 45 46 template<typename T> class SmallVectorImpl; 47 48 //===----------------------------------------------------------------------===// 49 // Local constant propagation. 50 // 51 52 /// ConstantFoldTerminator - If a terminator instruction is predicated on a 53 /// constant value, convert it into an unconditional branch to the constant 54 /// destination. This is a nontrivial operation because the successors of this 55 /// basic block must have their PHI nodes updated. 56 /// Also calls RecursivelyDeleteTriviallyDeadInstructions() on any branch/switch 57 /// conditions and indirectbr addresses this might make dead if 58 /// DeleteDeadConditions is true. 59 bool ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions = false, 60 const TargetLibraryInfo *TLI = nullptr); 61 62 //===----------------------------------------------------------------------===// 63 // Local dead code elimination. 64 // 65 66 /// isInstructionTriviallyDead - Return true if the result produced by the 67 /// instruction is not used, and the instruction has no side effects. 68 /// 69 bool isInstructionTriviallyDead(Instruction *I, 70 const TargetLibraryInfo *TLI = nullptr); 71 72 /// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a 73 /// trivially dead instruction, delete it. If that makes any of its operands 74 /// trivially dead, delete them too, recursively. Return true if any 75 /// instructions were deleted. 76 bool RecursivelyDeleteTriviallyDeadInstructions(Value *V, 77 const TargetLibraryInfo *TLI = nullptr); 78 79 /// RecursivelyDeleteDeadPHINode - If the specified value is an effectively 80 /// dead PHI node, due to being a def-use chain of single-use nodes that 81 /// either forms a cycle or is terminated by a trivially dead instruction, 82 /// delete it. If that makes any of its operands trivially dead, delete them 83 /// too, recursively. Return true if a change was made. 84 bool RecursivelyDeleteDeadPHINode(PHINode *PN, 85 const TargetLibraryInfo *TLI = nullptr); 86 87 /// SimplifyInstructionsInBlock - Scan the specified basic block and try to 88 /// simplify any instructions in it and recursively delete dead instructions. 89 /// 90 /// This returns true if it changed the code, note that it can delete 91 /// instructions in other blocks as well in this block. 92 bool SimplifyInstructionsInBlock(BasicBlock *BB, const DataLayout *TD = nullptr, 93 const TargetLibraryInfo *TLI = nullptr); 94 95 //===----------------------------------------------------------------------===// 96 // Control Flow Graph Restructuring. 97 // 98 99 /// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this 100 /// method is called when we're about to delete Pred as a predecessor of BB. If 101 /// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred. 102 /// 103 /// Unlike the removePredecessor method, this attempts to simplify uses of PHI 104 /// nodes that collapse into identity values. For example, if we have: 105 /// x = phi(1, 0, 0, 0) 106 /// y = and x, z 107 /// 108 /// .. and delete the predecessor corresponding to the '1', this will attempt to 109 /// recursively fold the 'and' to 0. 110 void RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred, 111 DataLayout *TD = nullptr); 112 113 /// MergeBasicBlockIntoOnlyPred - BB is a block with one predecessor and its 114 /// predecessor is known to have one successor (BB!). Eliminate the edge 115 /// between them, moving the instructions in the predecessor into BB. This 116 /// deletes the predecessor block. 117 /// 118 void MergeBasicBlockIntoOnlyPred(BasicBlock *BB, Pass *P = nullptr); 119 120 /// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an 121 /// unconditional branch, and contains no instructions other than PHI nodes, 122 /// potential debug intrinsics and the branch. If possible, eliminate BB by 123 /// rewriting all the predecessors to branch to the successor block and return 124 /// true. If we can't transform, return false. 125 bool TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB); 126 127 /// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI 128 /// nodes in this block. This doesn't try to be clever about PHI nodes 129 /// which differ only in the order of the incoming values, but instcombine 130 /// orders them so it usually won't matter. 131 /// 132 bool EliminateDuplicatePHINodes(BasicBlock *BB); 133 134 /// SimplifyCFG - This function is used to do simplification of a CFG. For 135 /// example, it adjusts branches to branches to eliminate the extra hop, it 136 /// eliminates unreachable basic blocks, and does other "peephole" optimization 137 /// of the CFG. It returns true if a modification was made, possibly deleting 138 /// the basic block that was pointed to. 139 /// 140 bool SimplifyCFG(BasicBlock *BB, const TargetTransformInfo &TTI, 141 unsigned BonusInstThreshold, const DataLayout *TD = nullptr, 142 AssumptionCache *AC = nullptr); 143 144 /// FlatternCFG - This function is used to flatten a CFG. For 145 /// example, it uses parallel-and and parallel-or mode to collapse 146 // if-conditions and merge if-regions with identical statements. 147 /// 148 bool FlattenCFG(BasicBlock *BB, AliasAnalysis *AA = nullptr); 149 150 /// FoldBranchToCommonDest - If this basic block is ONLY a setcc and a branch, 151 /// and if a predecessor branches to us and one of our successors, fold the 152 /// setcc into the predecessor and use logical operations to pick the right 153 /// destination. 154 bool FoldBranchToCommonDest(BranchInst *BI, const DataLayout *DL = nullptr, 155 unsigned BonusInstThreshold = 1); 156 157 /// DemoteRegToStack - This function takes a virtual register computed by an 158 /// Instruction and replaces it with a slot in the stack frame, allocated via 159 /// alloca. This allows the CFG to be changed around without fear of 160 /// invalidating the SSA information for the value. It returns the pointer to 161 /// the alloca inserted to create a stack slot for X. 162 /// 163 AllocaInst *DemoteRegToStack(Instruction &X, 164 bool VolatileLoads = false, 165 Instruction *AllocaPoint = nullptr); 166 167 /// DemotePHIToStack - This function takes a virtual register computed by a phi 168 /// node and replaces it with a slot in the stack frame, allocated via alloca. 169 /// The phi node is deleted and it returns the pointer to the alloca inserted. 170 AllocaInst *DemotePHIToStack(PHINode *P, Instruction *AllocaPoint = nullptr); 171 172 /// getOrEnforceKnownAlignment - If the specified pointer has an alignment that 173 /// we can determine, return it, otherwise return 0. If PrefAlign is specified, 174 /// and it is more than the alignment of the ultimate object, see if we can 175 /// increase the alignment of the ultimate object, making this check succeed. 176 unsigned getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign, 177 const DataLayout *TD = nullptr, 178 AssumptionCache *AC = nullptr, 179 const Instruction *CxtI = nullptr, 180 const DominatorTree *DT = nullptr); 181 182 /// getKnownAlignment - Try to infer an alignment for the specified pointer. 183 static inline unsigned getKnownAlignment(Value *V, 184 const DataLayout *TD = nullptr, 185 AssumptionCache *AC = nullptr, 186 const Instruction *CxtI = nullptr, 187 const DominatorTree *DT = nullptr) { 188 return getOrEnforceKnownAlignment(V, 0, TD, AC, CxtI, DT); 189 } 190 191 /// EmitGEPOffset - Given a getelementptr instruction/constantexpr, emit the 192 /// code necessary to compute the offset from the base pointer (without adding 193 /// in the base pointer). Return the result as a signed integer of intptr size. 194 /// When NoAssumptions is true, no assumptions about index computation not 195 /// overflowing is made. 196 template<typename IRBuilderTy> 197 Value *EmitGEPOffset(IRBuilderTy *Builder, const DataLayout &TD, User *GEP, 198 bool NoAssumptions = false) { 199 GEPOperator *GEPOp = cast<GEPOperator>(GEP); 200 Type *IntPtrTy = TD.getIntPtrType(GEP->getType()); 201 Value *Result = Constant::getNullValue(IntPtrTy); 202 203 // If the GEP is inbounds, we know that none of the addressing operations will 204 // overflow in an unsigned sense. 205 bool isInBounds = GEPOp->isInBounds() && !NoAssumptions; 206 207 // Build a mask for high order bits. 208 unsigned IntPtrWidth = IntPtrTy->getScalarType()->getIntegerBitWidth(); 209 uint64_t PtrSizeMask = ~0ULL >> (64 - IntPtrWidth); 210 211 gep_type_iterator GTI = gep_type_begin(GEP); 212 for (User::op_iterator i = GEP->op_begin() + 1, e = GEP->op_end(); i != e; 213 ++i, ++GTI) { 214 Value *Op = *i; 215 uint64_t Size = TD.getTypeAllocSize(GTI.getIndexedType()) & PtrSizeMask; 216 if (Constant *OpC = dyn_cast<Constant>(Op)) { 217 if (OpC->isZeroValue()) 218 continue; 219 220 // Handle a struct index, which adds its field offset to the pointer. 221 if (StructType *STy = dyn_cast<StructType>(*GTI)) { 222 if (OpC->getType()->isVectorTy()) 223 OpC = OpC->getSplatValue(); 224 225 uint64_t OpValue = cast<ConstantInt>(OpC)->getZExtValue(); 226 Size = TD.getStructLayout(STy)->getElementOffset(OpValue); 227 228 if (Size) 229 Result = Builder->CreateAdd(Result, ConstantInt::get(IntPtrTy, Size), 230 GEP->getName()+".offs"); 231 continue; 232 } 233 234 Constant *Scale = ConstantInt::get(IntPtrTy, Size); 235 Constant *OC = ConstantExpr::getIntegerCast(OpC, IntPtrTy, true /*SExt*/); 236 Scale = ConstantExpr::getMul(OC, Scale, isInBounds/*NUW*/); 237 // Emit an add instruction. 238 Result = Builder->CreateAdd(Result, Scale, GEP->getName()+".offs"); 239 continue; 240 } 241 // Convert to correct type. 242 if (Op->getType() != IntPtrTy) 243 Op = Builder->CreateIntCast(Op, IntPtrTy, true, Op->getName()+".c"); 244 if (Size != 1) { 245 // We'll let instcombine(mul) convert this to a shl if possible. 246 Op = Builder->CreateMul(Op, ConstantInt::get(IntPtrTy, Size), 247 GEP->getName()+".idx", isInBounds /*NUW*/); 248 } 249 250 // Emit an add instruction. 251 Result = Builder->CreateAdd(Op, Result, GEP->getName()+".offs"); 252 } 253 return Result; 254 } 255 256 ///===---------------------------------------------------------------------===// 257 /// Dbg Intrinsic utilities 258 /// 259 260 /// Inserts a llvm.dbg.value intrinsic before a store to an alloca'd value 261 /// that has an associated llvm.dbg.decl intrinsic. 262 bool ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI, 263 StoreInst *SI, DIBuilder &Builder); 264 265 /// Inserts a llvm.dbg.value intrinsic before a load of an alloca'd value 266 /// that has an associated llvm.dbg.decl intrinsic. 267 bool ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI, 268 LoadInst *LI, DIBuilder &Builder); 269 270 /// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set 271 /// of llvm.dbg.value intrinsics. 272 bool LowerDbgDeclare(Function &F); 273 274 /// FindAllocaDbgDeclare - Finds the llvm.dbg.declare intrinsic corresponding to 275 /// an alloca, if any. 276 DbgDeclareInst *FindAllocaDbgDeclare(Value *V); 277 278 /// replaceDbgDeclareForAlloca - Replaces llvm.dbg.declare instruction when 279 /// alloca is replaced with a new value. 280 bool replaceDbgDeclareForAlloca(AllocaInst *AI, Value *NewAllocaAddress, 281 DIBuilder &Builder); 282 283 /// \brief Remove all blocks that can not be reached from the function's entry. 284 /// 285 /// Returns true if any basic block was removed. 286 bool removeUnreachableBlocks(Function &F); 287 288 /// \brief Combine the metadata of two instructions so that K can replace J 289 /// 290 /// Metadata not listed as known via KnownIDs is removed 291 void combineMetadata(Instruction *K, const Instruction *J, ArrayRef<unsigned> KnownIDs); 292 293 } // End llvm namespace 294 295 #endif 296