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/Analysis/AliasAnalysis.h" 19 #include "llvm/IR/DataLayout.h" 20 #include "llvm/IR/Dominators.h" 21 #include "llvm/IR/GetElementPtrTypeIterator.h" 22 #include "llvm/IR/IRBuilder.h" 23 #include "llvm/IR/Operator.h" 24 25 namespace llvm { 26 27 class User; 28 class BasicBlock; 29 class Function; 30 class BranchInst; 31 class Instruction; 32 class DbgDeclareInst; 33 class StoreInst; 34 class LoadInst; 35 class Value; 36 class PHINode; 37 class AllocaInst; 38 class AssumptionCache; 39 class ConstantExpr; 40 class DataLayout; 41 class TargetLibraryInfo; 42 class TargetTransformInfo; 43 class DIBuilder; 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, 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); 111 112 /// MergeBasicBlockIntoOnlyPred - BB is a block with one predecessor and its 113 /// predecessor is known to have one successor (BB!). Eliminate the edge 114 /// between them, moving the instructions in the predecessor into BB. This 115 /// deletes the predecessor block. 116 /// 117 void MergeBasicBlockIntoOnlyPred(BasicBlock *BB, DominatorTree *DT = nullptr); 118 119 /// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an 120 /// unconditional branch, and contains no instructions other than PHI nodes, 121 /// potential debug intrinsics and the branch. If possible, eliminate BB by 122 /// rewriting all the predecessors to branch to the successor block and return 123 /// true. If we can't transform, return false. 124 bool TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB); 125 126 /// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI 127 /// nodes in this block. This doesn't try to be clever about PHI nodes 128 /// which differ only in the order of the incoming values, but instcombine 129 /// orders them so it usually won't matter. 130 /// 131 bool EliminateDuplicatePHINodes(BasicBlock *BB); 132 133 /// SimplifyCFG - This function is used to do simplification of a CFG. For 134 /// example, it adjusts branches to branches to eliminate the extra hop, it 135 /// eliminates unreachable basic blocks, and does other "peephole" optimization 136 /// of the CFG. It returns true if a modification was made, possibly deleting 137 /// the basic block that was pointed to. 138 /// 139 bool SimplifyCFG(BasicBlock *BB, const TargetTransformInfo &TTI, 140 unsigned BonusInstThreshold, AssumptionCache *AC = nullptr); 141 142 /// FlatternCFG - This function is used to flatten a CFG. For 143 /// example, it uses parallel-and and parallel-or mode to collapse 144 // if-conditions and merge if-regions with identical statements. 145 /// 146 bool FlattenCFG(BasicBlock *BB, AliasAnalysis *AA = nullptr); 147 148 /// FoldBranchToCommonDest - If this basic block is ONLY a setcc and a branch, 149 /// and if a predecessor branches to us and one of our successors, fold the 150 /// setcc into the predecessor and use logical operations to pick the right 151 /// destination. 152 bool FoldBranchToCommonDest(BranchInst *BI, unsigned BonusInstThreshold = 1); 153 154 /// DemoteRegToStack - This function takes a virtual register computed by an 155 /// Instruction and replaces it with a slot in the stack frame, allocated via 156 /// alloca. This allows the CFG to be changed around without fear of 157 /// invalidating the SSA information for the value. It returns the pointer to 158 /// the alloca inserted to create a stack slot for X. 159 /// 160 AllocaInst *DemoteRegToStack(Instruction &X, 161 bool VolatileLoads = false, 162 Instruction *AllocaPoint = nullptr); 163 164 /// DemotePHIToStack - This function takes a virtual register computed by a phi 165 /// node and replaces it with a slot in the stack frame, allocated via alloca. 166 /// The phi node is deleted and it returns the pointer to the alloca inserted. 167 AllocaInst *DemotePHIToStack(PHINode *P, Instruction *AllocaPoint = nullptr); 168 169 /// getOrEnforceKnownAlignment - If the specified pointer has an alignment that 170 /// we can determine, return it, otherwise return 0. If PrefAlign is specified, 171 /// and it is more than the alignment of the ultimate object, see if we can 172 /// increase the alignment of the ultimate object, making this check succeed. 173 unsigned getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign, 174 const DataLayout &DL, 175 const Instruction *CxtI = nullptr, 176 AssumptionCache *AC = nullptr, 177 const DominatorTree *DT = nullptr); 178 179 /// getKnownAlignment - Try to infer an alignment for the specified pointer. 180 static inline unsigned getKnownAlignment(Value *V, const DataLayout &DL, 181 const Instruction *CxtI = nullptr, 182 AssumptionCache *AC = nullptr, 183 const DominatorTree *DT = nullptr) { 184 return getOrEnforceKnownAlignment(V, 0, DL, CxtI, AC, DT); 185 } 186 187 /// EmitGEPOffset - Given a getelementptr instruction/constantexpr, emit the 188 /// code necessary to compute the offset from the base pointer (without adding 189 /// in the base pointer). Return the result as a signed integer of intptr size. 190 /// When NoAssumptions is true, no assumptions about index computation not 191 /// overflowing is made. 192 template <typename IRBuilderTy> 193 Value *EmitGEPOffset(IRBuilderTy *Builder, const DataLayout &DL, User *GEP, 194 bool NoAssumptions = false) { 195 GEPOperator *GEPOp = cast<GEPOperator>(GEP); 196 Type *IntPtrTy = DL.getIntPtrType(GEP->getType()); 197 Value *Result = Constant::getNullValue(IntPtrTy); 198 199 // If the GEP is inbounds, we know that none of the addressing operations will 200 // overflow in an unsigned sense. 201 bool isInBounds = GEPOp->isInBounds() && !NoAssumptions; 202 203 // Build a mask for high order bits. 204 unsigned IntPtrWidth = IntPtrTy->getScalarType()->getIntegerBitWidth(); 205 uint64_t PtrSizeMask = ~0ULL >> (64 - IntPtrWidth); 206 207 gep_type_iterator GTI = gep_type_begin(GEP); 208 for (User::op_iterator i = GEP->op_begin() + 1, e = GEP->op_end(); i != e; 209 ++i, ++GTI) { 210 Value *Op = *i; 211 uint64_t Size = DL.getTypeAllocSize(GTI.getIndexedType()) & PtrSizeMask; 212 if (Constant *OpC = dyn_cast<Constant>(Op)) { 213 if (OpC->isZeroValue()) 214 continue; 215 216 // Handle a struct index, which adds its field offset to the pointer. 217 if (StructType *STy = dyn_cast<StructType>(*GTI)) { 218 if (OpC->getType()->isVectorTy()) 219 OpC = OpC->getSplatValue(); 220 221 uint64_t OpValue = cast<ConstantInt>(OpC)->getZExtValue(); 222 Size = DL.getStructLayout(STy)->getElementOffset(OpValue); 223 224 if (Size) 225 Result = Builder->CreateAdd(Result, ConstantInt::get(IntPtrTy, Size), 226 GEP->getName()+".offs"); 227 continue; 228 } 229 230 Constant *Scale = ConstantInt::get(IntPtrTy, Size); 231 Constant *OC = ConstantExpr::getIntegerCast(OpC, IntPtrTy, true /*SExt*/); 232 Scale = ConstantExpr::getMul(OC, Scale, isInBounds/*NUW*/); 233 // Emit an add instruction. 234 Result = Builder->CreateAdd(Result, Scale, GEP->getName()+".offs"); 235 continue; 236 } 237 // Convert to correct type. 238 if (Op->getType() != IntPtrTy) 239 Op = Builder->CreateIntCast(Op, IntPtrTy, true, Op->getName()+".c"); 240 if (Size != 1) { 241 // We'll let instcombine(mul) convert this to a shl if possible. 242 Op = Builder->CreateMul(Op, ConstantInt::get(IntPtrTy, Size), 243 GEP->getName()+".idx", isInBounds /*NUW*/); 244 } 245 246 // Emit an add instruction. 247 Result = Builder->CreateAdd(Op, Result, GEP->getName()+".offs"); 248 } 249 return Result; 250 } 251 252 ///===---------------------------------------------------------------------===// 253 /// Dbg Intrinsic utilities 254 /// 255 256 /// Inserts a llvm.dbg.value intrinsic before a store to an alloca'd value 257 /// that has an associated llvm.dbg.decl intrinsic. 258 bool ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI, 259 StoreInst *SI, DIBuilder &Builder); 260 261 /// Inserts a llvm.dbg.value intrinsic before a load of an alloca'd value 262 /// that has an associated llvm.dbg.decl intrinsic. 263 bool ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI, 264 LoadInst *LI, DIBuilder &Builder); 265 266 /// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set 267 /// of llvm.dbg.value intrinsics. 268 bool LowerDbgDeclare(Function &F); 269 270 /// FindAllocaDbgDeclare - Finds the llvm.dbg.declare intrinsic corresponding to 271 /// an alloca, if any. 272 DbgDeclareInst *FindAllocaDbgDeclare(Value *V); 273 274 /// \brief Replaces llvm.dbg.declare instruction when the address it describes 275 /// is replaced with a new value. If Deref is true, an additional DW_OP_deref is 276 /// prepended to the expression. If Offset is non-zero, a constant displacement 277 /// is added to the expression (after the optional Deref). Offset can be 278 /// negative. 279 bool replaceDbgDeclare(Value *Address, Value *NewAddress, 280 Instruction *InsertBefore, DIBuilder &Builder, 281 bool Deref, int Offset); 282 283 /// \brief Replaces llvm.dbg.declare instruction when the alloca it describes 284 /// is replaced with a new value. If Deref is true, an additional DW_OP_deref is 285 /// prepended to the expression. If Offset is non-zero, a constant displacement 286 /// is added to the expression (after the optional Deref). Offset can be 287 /// negative. New llvm.dbg.declare is inserted immediately before AI. 288 bool replaceDbgDeclareForAlloca(AllocaInst *AI, Value *NewAllocaAddress, 289 DIBuilder &Builder, bool Deref, int Offset = 0); 290 291 /// \brief Insert an unreachable instruction before the specified 292 /// instruction, making it and the rest of the code in the block dead. 293 void changeToUnreachable(Instruction *I, bool UseLLVMTrap); 294 295 /// Replace 'BB's terminator with one that does not have an unwind successor 296 /// block. Rewrites `invoke` to `call`, etc. Updates any PHIs in unwind 297 /// successor. 298 /// 299 /// \param BB Block whose terminator will be replaced. Its terminator must 300 /// have an unwind successor. 301 void removeUnwindEdge(BasicBlock *BB); 302 303 /// \brief Remove all blocks that can not be reached from the function's entry. 304 /// 305 /// Returns true if any basic block was removed. 306 bool removeUnreachableBlocks(Function &F); 307 308 /// \brief Combine the metadata of two instructions so that K can replace J 309 /// 310 /// Metadata not listed as known via KnownIDs is removed 311 void combineMetadata(Instruction *K, const Instruction *J, ArrayRef<unsigned> KnownIDs); 312 313 /// \brief Replace each use of 'From' with 'To' if that use is dominated by 314 /// the given edge. Returns the number of replacements made. 315 unsigned replaceDominatedUsesWith(Value *From, Value *To, DominatorTree &DT, 316 const BasicBlockEdge &Edge); 317 /// \brief Replace each use of 'From' with 'To' if that use is dominated by 318 /// the given BasicBlock. Returns the number of replacements made. 319 unsigned replaceDominatedUsesWith(Value *From, Value *To, DominatorTree &DT, 320 const BasicBlock *BB); 321 322 323 /// \brief Return true if the CallSite CS calls a gc leaf function. 324 /// 325 /// A leaf function is a function that does not safepoint the thread during its 326 /// execution. During a call or invoke to such a function, the callers stack 327 /// does not have to be made parseable. 328 /// 329 /// Most passes can and should ignore this information, and it is only used 330 /// during lowering by the GC infrastructure. 331 bool callsGCLeafFunction(ImmutableCallSite CS); 332 333 } // End llvm namespace 334 335 #endif 336