LLVM API Documentation

Local.h
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00001 //===-- Local.h - Functions to perform local transformations ----*- C++ -*-===//
00002 //
00003 //                     The LLVM Compiler Infrastructure
00004 //
00005 // This file is distributed under the University of Illinois Open Source
00006 // License. See LICENSE.TXT for details.
00007 //
00008 //===----------------------------------------------------------------------===//
00009 //
00010 // This family of functions perform various local transformations to the
00011 // program.
00012 //
00013 //===----------------------------------------------------------------------===//
00014 
00015 #ifndef LLVM_TRANSFORMS_UTILS_LOCAL_H
00016 #define LLVM_TRANSFORMS_UTILS_LOCAL_H
00017 
00018 #include "llvm/IR/DataLayout.h"
00019 #include "llvm/IR/GetElementPtrTypeIterator.h"
00020 #include "llvm/IR/IRBuilder.h"
00021 #include "llvm/IR/Operator.h"
00022 
00023 namespace llvm {
00024 
00025 class User;
00026 class BasicBlock;
00027 class Function;
00028 class BranchInst;
00029 class Instruction;
00030 class DbgDeclareInst;
00031 class StoreInst;
00032 class LoadInst;
00033 class Value;
00034 class PHINode;
00035 class AllocaInst;
00036 class AssumptionCache;
00037 class ConstantExpr;
00038 class DataLayout;
00039 class TargetLibraryInfo;
00040 class TargetTransformInfo;
00041 class DIBuilder;
00042 class AliasAnalysis;
00043 class DominatorTree;
00044 
00045 template<typename T> class SmallVectorImpl;
00046 
00047 //===----------------------------------------------------------------------===//
00048 //  Local constant propagation.
00049 //
00050 
00051 /// ConstantFoldTerminator - If a terminator instruction is predicated on a
00052 /// constant value, convert it into an unconditional branch to the constant
00053 /// destination.  This is a nontrivial operation because the successors of this
00054 /// basic block must have their PHI nodes updated.
00055 /// Also calls RecursivelyDeleteTriviallyDeadInstructions() on any branch/switch
00056 /// conditions and indirectbr addresses this might make dead if
00057 /// DeleteDeadConditions is true.
00058 bool ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions = false,
00059                             const TargetLibraryInfo *TLI = nullptr);
00060 
00061 //===----------------------------------------------------------------------===//
00062 //  Local dead code elimination.
00063 //
00064 
00065 /// isInstructionTriviallyDead - Return true if the result produced by the
00066 /// instruction is not used, and the instruction has no side effects.
00067 ///
00068 bool isInstructionTriviallyDead(Instruction *I,
00069                                 const TargetLibraryInfo *TLI = nullptr);
00070 
00071 /// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a
00072 /// trivially dead instruction, delete it.  If that makes any of its operands
00073 /// trivially dead, delete them too, recursively.  Return true if any
00074 /// instructions were deleted.
00075 bool RecursivelyDeleteTriviallyDeadInstructions(Value *V,
00076                                         const TargetLibraryInfo *TLI = nullptr);
00077 
00078 /// RecursivelyDeleteDeadPHINode - If the specified value is an effectively
00079 /// dead PHI node, due to being a def-use chain of single-use nodes that
00080 /// either forms a cycle or is terminated by a trivially dead instruction,
00081 /// delete it.  If that makes any of its operands trivially dead, delete them
00082 /// too, recursively.  Return true if a change was made.
00083 bool RecursivelyDeleteDeadPHINode(PHINode *PN,
00084                                   const TargetLibraryInfo *TLI = nullptr);
00085 
00086 /// SimplifyInstructionsInBlock - Scan the specified basic block and try to
00087 /// simplify any instructions in it and recursively delete dead instructions.
00088 ///
00089 /// This returns true if it changed the code, note that it can delete
00090 /// instructions in other blocks as well in this block.
00091 bool SimplifyInstructionsInBlock(BasicBlock *BB, const DataLayout *TD = nullptr,
00092                                  const TargetLibraryInfo *TLI = nullptr);
00093 
00094 //===----------------------------------------------------------------------===//
00095 //  Control Flow Graph Restructuring.
00096 //
00097 
00098 /// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this
00099 /// method is called when we're about to delete Pred as a predecessor of BB.  If
00100 /// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred.
00101 ///
00102 /// Unlike the removePredecessor method, this attempts to simplify uses of PHI
00103 /// nodes that collapse into identity values.  For example, if we have:
00104 ///   x = phi(1, 0, 0, 0)
00105 ///   y = and x, z
00106 ///
00107 /// .. and delete the predecessor corresponding to the '1', this will attempt to
00108 /// recursively fold the 'and' to 0.
00109 void RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred,
00110                                   DataLayout *TD = nullptr);
00111 
00112 /// MergeBasicBlockIntoOnlyPred - BB is a block with one predecessor and its
00113 /// predecessor is known to have one successor (BB!).  Eliminate the edge
00114 /// between them, moving the instructions in the predecessor into BB.  This
00115 /// deletes the predecessor block.
00116 ///
00117 void MergeBasicBlockIntoOnlyPred(BasicBlock *BB, DominatorTree *DT = nullptr);
00118 
00119 /// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an
00120 /// unconditional branch, and contains no instructions other than PHI nodes,
00121 /// potential debug intrinsics and the branch.  If possible, eliminate BB by
00122 /// rewriting all the predecessors to branch to the successor block and return
00123 /// true.  If we can't transform, return false.
00124 bool TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB);
00125 
00126 /// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI
00127 /// nodes in this block. This doesn't try to be clever about PHI nodes
00128 /// which differ only in the order of the incoming values, but instcombine
00129 /// orders them so it usually won't matter.
00130 ///
00131 bool EliminateDuplicatePHINodes(BasicBlock *BB);
00132 
00133 /// SimplifyCFG - This function is used to do simplification of a CFG.  For
00134 /// example, it adjusts branches to branches to eliminate the extra hop, it
00135 /// eliminates unreachable basic blocks, and does other "peephole" optimization
00136 /// of the CFG.  It returns true if a modification was made, possibly deleting
00137 /// the basic block that was pointed to.
00138 ///
00139 bool SimplifyCFG(BasicBlock *BB, const TargetTransformInfo &TTI,
00140                  unsigned BonusInstThreshold, const DataLayout *TD = nullptr,
00141                  AssumptionCache *AC = nullptr);
00142 
00143 /// FlatternCFG - This function is used to flatten a CFG.  For
00144 /// example, it uses parallel-and and parallel-or mode to collapse
00145 //  if-conditions and merge if-regions with identical statements.
00146 ///
00147 bool FlattenCFG(BasicBlock *BB, AliasAnalysis *AA = nullptr);
00148 
00149 /// FoldBranchToCommonDest - If this basic block is ONLY a setcc and a branch,
00150 /// and if a predecessor branches to us and one of our successors, fold the
00151 /// setcc into the predecessor and use logical operations to pick the right
00152 /// destination.
00153 bool FoldBranchToCommonDest(BranchInst *BI, const DataLayout *DL = nullptr,
00154                             unsigned BonusInstThreshold = 1);
00155 
00156 /// DemoteRegToStack - This function takes a virtual register computed by an
00157 /// Instruction and replaces it with a slot in the stack frame, allocated via
00158 /// alloca.  This allows the CFG to be changed around without fear of
00159 /// invalidating the SSA information for the value.  It returns the pointer to
00160 /// the alloca inserted to create a stack slot for X.
00161 ///
00162 AllocaInst *DemoteRegToStack(Instruction &X,
00163                              bool VolatileLoads = false,
00164                              Instruction *AllocaPoint = nullptr);
00165 
00166 /// DemotePHIToStack - This function takes a virtual register computed by a phi
00167 /// node and replaces it with a slot in the stack frame, allocated via alloca.
00168 /// The phi node is deleted and it returns the pointer to the alloca inserted.
00169 AllocaInst *DemotePHIToStack(PHINode *P, Instruction *AllocaPoint = nullptr);
00170 
00171 /// getOrEnforceKnownAlignment - If the specified pointer has an alignment that
00172 /// we can determine, return it, otherwise return 0.  If PrefAlign is specified,
00173 /// and it is more than the alignment of the ultimate object, see if we can
00174 /// increase the alignment of the ultimate object, making this check succeed.
00175 unsigned getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign,
00176                                     const DataLayout *TD = nullptr,
00177                                     AssumptionCache *AC = nullptr,
00178                                     const Instruction *CxtI = nullptr,
00179                                     const DominatorTree *DT = nullptr);
00180 
00181 /// getKnownAlignment - Try to infer an alignment for the specified pointer.
00182 static inline unsigned getKnownAlignment(Value *V,
00183                                          const DataLayout *TD = nullptr,
00184                                          AssumptionCache *AC = nullptr,
00185                                          const Instruction *CxtI = nullptr,
00186                                          const DominatorTree *DT = nullptr) {
00187   return getOrEnforceKnownAlignment(V, 0, TD, AC, CxtI, DT);
00188 }
00189 
00190 /// EmitGEPOffset - Given a getelementptr instruction/constantexpr, emit the
00191 /// code necessary to compute the offset from the base pointer (without adding
00192 /// in the base pointer).  Return the result as a signed integer of intptr size.
00193 /// When NoAssumptions is true, no assumptions about index computation not
00194 /// overflowing is made.
00195 template<typename IRBuilderTy>
00196 Value *EmitGEPOffset(IRBuilderTy *Builder, const DataLayout &TD, User *GEP,
00197                      bool NoAssumptions = false) {
00198   GEPOperator *GEPOp = cast<GEPOperator>(GEP);
00199   Type *IntPtrTy = TD.getIntPtrType(GEP->getType());
00200   Value *Result = Constant::getNullValue(IntPtrTy);
00201 
00202   // If the GEP is inbounds, we know that none of the addressing operations will
00203   // overflow in an unsigned sense.
00204   bool isInBounds = GEPOp->isInBounds() && !NoAssumptions;
00205 
00206   // Build a mask for high order bits.
00207   unsigned IntPtrWidth = IntPtrTy->getScalarType()->getIntegerBitWidth();
00208   uint64_t PtrSizeMask = ~0ULL >> (64 - IntPtrWidth);
00209 
00210   gep_type_iterator GTI = gep_type_begin(GEP);
00211   for (User::op_iterator i = GEP->op_begin() + 1, e = GEP->op_end(); i != e;
00212        ++i, ++GTI) {
00213     Value *Op = *i;
00214     uint64_t Size = TD.getTypeAllocSize(GTI.getIndexedType()) & PtrSizeMask;
00215     if (Constant *OpC = dyn_cast<Constant>(Op)) {
00216       if (OpC->isZeroValue())
00217         continue;
00218 
00219       // Handle a struct index, which adds its field offset to the pointer.
00220       if (StructType *STy = dyn_cast<StructType>(*GTI)) {
00221         if (OpC->getType()->isVectorTy())
00222           OpC = OpC->getSplatValue();
00223 
00224         uint64_t OpValue = cast<ConstantInt>(OpC)->getZExtValue();
00225         Size = TD.getStructLayout(STy)->getElementOffset(OpValue);
00226 
00227         if (Size)
00228           Result = Builder->CreateAdd(Result, ConstantInt::get(IntPtrTy, Size),
00229                                       GEP->getName()+".offs");
00230         continue;
00231       }
00232 
00233       Constant *Scale = ConstantInt::get(IntPtrTy, Size);
00234       Constant *OC = ConstantExpr::getIntegerCast(OpC, IntPtrTy, true /*SExt*/);
00235       Scale = ConstantExpr::getMul(OC, Scale, isInBounds/*NUW*/);
00236       // Emit an add instruction.
00237       Result = Builder->CreateAdd(Result, Scale, GEP->getName()+".offs");
00238       continue;
00239     }
00240     // Convert to correct type.
00241     if (Op->getType() != IntPtrTy)
00242       Op = Builder->CreateIntCast(Op, IntPtrTy, true, Op->getName()+".c");
00243     if (Size != 1) {
00244       // We'll let instcombine(mul) convert this to a shl if possible.
00245       Op = Builder->CreateMul(Op, ConstantInt::get(IntPtrTy, Size),
00246                               GEP->getName()+".idx", isInBounds /*NUW*/);
00247     }
00248 
00249     // Emit an add instruction.
00250     Result = Builder->CreateAdd(Op, Result, GEP->getName()+".offs");
00251   }
00252   return Result;
00253 }
00254 
00255 ///===---------------------------------------------------------------------===//
00256 ///  Dbg Intrinsic utilities
00257 ///
00258 
00259 /// Inserts a llvm.dbg.value intrinsic before a store to an alloca'd value
00260 /// that has an associated llvm.dbg.decl intrinsic.
00261 bool ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
00262                                      StoreInst *SI, DIBuilder &Builder);
00263 
00264 /// Inserts a llvm.dbg.value intrinsic before a load of an alloca'd value
00265 /// that has an associated llvm.dbg.decl intrinsic.
00266 bool ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
00267                                      LoadInst *LI, DIBuilder &Builder);
00268 
00269 /// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set
00270 /// of llvm.dbg.value intrinsics.
00271 bool LowerDbgDeclare(Function &F);
00272 
00273 /// FindAllocaDbgDeclare - Finds the llvm.dbg.declare intrinsic corresponding to
00274 /// an alloca, if any.
00275 DbgDeclareInst *FindAllocaDbgDeclare(Value *V);
00276 
00277 /// replaceDbgDeclareForAlloca - Replaces llvm.dbg.declare instruction when
00278 /// alloca is replaced with a new value.
00279 bool replaceDbgDeclareForAlloca(AllocaInst *AI, Value *NewAllocaAddress,
00280                                 DIBuilder &Builder);
00281 
00282 /// \brief Remove all blocks that can not be reached from the function's entry.
00283 ///
00284 /// Returns true if any basic block was removed.
00285 bool removeUnreachableBlocks(Function &F);
00286 
00287 /// \brief Combine the metadata of two instructions so that K can replace J
00288 ///
00289 /// Metadata not listed as known via KnownIDs is removed
00290 void combineMetadata(Instruction *K, const Instruction *J, ArrayRef<unsigned> KnownIDs);
00291 
00292 } // End llvm namespace
00293 
00294 #endif