1 //===-- Local.h - Functions to perform local transformations ----*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This family of functions perform various local transformations to the
13 //===----------------------------------------------------------------------===//
15 #ifndef LLVM_TRANSFORMS_UTILS_LOCAL_H
16 #define LLVM_TRANSFORMS_UTILS_LOCAL_H
18 #include "llvm/IR/DataLayout.h"
19 #include "llvm/IR/GetElementPtrTypeIterator.h"
20 #include "llvm/IR/IRBuilder.h"
21 #include "llvm/IR/Operator.h"
37 class AssumptionTracker;
40 class TargetLibraryInfo;
41 class TargetTransformInfo;
46 template<typename T> class SmallVectorImpl;
48 //===----------------------------------------------------------------------===//
49 // Local constant propagation.
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);
62 //===----------------------------------------------------------------------===//
63 // Local dead code elimination.
66 /// isInstructionTriviallyDead - Return true if the result produced by the
67 /// instruction is not used, and the instruction has no side effects.
69 bool isInstructionTriviallyDead(Instruction *I,
70 const TargetLibraryInfo *TLI = nullptr);
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);
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);
87 /// SimplifyInstructionsInBlock - Scan the specified basic block and try to
88 /// simplify any instructions in it and recursively delete dead instructions.
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);
95 //===----------------------------------------------------------------------===//
96 // Control Flow Graph Restructuring.
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.
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)
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);
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.
118 void MergeBasicBlockIntoOnlyPred(BasicBlock *BB, Pass *P = nullptr);
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);
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.
132 bool EliminateDuplicatePHINodes(BasicBlock *BB);
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.
140 bool SimplifyCFG(BasicBlock *BB, const TargetTransformInfo &TTI,
141 unsigned BonusInstThreshold,
142 const DataLayout *TD = nullptr,
143 AssumptionTracker *AT = nullptr);
145 /// FlatternCFG - This function is used to flatten a CFG. For
146 /// example, it uses parallel-and and parallel-or mode to collapse
147 // if-conditions and merge if-regions with identical statements.
149 bool FlattenCFG(BasicBlock *BB, AliasAnalysis *AA = nullptr);
151 /// FoldBranchToCommonDest - If this basic block is ONLY a setcc and a branch,
152 /// and if a predecessor branches to us and one of our successors, fold the
153 /// setcc into the predecessor and use logical operations to pick the right
155 bool FoldBranchToCommonDest(BranchInst *BI, const DataLayout *DL = nullptr,
156 unsigned BonusInstThreshold = 1);
158 /// DemoteRegToStack - This function takes a virtual register computed by an
159 /// Instruction and replaces it with a slot in the stack frame, allocated via
160 /// alloca. This allows the CFG to be changed around without fear of
161 /// invalidating the SSA information for the value. It returns the pointer to
162 /// the alloca inserted to create a stack slot for X.
164 AllocaInst *DemoteRegToStack(Instruction &X,
165 bool VolatileLoads = false,
166 Instruction *AllocaPoint = nullptr);
168 /// DemotePHIToStack - This function takes a virtual register computed by a phi
169 /// node and replaces it with a slot in the stack frame, allocated via alloca.
170 /// The phi node is deleted and it returns the pointer to the alloca inserted.
171 AllocaInst *DemotePHIToStack(PHINode *P, Instruction *AllocaPoint = nullptr);
173 /// getOrEnforceKnownAlignment - If the specified pointer has an alignment that
174 /// we can determine, return it, otherwise return 0. If PrefAlign is specified,
175 /// and it is more than the alignment of the ultimate object, see if we can
176 /// increase the alignment of the ultimate object, making this check succeed.
177 unsigned getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign,
178 const DataLayout *TD = nullptr,
179 AssumptionTracker *AT = nullptr,
180 const Instruction *CxtI = nullptr,
181 const DominatorTree *DT = nullptr);
183 /// getKnownAlignment - Try to infer an alignment for the specified pointer.
184 static inline unsigned getKnownAlignment(Value *V,
185 const DataLayout *TD = nullptr,
186 AssumptionTracker *AT = nullptr,
187 const Instruction *CxtI = nullptr,
188 const DominatorTree *DT = nullptr) {
189 return getOrEnforceKnownAlignment(V, 0, TD, AT, CxtI, DT);
192 /// EmitGEPOffset - Given a getelementptr instruction/constantexpr, emit the
193 /// code necessary to compute the offset from the base pointer (without adding
194 /// in the base pointer). Return the result as a signed integer of intptr size.
195 /// When NoAssumptions is true, no assumptions about index computation not
196 /// overflowing is made.
197 template<typename IRBuilderTy>
198 Value *EmitGEPOffset(IRBuilderTy *Builder, const DataLayout &TD, User *GEP,
199 bool NoAssumptions = false) {
200 GEPOperator *GEPOp = cast<GEPOperator>(GEP);
201 Type *IntPtrTy = TD.getIntPtrType(GEP->getType());
202 Value *Result = Constant::getNullValue(IntPtrTy);
204 // If the GEP is inbounds, we know that none of the addressing operations will
205 // overflow in an unsigned sense.
206 bool isInBounds = GEPOp->isInBounds() && !NoAssumptions;
208 // Build a mask for high order bits.
209 unsigned IntPtrWidth = IntPtrTy->getScalarType()->getIntegerBitWidth();
210 uint64_t PtrSizeMask = ~0ULL >> (64 - IntPtrWidth);
212 gep_type_iterator GTI = gep_type_begin(GEP);
213 for (User::op_iterator i = GEP->op_begin() + 1, e = GEP->op_end(); i != e;
216 uint64_t Size = TD.getTypeAllocSize(GTI.getIndexedType()) & PtrSizeMask;
217 if (Constant *OpC = dyn_cast<Constant>(Op)) {
218 if (OpC->isZeroValue())
221 // Handle a struct index, which adds its field offset to the pointer.
222 if (StructType *STy = dyn_cast<StructType>(*GTI)) {
223 if (OpC->getType()->isVectorTy())
224 OpC = OpC->getSplatValue();
226 uint64_t OpValue = cast<ConstantInt>(OpC)->getZExtValue();
227 Size = TD.getStructLayout(STy)->getElementOffset(OpValue);
230 Result = Builder->CreateAdd(Result, ConstantInt::get(IntPtrTy, Size),
231 GEP->getName()+".offs");
235 Constant *Scale = ConstantInt::get(IntPtrTy, Size);
236 Constant *OC = ConstantExpr::getIntegerCast(OpC, IntPtrTy, true /*SExt*/);
237 Scale = ConstantExpr::getMul(OC, Scale, isInBounds/*NUW*/);
238 // Emit an add instruction.
239 Result = Builder->CreateAdd(Result, Scale, GEP->getName()+".offs");
242 // Convert to correct type.
243 if (Op->getType() != IntPtrTy)
244 Op = Builder->CreateIntCast(Op, IntPtrTy, true, Op->getName()+".c");
246 // We'll let instcombine(mul) convert this to a shl if possible.
247 Op = Builder->CreateMul(Op, ConstantInt::get(IntPtrTy, Size),
248 GEP->getName()+".idx", isInBounds /*NUW*/);
251 // Emit an add instruction.
252 Result = Builder->CreateAdd(Op, Result, GEP->getName()+".offs");
257 ///===---------------------------------------------------------------------===//
258 /// Dbg Intrinsic utilities
261 /// Inserts a llvm.dbg.value intrinsic before a store to an alloca'd value
262 /// that has an associated llvm.dbg.decl intrinsic.
263 bool ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
264 StoreInst *SI, DIBuilder &Builder);
266 /// Inserts a llvm.dbg.value intrinsic before a load of an alloca'd value
267 /// that has an associated llvm.dbg.decl intrinsic.
268 bool ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
269 LoadInst *LI, DIBuilder &Builder);
271 /// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set
272 /// of llvm.dbg.value intrinsics.
273 bool LowerDbgDeclare(Function &F);
275 /// FindAllocaDbgDeclare - Finds the llvm.dbg.declare intrinsic corresponding to
276 /// an alloca, if any.
277 DbgDeclareInst *FindAllocaDbgDeclare(Value *V);
279 /// replaceDbgDeclareForAlloca - Replaces llvm.dbg.declare instruction when
280 /// alloca is replaced with a new value.
281 bool replaceDbgDeclareForAlloca(AllocaInst *AI, Value *NewAllocaAddress,
284 /// \brief Remove all blocks that can not be reached from the function's entry.
286 /// Returns true if any basic block was removed.
287 bool removeUnreachableBlocks(Function &F);
289 /// \brief Combine the metadata of two instructions so that K can replace J
291 /// Metadata not listed as known via KnownIDs is removed
292 void combineMetadata(Instruction *K, const Instruction *J, ArrayRef<unsigned> KnownIDs);
294 } // End llvm namespace