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/Dominators.h"
20 #include "llvm/IR/GetElementPtrTypeIterator.h"
21 #include "llvm/IR/IRBuilder.h"
22 #include "llvm/IR/Operator.h"
37 class AssumptionCache;
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,
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);
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.
117 void MergeBasicBlockIntoOnlyPred(BasicBlock *BB, DominatorTree *DT = nullptr);
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);
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.
131 bool EliminateDuplicatePHINodes(BasicBlock *BB);
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.
139 bool SimplifyCFG(BasicBlock *BB, const TargetTransformInfo &TTI,
140 unsigned BonusInstThreshold, AssumptionCache *AC = nullptr);
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.
146 bool FlattenCFG(BasicBlock *BB, AliasAnalysis *AA = nullptr);
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
152 bool FoldBranchToCommonDest(BranchInst *BI, unsigned BonusInstThreshold = 1);
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.
160 AllocaInst *DemoteRegToStack(Instruction &X,
161 bool VolatileLoads = false,
162 Instruction *AllocaPoint = nullptr);
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);
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);
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);
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);
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;
203 // Build a mask for high order bits.
204 unsigned IntPtrWidth = IntPtrTy->getScalarType()->getIntegerBitWidth();
205 uint64_t PtrSizeMask = ~0ULL >> (64 - IntPtrWidth);
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;
211 uint64_t Size = DL.getTypeAllocSize(GTI.getIndexedType()) & PtrSizeMask;
212 if (Constant *OpC = dyn_cast<Constant>(Op)) {
213 if (OpC->isZeroValue())
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();
221 uint64_t OpValue = cast<ConstantInt>(OpC)->getZExtValue();
222 Size = DL.getStructLayout(STy)->getElementOffset(OpValue);
225 Result = Builder->CreateAdd(Result, ConstantInt::get(IntPtrTy, Size),
226 GEP->getName()+".offs");
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");
237 // Convert to correct type.
238 if (Op->getType() != IntPtrTy)
239 Op = Builder->CreateIntCast(Op, IntPtrTy, true, Op->getName()+".c");
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*/);
246 // Emit an add instruction.
247 Result = Builder->CreateAdd(Op, Result, GEP->getName()+".offs");
252 ///===---------------------------------------------------------------------===//
253 /// Dbg Intrinsic utilities
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);
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);
266 /// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set
267 /// of llvm.dbg.value intrinsics.
268 bool LowerDbgDeclare(Function &F);
270 /// FindAllocaDbgDeclare - Finds the llvm.dbg.declare intrinsic corresponding to
271 /// an alloca, if any.
272 DbgDeclareInst *FindAllocaDbgDeclare(Value *V);
274 /// \brief Replaces llvm.dbg.declare instruction when an alloca is replaced with
275 /// a new value. If Deref is true, tan additional DW_OP_deref is prepended to
277 bool replaceDbgDeclareForAlloca(AllocaInst *AI, Value *NewAllocaAddress,
278 DIBuilder &Builder, bool Deref);
280 /// \brief Remove all blocks that can not be reached from the function's entry.
282 /// Returns true if any basic block was removed.
283 bool removeUnreachableBlocks(Function &F);
285 /// \brief Combine the metadata of two instructions so that K can replace J
287 /// Metadata not listed as known via KnownIDs is removed
288 void combineMetadata(Instruction *K, const Instruction *J, ArrayRef<unsigned> KnownIDs);
290 /// \brief Replace each use of 'From' with 'To' if that use is dominated by
291 /// the given edge. Returns the number of replacements made.
292 unsigned replaceDominatedUsesWith(Value *From, Value *To, DominatorTree &DT,
293 const BasicBlockEdge &Edge);
294 } // End llvm namespace