LLVM API Documentation
00001 //===- ValueNumbering.cpp - Value #'ing Implementation ----------*- C++ -*-===// 00002 // 00003 // The LLVM Compiler Infrastructure 00004 // 00005 // This file was developed by the LLVM research group and is distributed under 00006 // the University of Illinois Open Source License. See LICENSE.TXT for details. 00007 // 00008 //===----------------------------------------------------------------------===// 00009 // 00010 // This file implements the non-abstract Value Numbering methods as well as a 00011 // default implementation for the analysis group. 00012 // 00013 //===----------------------------------------------------------------------===// 00014 00015 #include "llvm/Analysis/Passes.h" 00016 #include "llvm/Analysis/ValueNumbering.h" 00017 #include "llvm/Support/InstVisitor.h" 00018 #include "llvm/BasicBlock.h" 00019 #include "llvm/Instructions.h" 00020 #include "llvm/Pass.h" 00021 #include "llvm/Type.h" 00022 using namespace llvm; 00023 00024 // Register the ValueNumbering interface, providing a nice name to refer to. 00025 static RegisterAnalysisGroup<ValueNumbering> X("Value Numbering"); 00026 00027 /// ValueNumbering destructor: DO NOT move this to the header file for 00028 /// ValueNumbering or else clients of the ValueNumbering class may not depend on 00029 /// the ValueNumbering.o file in the current .a file, causing alias analysis 00030 /// support to not be included in the tool correctly! 00031 /// 00032 ValueNumbering::~ValueNumbering() {} 00033 00034 //===----------------------------------------------------------------------===// 00035 // Basic ValueNumbering Pass Implementation 00036 //===----------------------------------------------------------------------===// 00037 // 00038 // Because of the way .a files work, the implementation of the BasicVN class 00039 // MUST be in the ValueNumbering file itself, or else we run the risk of 00040 // ValueNumbering being used, but the default implementation not being linked 00041 // into the tool that uses it. As such, we register and implement the class 00042 // here. 00043 // 00044 00045 namespace { 00046 /// BasicVN - This class is the default implementation of the ValueNumbering 00047 /// interface. It walks the SSA def-use chains to trivially identify 00048 /// lexically identical expressions. This does not require any ahead of time 00049 /// analysis, so it is a very fast default implementation. 00050 /// 00051 struct BasicVN : public ImmutablePass, public ValueNumbering { 00052 /// getEqualNumberNodes - Return nodes with the same value number as the 00053 /// specified Value. This fills in the argument vector with any equal 00054 /// values. 00055 /// 00056 /// This is where our implementation is. 00057 /// 00058 virtual void getEqualNumberNodes(Value *V1, 00059 std::vector<Value*> &RetVals) const; 00060 }; 00061 00062 // Register this pass... 00063 RegisterOpt<BasicVN> 00064 X("basicvn", "Basic Value Numbering (default GVN impl)"); 00065 00066 // Declare that we implement the ValueNumbering interface 00067 RegisterAnalysisGroup<ValueNumbering, BasicVN, true> Y; 00068 00069 /// BVNImpl - Implement BasicVN in terms of a visitor class that 00070 /// handles the different types of instructions as appropriate. 00071 /// 00072 struct BVNImpl : public InstVisitor<BVNImpl> { 00073 std::vector<Value*> &RetVals; 00074 BVNImpl(std::vector<Value*> &RV) : RetVals(RV) {} 00075 00076 void handleBinaryInst(Instruction &I); 00077 void visitBinaryOperator(BinaryOperator &I) { 00078 handleBinaryInst((Instruction&)I); 00079 } 00080 void visitGetElementPtrInst(GetElementPtrInst &I); 00081 void visitCastInst(CastInst &I); 00082 void visitShiftInst(ShiftInst &I) { handleBinaryInst((Instruction&)I); } 00083 void visitSelectInst(SelectInst &I); 00084 void visitInstruction(Instruction &) { 00085 // Cannot value number calls or terminator instructions. 00086 } 00087 }; 00088 } 00089 00090 ImmutablePass *llvm::createBasicVNPass() { return new BasicVN(); } 00091 00092 // getEqualNumberNodes - Return nodes with the same value number as the 00093 // specified Value. This fills in the argument vector with any equal values. 00094 // 00095 void BasicVN::getEqualNumberNodes(Value *V, std::vector<Value*> &RetVals) const{ 00096 assert(V->getType() != Type::VoidTy && 00097 "Can only value number non-void values!"); 00098 // We can only handle the case where I is an instruction! 00099 if (Instruction *I = dyn_cast<Instruction>(V)) 00100 BVNImpl(RetVals).visit(I); 00101 } 00102 00103 void BVNImpl::visitCastInst(CastInst &CI) { 00104 Instruction &I = (Instruction&)CI; 00105 Value *Op = I.getOperand(0); 00106 Function *F = I.getParent()->getParent(); 00107 00108 for (Value::use_iterator UI = Op->use_begin(), UE = Op->use_end(); 00109 UI != UE; ++UI) 00110 if (CastInst *Other = dyn_cast<CastInst>(*UI)) 00111 // Check that the types are the same, since this code handles casts... 00112 if (Other->getType() == I.getType() && 00113 // Is it embedded in the same function? (This could be false if LHS 00114 // is a constant or global!) 00115 Other->getParent()->getParent() == F && 00116 // Check to see if this new cast is not I. 00117 Other != &I) { 00118 // These instructions are identical. Add to list... 00119 RetVals.push_back(Other); 00120 } 00121 } 00122 00123 00124 // isIdenticalBinaryInst - Return true if the two binary instructions are 00125 // identical. 00126 // 00127 static inline bool isIdenticalBinaryInst(const Instruction &I1, 00128 const Instruction *I2) { 00129 // Is it embedded in the same function? (This could be false if LHS 00130 // is a constant or global!) 00131 if (I1.getOpcode() != I2->getOpcode() || 00132 I1.getParent()->getParent() != I2->getParent()->getParent()) 00133 return false; 00134 00135 // They are identical if both operands are the same! 00136 if (I1.getOperand(0) == I2->getOperand(0) && 00137 I1.getOperand(1) == I2->getOperand(1)) 00138 return true; 00139 00140 // If the instruction is commutative, the instruction can match if the 00141 // operands are swapped! 00142 // 00143 if ((I1.getOperand(0) == I2->getOperand(1) && 00144 I1.getOperand(1) == I2->getOperand(0)) && 00145 I1.isCommutative()) 00146 return true; 00147 00148 return false; 00149 } 00150 00151 void BVNImpl::handleBinaryInst(Instruction &I) { 00152 Value *LHS = I.getOperand(0); 00153 00154 for (Value::use_iterator UI = LHS->use_begin(), UE = LHS->use_end(); 00155 UI != UE; ++UI) 00156 if (Instruction *Other = dyn_cast<Instruction>(*UI)) 00157 // Check to see if this new binary operator is not I, but same operand... 00158 if (Other != &I && isIdenticalBinaryInst(I, Other)) { 00159 // These instructions are identical. Handle the situation. 00160 RetVals.push_back(Other); 00161 } 00162 } 00163 00164 // IdenticalComplexInst - Return true if the two instructions are the same, by 00165 // using a brute force comparison. This is useful for instructions with an 00166 // arbitrary number of arguments. 00167 // 00168 static inline bool IdenticalComplexInst(const Instruction *I1, 00169 const Instruction *I2) { 00170 assert(I1->getOpcode() == I2->getOpcode()); 00171 // Equal if they are in the same function... 00172 return I1->getParent()->getParent() == I2->getParent()->getParent() && 00173 // And return the same type... 00174 I1->getType() == I2->getType() && 00175 // And have the same number of operands... 00176 I1->getNumOperands() == I2->getNumOperands() && 00177 // And all of the operands are equal. 00178 std::equal(I1->op_begin(), I1->op_end(), I2->op_begin()); 00179 } 00180 00181 void BVNImpl::visitGetElementPtrInst(GetElementPtrInst &I) { 00182 Value *Op = I.getOperand(0); 00183 00184 // Try to pick a local operand if possible instead of a constant or a global 00185 // that might have a lot of uses. 00186 for (unsigned i = 1, e = I.getNumOperands(); i != e; ++i) 00187 if (isa<Instruction>(I.getOperand(i)) || isa<Argument>(I.getOperand(i))) { 00188 Op = I.getOperand(i); 00189 break; 00190 } 00191 00192 for (Value::use_iterator UI = Op->use_begin(), UE = Op->use_end(); 00193 UI != UE; ++UI) 00194 if (GetElementPtrInst *Other = dyn_cast<GetElementPtrInst>(*UI)) 00195 // Check to see if this new getelementptr is not I, but same operand... 00196 if (Other != &I && IdenticalComplexInst(&I, Other)) { 00197 // These instructions are identical. Handle the situation. 00198 RetVals.push_back(Other); 00199 } 00200 } 00201 00202 // isIdenticalSelectInst - Return true if the two select instructions are 00203 // identical. 00204 // 00205 static inline bool isIdenticalSelectInst(const SelectInst &I1, 00206 const SelectInst *I2) { 00207 // Is it embedded in the same function? (This could be false if LHS 00208 // is a constant or global!) 00209 if (I1.getParent()->getParent() != I2->getParent()->getParent()) 00210 return false; 00211 00212 // They are identical if both operands are the same! 00213 return I1.getOperand(0) == I2->getOperand(0) && 00214 I1.getOperand(1) == I2->getOperand(1) && 00215 I1.getOperand(2) == I2->getOperand(2); 00216 return true; 00217 00218 return false; 00219 } 00220 00221 void BVNImpl::visitSelectInst(SelectInst &I) { 00222 Value *Cond = I.getOperand(0); 00223 00224 for (Value::use_iterator UI = Cond->use_begin(), UE = Cond->use_end(); 00225 UI != UE; ++UI) 00226 if (SelectInst *Other = dyn_cast<SelectInst>(*UI)) 00227 // Check to see if this new select is not I, but has the same operands. 00228 if (Other != &I && isIdenticalSelectInst(I, Other)) { 00229 // These instructions are identical. Handle the situation. 00230 RetVals.push_back(Other); 00231 } 00232 00233 } 00234 00235 00236 void llvm::BasicValueNumberingStub() { }