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 visitCastInst(CastInst &I); 00077 void visitGetElementPtrInst(GetElementPtrInst &I); 00078 00079 void handleBinaryInst(Instruction &I); 00080 void visitBinaryOperator(Instruction &I) { handleBinaryInst(I); } 00081 void visitShiftInst(Instruction &I) { handleBinaryInst(I); } 00082 void visitExtractElementInst(Instruction &I) { handleBinaryInst(I); } 00083 00084 void handleTernaryInst(Instruction &I); 00085 void visitSelectInst(Instruction &I) { handleTernaryInst(I); } 00086 void visitInsertElementInst(Instruction &I) { handleTernaryInst(I); } 00087 void visitShuffleVectorInst(Instruction &I) { handleTernaryInst(I); } 00088 void visitInstruction(Instruction &) { 00089 // Cannot value number calls or terminator instructions. 00090 } 00091 }; 00092 } 00093 00094 ImmutablePass *llvm::createBasicVNPass() { return new BasicVN(); } 00095 00096 // getEqualNumberNodes - Return nodes with the same value number as the 00097 // specified Value. This fills in the argument vector with any equal values. 00098 // 00099 void BasicVN::getEqualNumberNodes(Value *V, std::vector<Value*> &RetVals) const{ 00100 assert(V->getType() != Type::VoidTy && 00101 "Can only value number non-void values!"); 00102 // We can only handle the case where I is an instruction! 00103 if (Instruction *I = dyn_cast<Instruction>(V)) 00104 BVNImpl(RetVals).visit(I); 00105 } 00106 00107 void BVNImpl::visitCastInst(CastInst &CI) { 00108 Instruction &I = (Instruction&)CI; 00109 Value *Op = I.getOperand(0); 00110 Function *F = I.getParent()->getParent(); 00111 00112 for (Value::use_iterator UI = Op->use_begin(), UE = Op->use_end(); 00113 UI != UE; ++UI) 00114 if (CastInst *Other = dyn_cast<CastInst>(*UI)) 00115 // Check that the types are the same, since this code handles casts... 00116 if (Other->getType() == I.getType() && 00117 // Is it embedded in the same function? (This could be false if LHS 00118 // is a constant or global!) 00119 Other->getParent()->getParent() == F && 00120 // Check to see if this new cast is not I. 00121 Other != &I) { 00122 // These instructions are identical. Add to list... 00123 RetVals.push_back(Other); 00124 } 00125 } 00126 00127 00128 // isIdenticalBinaryInst - Return true if the two binary instructions are 00129 // identical. 00130 // 00131 static inline bool isIdenticalBinaryInst(const Instruction &I1, 00132 const Instruction *I2) { 00133 // Is it embedded in the same function? (This could be false if LHS 00134 // is a constant or global!) 00135 if (I1.getOpcode() != I2->getOpcode() || 00136 I1.getParent()->getParent() != I2->getParent()->getParent()) 00137 return false; 00138 00139 // They are identical if both operands are the same! 00140 if (I1.getOperand(0) == I2->getOperand(0) && 00141 I1.getOperand(1) == I2->getOperand(1)) 00142 return true; 00143 00144 // If the instruction is commutative, the instruction can match if the 00145 // operands are swapped! 00146 // 00147 if ((I1.getOperand(0) == I2->getOperand(1) && 00148 I1.getOperand(1) == I2->getOperand(0)) && 00149 I1.isCommutative()) 00150 return true; 00151 00152 return false; 00153 } 00154 00155 // isIdenticalTernaryInst - Return true if the two ternary instructions are 00156 // identical. 00157 // 00158 static inline bool isIdenticalTernaryInst(const Instruction &I1, 00159 const Instruction *I2) { 00160 // Is it embedded in the same function? (This could be false if LHS 00161 // is a constant or global!) 00162 if (I1.getParent()->getParent() != I2->getParent()->getParent()) 00163 return false; 00164 00165 // They are identical if all operands are the same! 00166 return I1.getOperand(0) == I2->getOperand(0) && 00167 I1.getOperand(1) == I2->getOperand(1) && 00168 I1.getOperand(2) == I2->getOperand(2); 00169 } 00170 00171 00172 00173 void BVNImpl::handleBinaryInst(Instruction &I) { 00174 Value *LHS = I.getOperand(0); 00175 00176 for (Value::use_iterator UI = LHS->use_begin(), UE = LHS->use_end(); 00177 UI != UE; ++UI) 00178 if (Instruction *Other = dyn_cast<Instruction>(*UI)) 00179 // Check to see if this new binary operator is not I, but same operand... 00180 if (Other != &I && isIdenticalBinaryInst(I, Other)) { 00181 // These instructions are identical. Handle the situation. 00182 RetVals.push_back(Other); 00183 } 00184 } 00185 00186 // IdenticalComplexInst - Return true if the two instructions are the same, by 00187 // using a brute force comparison. This is useful for instructions with an 00188 // arbitrary number of arguments. 00189 // 00190 static inline bool IdenticalComplexInst(const Instruction *I1, 00191 const Instruction *I2) { 00192 assert(I1->getOpcode() == I2->getOpcode()); 00193 // Equal if they are in the same function... 00194 return I1->getParent()->getParent() == I2->getParent()->getParent() && 00195 // And return the same type... 00196 I1->getType() == I2->getType() && 00197 // And have the same number of operands... 00198 I1->getNumOperands() == I2->getNumOperands() && 00199 // And all of the operands are equal. 00200 std::equal(I1->op_begin(), I1->op_end(), I2->op_begin()); 00201 } 00202 00203 void BVNImpl::visitGetElementPtrInst(GetElementPtrInst &I) { 00204 Value *Op = I.getOperand(0); 00205 00206 // Try to pick a local operand if possible instead of a constant or a global 00207 // that might have a lot of uses. 00208 for (unsigned i = 1, e = I.getNumOperands(); i != e; ++i) 00209 if (isa<Instruction>(I.getOperand(i)) || isa<Argument>(I.getOperand(i))) { 00210 Op = I.getOperand(i); 00211 break; 00212 } 00213 00214 for (Value::use_iterator UI = Op->use_begin(), UE = Op->use_end(); 00215 UI != UE; ++UI) 00216 if (GetElementPtrInst *Other = dyn_cast<GetElementPtrInst>(*UI)) 00217 // Check to see if this new getelementptr is not I, but same operand... 00218 if (Other != &I && IdenticalComplexInst(&I, Other)) { 00219 // These instructions are identical. Handle the situation. 00220 RetVals.push_back(Other); 00221 } 00222 } 00223 00224 void BVNImpl::handleTernaryInst(Instruction &I) { 00225 Value *Op0 = I.getOperand(0); 00226 Instruction *OtherInst; 00227 00228 for (Value::use_iterator UI = Op0->use_begin(), UE = Op0->use_end(); 00229 UI != UE; ++UI) 00230 if ((OtherInst = dyn_cast<Instruction>(*UI)) && 00231 OtherInst->getOpcode() == I.getOpcode()) { 00232 // Check to see if this new select is not I, but has the same operands. 00233 if (OtherInst != &I && isIdenticalTernaryInst(I, OtherInst)) { 00234 // These instructions are identical. Handle the situation. 00235 RetVals.push_back(OtherInst); 00236 } 00237 00238 } 00239 } 00240 00241 00242 // Ensure that users of ValueNumbering.h will link with this file 00243 DEFINING_FILE_FOR(BasicValueNumbering)