InlineCost.h revision 52d55bd224ac08dfef959527ca8257f82a80dbb0
1//===- InlineCost.cpp - Cost analysis for inliner ---------------*- C++ -*-===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This file implements heuristics for inlining decisions. 11// 12//===----------------------------------------------------------------------===// 13 14#ifndef LLVM_ANALYSIS_INLINECOST_H 15#define LLVM_ANALYSIS_INLINECOST_H 16 17#include <cassert> 18#include <climits> 19#include <map> 20#include <vector> 21#include "llvm/ADT/DenseMap.h" 22 23namespace llvm { 24 25 class Value; 26 class Function; 27 class BasicBlock; 28 class CallSite; 29 template<class PtrType, unsigned SmallSize> 30 class SmallPtrSet; 31 32 // CodeMetrics - Calculate size and a few similar metrics for a set of 33 // basic blocks. 34 struct CodeMetrics { 35 /// NeverInline - True if this callee should never be inlined into a 36 /// caller. 37 bool NeverInline; 38 39 /// usesDynamicAlloca - True if this function calls alloca (in the C sense). 40 bool usesDynamicAlloca; 41 42 /// NumInsts, NumBlocks - Keep track of how large each function is, which 43 /// is used to estimate the code size cost of inlining it. 44 unsigned NumInsts, NumBlocks; 45 46 /// NumBBInsts - Keeps track of basic block code size estimates. 47 DenseMap<const BasicBlock *, unsigned> NumBBInsts; 48 49 /// NumCalls - Keep track of the number of calls to 'big' functions. 50 unsigned NumCalls; 51 52 /// NumVectorInsts - Keep track of how many instructions produce vector 53 /// values. The inliner is being more aggressive with inlining vector 54 /// kernels. 55 unsigned NumVectorInsts; 56 57 /// NumRets - Keep track of how many Ret instructions the block contains. 58 unsigned NumRets; 59 60 CodeMetrics() : NeverInline(false), usesDynamicAlloca(false), NumInsts(0), 61 NumBlocks(0), NumCalls(0), NumVectorInsts(0), NumRets(0) {} 62 63 /// analyzeBasicBlock - Add information about the specified basic block 64 /// to the current structure. 65 void analyzeBasicBlock(const BasicBlock *BB); 66 67 /// analyzeFunction - Add information about the specified function 68 /// to the current structure. 69 void analyzeFunction(Function *F); 70 }; 71 72 namespace InlineConstants { 73 // Various magic constants used to adjust heuristics. 74 const int InstrCost = 5; 75 const int IndirectCallBonus = 500; 76 const int CallPenalty = 25; 77 const int LastCallToStaticBonus = -15000; 78 const int ColdccPenalty = 2000; 79 const int NoreturnPenalty = 10000; 80 } 81 82 /// InlineCost - Represent the cost of inlining a function. This 83 /// supports special values for functions which should "always" or 84 /// "never" be inlined. Otherwise, the cost represents a unitless 85 /// amount; smaller values increase the likelyhood of the function 86 /// being inlined. 87 class InlineCost { 88 enum Kind { 89 Value, 90 Always, 91 Never 92 }; 93 94 // This is a do-it-yourself implementation of 95 // int Cost : 30; 96 // unsigned Type : 2; 97 // We used to use bitfields, but they were sometimes miscompiled (PR3822). 98 enum { TYPE_BITS = 2 }; 99 enum { COST_BITS = unsigned(sizeof(unsigned)) * CHAR_BIT - TYPE_BITS }; 100 unsigned TypedCost; // int Cost : COST_BITS; unsigned Type : TYPE_BITS; 101 102 Kind getType() const { 103 return Kind(TypedCost >> COST_BITS); 104 } 105 106 int getCost() const { 107 // Sign-extend the bottom COST_BITS bits. 108 return (int(TypedCost << TYPE_BITS)) >> TYPE_BITS; 109 } 110 111 InlineCost(int C, int T) { 112 TypedCost = (unsigned(C << TYPE_BITS) >> TYPE_BITS) | (T << COST_BITS); 113 assert(getCost() == C && "Cost exceeds InlineCost precision"); 114 } 115 public: 116 static InlineCost get(int Cost) { return InlineCost(Cost, Value); } 117 static InlineCost getAlways() { return InlineCost(0, Always); } 118 static InlineCost getNever() { return InlineCost(0, Never); } 119 120 bool isVariable() const { return getType() == Value; } 121 bool isAlways() const { return getType() == Always; } 122 bool isNever() const { return getType() == Never; } 123 124 /// getValue() - Return a "variable" inline cost's amount. It is 125 /// an error to call this on an "always" or "never" InlineCost. 126 int getValue() const { 127 assert(getType() == Value && "Invalid access of InlineCost"); 128 return getCost(); 129 } 130 }; 131 132 /// InlineCostAnalyzer - Cost analyzer used by inliner. 133 class InlineCostAnalyzer { 134 struct ArgInfo { 135 public: 136 unsigned ConstantWeight; 137 unsigned AllocaWeight; 138 139 ArgInfo(unsigned CWeight, unsigned AWeight) 140 : ConstantWeight(CWeight), AllocaWeight(AWeight) {} 141 }; 142 143 struct FunctionInfo { 144 CodeMetrics Metrics; 145 146 /// ArgumentWeights - Each formal argument of the function is inspected to 147 /// see if it is used in any contexts where making it a constant or alloca 148 /// would reduce the code size. If so, we add some value to the argument 149 /// entry here. 150 std::vector<ArgInfo> ArgumentWeights; 151 152 /// CountCodeReductionForConstant - Figure out an approximation for how 153 /// many instructions will be constant folded if the specified value is 154 /// constant. 155 unsigned CountCodeReductionForConstant(Value *V); 156 157 /// CountCodeReductionForAlloca - Figure out an approximation of how much 158 /// smaller the function will be if it is inlined into a context where an 159 /// argument becomes an alloca. 160 /// 161 unsigned CountCodeReductionForAlloca(Value *V); 162 163 /// analyzeFunction - Add information about the specified function 164 /// to the current structure. 165 void analyzeFunction(Function *F); 166 }; 167 168 std::map<const Function *, FunctionInfo> CachedFunctionInfo; 169 170 public: 171 172 /// getInlineCost - The heuristic used to determine if we should inline the 173 /// function call or not. 174 /// 175 InlineCost getInlineCost(CallSite CS, 176 SmallPtrSet<const Function *, 16> &NeverInline); 177 178 /// getInlineFudgeFactor - Return a > 1.0 factor if the inliner should use a 179 /// higher threshold to determine if the function call should be inlined. 180 float getInlineFudgeFactor(CallSite CS); 181 182 /// resetCachedFunctionInfo - erase any cached cost info for this function. 183 void resetCachedCostInfo(Function* Caller) { 184 CachedFunctionInfo[Caller] = FunctionInfo(); 185 } 186 187 /// growCachedCostInfo - update the cached cost info for Caller after Callee 188 /// has been inlined. If Callee is NULL it means a dead call has been 189 /// eliminated. 190 void growCachedCostInfo(Function* Caller, Function* Callee); 191 }; 192 193 /// callIsSmall - If a call is likely to lower to a single target instruction, 194 /// or is otherwise deemed small return true. 195 bool callIsSmall(const Function *Callee); 196} 197 198#endif 199