InlineCost.h revision aa034fa2299e41b73f60d3993f5460260e239fab
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 22namespace llvm { 23 24 class Value; 25 class Function; 26 class BasicBlock; 27 class CallSite; 28 template<class PtrType, unsigned SmallSize> 29 class SmallPtrSet; 30 31 // CodeMetrics - Calculate size and a few similar metrics for a set of 32 // basic blocks. 33 struct CodeMetrics { 34 /// NeverInline - True if this callee should never be inlined into a 35 /// caller. 36 bool NeverInline; 37 38 /// usesDynamicAlloca - True if this function calls alloca (in the C sense). 39 bool usesDynamicAlloca; 40 41 /// NumInsts, NumBlocks - Keep track of how large each function is, which 42 /// is used to estimate the code size cost of inlining it. 43 unsigned NumInsts, NumBlocks; 44 45 /// NumCalls - Keep track of the number of calls to 'big' functions. 46 unsigned NumCalls; 47 48 /// NumVectorInsts - Keep track of how many instructions produce vector 49 /// values. The inliner is being more aggressive with inlining vector 50 /// kernels. 51 unsigned NumVectorInsts; 52 53 /// NumRets - Keep track of how many Ret instructions the block contains. 54 unsigned NumRets; 55 56 CodeMetrics() : NeverInline(false), usesDynamicAlloca(false), NumInsts(0), 57 NumBlocks(0), NumCalls(0), NumVectorInsts(0), NumRets(0) {} 58 59 /// analyzeBasicBlock - Add information about the specified basic block 60 /// to the current structure. 61 void analyzeBasicBlock(const BasicBlock *BB); 62 63 /// analyzeFunction - Add information about the specified function 64 /// to the current structure. 65 void analyzeFunction(Function *F); 66 }; 67 68 namespace InlineConstants { 69 // Various magic constants used to adjust heuristics. 70 const int InstrCost = 5; 71 const int IndirectCallBonus = 500; 72 const int CallPenalty = 25; 73 const int LastCallToStaticBonus = -15000; 74 const int ColdccPenalty = 2000; 75 const int NoreturnPenalty = 10000; 76 } 77 78 /// InlineCost - Represent the cost of inlining a function. This 79 /// supports special values for functions which should "always" or 80 /// "never" be inlined. Otherwise, the cost represents a unitless 81 /// amount; smaller values increase the likelyhood of the function 82 /// being inlined. 83 class InlineCost { 84 enum Kind { 85 Value, 86 Always, 87 Never 88 }; 89 90 // This is a do-it-yourself implementation of 91 // int Cost : 30; 92 // unsigned Type : 2; 93 // We used to use bitfields, but they were sometimes miscompiled (PR3822). 94 enum { TYPE_BITS = 2 }; 95 enum { COST_BITS = unsigned(sizeof(unsigned)) * CHAR_BIT - TYPE_BITS }; 96 unsigned TypedCost; // int Cost : COST_BITS; unsigned Type : TYPE_BITS; 97 98 Kind getType() const { 99 return Kind(TypedCost >> COST_BITS); 100 } 101 102 int getCost() const { 103 // Sign-extend the bottom COST_BITS bits. 104 return (int(TypedCost << TYPE_BITS)) >> TYPE_BITS; 105 } 106 107 InlineCost(int C, int T) { 108 TypedCost = (unsigned(C << TYPE_BITS) >> TYPE_BITS) | (T << COST_BITS); 109 assert(getCost() == C && "Cost exceeds InlineCost precision"); 110 } 111 public: 112 static InlineCost get(int Cost) { return InlineCost(Cost, Value); } 113 static InlineCost getAlways() { return InlineCost(0, Always); } 114 static InlineCost getNever() { return InlineCost(0, Never); } 115 116 bool isVariable() const { return getType() == Value; } 117 bool isAlways() const { return getType() == Always; } 118 bool isNever() const { return getType() == Never; } 119 120 /// getValue() - Return a "variable" inline cost's amount. It is 121 /// an error to call this on an "always" or "never" InlineCost. 122 int getValue() const { 123 assert(getType() == Value && "Invalid access of InlineCost"); 124 return getCost(); 125 } 126 }; 127 128 /// InlineCostAnalyzer - Cost analyzer used by inliner. 129 class InlineCostAnalyzer { 130 struct ArgInfo { 131 public: 132 unsigned ConstantWeight; 133 unsigned AllocaWeight; 134 135 ArgInfo(unsigned CWeight, unsigned AWeight) 136 : ConstantWeight(CWeight), AllocaWeight(AWeight) {} 137 }; 138 139 struct FunctionInfo { 140 CodeMetrics Metrics; 141 142 /// ArgumentWeights - Each formal argument of the function is inspected to 143 /// see if it is used in any contexts where making it a constant or alloca 144 /// would reduce the code size. If so, we add some value to the argument 145 /// entry here. 146 std::vector<ArgInfo> ArgumentWeights; 147 148 /// CountCodeReductionForConstant - Figure out an approximation for how 149 /// many instructions will be constant folded if the specified value is 150 /// constant. 151 unsigned CountCodeReductionForConstant(Value *V); 152 153 /// CountCodeReductionForAlloca - Figure out an approximation of how much 154 /// smaller the function will be if it is inlined into a context where an 155 /// argument becomes an alloca. 156 /// 157 unsigned CountCodeReductionForAlloca(Value *V); 158 159 /// analyzeFunction - Add information about the specified function 160 /// to the current structure. 161 void analyzeFunction(Function *F); 162 }; 163 164 std::map<const Function *, FunctionInfo> CachedFunctionInfo; 165 166 public: 167 168 /// getInlineCost - The heuristic used to determine if we should inline the 169 /// function call or not. 170 /// 171 InlineCost getInlineCost(CallSite CS, 172 SmallPtrSet<const Function *, 16> &NeverInline); 173 174 /// getInlineFudgeFactor - Return a > 1.0 factor if the inliner should use a 175 /// higher threshold to determine if the function call should be inlined. 176 float getInlineFudgeFactor(CallSite CS); 177 178 /// resetCachedFunctionInfo - erase any cached cost info for this function. 179 void resetCachedCostInfo(Function* Caller) { 180 CachedFunctionInfo[Caller] = FunctionInfo(); 181 } 182 }; 183} 184 185#endif 186