InlineCost.h revision e4aeec003f82a5263ffb168e175e6fca8b6f681d
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 namespace InlineConstants { 32 // Various magic constants used to adjust heuristics. 33 const int CallPenalty = 5; 34 const int LastCallToStaticBonus = -15000; 35 const int ColdccPenalty = 2000; 36 const int NoreturnPenalty = 10000; 37 } 38 39 /// InlineCost - Represent the cost of inlining a function. This 40 /// supports special values for functions which should "always" or 41 /// "never" be inlined. Otherwise, the cost represents a unitless 42 /// amount; smaller values increase the likelyhood of the function 43 /// being inlined. 44 class InlineCost { 45 enum Kind { 46 Value, 47 Always, 48 Never 49 }; 50 51 // This is a do-it-yourself implementation of 52 // int Cost : 30; 53 // unsigned Type : 2; 54 // We used to use bitfields, but they were sometimes miscompiled (PR3822). 55 enum { TYPE_BITS = 2 }; 56 enum { COST_BITS = unsigned(sizeof(unsigned)) * CHAR_BIT - TYPE_BITS }; 57 unsigned TypedCost; // int Cost : COST_BITS; unsigned Type : TYPE_BITS; 58 59 Kind getType() const { 60 return Kind(TypedCost >> COST_BITS); 61 } 62 63 int getCost() const { 64 // Sign-extend the bottom COST_BITS bits. 65 return (int(TypedCost << TYPE_BITS)) >> TYPE_BITS; 66 } 67 68 InlineCost(int C, int T) { 69 TypedCost = (unsigned(C << TYPE_BITS) >> TYPE_BITS) | (T << COST_BITS); 70 assert(getCost() == C && "Cost exceeds InlineCost precision"); 71 } 72 public: 73 static InlineCost get(int Cost) { return InlineCost(Cost, Value); } 74 static InlineCost getAlways() { return InlineCost(0, Always); } 75 static InlineCost getNever() { return InlineCost(0, Never); } 76 77 bool isVariable() const { return getType() == Value; } 78 bool isAlways() const { return getType() == Always; } 79 bool isNever() const { return getType() == Never; } 80 81 /// getValue() - Return a "variable" inline cost's amount. It is 82 /// an error to call this on an "always" or "never" InlineCost. 83 int getValue() const { 84 assert(getType() == Value && "Invalid access of InlineCost"); 85 return getCost(); 86 } 87 }; 88 89 /// InlineCostAnalyzer - Cost analyzer used by inliner. 90 class InlineCostAnalyzer { 91 struct ArgInfo { 92 public: 93 unsigned ConstantWeight; 94 unsigned AllocaWeight; 95 96 ArgInfo(unsigned CWeight, unsigned AWeight) 97 : ConstantWeight(CWeight), AllocaWeight(AWeight) {} 98 }; 99 100 // RegionInfo - Calculate size and a few related metrics for a set of 101 // basic blocks. 102 struct RegionInfo { 103 /// NeverInline - True if this callee should never be inlined into a 104 /// caller. 105 bool NeverInline; 106 107 /// usesDynamicAlloca - True if this function calls alloca (in the C sense). 108 bool usesDynamicAlloca; 109 110 /// NumInsts, NumBlocks - Keep track of how large each function is, which 111 /// is used to estimate the code size cost of inlining it. 112 unsigned NumInsts, NumBlocks; 113 114 /// NumVectorInsts - Keep track of how many instructions produce vector 115 /// values. The inliner is being more aggressive with inlining vector 116 /// kernels. 117 unsigned NumVectorInsts; 118 119 /// NumRets - Keep track of how many Ret instructions the block contains. 120 unsigned NumRets; 121 122 /// ArgumentWeights - Each formal argument of the function is inspected to 123 /// see if it is used in any contexts where making it a constant or alloca 124 /// would reduce the code size. If so, we add some value to the argument 125 /// entry here. 126 std::vector<ArgInfo> ArgumentWeights; 127 128 RegionInfo() : NeverInline(false), usesDynamicAlloca(false), NumInsts(0), 129 NumBlocks(0), NumVectorInsts(0), NumRets(0) {} 130 131 /// analyzeBasicBlock - Add information about the specified basic block 132 /// to the current structure. 133 void analyzeBasicBlock(const BasicBlock *BB); 134 135 /// analyzeFunction - Add information about the specified function 136 /// to the current structure. 137 void analyzeFunction(Function *F); 138 139 /// CountCodeReductionForConstant - Figure out an approximation for how 140 /// many instructions will be constant folded if the specified value is 141 /// constant. 142 unsigned CountCodeReductionForConstant(Value *V); 143 144 /// CountCodeReductionForAlloca - Figure out an approximation of how much 145 /// smaller the function will be if it is inlined into a context where an 146 /// argument becomes an alloca. 147 /// 148 unsigned CountCodeReductionForAlloca(Value *V); 149 }; 150 151 std::map<const Function *, RegionInfo> CachedFunctionInfo; 152 153 public: 154 155 /// getInlineCost - The heuristic used to determine if we should inline the 156 /// function call or not. 157 /// 158 InlineCost getInlineCost(CallSite CS, 159 SmallPtrSet<const Function *, 16> &NeverInline); 160 161 /// getInlineFudgeFactor - Return a > 1.0 factor if the inliner should use a 162 /// higher threshold to determine if the function call should be inlined. 163 float getInlineFudgeFactor(CallSite CS); 164 165 /// resetCachedFunctionInfo - erase any cached cost info for this function. 166 void resetCachedCostInfo(Function* Caller) { 167 CachedFunctionInfo[Caller].NumBlocks = 0; 168 } 169 }; 170} 171 172#endif 173