• Home
  • Line#
  • Scopes#
  • Navigate#
  • Raw
  • Download
1 //===- InlineCost.h - 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 <vector>
20 #include "llvm/ADT/DenseMap.h"
21 #include "llvm/ADT/ValueMap.h"
22 #include "llvm/Analysis/CodeMetrics.h"
23 
24 namespace llvm {
25 
26   class Value;
27   class Function;
28   class BasicBlock;
29   class CallSite;
30   template<class PtrType, unsigned SmallSize>
31   class SmallPtrSet;
32   class TargetData;
33 
34   namespace InlineConstants {
35     // Various magic constants used to adjust heuristics.
36     const int InstrCost = 5;
37     const int IndirectCallBonus = -100;
38     const int CallPenalty = 25;
39     const int LastCallToStaticBonus = -15000;
40     const int ColdccPenalty = 2000;
41     const int NoreturnPenalty = 10000;
42   }
43 
44   /// InlineCost - Represent the cost of inlining a function. This
45   /// supports special values for functions which should "always" or
46   /// "never" be inlined. Otherwise, the cost represents a unitless
47   /// amount; smaller values increase the likelihood of the function
48   /// being inlined.
49   class InlineCost {
50     enum Kind {
51       Value,
52       Always,
53       Never
54     };
55 
56     // This is a do-it-yourself implementation of
57     //   int Cost : 30;
58     //   unsigned Type : 2;
59     // We used to use bitfields, but they were sometimes miscompiled (PR3822).
60     enum { TYPE_BITS = 2 };
61     enum { COST_BITS = unsigned(sizeof(unsigned)) * CHAR_BIT - TYPE_BITS };
62     unsigned TypedCost; // int Cost : COST_BITS; unsigned Type : TYPE_BITS;
63 
getType()64     Kind getType() const {
65       return Kind(TypedCost >> COST_BITS);
66     }
67 
getCost()68     int getCost() const {
69       // Sign-extend the bottom COST_BITS bits.
70       return (int(TypedCost << TYPE_BITS)) >> TYPE_BITS;
71     }
72 
InlineCost(int C,int T)73     InlineCost(int C, int T) {
74       TypedCost = (unsigned(C << TYPE_BITS) >> TYPE_BITS) | (T << COST_BITS);
75       assert(getCost() == C && "Cost exceeds InlineCost precision");
76     }
77   public:
get(int Cost)78     static InlineCost get(int Cost) { return InlineCost(Cost, Value); }
getAlways()79     static InlineCost getAlways() { return InlineCost(0, Always); }
getNever()80     static InlineCost getNever() { return InlineCost(0, Never); }
81 
isVariable()82     bool isVariable() const { return getType() == Value; }
isAlways()83     bool isAlways() const { return getType() == Always; }
isNever()84     bool isNever() const { return getType() == Never; }
85 
86     /// getValue() - Return a "variable" inline cost's amount. It is
87     /// an error to call this on an "always" or "never" InlineCost.
getValue()88     int getValue() const {
89       assert(getType() == Value && "Invalid access of InlineCost");
90       return getCost();
91     }
92   };
93 
94   /// InlineCostAnalyzer - Cost analyzer used by inliner.
95   class InlineCostAnalyzer {
96     struct ArgInfo {
97     public:
98       unsigned ConstantWeight;
99       unsigned AllocaWeight;
100 
ArgInfoArgInfo101       ArgInfo(unsigned CWeight, unsigned AWeight)
102         : ConstantWeight(CWeight), AllocaWeight(AWeight)
103           {}
104     };
105 
106     struct FunctionInfo {
107       CodeMetrics Metrics;
108 
109       /// ArgumentWeights - Each formal argument of the function is inspected to
110       /// see if it is used in any contexts where making it a constant or alloca
111       /// would reduce the code size.  If so, we add some value to the argument
112       /// entry here.
113       std::vector<ArgInfo> ArgumentWeights;
114 
115       /// analyzeFunction - Add information about the specified function
116       /// to the current structure.
117       void analyzeFunction(Function *F, const TargetData *TD);
118 
119       /// NeverInline - Returns true if the function should never be
120       /// inlined into any caller.
121       bool NeverInline();
122     };
123 
124     // The Function* for a function can be changed (by ArgumentPromotion);
125     // the ValueMap will update itself when this happens.
126     ValueMap<const Function *, FunctionInfo> CachedFunctionInfo;
127 
128     // TargetData if available, or null.
129     const TargetData *TD;
130 
131     int CountBonusForConstant(Value *V, Constant *C = NULL);
132     int ConstantFunctionBonus(CallSite CS, Constant *C);
133     int getInlineSize(CallSite CS, Function *Callee);
134     int getInlineBonuses(CallSite CS, Function *Callee);
135   public:
InlineCostAnalyzer()136     InlineCostAnalyzer(): TD(0) {}
137 
setTargetData(const TargetData * TData)138     void setTargetData(const TargetData *TData) { TD = TData; }
139 
140     /// getInlineCost - The heuristic used to determine if we should inline the
141     /// function call or not.
142     ///
143     InlineCost getInlineCost(CallSite CS,
144                              SmallPtrSet<const Function *, 16> &NeverInline);
145     /// getCalledFunction - The heuristic used to determine if we should inline
146     /// the function call or not.  The callee is explicitly specified, to allow
147     /// you to calculate the cost of inlining a function via a pointer.  The
148     /// result assumes that the inlined version will always be used.  You should
149     /// weight it yourself in cases where this callee will not always be called.
150     InlineCost getInlineCost(CallSite CS,
151                              Function *Callee,
152                              SmallPtrSet<const Function *, 16> &NeverInline);
153 
154     /// getSpecializationBonus - The heuristic used to determine the per-call
155     /// performance boost for using a specialization of Callee with argument
156     /// SpecializedArgNos replaced by a constant.
157     int getSpecializationBonus(Function *Callee,
158              SmallVectorImpl<unsigned> &SpecializedArgNo);
159 
160     /// getSpecializationCost - The heuristic used to determine the code-size
161     /// impact of creating a specialized version of Callee with argument
162     /// SpecializedArgNo replaced by a constant.
163     InlineCost getSpecializationCost(Function *Callee,
164                SmallVectorImpl<unsigned> &SpecializedArgNo);
165 
166     /// getInlineFudgeFactor - Return a > 1.0 factor if the inliner should use a
167     /// higher threshold to determine if the function call should be inlined.
168     float getInlineFudgeFactor(CallSite CS);
169 
170     /// resetCachedFunctionInfo - erase any cached cost info for this function.
resetCachedCostInfo(Function * Caller)171     void resetCachedCostInfo(Function* Caller) {
172       CachedFunctionInfo[Caller] = FunctionInfo();
173     }
174 
175     /// growCachedCostInfo - update the cached cost info for Caller after Callee
176     /// has been inlined. If Callee is NULL it means a dead call has been
177     /// eliminated.
178     void growCachedCostInfo(Function* Caller, Function* Callee);
179 
180     /// clear - empty the cache of inline costs
181     void clear();
182   };
183 
184   /// callIsSmall - If a call is likely to lower to a single target instruction,
185   /// or is otherwise deemed small return true.
186   bool callIsSmall(const Function *Callee);
187 }
188 
189 #endif
190