InlineCost.h revision f7477470d37ee2ab9075eaee4745fa084d424ab8 
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    /// growCachedCostInfo - update the cached cost info for Caller after Callee
184    /// has been inlined. If Callee is NULL it means a dead call has been
185    /// eliminated.
186    void growCachedCostInfo(Function* Caller, Function* Callee);
187  };
188}
189
190#endif
191