InlineCost.h revision 4e8af6db184118638c21f713ad98e3292c6891c9 
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
24namespace llvm {
25
26  class Value;
27  class Function;
28  class BasicBlock;
29  class CallSite;
30  template<class PtrType, unsigned SmallSize>
31  class SmallPtrSet;
32
33  namespace InlineConstants {
34    // Various magic constants used to adjust heuristics.
35    const int InstrCost = 5;
36    const int IndirectCallBonus = -100;
37    const int CallPenalty = 25;
38    const int LastCallToStaticBonus = -15000;
39    const int ColdccPenalty = 2000;
40    const int NoreturnPenalty = 10000;
41  }
42
43  /// InlineCost - Represent the cost of inlining a function. This
44  /// supports special values for functions which should "always" or
45  /// "never" be inlined. Otherwise, the cost represents a unitless
46  /// amount; smaller values increase the likelyhood of the function
47  /// being inlined.
48  class InlineCost {
49    enum Kind {
50      Value,
51      Always,
52      Never
53    };
54
55    // This is a do-it-yourself implementation of
56    //   int Cost : 30;
57    //   unsigned Type : 2;
58    // We used to use bitfields, but they were sometimes miscompiled (PR3822).
59    enum { TYPE_BITS = 2 };
60    enum { COST_BITS = unsigned(sizeof(unsigned)) * CHAR_BIT - TYPE_BITS };
61    unsigned TypedCost; // int Cost : COST_BITS; unsigned Type : TYPE_BITS;
62
63    Kind getType() const {
64      return Kind(TypedCost >> COST_BITS);
65    }
66
67    int getCost() const {
68      // Sign-extend the bottom COST_BITS bits.
69      return (int(TypedCost << TYPE_BITS)) >> TYPE_BITS;
70    }
71
72    InlineCost(int C, int T) {
73      TypedCost = (unsigned(C << TYPE_BITS) >> TYPE_BITS) | (T << COST_BITS);
74      assert(getCost() == C && "Cost exceeds InlineCost precision");
75    }
76  public:
77    static InlineCost get(int Cost) { return InlineCost(Cost, Value); }
78    static InlineCost getAlways() { return InlineCost(0, Always); }
79    static InlineCost getNever() { return InlineCost(0, Never); }
80
81    bool isVariable() const { return getType() == Value; }
82    bool isAlways() const { return getType() == Always; }
83    bool isNever() const { return getType() == Never; }
84
85    /// getValue() - Return a "variable" inline cost's amount. It is
86    /// an error to call this on an "always" or "never" InlineCost.
87    int getValue() const {
88      assert(getType() == Value && "Invalid access of InlineCost");
89      return getCost();
90    }
91  };
92
93  /// InlineCostAnalyzer - Cost analyzer used by inliner.
94  class InlineCostAnalyzer {
95    struct ArgInfo {
96    public:
97      unsigned ConstantWeight;
98      unsigned AllocaWeight;
99
100      ArgInfo(unsigned CWeight, unsigned AWeight)
101        : ConstantWeight(CWeight), AllocaWeight(AWeight)
102          {}
103    };
104
105    struct FunctionInfo {
106      CodeMetrics Metrics;
107
108      /// ArgumentWeights - Each formal argument of the function is inspected to
109      /// see if it is used in any contexts where making it a constant or alloca
110      /// would reduce the code size.  If so, we add some value to the argument
111      /// entry here.
112      std::vector<ArgInfo> ArgumentWeights;
113
114      /// analyzeFunction - Add information about the specified function
115      /// to the current structure.
116      void analyzeFunction(Function *F);
117
118      /// NeverInline - Returns true if the function should never be
119      /// inlined into any caller.
120      bool NeverInline();
121    };
122
123    // The Function* for a function can be changed (by ArgumentPromotion);
124    // the ValueMap will update itself when this happens.
125    ValueMap<const Function *, FunctionInfo> CachedFunctionInfo;
126
127    int CountBonusForConstant(Value *V, Constant *C = NULL);
128    int ConstantFunctionBonus(CallSite CS, Constant *C);
129    int getInlineSize(CallSite CS, Function *Callee);
130    int getInlineBonuses(CallSite CS, Function *Callee);
131  public:
132
133    /// getInlineCost - The heuristic used to determine if we should inline the
134    /// function call or not.
135    ///
136    InlineCost getInlineCost(CallSite CS,
137                             SmallPtrSet<const Function *, 16> &NeverInline);
138    /// getCalledFunction - The heuristic used to determine if we should inline
139    /// the function call or not.  The callee is explicitly specified, to allow
140    /// you to calculate the cost of inlining a function via a pointer.  The
141    /// result assumes that the inlined version will always be used.  You should
142    /// weight it yourself in cases where this callee will not always be called.
143    InlineCost getInlineCost(CallSite CS,
144                             Function *Callee,
145                             SmallPtrSet<const Function *, 16> &NeverInline);
146
147    /// getSpecializationBonus - The heuristic used to determine the per-call
148    /// performance boost for using a specialization of Callee with argument
149    /// SpecializedArgNos replaced by a constant.
150    int getSpecializationBonus(Function *Callee,
151             SmallVectorImpl<unsigned> &SpecializedArgNo);
152
153    /// getSpecializationCost - The heuristic used to determine the code-size
154    /// impact of creating a specialized version of Callee with argument
155    /// SpecializedArgNo replaced by a constant.
156    InlineCost getSpecializationCost(Function *Callee,
157               SmallVectorImpl<unsigned> &SpecializedArgNo);
158
159    /// getInlineFudgeFactor - Return a > 1.0 factor if the inliner should use a
160    /// higher threshold to determine if the function call should be inlined.
161    float getInlineFudgeFactor(CallSite CS);
162
163    /// resetCachedFunctionInfo - erase any cached cost info for this function.
164    void resetCachedCostInfo(Function* Caller) {
165      CachedFunctionInfo[Caller] = FunctionInfo();
166    }
167
168    /// growCachedCostInfo - update the cached cost info for Caller after Callee
169    /// has been inlined. If Callee is NULL it means a dead call has been
170    /// eliminated.
171    void growCachedCostInfo(Function* Caller, Function* Callee);
172
173    /// clear - empty the cache of inline costs
174    void clear();
175  };
176
177  /// callIsSmall - If a call is likely to lower to a single target instruction,
178  /// or is otherwise deemed small return true.
179  bool callIsSmall(const Function *Callee);
180}
181
182#endif
183