InlineCost.h revision 42c7d23c6d56e0743169d94025264eaf17eb799d 
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 = 500;
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    struct FunctionInfo {
105      CodeMetrics Metrics;
106
107      /// ArgumentWeights - Each formal argument of the function is inspected to
108      /// see if it is used in any contexts where making it a constant or alloca
109      /// would reduce the code size.  If so, we add some value to the argument
110      /// entry here.
111      std::vector<ArgInfo> ArgumentWeights;
112
113      /// CountCodeReductionForConstant - Figure out an approximation for how
114      /// many instructions will be constant folded if the specified value is
115      /// constant.
116      unsigned CountCodeReductionForConstant(Value *V);
117
118      /// CountCodeReductionForAlloca - Figure out an approximation of how much
119      /// smaller the function will be if it is inlined into a context where an
120      /// argument becomes an alloca.
121      ///
122      unsigned CountCodeReductionForAlloca(Value *V);
123
124      /// analyzeFunction - Add information about the specified function
125      /// to the current structure.
126      void analyzeFunction(Function *F);
127
128      /// NeverInline - Returns true if the function should never be
129      /// inlined into any caller.
130      bool NeverInline();
131    };
132
133    // The Function* for a function can be changed (by ArgumentPromotion);
134    // the ValueMap will update itself when this happens.
135    ValueMap<const Function *, FunctionInfo> CachedFunctionInfo;
136
137  public:
138
139    /// getInlineCost - The heuristic used to determine if we should inline the
140    /// function call or not.
141    ///
142    InlineCost getInlineCost(CallSite CS,
143                             SmallPtrSet<const Function *, 16> &NeverInline);
144    /// getCalledFunction - The heuristic used to determine if we should inline
145    /// the function call or not.  The callee is explicitly specified, to allow
146    /// you to calculate the cost of inlining a function via a pointer.  The
147    /// result assumes that the inlined version will always be used.  You should
148    /// weight it yourself in cases where this callee will not always be called.
149    InlineCost getInlineCost(CallSite CS,
150                             Function *Callee,
151                             SmallPtrSet<const Function *, 16> &NeverInline);
152
153    /// getInlineFudgeFactor - Return a > 1.0 factor if the inliner should use a
154    /// higher threshold to determine if the function call should be inlined.
155    float getInlineFudgeFactor(CallSite CS);
156
157    /// resetCachedFunctionInfo - erase any cached cost info for this function.
158    void resetCachedCostInfo(Function* Caller) {
159      CachedFunctionInfo[Caller] = FunctionInfo();
160    }
161
162    /// growCachedCostInfo - update the cached cost info for Caller after Callee
163    /// has been inlined. If Callee is NULL it means a dead call has been
164    /// eliminated.
165    void growCachedCostInfo(Function* Caller, Function* Callee);
166
167    /// clear - empty the cache of inline costs
168    void clear();
169  };
170
171  /// callIsSmall - If a call is likely to lower to a single target instruction,
172  /// or is otherwise deemed small return true.
173  bool callIsSmall(const Function *Callee);
174}
175
176#endif
177