InlineCost.h revision 220d2d7b50ddbbab1fe5e57fe9f39e72ef430a89 
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 "llvm/Function.h"
18#include "llvm/ADT/DenseMap.h"
19#include "llvm/ADT/ValueMap.h"
20#include "llvm/Analysis/CodeMetrics.h"
21#include <cassert>
22#include <climits>
23#include <vector>
24
25namespace llvm {
26
27  class CallSite;
28  template<class PtrType, unsigned SmallSize>
29  class SmallPtrSet;
30  class TargetData;
31
32  namespace InlineConstants {
33    // Various magic constants used to adjust heuristics.
34    const int InstrCost = 5;
35    const int IndirectCallBonus = -100;
36    const int CallPenalty = 25;
37    const int LastCallToStaticBonus = -15000;
38    const int ColdccPenalty = 2000;
39    const int NoreturnPenalty = 10000;
40  }
41
42  /// InlineCost - Represent the cost of inlining a function. This
43  /// supports special values for functions which should "always" or
44  /// "never" be inlined. Otherwise, the cost represents a unitless
45  /// amount; smaller values increase the likelihood of the function
46  /// being inlined.
47  class InlineCost {
48    enum Kind {
49      Value,
50      Always,
51      Never
52    };
53
54    // This is a do-it-yourself implementation of
55    //   int Cost : 30;
56    //   unsigned Type : 2;
57    // We used to use bitfields, but they were sometimes miscompiled (PR3822).
58    enum { TYPE_BITS = 2 };
59    enum { COST_BITS = unsigned(sizeof(unsigned)) * CHAR_BIT - TYPE_BITS };
60    unsigned TypedCost; // int Cost : COST_BITS; unsigned Type : TYPE_BITS;
61
62    Kind getType() const {
63      return Kind(TypedCost >> COST_BITS);
64    }
65
66    int getCost() const {
67      // Sign-extend the bottom COST_BITS bits.
68      return (int(TypedCost << TYPE_BITS)) >> TYPE_BITS;
69    }
70
71    InlineCost(int C, int T) {
72      TypedCost = (unsigned(C << TYPE_BITS) >> TYPE_BITS) | (T << COST_BITS);
73      assert(getCost() == C && "Cost exceeds InlineCost precision");
74    }
75  public:
76    static InlineCost get(int Cost) { return InlineCost(Cost, Value); }
77    static InlineCost getAlways() { return InlineCost(0, Always); }
78    static InlineCost getNever() { return InlineCost(0, Never); }
79
80    bool isVariable() const { return getType() == Value; }
81    bool isAlways() const { return getType() == Always; }
82    bool isNever() const { return getType() == Never; }
83
84    /// getValue() - Return a "variable" inline cost's amount. It is
85    /// an error to call this on an "always" or "never" InlineCost.
86    int getValue() const {
87      assert(getType() == Value && "Invalid access of InlineCost");
88      return getCost();
89    }
90  };
91
92  /// InlineCostAnalyzer - Cost analyzer used by inliner.
93  class InlineCostAnalyzer {
94    struct ArgInfo {
95    public:
96      unsigned ConstantWeight;
97      unsigned AllocaWeight;
98
99      ArgInfo(unsigned CWeight, unsigned AWeight)
100        : ConstantWeight(CWeight), AllocaWeight(AWeight)
101          {}
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      /// PointerArgPairWeights - Weights to use when giving an inline bonus to
114      /// a call site due to correlated pairs of pointers.
115      DenseMap<std::pair<unsigned, unsigned>, unsigned> PointerArgPairWeights;
116
117      /// countCodeReductionForConstant - Figure out an approximation for how
118      /// many instructions will be constant folded if the specified value is
119      /// constant.
120      unsigned countCodeReductionForConstant(const CodeMetrics &Metrics,
121                                             Value *V);
122
123      /// countCodeReductionForAlloca - Figure out an approximation of how much
124      /// smaller the function will be if it is inlined into a context where an
125      /// argument becomes an alloca.
126      unsigned countCodeReductionForAlloca(const CodeMetrics &Metrics,
127                                           Value *V);
128
129      /// countCodeReductionForPointerPair - Count the bonus to apply to an
130      /// inline call site where a pair of arguments are pointers and one
131      /// argument is a constant offset from the other. The idea is to
132      /// recognize a common C++ idiom where a begin and end iterator are
133      /// actually pointers, and many operations on the pair of them will be
134      /// constants if the function is called with arguments that have
135      /// a constant offset.
136      void countCodeReductionForPointerPair(
137          const CodeMetrics &Metrics,
138          DenseMap<Value *, unsigned> &PointerArgs,
139          Value *V, unsigned ArgIdx);
140
141      /// analyzeFunction - Add information about the specified function
142      /// to the current structure.
143      void analyzeFunction(Function *F, const TargetData *TD);
144
145      /// NeverInline - Returns true if the function should never be
146      /// inlined into any caller.
147      bool NeverInline();
148    };
149
150    // The Function* for a function can be changed (by ArgumentPromotion);
151    // the ValueMap will update itself when this happens.
152    ValueMap<const Function *, FunctionInfo> CachedFunctionInfo;
153
154    // TargetData if available, or null.
155    const TargetData *TD;
156
157    int CountBonusForConstant(Value *V, Constant *C = NULL);
158    int ConstantFunctionBonus(CallSite CS, Constant *C);
159    int getInlineSize(CallSite CS, Function *Callee);
160    int getInlineBonuses(CallSite CS, Function *Callee);
161  public:
162    InlineCostAnalyzer(): TD(0) {}
163
164    void setTargetData(const TargetData *TData) { TD = TData; }
165
166    /// getInlineCost - The heuristic used to determine if we should inline the
167    /// function call or not.
168    ///
169    InlineCost getInlineCost(CallSite CS,
170                             SmallPtrSet<const Function *, 16> &NeverInline);
171    /// getCalledFunction - The heuristic used to determine if we should inline
172    /// the function call or not.  The callee is explicitly specified, to allow
173    /// you to calculate the cost of inlining a function via a pointer.  The
174    /// result assumes that the inlined version will always be used.  You should
175    /// weight it yourself in cases where this callee will not always be called.
176    InlineCost getInlineCost(CallSite CS,
177                             Function *Callee,
178                             SmallPtrSet<const Function *, 16> &NeverInline);
179
180    /// getInlineFudgeFactor - Return a > 1.0 factor if the inliner should use a
181    /// higher threshold to determine if the function call should be inlined.
182    float getInlineFudgeFactor(CallSite CS);
183
184    /// resetCachedFunctionInfo - erase any cached cost info for this function.
185    void resetCachedCostInfo(Function* Caller) {
186      CachedFunctionInfo[Caller] = FunctionInfo();
187    }
188
189    /// growCachedCostInfo - update the cached cost info for Caller after Callee
190    /// has been inlined. If Callee is NULL it means a dead call has been
191    /// eliminated.
192    void growCachedCostInfo(Function* Caller, Function* Callee);
193
194    /// clear - empty the cache of inline costs
195    void clear();
196  };
197
198  /// callIsSmall - If a call is likely to lower to a single target instruction,
199  /// or is otherwise deemed small return true.
200  bool callIsSmall(const Function *Callee);
201}
202
203#endif
204