InlineCost.h revision 36b56886974eae4f9c5ebc96befd3e7bfe5de338 
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/Analysis/CallGraphSCCPass.h"
18#include <cassert>
19#include <climits>
20
21namespace llvm {
22class CallSite;
23class DataLayout;
24class Function;
25class TargetTransformInfo;
26
27namespace InlineConstants {
28  // Various magic constants used to adjust heuristics.
29  const int InstrCost = 5;
30  const int IndirectCallThreshold = 100;
31  const int CallPenalty = 25;
32  const int LastCallToStaticBonus = -15000;
33  const int ColdccPenalty = 2000;
34  const int NoreturnPenalty = 10000;
35  /// Do not inline functions which allocate this many bytes on the stack
36  /// when the caller is recursive.
37  const unsigned TotalAllocaSizeRecursiveCaller = 1024;
38}
39
40/// \brief Represents the cost of inlining a function.
41///
42/// This supports special values for functions which should "always" or
43/// "never" be inlined. Otherwise, the cost represents a unitless amount;
44/// smaller values increase the likelihood of the function being inlined.
45///
46/// Objects of this type also provide the adjusted threshold for inlining
47/// based on the information available for a particular callsite. They can be
48/// directly tested to determine if inlining should occur given the cost and
49/// threshold for this cost metric.
50class InlineCost {
51  enum SentinelValues {
52    AlwaysInlineCost = INT_MIN,
53    NeverInlineCost = INT_MAX
54  };
55
56  /// \brief The estimated cost of inlining this callsite.
57  const int Cost;
58
59  /// \brief The adjusted threshold against which this cost was computed.
60  const int Threshold;
61
62  // Trivial constructor, interesting logic in the factory functions below.
63  InlineCost(int Cost, int Threshold) : Cost(Cost), Threshold(Threshold) {}
64
65public:
66  static InlineCost get(int Cost, int Threshold) {
67    assert(Cost > AlwaysInlineCost && "Cost crosses sentinel value");
68    assert(Cost < NeverInlineCost && "Cost crosses sentinel value");
69    return InlineCost(Cost, Threshold);
70  }
71  static InlineCost getAlways() {
72    return InlineCost(AlwaysInlineCost, 0);
73  }
74  static InlineCost getNever() {
75    return InlineCost(NeverInlineCost, 0);
76  }
77
78  /// \brief Test whether the inline cost is low enough for inlining.
79  LLVM_EXPLICIT operator bool() const {
80    return Cost < Threshold;
81  }
82
83  bool isAlways() const { return Cost == AlwaysInlineCost; }
84  bool isNever() const { return Cost == NeverInlineCost; }
85  bool isVariable() const { return !isAlways() && !isNever(); }
86
87  /// \brief Get the inline cost estimate.
88  /// It is an error to call this on an "always" or "never" InlineCost.
89  int getCost() const {
90    assert(isVariable() && "Invalid access of InlineCost");
91    return Cost;
92  }
93
94  /// \brief Get the cost delta from the threshold for inlining.
95  /// Only valid if the cost is of the variable kind. Returns a negative
96  /// value if the cost is too high to inline.
97  int getCostDelta() const { return Threshold - getCost(); }
98};
99
100/// \brief Cost analyzer used by inliner.
101class InlineCostAnalysis : public CallGraphSCCPass {
102  const TargetTransformInfo *TTI;
103
104public:
105  static char ID;
106
107  InlineCostAnalysis();
108  ~InlineCostAnalysis();
109
110  // Pass interface implementation.
111  void getAnalysisUsage(AnalysisUsage &AU) const override;
112  bool runOnSCC(CallGraphSCC &SCC) override;
113
114  /// \brief Get an InlineCost object representing the cost of inlining this
115  /// callsite.
116  ///
117  /// Note that threshold is passed into this function. Only costs below the
118  /// threshold are computed with any accuracy. The threshold can be used to
119  /// bound the computation necessary to determine whether the cost is
120  /// sufficiently low to warrant inlining.
121  ///
122  /// Also note that calling this function *dynamically* computes the cost of
123  /// inlining the callsite. It is an expensive, heavyweight call.
124  InlineCost getInlineCost(CallSite CS, int Threshold);
125
126  /// \brief Get an InlineCost with the callee explicitly specified.
127  /// This allows you to calculate the cost of inlining a function via a
128  /// pointer. This behaves exactly as the version with no explicit callee
129  /// parameter in all other respects.
130  //
131  //  Note: This is used by out-of-tree passes, please do not remove without
132  //  adding a replacement API.
133  InlineCost getInlineCost(CallSite CS, Function *Callee, int Threshold);
134
135  /// \brief Minimal filter to detect invalid constructs for inlining.
136  bool isInlineViable(Function &Callee);
137};
138
139}
140
141#endif
142