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/AssumptionCache.h"
18#include "llvm/Analysis/CallGraphSCCPass.h"
19#include "llvm/Analysis/OptimizationRemarkEmitter.h"
20#include <cassert>
21#include <climits>
22
23namespace llvm {
24class AssumptionCacheTracker;
25class BlockFrequencyInfo;
26class CallSite;
27class DataLayout;
28class Function;
29class ProfileSummaryInfo;
30class TargetTransformInfo;
31
32namespace InlineConstants {
33// Various thresholds used by inline cost analysis.
34/// Use when optsize (-Os) is specified.
35const int OptSizeThreshold = 50;
36
37/// Use when minsize (-Oz) is specified.
38const int OptMinSizeThreshold = 5;
39
40/// Use when -O3 is specified.
41const int OptAggressiveThreshold = 250;
42
43// Various magic constants used to adjust heuristics.
44const int InstrCost = 5;
45const int IndirectCallThreshold = 100;
46const int CallPenalty = 25;
47const int LastCallToStaticBonus = 15000;
48const int ColdccPenalty = 2000;
49const int NoreturnPenalty = 10000;
50/// Do not inline functions which allocate this many bytes on the stack
51/// when the caller is recursive.
52const unsigned TotalAllocaSizeRecursiveCaller = 1024;
53}
54
55/// \brief Represents the cost of inlining a function.
56///
57/// This supports special values for functions which should "always" or
58/// "never" be inlined. Otherwise, the cost represents a unitless amount;
59/// smaller values increase the likelihood of the function being inlined.
60///
61/// Objects of this type also provide the adjusted threshold for inlining
62/// based on the information available for a particular callsite. They can be
63/// directly tested to determine if inlining should occur given the cost and
64/// threshold for this cost metric.
65class InlineCost {
66  enum SentinelValues {
67    AlwaysInlineCost = INT_MIN,
68    NeverInlineCost = INT_MAX
69  };
70
71  /// \brief The estimated cost of inlining this callsite.
72  const int Cost;
73
74  /// \brief The adjusted threshold against which this cost was computed.
75  const int Threshold;
76
77  // Trivial constructor, interesting logic in the factory functions below.
78  InlineCost(int Cost, int Threshold) : Cost(Cost), Threshold(Threshold) {}
79
80public:
81  static InlineCost get(int Cost, int Threshold) {
82    assert(Cost > AlwaysInlineCost && "Cost crosses sentinel value");
83    assert(Cost < NeverInlineCost && "Cost crosses sentinel value");
84    return InlineCost(Cost, Threshold);
85  }
86  static InlineCost getAlways() {
87    return InlineCost(AlwaysInlineCost, 0);
88  }
89  static InlineCost getNever() {
90    return InlineCost(NeverInlineCost, 0);
91  }
92
93  /// \brief Test whether the inline cost is low enough for inlining.
94  explicit operator bool() const {
95    return Cost < Threshold;
96  }
97
98  bool isAlways() const { return Cost == AlwaysInlineCost; }
99  bool isNever() const { return Cost == NeverInlineCost; }
100  bool isVariable() const { return !isAlways() && !isNever(); }
101
102  /// \brief Get the inline cost estimate.
103  /// It is an error to call this on an "always" or "never" InlineCost.
104  int getCost() const {
105    assert(isVariable() && "Invalid access of InlineCost");
106    return Cost;
107  }
108
109  /// \brief Get the threshold against which the cost was computed
110  int getThreshold() const {
111    assert(isVariable() && "Invalid access of InlineCost");
112    return Threshold;
113  }
114
115  /// \brief Get the cost delta from the threshold for inlining.
116  /// Only valid if the cost is of the variable kind. Returns a negative
117  /// value if the cost is too high to inline.
118  int getCostDelta() const { return Threshold - getCost(); }
119};
120
121/// Thresholds to tune inline cost analysis. The inline cost analysis decides
122/// the condition to apply a threshold and applies it. Otherwise,
123/// DefaultThreshold is used. If a threshold is Optional, it is applied only
124/// when it has a valid value. Typically, users of inline cost analysis
125/// obtain an InlineParams object through one of the \c getInlineParams methods
126/// and pass it to \c getInlineCost. Some specialized versions of inliner
127/// (such as the pre-inliner) might have custom logic to compute \c InlineParams
128/// object.
129
130struct InlineParams {
131  /// The default threshold to start with for a callee.
132  int DefaultThreshold;
133
134  /// Threshold to use for callees with inline hint.
135  Optional<int> HintThreshold;
136
137  /// Threshold to use for cold callees.
138  Optional<int> ColdThreshold;
139
140  /// Threshold to use when the caller is optimized for size.
141  Optional<int> OptSizeThreshold;
142
143  /// Threshold to use when the caller is optimized for minsize.
144  Optional<int> OptMinSizeThreshold;
145
146  /// Threshold to use when the callsite is considered hot.
147  Optional<int> HotCallSiteThreshold;
148
149  /// Threshold to use when the callsite is considered hot relative to function
150  /// entry.
151  Optional<int> LocallyHotCallSiteThreshold;
152
153  /// Threshold to use when the callsite is considered cold.
154  Optional<int> ColdCallSiteThreshold;
155
156  /// Compute inline cost even when the cost has exceeded the threshold.
157  Optional<bool> ComputeFullInlineCost;
158};
159
160/// Generate the parameters to tune the inline cost analysis based only on the
161/// commandline options.
162InlineParams getInlineParams();
163
164/// Generate the parameters to tune the inline cost analysis based on command
165/// line options. If -inline-threshold option is not explicitly passed,
166/// \p Threshold is used as the default threshold.
167InlineParams getInlineParams(int Threshold);
168
169/// Generate the parameters to tune the inline cost analysis based on command
170/// line options. If -inline-threshold option is not explicitly passed,
171/// the default threshold is computed from \p OptLevel and \p SizeOptLevel.
172/// An \p OptLevel value above 3 is considered an aggressive optimization mode.
173/// \p SizeOptLevel of 1 corresponds to the the -Os flag and 2 corresponds to
174/// the -Oz flag.
175InlineParams getInlineParams(unsigned OptLevel, unsigned SizeOptLevel);
176
177/// Return the cost associated with a callsite, including parameter passing
178/// and the call/return instruction.
179int getCallsiteCost(CallSite CS, const DataLayout &DL);
180
181/// \brief Get an InlineCost object representing the cost of inlining this
182/// callsite.
183///
184/// Note that a default threshold is passed into this function. This threshold
185/// could be modified based on callsite's properties and only costs below this
186/// new threshold are computed with any accuracy. The new threshold can be
187/// used to bound the computation necessary to determine whether the cost is
188/// sufficiently low to warrant inlining.
189///
190/// Also note that calling this function *dynamically* computes the cost of
191/// inlining the callsite. It is an expensive, heavyweight call.
192InlineCost getInlineCost(
193    CallSite CS, const InlineParams &Params, TargetTransformInfo &CalleeTTI,
194    std::function<AssumptionCache &(Function &)> &GetAssumptionCache,
195    Optional<function_ref<BlockFrequencyInfo &(Function &)>> GetBFI,
196    ProfileSummaryInfo *PSI, OptimizationRemarkEmitter *ORE = nullptr);
197
198/// \brief Get an InlineCost with the callee explicitly specified.
199/// This allows you to calculate the cost of inlining a function via a
200/// pointer. This behaves exactly as the version with no explicit callee
201/// parameter in all other respects.
202//
203InlineCost
204getInlineCost(CallSite CS, Function *Callee, const InlineParams &Params,
205              TargetTransformInfo &CalleeTTI,
206              std::function<AssumptionCache &(Function &)> &GetAssumptionCache,
207              Optional<function_ref<BlockFrequencyInfo &(Function &)>> GetBFI,
208              ProfileSummaryInfo *PSI, OptimizationRemarkEmitter *ORE);
209
210/// \brief Minimal filter to detect invalid constructs for inlining.
211bool isInlineViable(Function &Callee);
212}
213
214#endif
215