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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 :
23 : namespace llvm {
24 : class AssumptionCacheTracker;
25 : class BlockFrequencyInfo;
26 : class CallSite;
27 : class DataLayout;
28 : class Function;
29 : class ProfileSummaryInfo;
30 : class TargetTransformInfo;
31 :
32 : namespace InlineConstants {
33 : // Various thresholds used by inline cost analysis.
34 : /// Use when optsize (-Os) is specified.
35 : const int OptSizeThreshold = 50;
36 :
37 : /// Use when minsize (-Oz) is specified.
38 : const int OptMinSizeThreshold = 5;
39 :
40 : /// Use when -O3 is specified.
41 : const int OptAggressiveThreshold = 250;
42 :
43 : // Various magic constants used to adjust heuristics.
44 : const int InstrCost = 5;
45 : const int IndirectCallThreshold = 100;
46 : const int CallPenalty = 25;
47 : const int LastCallToStaticBonus = 15000;
48 : const int ColdccPenalty = 2000;
49 : const int NoreturnPenalty = 10000;
50 : /// Do not inline functions which allocate this many bytes on the stack
51 : /// when the caller is recursive.
52 : const unsigned TotalAllocaSizeRecursiveCaller = 1024;
53 : }
54 :
55 : /// 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.
65 : class InlineCost {
66 : enum SentinelValues {
67 : AlwaysInlineCost = INT_MIN,
68 : NeverInlineCost = INT_MAX
69 : };
70 :
71 : /// The estimated cost of inlining this callsite.
72 : const int Cost;
73 :
74 : /// The adjusted threshold against which this cost was computed.
75 : const int Threshold;
76 :
77 : /// Must be set for Always and Never instances.
78 : const char *Reason = nullptr;
79 :
80 : // Trivial constructor, interesting logic in the factory functions below.
81 : InlineCost(int Cost, int Threshold, const char *Reason = nullptr)
82 : : Cost(Cost), Threshold(Threshold), Reason(Reason) {
83 : assert((isVariable() || Reason) &&
84 : "Reason must be provided for Never or Always");
85 : }
86 :
87 : public:
88 : static InlineCost get(int Cost, int Threshold) {
89 : assert(Cost > AlwaysInlineCost && "Cost crosses sentinel value");
90 : assert(Cost < NeverInlineCost && "Cost crosses sentinel value");
91 : return InlineCost(Cost, Threshold);
92 : }
93 : static InlineCost getAlways(const char *Reason) {
94 : return InlineCost(AlwaysInlineCost, 0, Reason);
95 : }
96 : static InlineCost getNever(const char *Reason) {
97 : return InlineCost(NeverInlineCost, 0, Reason);
98 : }
99 :
100 : /// Test whether the inline cost is low enough for inlining.
101 0 : explicit operator bool() const {
102 0 : return Cost < Threshold;
103 : }
104 :
105 0 : bool isAlways() const { return Cost == AlwaysInlineCost; }
106 0 : bool isNever() const { return Cost == NeverInlineCost; }
107 : bool isVariable() const { return !isAlways() && !isNever(); }
108 :
109 : /// Get the inline cost estimate.
110 : /// It is an error to call this on an "always" or "never" InlineCost.
111 0 : int getCost() const {
112 : assert(isVariable() && "Invalid access of InlineCost");
113 0 : return Cost;
114 : }
115 :
116 : /// Get the threshold against which the cost was computed
117 0 : int getThreshold() const {
118 : assert(isVariable() && "Invalid access of InlineCost");
119 0 : return Threshold;
120 : }
121 :
122 : /// Get the reason of Always or Never.
123 0 : const char *getReason() const {
124 : assert((Reason || isVariable()) &&
125 : "InlineCost reason must be set for Always or Never");
126 0 : return Reason;
127 : }
128 :
129 : /// Get the cost delta from the threshold for inlining.
130 : /// Only valid if the cost is of the variable kind. Returns a negative
131 : /// value if the cost is too high to inline.
132 0 : int getCostDelta() const { return Threshold - getCost(); }
133 : };
134 :
135 : /// InlineResult is basically true or false. For false results the message
136 : /// describes a reason why it is decided not to inline.
137 : struct InlineResult {
138 : const char *message = nullptr;
139 : InlineResult(bool result, const char *message = nullptr)
140 215300 : : message(result ? nullptr : (message ? message : "cost > threshold")) {}
141 18196401 : InlineResult(const char *message = nullptr) : message(message) {}
142 31 : operator bool() const { return !message; }
143 0 : operator const char *() const { return message; }
144 : };
145 :
146 : /// Thresholds to tune inline cost analysis. The inline cost analysis decides
147 : /// the condition to apply a threshold and applies it. Otherwise,
148 : /// DefaultThreshold is used. If a threshold is Optional, it is applied only
149 : /// when it has a valid value. Typically, users of inline cost analysis
150 : /// obtain an InlineParams object through one of the \c getInlineParams methods
151 : /// and pass it to \c getInlineCost. Some specialized versions of inliner
152 : /// (such as the pre-inliner) might have custom logic to compute \c InlineParams
153 : /// object.
154 :
155 103 : struct InlineParams {
156 : /// The default threshold to start with for a callee.
157 : int DefaultThreshold;
158 :
159 : /// Threshold to use for callees with inline hint.
160 : Optional<int> HintThreshold;
161 :
162 : /// Threshold to use for cold callees.
163 : Optional<int> ColdThreshold;
164 :
165 : /// Threshold to use when the caller is optimized for size.
166 : Optional<int> OptSizeThreshold;
167 :
168 : /// Threshold to use when the caller is optimized for minsize.
169 : Optional<int> OptMinSizeThreshold;
170 :
171 : /// Threshold to use when the callsite is considered hot.
172 : Optional<int> HotCallSiteThreshold;
173 :
174 : /// Threshold to use when the callsite is considered hot relative to function
175 : /// entry.
176 : Optional<int> LocallyHotCallSiteThreshold;
177 :
178 : /// Threshold to use when the callsite is considered cold.
179 : Optional<int> ColdCallSiteThreshold;
180 :
181 : /// Compute inline cost even when the cost has exceeded the threshold.
182 : Optional<bool> ComputeFullInlineCost;
183 : };
184 :
185 : /// Generate the parameters to tune the inline cost analysis based only on the
186 : /// commandline options.
187 : InlineParams getInlineParams();
188 :
189 : /// Generate the parameters to tune the inline cost analysis based on command
190 : /// line options. If -inline-threshold option is not explicitly passed,
191 : /// \p Threshold is used as the default threshold.
192 : InlineParams getInlineParams(int Threshold);
193 :
194 : /// Generate the parameters to tune the inline cost analysis based on command
195 : /// line options. If -inline-threshold option is not explicitly passed,
196 : /// the default threshold is computed from \p OptLevel and \p SizeOptLevel.
197 : /// An \p OptLevel value above 3 is considered an aggressive optimization mode.
198 : /// \p SizeOptLevel of 1 corresponds to the -Os flag and 2 corresponds to
199 : /// the -Oz flag.
200 : InlineParams getInlineParams(unsigned OptLevel, unsigned SizeOptLevel);
201 :
202 : /// Return the cost associated with a callsite, including parameter passing
203 : /// and the call/return instruction.
204 : int getCallsiteCost(CallSite CS, const DataLayout &DL);
205 :
206 : /// Get an InlineCost object representing the cost of inlining this
207 : /// callsite.
208 : ///
209 : /// Note that a default threshold is passed into this function. This threshold
210 : /// could be modified based on callsite's properties and only costs below this
211 : /// new threshold are computed with any accuracy. The new threshold can be
212 : /// used to bound the computation necessary to determine whether the cost is
213 : /// sufficiently low to warrant inlining.
214 : ///
215 : /// Also note that calling this function *dynamically* computes the cost of
216 : /// inlining the callsite. It is an expensive, heavyweight call.
217 : InlineCost getInlineCost(
218 : CallSite CS, const InlineParams &Params, TargetTransformInfo &CalleeTTI,
219 : std::function<AssumptionCache &(Function &)> &GetAssumptionCache,
220 : Optional<function_ref<BlockFrequencyInfo &(Function &)>> GetBFI,
221 : ProfileSummaryInfo *PSI, OptimizationRemarkEmitter *ORE = nullptr);
222 :
223 : /// Get an InlineCost with the callee explicitly specified.
224 : /// This allows you to calculate the cost of inlining a function via a
225 : /// pointer. This behaves exactly as the version with no explicit callee
226 : /// parameter in all other respects.
227 : //
228 : InlineCost
229 : getInlineCost(CallSite CS, Function *Callee, const InlineParams &Params,
230 : TargetTransformInfo &CalleeTTI,
231 : std::function<AssumptionCache &(Function &)> &GetAssumptionCache,
232 : Optional<function_ref<BlockFrequencyInfo &(Function &)>> GetBFI,
233 : ProfileSummaryInfo *PSI, OptimizationRemarkEmitter *ORE);
234 :
235 : /// Minimal filter to detect invalid constructs for inlining.
236 : bool isInlineViable(Function &Callee);
237 : }
238 :
239 : #endif
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