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;
49/// Do not inline functions which allocate this many bytes on the stack
50/// when the caller is recursive.
51const unsigned TotalAllocaSizeRecursiveCaller = 1024;
52}
53
54/// Represents the cost of inlining a function.
55///
56/// This supports special values for functions which should "always" or
57/// "never" be inlined. Otherwise, the cost represents a unitless amount;
58/// smaller values increase the likelihood of the function being inlined.
59///
60/// Objects of this type also provide the adjusted threshold for inlining
61/// based on the information available for a particular callsite. They can be
62/// directly tested to determine if inlining should occur given the cost and
63/// threshold for this cost metric.
64class InlineCost {
65 enum SentinelValues {
66 AlwaysInlineCost = INT_MIN,
67 NeverInlineCost = INT_MAX
68 };
69
70 /// The estimated cost of inlining this callsite.
71 const int Cost;
72
73 /// The adjusted threshold against which this cost was computed.
74 const int Threshold;
75
76 /// Must be set for Always and Never instances.
77 const char *Reason = nullptr;
78
79 // Trivial constructor, interesting logic in the factory functions below.
80 InlineCost(int Cost, int Threshold, const char *Reason = nullptr)
81 : Cost(Cost), Threshold(Threshold), Reason(Reason) {
82 assert((isVariable() || Reason) &&
83 "Reason must be provided for Never or Always");
84 }
85
86public:
87 static InlineCost get(int Cost, int Threshold) {
88 assert(Cost > AlwaysInlineCost && "Cost crosses sentinel value");
89 assert(Cost < NeverInlineCost && "Cost crosses sentinel value");
90 return InlineCost(Cost, Threshold);
91 }
92 static InlineCost getAlways(const char *Reason) {
93 return InlineCost(AlwaysInlineCost, 0, Reason);
94 }
95 static InlineCost getNever(const char *Reason) {
96 return InlineCost(NeverInlineCost, 0, Reason);
97 }
98
99 /// Test whether the inline cost is low enough for inlining.
100 explicit operator bool() const {
101 return Cost < Threshold;
102 }
103
104 bool isAlways() const { return Cost == AlwaysInlineCost; }
105 bool isNever() const { return Cost == NeverInlineCost; }
106 bool isVariable() const { return !isAlways() && !isNever(); }
107
108 /// Get the inline cost estimate.
109 /// It is an error to call this on an "always" or "never" InlineCost.
110 int getCost() const {
111 assert(isVariable() && "Invalid access of InlineCost");
112 return Cost;
113 }
114
115 /// Get the threshold against which the cost was computed
116 int getThreshold() const {
117 assert(isVariable() && "Invalid access of InlineCost");
118 return Threshold;
119 }
120
121 /// Get the reason of Always or Never.
122 const char *getReason() const {
123 assert((Reason || isVariable()) &&
124 "InlineCost reason must be set for Always or Never");
125 return Reason;
126 }
127
128 /// Get the cost delta from the threshold for inlining.
129 /// Only valid if the cost is of the variable kind. Returns a negative
130 /// value if the cost is too high to inline.
131 int getCostDelta() const { return Threshold - getCost(); }
132};
133
134/// InlineResult is basically true or false. For false results the message
135/// describes a reason why it is decided not to inline.
136struct InlineResult {
137 const char *message = nullptr;
138 InlineResult(bool result, const char *message = nullptr)
139 : message(result ? nullptr : (message ? message : "cost > threshold")) {}
140 InlineResult(const char *message = nullptr) : message(message) {}
141 operator bool() const { return !message; }
142 operator const char *() const { return message; }
143};
144
145/// Thresholds to tune inline cost analysis. The inline cost analysis decides
146/// the condition to apply a threshold and applies it. Otherwise,
147/// DefaultThreshold is used. If a threshold is Optional, it is applied only
148/// when it has a valid value. Typically, users of inline cost analysis
149/// obtain an InlineParams object through one of the \c getInlineParams methods
150/// and pass it to \c getInlineCost. Some specialized versions of inliner
151/// (such as the pre-inliner) might have custom logic to compute \c InlineParams
152/// object.
153
154struct InlineParams {
155 /// The default threshold to start with for a callee.
156 int DefaultThreshold;
157
158 /// Threshold to use for callees with inline hint.
159 Optional<int> HintThreshold;
160
161 /// Threshold to use for cold callees.
162 Optional<int> ColdThreshold;
163
164 /// Threshold to use when the caller is optimized for size.
165 Optional<int> OptSizeThreshold;
166
167 /// Threshold to use when the caller is optimized for minsize.
168 Optional<int> OptMinSizeThreshold;
169
170 /// Threshold to use when the callsite is considered hot.
171 Optional<int> HotCallSiteThreshold;
172
173 /// Threshold to use when the callsite is considered hot relative to function
174 /// entry.
175 Optional<int> LocallyHotCallSiteThreshold;
176
177 /// Threshold to use when the callsite is considered cold.
178 Optional<int> ColdCallSiteThreshold;
179
180 /// Compute inline cost even when the cost has exceeded the threshold.
181 Optional<bool> ComputeFullInlineCost;
182};
183
184/// Generate the parameters to tune the inline cost analysis based only on the
185/// commandline options.
186InlineParams getInlineParams();
187
188/// Generate the parameters to tune the inline cost analysis based on command
189/// line options. If -inline-threshold option is not explicitly passed,
190/// \p Threshold is used as the default threshold.
191InlineParams getInlineParams(int Threshold);
192
193/// Generate the parameters to tune the inline cost analysis based on command
194/// line options. If -inline-threshold option is not explicitly passed,
195/// the default threshold is computed from \p OptLevel and \p SizeOptLevel.
196/// An \p OptLevel value above 3 is considered an aggressive optimization mode.
197/// \p SizeOptLevel of 1 corresponds to the -Os flag and 2 corresponds to
198/// the -Oz flag.
199InlineParams getInlineParams(unsigned OptLevel, unsigned SizeOptLevel);
200
201/// Return the cost associated with a callsite, including parameter passing
202/// and the call/return instruction.
203int getCallsiteCost(CallSite CS, const DataLayout &DL);
204
205/// Get an InlineCost object representing the cost of inlining this
206/// callsite.
207///
208/// Note that a default threshold is passed into this function. This threshold
209/// could be modified based on callsite's properties and only costs below this
210/// new threshold are computed with any accuracy. The new threshold can be
211/// used to bound the computation necessary to determine whether the cost is
212/// sufficiently low to warrant inlining.
213///
214/// Also note that calling this function *dynamically* computes the cost of
215/// inlining the callsite. It is an expensive, heavyweight call.
216InlineCost getInlineCost(
217 CallSite CS, const InlineParams &Params, TargetTransformInfo &CalleeTTI,
218 std::function<AssumptionCache &(Function &)> &GetAssumptionCache,
219 Optional<function_ref<BlockFrequencyInfo &(Function &)>> GetBFI,
220 ProfileSummaryInfo *PSI, OptimizationRemarkEmitter *ORE = nullptr);
221
222/// Get an InlineCost with the callee explicitly specified.
223/// This allows you to calculate the cost of inlining a function via a
224/// pointer. This behaves exactly as the version with no explicit callee
225/// parameter in all other respects.
226//
227InlineCost
228getInlineCost(CallSite CS, Function *Callee, const InlineParams &Params,
229 TargetTransformInfo &CalleeTTI,
230 std::function<AssumptionCache &(Function &)> &GetAssumptionCache,
231 Optional<function_ref<BlockFrequencyInfo &(Function &)>> GetBFI,
232 ProfileSummaryInfo *PSI, OptimizationRemarkEmitter *ORE);
233
234/// Minimal filter to detect invalid constructs for inlining.
235bool isInlineViable(Function &Callee);
236}
237
238#endif
239