1 //===- InlineCost.h - Cost analysis for inliner -----------------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements heuristics for inlining decisions.
12 //===----------------------------------------------------------------------===//
14 #ifndef LLVM_ANALYSIS_INLINECOST_H
15 #define LLVM_ANALYSIS_INLINECOST_H
17 #include "llvm/Analysis/AssumptionCache.h"
18 #include "llvm/Analysis/CallGraphSCCPass.h"
19 #include "llvm/Analysis/OptimizationRemarkEmitter.h"
24 class AssumptionCacheTracker;
25 class BlockFrequencyInfo;
29 class ProfileSummaryInfo;
30 class TargetTransformInfo;
32 namespace InlineConstants {
33 // Various thresholds used by inline cost analysis.
34 /// Use when optsize (-Os) is specified.
35 const int OptSizeThreshold = 50;
37 /// Use when minsize (-Oz) is specified.
38 const int OptMinSizeThreshold = 5;
40 /// Use when -O3 is specified.
41 const int OptAggressiveThreshold = 250;
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 /// Do not inline functions which allocate this many bytes on the stack
50 /// when the caller is recursive.
51 const unsigned TotalAllocaSizeRecursiveCaller = 1024;
54 /// Represents the cost of inlining a function.
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.
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.
66 AlwaysInlineCost = INT_MIN,
67 NeverInlineCost = INT_MAX
70 /// The estimated cost of inlining this callsite.
73 /// The adjusted threshold against which this cost was computed.
76 /// Must be set for Always and Never instances.
77 const char *Reason = nullptr;
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");
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);
92 static InlineCost getAlways(const char *Reason) {
93 return InlineCost(AlwaysInlineCost, 0, Reason);
95 static InlineCost getNever(const char *Reason) {
96 return InlineCost(NeverInlineCost, 0, Reason);
99 /// Test whether the inline cost is low enough for inlining.
100 explicit operator bool() const {
101 return Cost < Threshold;
104 bool isAlways() const { return Cost == AlwaysInlineCost; }
105 bool isNever() const { return Cost == NeverInlineCost; }
106 bool isVariable() const { return !isAlways() && !isNever(); }
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");
115 /// Get the threshold against which the cost was computed
116 int getThreshold() const {
117 assert(isVariable() && "Invalid access of InlineCost");
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");
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(); }
134 /// InlineResult is basically true or false. For false results the message
135 /// describes a reason why it is decided not to inline.
136 struct 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; }
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
154 struct InlineParams {
155 /// The default threshold to start with for a callee.
156 int DefaultThreshold;
158 /// Threshold to use for callees with inline hint.
159 Optional<int> HintThreshold;
161 /// Threshold to use for cold callees.
162 Optional<int> ColdThreshold;
164 /// Threshold to use when the caller is optimized for size.
165 Optional<int> OptSizeThreshold;
167 /// Threshold to use when the caller is optimized for minsize.
168 Optional<int> OptMinSizeThreshold;
170 /// Threshold to use when the callsite is considered hot.
171 Optional<int> HotCallSiteThreshold;
173 /// Threshold to use when the callsite is considered hot relative to function
175 Optional<int> LocallyHotCallSiteThreshold;
177 /// Threshold to use when the callsite is considered cold.
178 Optional<int> ColdCallSiteThreshold;
180 /// Compute inline cost even when the cost has exceeded the threshold.
181 Optional<bool> ComputeFullInlineCost;
184 /// Generate the parameters to tune the inline cost analysis based only on the
185 /// commandline options.
186 InlineParams getInlineParams();
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.
191 InlineParams getInlineParams(int Threshold);
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
199 InlineParams getInlineParams(unsigned OptLevel, unsigned SizeOptLevel);
201 /// Return the cost associated with a callsite, including parameter passing
202 /// and the call/return instruction.
203 int getCallsiteCost(CallSite CS, const DataLayout &DL);
205 /// Get an InlineCost object representing the cost of inlining this
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.
214 /// Also note that calling this function *dynamically* computes the cost of
215 /// inlining the callsite. It is an expensive, heavyweight call.
216 InlineCost 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);
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.
228 getInlineCost(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);
234 /// Minimal filter to detect invalid constructs for inlining.
235 bool isInlineViable(Function &Callee);