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 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;
55 /// \brief Represents the cost of inlining a function.
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.
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.
67 AlwaysInlineCost = INT_MIN,
68 NeverInlineCost = INT_MAX
71 /// \brief The estimated cost of inlining this callsite.
74 /// \brief The adjusted threshold against which this cost was computed.
77 // Trivial constructor, interesting logic in the factory functions below.
78 InlineCost(int Cost, int Threshold) : Cost(Cost), Threshold(Threshold) {}
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);
86 static InlineCost getAlways() {
87 return InlineCost(AlwaysInlineCost, 0);
89 static InlineCost getNever() {
90 return InlineCost(NeverInlineCost, 0);
93 /// \brief Test whether the inline cost is low enough for inlining.
94 explicit operator bool() const {
95 return Cost < Threshold;
98 bool isAlways() const { return Cost == AlwaysInlineCost; }
99 bool isNever() const { return Cost == NeverInlineCost; }
100 bool isVariable() const { return !isAlways() && !isNever(); }
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");
109 /// \brief Get the threshold against which the cost was computed
110 int getThreshold() const {
111 assert(isVariable() && "Invalid access of InlineCost");
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(); }
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
130 struct InlineParams {
131 /// The default threshold to start with for a callee.
132 int DefaultThreshold;
134 /// Threshold to use for callees with inline hint.
135 Optional<int> HintThreshold;
137 /// Threshold to use for cold callees.
138 Optional<int> ColdThreshold;
140 /// Threshold to use when the caller is optimized for size.
141 Optional<int> OptSizeThreshold;
143 /// Threshold to use when the caller is optimized for minsize.
144 Optional<int> OptMinSizeThreshold;
146 /// Threshold to use when the callsite is considered hot.
147 Optional<int> HotCallSiteThreshold;
149 /// Threshold to use when the callsite is considered hot relative to function
151 Optional<int> LocallyHotCallSiteThreshold;
153 /// Threshold to use when the callsite is considered cold.
154 Optional<int> ColdCallSiteThreshold;
156 /// Compute inline cost even when the cost has exceeded the threshold.
157 Optional<bool> ComputeFullInlineCost;
160 /// Generate the parameters to tune the inline cost analysis based only on the
161 /// commandline options.
162 InlineParams getInlineParams();
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.
167 InlineParams getInlineParams(int Threshold);
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
175 InlineParams getInlineParams(unsigned OptLevel, unsigned SizeOptLevel);
177 /// Return the cost associated with a callsite, including parameter passing
178 /// and the call/return instruction.
179 int getCallsiteCost(CallSite CS, const DataLayout &DL);
181 /// \brief Get an InlineCost object representing the cost of inlining this
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.
190 /// Also note that calling this function *dynamically* computes the cost of
191 /// inlining the callsite. It is an expensive, heavyweight call.
192 InlineCost 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);
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.
204 getInlineCost(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);
210 /// \brief Minimal filter to detect invalid constructs for inlining.
211 bool isInlineViable(Function &Callee);