1//===- InlineCost.h - Cost analysis for inliner -----------------*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file implements heuristics for inlining decisions.
10//
11//===----------------------------------------------------------------------===//
12
13#ifndef LLVM_ANALYSIS_INLINECOST_H
14#define LLVM_ANALYSIS_INLINECOST_H
15
16#include "llvm/ADT/APInt.h"
17#include "llvm/ADT/STLFunctionalExtras.h"
18#include "llvm/Analysis/InlineModelFeatureMaps.h"
19#include "llvm/IR/PassManager.h"
20#include <cassert>
21#include <climits>
22#include <optional>
23
24namespace llvm {
25class AssumptionCache;
26class OptimizationRemarkEmitter;
27class BlockFrequencyInfo;
28class CallBase;
29class DataLayout;
30class Function;
31class ProfileSummaryInfo;
32class TargetTransformInfo;
33class TargetLibraryInfo;
34
35namespace InlineConstants {
36// Various thresholds used by inline cost analysis.
37/// Use when optsize (-Os) is specified.
38const int OptSizeThreshold = 50;
39
40/// Use when minsize (-Oz) is specified.
41const int OptMinSizeThreshold = 5;
42
43/// Use when -O3 is specified.
44const int OptAggressiveThreshold = 250;
45
46// Various magic constants used to adjust heuristics.
47int getInstrCost();
48const int IndirectCallThreshold = 100;
49const int LoopPenalty = 25;
50const int LastCallToStaticBonus = 15000;
51const int ColdccPenalty = 2000;
52/// Do not inline functions which allocate this many bytes on the stack
53/// when the caller is recursive.
54const unsigned TotalAllocaSizeRecursiveCaller = 1024;
55/// Do not inline dynamic allocas that have been constant propagated to be
56/// static allocas above this amount in bytes.
57const uint64_t MaxSimplifiedDynamicAllocaToInline = 65536;
58
59const char FunctionInlineCostMultiplierAttributeName[] =
60 "function-inline-cost-multiplier";
61
62const char MaxInlineStackSizeAttributeName[] = "inline-max-stacksize";
63} // namespace InlineConstants
64
65// The cost-benefit pair computed by cost-benefit analysis.
66class CostBenefitPair {
67public:
68 CostBenefitPair(APInt Cost, APInt Benefit) : Cost(Cost), Benefit(Benefit) {}
69
70 const APInt &getCost() const { return Cost; }
71
72 const APInt &getBenefit() const { return Benefit; }
73
74private:
75 APInt Cost;
76 APInt Benefit;
77};
78
79/// Represents the cost of inlining a function.
80///
81/// This supports special values for functions which should "always" or
82/// "never" be inlined. Otherwise, the cost represents a unitless amount;
83/// smaller values increase the likelihood of the function being inlined.
84///
85/// Objects of this type also provide the adjusted threshold for inlining
86/// based on the information available for a particular callsite. They can be
87/// directly tested to determine if inlining should occur given the cost and
88/// threshold for this cost metric.
89class InlineCost {
90 enum SentinelValues { AlwaysInlineCost = INT_MIN, NeverInlineCost = INT_MAX };
91
92 /// The estimated cost of inlining this callsite.
93 int Cost = 0;
94
95 /// The adjusted threshold against which this cost was computed.
96 int Threshold = 0;
97
98 /// The amount of StaticBonus that has been applied.
99 int StaticBonusApplied = 0;
100
101 /// Must be set for Always and Never instances.
102 const char *Reason = nullptr;
103
104 /// The cost-benefit pair computed by cost-benefit analysis.
105 std::optional<CostBenefitPair> CostBenefit;
106
107 // Trivial constructor, interesting logic in the factory functions below.
108 InlineCost(int Cost, int Threshold, int StaticBonusApplied,
109 const char *Reason = nullptr,
110 std::optional<CostBenefitPair> CostBenefit = std::nullopt)
111 : Cost(Cost), Threshold(Threshold),
112 StaticBonusApplied(StaticBonusApplied), Reason(Reason),
113 CostBenefit(CostBenefit) {
114 assert((isVariable() || Reason) &&
115 "Reason must be provided for Never or Always");
116 }
117
118public:
119 static InlineCost get(int Cost, int Threshold, int StaticBonus = 0) {
120 assert(Cost > AlwaysInlineCost && "Cost crosses sentinel value");
121 assert(Cost < NeverInlineCost && "Cost crosses sentinel value");
122 return InlineCost(Cost, Threshold, StaticBonus);
123 }
124 static InlineCost
125 getAlways(const char *Reason,
126 std::optional<CostBenefitPair> CostBenefit = std::nullopt) {
127 return InlineCost(AlwaysInlineCost, 0, 0, Reason, CostBenefit);
128 }
129 static InlineCost
130 getNever(const char *Reason,
131 std::optional<CostBenefitPair> CostBenefit = std::nullopt) {
132 return InlineCost(NeverInlineCost, 0, 0, Reason, CostBenefit);
133 }
134
135 /// Test whether the inline cost is low enough for inlining.
136 explicit operator bool() const { return Cost < Threshold; }
137
138 bool isAlways() const { return Cost == AlwaysInlineCost; }
139 bool isNever() const { return Cost == NeverInlineCost; }
140 bool isVariable() const { return !isAlways() && !isNever(); }
141
142 /// Get the inline cost estimate.
143 /// It is an error to call this on an "always" or "never" InlineCost.
144 int getCost() const {
145 assert(isVariable() && "Invalid access of InlineCost");
146 return Cost;
147 }
148
149 /// Get the threshold against which the cost was computed
150 int getThreshold() const {
151 assert(isVariable() && "Invalid access of InlineCost");
152 return Threshold;
153 }
154
155 /// Get the amount of StaticBonus applied.
156 int getStaticBonusApplied() const {
157 assert(isVariable() && "Invalid access of InlineCost");
158 return StaticBonusApplied;
159 }
160
161 /// Get the cost-benefit pair which was computed by cost-benefit analysis
162 std::optional<CostBenefitPair> getCostBenefit() const { return CostBenefit; }
163
164 /// Get the reason of Always or Never.
165 const char *getReason() const {
166 assert((Reason || isVariable()) &&
167 "InlineCost reason must be set for Always or Never");
168 return Reason;
169 }
170
171 /// Get the cost delta from the threshold for inlining.
172 /// Only valid if the cost is of the variable kind. Returns a negative
173 /// value if the cost is too high to inline.
174 int getCostDelta() const { return Threshold - getCost(); }
175};
176
177/// InlineResult is basically true or false. For false results the message
178/// describes a reason.
179class InlineResult {
180 const char *Message = nullptr;
181 InlineResult(const char *Message = nullptr) : Message(Message) {}
182
183public:
184 static InlineResult success() { return {}; }
185 static InlineResult failure(const char *Reason) {
186 return InlineResult(Reason);
187 }
188 bool isSuccess() const { return Message == nullptr; }
189 const char *getFailureReason() const {
190 assert(!isSuccess() &&
191 "getFailureReason should only be called in failure cases");
192 return Message;
193 }
194};
195
196/// Thresholds to tune inline cost analysis. The inline cost analysis decides
197/// the condition to apply a threshold and applies it. Otherwise,
198/// DefaultThreshold is used. If a threshold is Optional, it is applied only
199/// when it has a valid value. Typically, users of inline cost analysis
200/// obtain an InlineParams object through one of the \c getInlineParams methods
201/// and pass it to \c getInlineCost. Some specialized versions of inliner
202/// (such as the pre-inliner) might have custom logic to compute \c InlineParams
203/// object.
204
205struct InlineParams {
206 /// The default threshold to start with for a callee.
207 int DefaultThreshold = -1;
208
209 /// Threshold to use for callees with inline hint.
210 std::optional<int> HintThreshold;
211
212 /// Threshold to use for cold callees.
213 std::optional<int> ColdThreshold;
214
215 /// Threshold to use when the caller is optimized for size.
216 std::optional<int> OptSizeThreshold;
217
218 /// Threshold to use when the caller is optimized for minsize.
219 std::optional<int> OptMinSizeThreshold;
220
221 /// Threshold to use when the callsite is considered hot.
222 std::optional<int> HotCallSiteThreshold;
223
224 /// Threshold to use when the callsite is considered hot relative to function
225 /// entry.
226 std::optional<int> LocallyHotCallSiteThreshold;
227
228 /// Threshold to use when the callsite is considered cold.
229 std::optional<int> ColdCallSiteThreshold;
230
231 /// Compute inline cost even when the cost has exceeded the threshold.
232 std::optional<bool> ComputeFullInlineCost;
233
234 /// Indicate whether we should allow inline deferral.
235 std::optional<bool> EnableDeferral;
236
237 /// Indicate whether we allow inlining for recursive call.
238 std::optional<bool> AllowRecursiveCall = false;
239};
240
241std::optional<int> getStringFnAttrAsInt(CallBase &CB, StringRef AttrKind);
242
243/// Generate the parameters to tune the inline cost analysis based only on the
244/// commandline options.
245InlineParams getInlineParams();
246
247/// Generate the parameters to tune the inline cost analysis based on command
248/// line options. If -inline-threshold option is not explicitly passed,
249/// \p Threshold is used as the default threshold.
250InlineParams getInlineParams(int Threshold);
251
252/// Generate the parameters to tune the inline cost analysis based on command
253/// line options. If -inline-threshold option is not explicitly passed,
254/// the default threshold is computed from \p OptLevel and \p SizeOptLevel.
255/// An \p OptLevel value above 3 is considered an aggressive optimization mode.
256/// \p SizeOptLevel of 1 corresponds to the -Os flag and 2 corresponds to
257/// the -Oz flag.
258InlineParams getInlineParams(unsigned OptLevel, unsigned SizeOptLevel);
259
260/// Return the cost associated with a callsite, including parameter passing
261/// and the call/return instruction.
262int getCallsiteCost(const TargetTransformInfo &TTI, const CallBase &Call,
263 const DataLayout &DL);
264
265/// Get an InlineCost object representing the cost of inlining this
266/// callsite.
267///
268/// Note that a default threshold is passed into this function. This threshold
269/// could be modified based on callsite's properties and only costs below this
270/// new threshold are computed with any accuracy. The new threshold can be
271/// used to bound the computation necessary to determine whether the cost is
272/// sufficiently low to warrant inlining.
273///
274/// Also note that calling this function *dynamically* computes the cost of
275/// inlining the callsite. It is an expensive, heavyweight call.
276InlineCost
277getInlineCost(CallBase &Call, const InlineParams &Params,
278 TargetTransformInfo &CalleeTTI,
279 function_ref<AssumptionCache &(Function &)> GetAssumptionCache,
280 function_ref<const TargetLibraryInfo &(Function &)> GetTLI,
281 function_ref<BlockFrequencyInfo &(Function &)> GetBFI = nullptr,
282 ProfileSummaryInfo *PSI = nullptr,
283 OptimizationRemarkEmitter *ORE = nullptr);
284
285/// Get an InlineCost with the callee explicitly specified.
286/// This allows you to calculate the cost of inlining a function via a
287/// pointer. This behaves exactly as the version with no explicit callee
288/// parameter in all other respects.
289//
290InlineCost
291getInlineCost(CallBase &Call, Function *Callee, const InlineParams &Params,
292 TargetTransformInfo &CalleeTTI,
293 function_ref<AssumptionCache &(Function &)> GetAssumptionCache,
294 function_ref<const TargetLibraryInfo &(Function &)> GetTLI,
295 function_ref<BlockFrequencyInfo &(Function &)> GetBFI = nullptr,
296 ProfileSummaryInfo *PSI = nullptr,
297 OptimizationRemarkEmitter *ORE = nullptr);
298
299/// Returns InlineResult::success() if the call site should be always inlined
300/// because of user directives, and the inlining is viable. Returns
301/// InlineResult::failure() if the inlining may never happen because of user
302/// directives or incompatibilities detectable without needing callee traversal.
303/// Otherwise returns std::nullopt, meaning that inlining should be decided
304/// based on other criteria (e.g. cost modeling).
305std::optional<InlineResult> getAttributeBasedInliningDecision(
306 CallBase &Call, Function *Callee, TargetTransformInfo &CalleeTTI,
307 function_ref<const TargetLibraryInfo &(Function &)> GetTLI);
308
309/// Get the cost estimate ignoring thresholds. This is similar to getInlineCost
310/// when passed InlineParams::ComputeFullInlineCost, or a non-null ORE. It
311/// uses default InlineParams otherwise.
312/// Contrary to getInlineCost, which makes a threshold-based final evaluation of
313/// should/shouldn't inline, captured in InlineResult, getInliningCostEstimate
314/// returns:
315/// - std::nullopt, if the inlining cannot happen (is illegal)
316/// - an integer, representing the cost.
317std::optional<int> getInliningCostEstimate(
318 CallBase &Call, TargetTransformInfo &CalleeTTI,
319 function_ref<AssumptionCache &(Function &)> GetAssumptionCache,
320 function_ref<BlockFrequencyInfo &(Function &)> GetBFI = nullptr,
321 ProfileSummaryInfo *PSI = nullptr,
322 OptimizationRemarkEmitter *ORE = nullptr);
323
324/// Get the expanded cost features. The features are returned unconditionally,
325/// even if inlining is impossible.
326std::optional<InlineCostFeatures> getInliningCostFeatures(
327 CallBase &Call, TargetTransformInfo &CalleeTTI,
328 function_ref<AssumptionCache &(Function &)> GetAssumptionCache,
329 function_ref<BlockFrequencyInfo &(Function &)> GetBFI = nullptr,
330 ProfileSummaryInfo *PSI = nullptr,
331 OptimizationRemarkEmitter *ORE = nullptr);
332
333/// Minimal filter to detect invalid constructs for inlining.
334InlineResult isInlineViable(Function &Callee);
335
336// This pass is used to annotate instructions during the inline process for
337// debugging and analysis. The main purpose of the pass is to see and test
338// inliner's decisions when creating new optimizations to InlineCost.
339struct InlineCostAnnotationPrinterPass
340 : PassInfoMixin<InlineCostAnnotationPrinterPass> {
341 raw_ostream &OS;
342
343public:
344 explicit InlineCostAnnotationPrinterPass(raw_ostream &OS) : OS(OS) {}
345 PreservedAnalyses run(Function &F, FunctionAnalysisManager &FAM);
346 static bool isRequired() { return true; }
347};
348} // namespace llvm
349
350#endif
351

source code of llvm/include/llvm/Analysis/InlineCost.h