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| 1 | +//===-- CSPreInliner.cpp - Profile guided preinliner -------------- 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 | +#include "CSPreInliner.h" |
| 10 | +#include "ProfiledBinary.h" |
| 11 | +#include "llvm/ADT/SCCIterator.h" |
| 12 | +#include "llvm/ADT/Statistic.h" |
| 13 | +#include "llvm/DebugInfo/Symbolize/SymbolizableModule.h" |
| 14 | +#include "llvm/Transforms/IPO/SampleProfile.h" |
| 15 | +#include <cstdint> |
| 16 | +#include <queue> |
| 17 | + |
| 18 | +#define DEBUG_TYPE "cs-preinliner" |
| 19 | + |
| 20 | +using namespace llvm; |
| 21 | +using namespace sampleprof; |
| 22 | + |
| 23 | +STATISTIC(PreInlNumCSInlined, |
| 24 | + "Number of functions inlined with context sensitive profile"); |
| 25 | +STATISTIC(PreInlNumCSNotInlined, |
| 26 | + "Number of functions not inlined with context sensitive profile"); |
| 27 | +STATISTIC(PreInlNumCSInlinedHitMinLimit, |
| 28 | + "Number of functions with FDO inline stopped due to min size limit"); |
| 29 | +STATISTIC(PreInlNumCSInlinedHitMaxLimit, |
| 30 | + "Number of functions with FDO inline stopped due to max size limit"); |
| 31 | +STATISTIC( |
| 32 | + PreInlNumCSInlinedHitGrowthLimit, |
| 33 | + "Number of functions with FDO inline stopped due to growth size limit"); |
| 34 | + |
| 35 | +// The switches specify inline thresholds used in SampleProfileLoader inlining. |
| 36 | +// TODO: the actual threshold to be tuned here because the size here is based |
| 37 | +// on machine code not LLVM IR. |
| 38 | +namespace llvm { |
| 39 | +cl::opt<bool> EnableCSPreInliner( |
| 40 | + "csspgo-preinliner", cl::Hidden, cl::init(true), |
| 41 | + cl::desc("Run a global pre-inliner to merge context profile based on " |
| 42 | + "estimated global top-down inline decisions")); |
| 43 | + |
| 44 | +cl::opt<bool> UseContextCostForPreInliner( |
| 45 | + "use-context-cost-for-preinliner", cl::Hidden, cl::init(true), |
| 46 | + cl::desc("Use context-sensitive byte size cost for preinliner decisions")); |
| 47 | +} // namespace llvm |
| 48 | + |
| 49 | +static cl::opt<bool> SamplePreInlineReplay( |
| 50 | + "csspgo-replay-preinline", cl::Hidden, cl::init(false), |
| 51 | + cl::desc( |
| 52 | + "Replay previous inlining and adjust context profile accordingly")); |
| 53 | + |
| 54 | +static cl::opt<int> CSPreinlMultiplierForPrevInl( |
| 55 | + "csspgo-preinliner-multiplier-for-previous-inlining", cl::Hidden, |
| 56 | + cl::init(100), |
| 57 | + cl::desc( |
| 58 | + "Multiplier to bump up callsite threshold for previous inlining.")); |
| 59 | + |
| 60 | +CSPreInliner::CSPreInliner(SampleContextTracker &Tracker, |
| 61 | + ProfiledBinary &Binary, ProfileSummary *Summary) |
| 62 | + : UseContextCost(UseContextCostForPreInliner), |
| 63 | + // TODO: Pass in a guid-to-name map in order for |
| 64 | + // ContextTracker.getFuncNameFor to work, if `Profiles` can have md5 codes |
| 65 | + // as their profile context. |
| 66 | + ContextTracker(Tracker), Binary(Binary), Summary(Summary) { |
| 67 | + // Set default preinliner hot/cold call site threshold tuned with CSSPGO. |
| 68 | + // for good performance with reasonable profile size. |
| 69 | + if (!SampleHotCallSiteThreshold.getNumOccurrences()) |
| 70 | + SampleHotCallSiteThreshold = 1500; |
| 71 | + if (!SampleColdCallSiteThreshold.getNumOccurrences()) |
| 72 | + SampleColdCallSiteThreshold = 0; |
| 73 | + if (!ProfileInlineLimitMax.getNumOccurrences()) |
| 74 | + ProfileInlineLimitMax = 50000; |
| 75 | +} |
| 76 | + |
| 77 | +std::vector<FunctionId> CSPreInliner::buildTopDownOrder() { |
| 78 | + std::vector<FunctionId> Order; |
| 79 | + // Trim cold edges to get a more stable call graph. This allows for a more |
| 80 | + // stable top-down order which in turns helps the stablity of the generated |
| 81 | + // profile from run to run. |
| 82 | + uint64_t ColdCountThreshold = ProfileSummaryBuilder::getColdCountThreshold( |
| 83 | + (Summary->getDetailedSummary())); |
| 84 | + ProfiledCallGraph ProfiledCG(ContextTracker, ColdCountThreshold); |
| 85 | + |
| 86 | + // Now that we have a profiled call graph, construct top-down order |
| 87 | + // by building up SCC and reversing SCC order. |
| 88 | + scc_iterator<ProfiledCallGraph *> I = scc_begin(&ProfiledCG); |
| 89 | + while (!I.isAtEnd()) { |
| 90 | + auto Range = *I; |
| 91 | + if (SortProfiledSCC) { |
| 92 | + // Sort nodes in one SCC based on callsite hotness. |
| 93 | + scc_member_iterator<ProfiledCallGraph *> SI(*I); |
| 94 | + Range = *SI; |
| 95 | + } |
| 96 | + for (auto *Node : Range) { |
| 97 | + if (Node != ProfiledCG.getEntryNode()) |
| 98 | + Order.push_back(Node->Name); |
| 99 | + } |
| 100 | + ++I; |
| 101 | + } |
| 102 | + std::reverse(Order.begin(), Order.end()); |
| 103 | + |
| 104 | + return Order; |
| 105 | +} |
| 106 | + |
| 107 | +bool CSPreInliner::getInlineCandidates(ProfiledCandidateQueue &CQueue, |
| 108 | + const FunctionSamples *CallerSamples) { |
| 109 | + assert(CallerSamples && "Expect non-null caller samples"); |
| 110 | + |
| 111 | + // Ideally we want to consider everything a function calls, but as far as |
| 112 | + // context profile is concerned, only those frames that are children of |
| 113 | + // current one in the trie is relavent. So we walk the trie instead of call |
| 114 | + // targets from function profile. |
| 115 | + ContextTrieNode *CallerNode = |
| 116 | + ContextTracker.getContextNodeForProfile(CallerSamples); |
| 117 | + |
| 118 | + bool HasNewCandidate = false; |
| 119 | + for (auto &Child : CallerNode->getAllChildContext()) { |
| 120 | + ContextTrieNode *CalleeNode = &Child.second; |
| 121 | + FunctionSamples *CalleeSamples = CalleeNode->getFunctionSamples(); |
| 122 | + if (!CalleeSamples) |
| 123 | + continue; |
| 124 | + |
| 125 | + // Call site count is more reliable, so we look up the corresponding call |
| 126 | + // target profile in caller's context profile to retrieve call site count. |
| 127 | + uint64_t CalleeEntryCount = CalleeSamples->getHeadSamplesEstimate(); |
| 128 | + uint64_t CallsiteCount = 0; |
| 129 | + LineLocation Callsite = CalleeNode->getCallSiteLoc(); |
| 130 | + if (auto CallTargets = CallerSamples->findCallTargetMapAt(Callsite)) { |
| 131 | + auto It = CallTargets->find(CalleeSamples->getFunction()); |
| 132 | + if (It != CallTargets->end()) |
| 133 | + CallsiteCount = It->second; |
| 134 | + } |
| 135 | + |
| 136 | + // TODO: call site and callee entry count should be mostly consistent, add |
| 137 | + // check for that. |
| 138 | + HasNewCandidate = true; |
| 139 | + uint32_t CalleeSize = getFuncSize(CalleeNode); |
| 140 | + CQueue.emplace(CalleeSamples, std::max(CallsiteCount, CalleeEntryCount), |
| 141 | + CalleeSize); |
| 142 | + } |
| 143 | + |
| 144 | + return HasNewCandidate; |
| 145 | +} |
| 146 | + |
| 147 | +uint32_t CSPreInliner::getFuncSize(const ContextTrieNode *ContextNode) { |
| 148 | + if (UseContextCost) |
| 149 | + return Binary.getFuncSizeForContext(ContextNode); |
| 150 | + |
| 151 | + return ContextNode->getFunctionSamples()->getBodySamples().size(); |
| 152 | +} |
| 153 | + |
| 154 | +bool CSPreInliner::shouldInline(ProfiledInlineCandidate &Candidate) { |
| 155 | + bool WasInlined = |
| 156 | + Candidate.CalleeSamples->getContext().hasAttribute(ContextWasInlined); |
| 157 | + // If replay inline is requested, simply follow the inline decision of the |
| 158 | + // profiled binary. |
| 159 | + if (SamplePreInlineReplay) |
| 160 | + return WasInlined; |
| 161 | + |
| 162 | + unsigned int SampleThreshold = SampleColdCallSiteThreshold; |
| 163 | + uint64_t ColdCountThreshold = ProfileSummaryBuilder::getColdCountThreshold( |
| 164 | + (Summary->getDetailedSummary())); |
| 165 | + |
| 166 | + if (Candidate.CallsiteCount <= ColdCountThreshold) |
| 167 | + SampleThreshold = SampleColdCallSiteThreshold; |
| 168 | + else { |
| 169 | + // Linearly adjust threshold based on normalized hotness, i.e, a value in |
| 170 | + // [0,1]. Use 10% cutoff instead of the max count as the normalization |
| 171 | + // upperbound for stability. |
| 172 | + double NormalizationUpperBound = |
| 173 | + ProfileSummaryBuilder::getEntryForPercentile( |
| 174 | + Summary->getDetailedSummary(), 100000 /* 10% */) |
| 175 | + .MinCount; |
| 176 | + double NormalizationLowerBound = ColdCountThreshold; |
| 177 | + double NormalizedHotness = |
| 178 | + (Candidate.CallsiteCount - NormalizationLowerBound) / |
| 179 | + (NormalizationUpperBound - NormalizationLowerBound); |
| 180 | + if (NormalizedHotness > 1.0) |
| 181 | + NormalizedHotness = 1.0; |
| 182 | + // Add 1 to ensure hot callsites get a non-zero threshold, which could |
| 183 | + // happen when SampleColdCallSiteThreshold is 0. This is when we do not |
| 184 | + // want any inlining for cold callsites. |
| 185 | + SampleThreshold = SampleHotCallSiteThreshold * NormalizedHotness * 100 + |
| 186 | + SampleColdCallSiteThreshold + 1; |
| 187 | + // Bump up the threshold to favor previous compiler inline decision. The |
| 188 | + // compiler has more insight and knowledge about functions based on their IR |
| 189 | + // and attribures and should be able to make a more reasonable inline |
| 190 | + // decision. |
| 191 | + if (WasInlined) |
| 192 | + SampleThreshold *= CSPreinlMultiplierForPrevInl; |
| 193 | + } |
| 194 | + |
| 195 | + return (Candidate.SizeCost < SampleThreshold); |
| 196 | +} |
| 197 | + |
| 198 | +void CSPreInliner::processFunction(const FunctionId Name) { |
| 199 | + FunctionSamples *FSamples = ContextTracker.getBaseSamplesFor(Name); |
| 200 | + if (!FSamples) |
| 201 | + return; |
| 202 | + |
| 203 | + unsigned FuncSize = |
| 204 | + getFuncSize(ContextTracker.getContextNodeForProfile(FSamples)); |
| 205 | + unsigned FuncFinalSize = FuncSize; |
| 206 | + unsigned SizeLimit = FuncSize * ProfileInlineGrowthLimit; |
| 207 | + SizeLimit = std::min(SizeLimit, (unsigned)ProfileInlineLimitMax); |
| 208 | + SizeLimit = std::max(SizeLimit, (unsigned)ProfileInlineLimitMin); |
| 209 | + |
| 210 | + LLVM_DEBUG(dbgs() << "Process " << Name |
| 211 | + << " for context-sensitive pre-inlining (pre-inline size: " |
| 212 | + << FuncSize << ", size limit: " << SizeLimit << ")\n"); |
| 213 | + |
| 214 | + ProfiledCandidateQueue CQueue; |
| 215 | + getInlineCandidates(CQueue, FSamples); |
| 216 | + |
| 217 | + while (!CQueue.empty() && FuncFinalSize < SizeLimit) { |
| 218 | + ProfiledInlineCandidate Candidate = CQueue.top(); |
| 219 | + CQueue.pop(); |
| 220 | + bool ShouldInline = false; |
| 221 | + if ((ShouldInline = shouldInline(Candidate))) { |
| 222 | + // We mark context as inlined as the corresponding context profile |
| 223 | + // won't be merged into that function's base profile. |
| 224 | + ++PreInlNumCSInlined; |
| 225 | + ContextTracker.markContextSamplesInlined(Candidate.CalleeSamples); |
| 226 | + Candidate.CalleeSamples->getContext().setAttribute( |
| 227 | + ContextShouldBeInlined); |
| 228 | + FuncFinalSize += Candidate.SizeCost; |
| 229 | + getInlineCandidates(CQueue, Candidate.CalleeSamples); |
| 230 | + } else { |
| 231 | + ++PreInlNumCSNotInlined; |
| 232 | + } |
| 233 | + LLVM_DEBUG( |
| 234 | + dbgs() << (ShouldInline ? " Inlined" : " Outlined") |
| 235 | + << " context profile for: " |
| 236 | + << ContextTracker.getContextString(*Candidate.CalleeSamples) |
| 237 | + << " (callee size: " << Candidate.SizeCost |
| 238 | + << ", call count:" << Candidate.CallsiteCount << ")\n"); |
| 239 | + } |
| 240 | + |
| 241 | + if (!CQueue.empty()) { |
| 242 | + if (SizeLimit == (unsigned)ProfileInlineLimitMax) |
| 243 | + ++PreInlNumCSInlinedHitMaxLimit; |
| 244 | + else if (SizeLimit == (unsigned)ProfileInlineLimitMin) |
| 245 | + ++PreInlNumCSInlinedHitMinLimit; |
| 246 | + else |
| 247 | + ++PreInlNumCSInlinedHitGrowthLimit; |
| 248 | + } |
| 249 | + |
| 250 | + LLVM_DEBUG({ |
| 251 | + if (!CQueue.empty()) |
| 252 | + dbgs() << " Inline candidates ignored due to size limit (inliner " |
| 253 | + "original size: " |
| 254 | + << FuncSize << ", inliner final size: " << FuncFinalSize |
| 255 | + << ", size limit: " << SizeLimit << ")\n"; |
| 256 | + |
| 257 | + while (!CQueue.empty()) { |
| 258 | + ProfiledInlineCandidate Candidate = CQueue.top(); |
| 259 | + CQueue.pop(); |
| 260 | + bool WasInlined = |
| 261 | + Candidate.CalleeSamples->getContext().hasAttribute(ContextWasInlined); |
| 262 | + dbgs() << " " |
| 263 | + << ContextTracker.getContextString(*Candidate.CalleeSamples) |
| 264 | + << " (candidate size:" << Candidate.SizeCost |
| 265 | + << ", call count: " << Candidate.CallsiteCount << ", previously " |
| 266 | + << (WasInlined ? "inlined)\n" : "not inlined)\n"); |
| 267 | + } |
| 268 | + }); |
| 269 | +} |
| 270 | + |
| 271 | +void CSPreInliner::run() { |
| 272 | +#ifndef NDEBUG |
| 273 | + auto printProfileNames = [](SampleContextTracker &ContextTracker, |
| 274 | + bool IsInput) { |
| 275 | + uint32_t Size = 0; |
| 276 | + for (auto *Node : ContextTracker) { |
| 277 | + FunctionSamples *FSamples = Node->getFunctionSamples(); |
| 278 | + if (FSamples) { |
| 279 | + Size++; |
| 280 | + dbgs() << " [" << ContextTracker.getContextString(Node) << "] " |
| 281 | + << FSamples->getTotalSamples() << ":" |
| 282 | + << FSamples->getHeadSamples() << "\n"; |
| 283 | + } |
| 284 | + } |
| 285 | + dbgs() << (IsInput ? "Input" : "Output") << " context-sensitive profiles (" |
| 286 | + << Size << " total):\n"; |
| 287 | + }; |
| 288 | +#endif |
| 289 | + |
| 290 | + LLVM_DEBUG(printProfileNames(ContextTracker, true)); |
| 291 | + |
| 292 | + // Execute global pre-inliner to estimate a global top-down inline |
| 293 | + // decision and merge profiles accordingly. This helps with profile |
| 294 | + // merge for ThinLTO otherwise we won't be able to merge profiles back |
| 295 | + // to base profile across module/thin-backend boundaries. |
| 296 | + // It also helps better compress context profile to control profile |
| 297 | + // size, as we now only need context profile for functions going to |
| 298 | + // be inlined. |
| 299 | + for (FunctionId FuncName : buildTopDownOrder()) { |
| 300 | + processFunction(FuncName); |
| 301 | + } |
| 302 | + |
| 303 | + // Not inlined context profiles are merged into its base, so we can |
| 304 | + // trim out such profiles from the output. |
| 305 | + for (auto *Node : ContextTracker) { |
| 306 | + FunctionSamples *FProfile = Node->getFunctionSamples(); |
| 307 | + if (FProfile && |
| 308 | + (Node->getParentContext() != &ContextTracker.getRootContext() && |
| 309 | + !FProfile->getContext().hasState(InlinedContext))) { |
| 310 | + Node->setFunctionSamples(nullptr); |
| 311 | + } |
| 312 | + } |
| 313 | + FunctionSamples::ProfileIsPreInlined = true; |
| 314 | + |
| 315 | + LLVM_DEBUG(printProfileNames(ContextTracker, false)); |
| 316 | +} |
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