tools/llvm-profgen/CSPreInliner.cpp - llvm-project/llvm - Git at Google

 //===-- CSPreInliner.cpp - Profile guided preinliner -------------- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//

 #include "CSPreInliner.h"
 #include "llvm/ADT/SCCIterator.h"
 #include <cstdint>
 #include <queue>

 #define DEBUG_TYPE "cs-preinliner"

 using namespace llvm;
 using namespace sampleprof;

 static cl::opt<bool> EnableCSPreInliner(
     "csspgo-preinliner", cl::Hidden, cl::init(false),
     cl::desc("Run a global pre-inliner to merge context profile based on "
              "estimated global top-down inline decisions"));

 // The switches specify inline thresholds used in SampleProfileLoader inlining.
 // TODO: the actual threshold to be tuned here because the size here is based
 // on machine code not LLVM IR.
 extern cl::opt<int> SampleHotCallSiteThreshold;
 extern cl::opt<int> SampleColdCallSiteThreshold;
 extern cl::opt<int> ProfileInlineGrowthLimit;
 extern cl::opt<int> ProfileInlineLimitMin;
 extern cl::opt<int> ProfileInlineLimitMax;

 static cl::opt<bool> SamplePreInlineReplay(
     "csspgo-replay-preinline", cl::Hidden, cl::init(false),
     cl::desc(
         "Replay previous inlining and adjust context profile accordingly"));

 CSPreInliner::CSPreInliner(StringMap<FunctionSamples> &Profiles,
                            uint64_t HotThreshold, uint64_t ColdThreshold)
     : ContextTracker(Profiles), ProfileMap(Profiles),
       HotCountThreshold(HotThreshold), ColdCountThreshold(ColdThreshold) {}

 std::vector<StringRef> CSPreInliner::buildTopDownOrder() {
   std::vector<StringRef> Order;
   ProfiledCallGraph ProfiledCG(ContextTracker);

   // Now that we have a profiled call graph, construct top-down order
   // by building up SCC and reversing SCC order.
   scc_iterator<ProfiledCallGraph *> I = scc_begin(&ProfiledCG);
   while (!I.isAtEnd()) {
     for (ProfiledCallGraphNode *Node : *I) {
       if (Node != ProfiledCG.getEntryNode())
         Order.push_back(Node->Name);
     }
     ++I;
   }
   std::reverse(Order.begin(), Order.end());

   return Order;
 }

 bool CSPreInliner::getInlineCandidates(ProfiledCandidateQueue &CQueue,
                                        const FunctionSamples *CallerSamples) {
   assert(CallerSamples && "Expect non-null caller samples");

   // Ideally we want to consider everything a function calls, but as far as
   // context profile is concerned, only those frames that are children of
   // current one in the trie is relavent. So we walk the trie instead of call
   // targets from function profile.
   ContextTrieNode *CallerNode =
       ContextTracker.getContextFor(CallerSamples->getContext());

   bool HasNewCandidate = false;
   for (auto &Child : CallerNode->getAllChildContext()) {
     ContextTrieNode *CalleeNode = &Child.second;
     FunctionSamples *CalleeSamples = CalleeNode->getFunctionSamples();
     if (!CalleeSamples)
       continue;

     // Call site count is more reliable, so we look up the corresponding call
     // target profile in caller's context profile to retrieve call site count.
     uint64_t CalleeEntryCount = CalleeSamples->getEntrySamples();
     uint64_t CallsiteCount = 0;
     LineLocation Callsite = CalleeNode->getCallSiteLoc();
     if (auto CallTargets = CallerSamples->findCallTargetMapAt(Callsite)) {
       SampleRecord::CallTargetMap &TargetCounts = CallTargets.get();
       auto It = TargetCounts.find(CalleeSamples->getName());
       if (It != TargetCounts.end())
         CallsiteCount = It->second;
     }

     // TODO: call site and callee entry count should be mostly consistent, add
     // check for that.
     HasNewCandidate = true;
     CQueue.emplace(CalleeSamples, std::max(CallsiteCount, CalleeEntryCount));
   }

   return HasNewCandidate;
 }

 bool CSPreInliner::shouldInline(ProfiledInlineCandidate &Candidate) {
   // If replay inline is requested, simply follow the inline decision of the
   // profiled binary.
   if (SamplePreInlineReplay)
     return Candidate.CalleeSamples->getContext().hasAttribute(
         ContextWasInlined);

   // Adjust threshold based on call site hotness, only do this for callsite
   // prioritized inliner because otherwise cost-benefit check is done earlier.
   unsigned int SampleThreshold = SampleColdCallSiteThreshold;
   if (Candidate.CallsiteCount > HotCountThreshold)
     SampleThreshold = SampleHotCallSiteThreshold;

   // TODO: for small cold functions, we may inlined them and we need to keep
   // context profile accordingly.
   if (Candidate.CallsiteCount < ColdCountThreshold)
     SampleThreshold = SampleColdCallSiteThreshold;

   return (Candidate.SizeCost < SampleThreshold);
 }

 void CSPreInliner::processFunction(const StringRef Name) {
   LLVM_DEBUG(dbgs() << "Process " << Name
                     << " for context-sensitive pre-inlining\n");

   FunctionSamples *FSamples = ContextTracker.getBaseSamplesFor(Name);
   if (!FSamples)
     return;

   // Use the number of lines/probes as proxy for function size for now.
   // TODO: retrieve accurate size from dwarf or binary instead.
   unsigned FuncSize = FSamples->getBodySamples().size();
   unsigned FuncFinalSize = FuncSize;
   unsigned SizeLimit = FuncSize * ProfileInlineGrowthLimit;
   SizeLimit = std::min(SizeLimit, (unsigned)ProfileInlineLimitMax);
   SizeLimit = std::max(SizeLimit, (unsigned)ProfileInlineLimitMin);

   ProfiledCandidateQueue CQueue;
   getInlineCandidates(CQueue, FSamples);

   while (!CQueue.empty() && FuncFinalSize < SizeLimit) {
     ProfiledInlineCandidate Candidate = CQueue.top();
     CQueue.pop();
     bool ShouldInline = false;
     if ((ShouldInline = shouldInline(Candidate))) {
       // We mark context as inlined as the corresponding context profile
       // won't be merged into that function's base profile.
       ContextTracker.markContextSamplesInlined(Candidate.CalleeSamples);
       Candidate.CalleeSamples->getContext().setAttribute(
           ContextShouldBeInlined);
       FuncFinalSize += Candidate.SizeCost;
       getInlineCandidates(CQueue, Candidate.CalleeSamples);
     }
     LLVM_DEBUG(dbgs() << (ShouldInline ? "  Inlined" : "  Outlined")
                       << " context profile for: "
                       << Candidate.CalleeSamples->getNameWithContext()
                       << " (callee size: " << Candidate.SizeCost
                       << ", call count:" << Candidate.CallsiteCount << ")\n");
   }

   LLVM_DEBUG({
     if (!CQueue.empty())
       dbgs() << "  Inline candidates ignored due to size limit (inliner "
                 "original size: "
              << FuncSize << ", inliner final size: " << FuncFinalSize
              << ", size limit: " << SizeLimit << ")\n";

     while (!CQueue.empty()) {
       ProfiledInlineCandidate Candidate = CQueue.top();
       CQueue.pop();
       bool WasInlined =
           Candidate.CalleeSamples->getContext().hasAttribute(ContextWasInlined);
       dbgs() << "    " << Candidate.CalleeSamples->getNameWithContext()
              << " (candidate size:" << Candidate.SizeCost
              << ", call count: " << Candidate.CallsiteCount << ", previously "
              << (WasInlined ? "inlined)\n" : "not inlined)\n");
     }
   });
 }

 void CSPreInliner::run() {
   if (!EnableCSPreInliner)
     return;

 #ifndef NDEBUG
   auto printProfileNames = [](StringMap<FunctionSamples> &Profiles,
                               bool IsInput) {
     dbgs() << (IsInput ? "Input" : "Output") << " context-sensitive profiles ("
            << Profiles.size() << " total):\n";
     for (auto &It : Profiles) {
       const FunctionSamples &Samples = It.second;
       dbgs() << "  [" << Samples.getNameWithContext() << "] "
              << Samples.getTotalSamples() << ":" << Samples.getHeadSamples()
              << "\n";
     }
   };
 #endif

   LLVM_DEBUG(printProfileNames(ProfileMap, true));

   // Execute global pre-inliner to estimate a global top-down inline
   // decision and merge profiles accordingly. This helps with profile
   // merge for ThinLTO otherwise we won't be able to merge profiles back
   // to base profile across module/thin-backend boundaries.
   // It also helps better compress context profile to control profile
   // size, as we now only need context profile for functions going to
   // be inlined.
   for (StringRef FuncName : buildTopDownOrder()) {
     processFunction(FuncName);
   }

   // Not inlined context profiles are merged into its base, so we can
   // trim out such profiles from the output.
   std::vector<StringRef> ProfilesToBeRemoved;
   for (auto &It : ProfileMap) {
     SampleContext Context = It.second.getContext();
     if (!Context.isBaseContext() && !Context.hasState(InlinedContext)) {
       assert(Context.hasState(MergedContext) &&
              "Not inlined context profile should be merged already");
       ProfilesToBeRemoved.push_back(It.first());
     }
   }

   for (StringRef ContextName : ProfilesToBeRemoved) {
     ProfileMap.erase(ContextName);
   }

   // Make sure ProfileMap's key is consistent with FunctionSamples' name.
   SampleContextTrimmer(ProfileMap).canonicalizeContextProfiles();

   LLVM_DEBUG(printProfileNames(ProfileMap, false));
 }
	//===-- CSPreInliner.cpp - Profile guided preinliner -------------- C++ -*-===//
	//
	// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
	// See https://llvm.org/LICENSE.txt for license information.
	// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
	//
	//===----------------------------------------------------------------------===//

	#include "CSPreInliner.h"
	#include "llvm/ADT/SCCIterator.h"
	#include <cstdint>
	#include <queue>

	#define DEBUG_TYPE "cs-preinliner"

	using namespace llvm;
	using namespace sampleprof;

	static cl::opt<bool> EnableCSPreInliner(
	"csspgo-preinliner", cl::Hidden, cl::init(false),
	cl::desc("Run a global pre-inliner to merge context profile based on "
	"estimated global top-down inline decisions"));

	// The switches specify inline thresholds used in SampleProfileLoader inlining.
	// TODO: the actual threshold to be tuned here because the size here is based
	// on machine code not LLVM IR.
	extern cl::opt<int> SampleHotCallSiteThreshold;
	extern cl::opt<int> SampleColdCallSiteThreshold;
	extern cl::opt<int> ProfileInlineGrowthLimit;
	extern cl::opt<int> ProfileInlineLimitMin;
	extern cl::opt<int> ProfileInlineLimitMax;

	static cl::opt<bool> SamplePreInlineReplay(
	"csspgo-replay-preinline", cl::Hidden, cl::init(false),
	cl::desc(
	"Replay previous inlining and adjust context profile accordingly"));

	CSPreInliner::CSPreInliner(StringMap<FunctionSamples> &Profiles,
	uint64_t HotThreshold, uint64_t ColdThreshold)
	: ContextTracker(Profiles), ProfileMap(Profiles),
	HotCountThreshold(HotThreshold), ColdCountThreshold(ColdThreshold) {}

	std::vector<StringRef> CSPreInliner::buildTopDownOrder() {
	std::vector<StringRef> Order;
	ProfiledCallGraph ProfiledCG(ContextTracker);

	// Now that we have a profiled call graph, construct top-down order
	// by building up SCC and reversing SCC order.
	scc_iterator<ProfiledCallGraph *> I = scc_begin(&ProfiledCG);
	while (!I.isAtEnd()) {
	for (ProfiledCallGraphNode Node : I) {
	if (Node != ProfiledCG.getEntryNode())
	Order.push_back(Node->Name);
	}
	++I;
	}
	std::reverse(Order.begin(), Order.end());

	return Order;
	}

	bool CSPreInliner::getInlineCandidates(ProfiledCandidateQueue &CQueue,
	const FunctionSamples *CallerSamples) {
	assert(CallerSamples && "Expect non-null caller samples");

	// Ideally we want to consider everything a function calls, but as far as
	// context profile is concerned, only those frames that are children of
	// current one in the trie is relavent. So we walk the trie instead of call
	// targets from function profile.
	ContextTrieNode *CallerNode =
	ContextTracker.getContextFor(CallerSamples->getContext());

	bool HasNewCandidate = false;
	for (auto &Child : CallerNode->getAllChildContext()) {
	ContextTrieNode *CalleeNode = &Child.second;
	FunctionSamples *CalleeSamples = CalleeNode->getFunctionSamples();
	if (!CalleeSamples)
	continue;

	// Call site count is more reliable, so we look up the corresponding call
	// target profile in caller's context profile to retrieve call site count.
	uint64_t CalleeEntryCount = CalleeSamples->getEntrySamples();
	uint64_t CallsiteCount = 0;
	LineLocation Callsite = CalleeNode->getCallSiteLoc();
	if (auto CallTargets = CallerSamples->findCallTargetMapAt(Callsite)) {
	SampleRecord::CallTargetMap &TargetCounts = CallTargets.get();
	auto It = TargetCounts.find(CalleeSamples->getName());
	if (It != TargetCounts.end())
	CallsiteCount = It->second;
	}

	// TODO: call site and callee entry count should be mostly consistent, add
	// check for that.
	HasNewCandidate = true;
	CQueue.emplace(CalleeSamples, std::max(CallsiteCount, CalleeEntryCount));
	}

	return HasNewCandidate;
	}

	bool CSPreInliner::shouldInline(ProfiledInlineCandidate &Candidate) {
	// If replay inline is requested, simply follow the inline decision of the
	// profiled binary.
	if (SamplePreInlineReplay)
	return Candidate.CalleeSamples->getContext().hasAttribute(
	ContextWasInlined);

	// Adjust threshold based on call site hotness, only do this for callsite
	// prioritized inliner because otherwise cost-benefit check is done earlier.
	unsigned int SampleThreshold = SampleColdCallSiteThreshold;
	if (Candidate.CallsiteCount > HotCountThreshold)
	SampleThreshold = SampleHotCallSiteThreshold;

	// TODO: for small cold functions, we may inlined them and we need to keep
	// context profile accordingly.
	if (Candidate.CallsiteCount < ColdCountThreshold)
	SampleThreshold = SampleColdCallSiteThreshold;

	return (Candidate.SizeCost < SampleThreshold);
	}

	void CSPreInliner::processFunction(const StringRef Name) {
	LLVM_DEBUG(dbgs() << "Process " << Name
	<< " for context-sensitive pre-inlining\n");

	FunctionSamples *FSamples = ContextTracker.getBaseSamplesFor(Name);
	if (!FSamples)
	return;

	// Use the number of lines/probes as proxy for function size for now.
	// TODO: retrieve accurate size from dwarf or binary instead.
	unsigned FuncSize = FSamples->getBodySamples().size();
	unsigned FuncFinalSize = FuncSize;
	unsigned SizeLimit = FuncSize * ProfileInlineGrowthLimit;
	SizeLimit = std::min(SizeLimit, (unsigned)ProfileInlineLimitMax);
	SizeLimit = std::max(SizeLimit, (unsigned)ProfileInlineLimitMin);

	ProfiledCandidateQueue CQueue;
	getInlineCandidates(CQueue, FSamples);

	while (!CQueue.empty() && FuncFinalSize < SizeLimit) {
	ProfiledInlineCandidate Candidate = CQueue.top();
	CQueue.pop();
	bool ShouldInline = false;
	if ((ShouldInline = shouldInline(Candidate))) {
	// We mark context as inlined as the corresponding context profile
	// won't be merged into that function's base profile.
	ContextTracker.markContextSamplesInlined(Candidate.CalleeSamples);
	Candidate.CalleeSamples->getContext().setAttribute(
	ContextShouldBeInlined);
	FuncFinalSize += Candidate.SizeCost;
	getInlineCandidates(CQueue, Candidate.CalleeSamples);
	}
	LLVM_DEBUG(dbgs() << (ShouldInline ? " Inlined" : " Outlined")
	<< " context profile for: "
	<< Candidate.CalleeSamples->getNameWithContext()
	<< " (callee size: " << Candidate.SizeCost
	<< ", call count:" << Candidate.CallsiteCount << ")\n");
	}

	LLVM_DEBUG({
	if (!CQueue.empty())
	dbgs() << " Inline candidates ignored due to size limit (inliner "
	"original size: "
	<< FuncSize << ", inliner final size: " << FuncFinalSize
	<< ", size limit: " << SizeLimit << ")\n";

	while (!CQueue.empty()) {
	ProfiledInlineCandidate Candidate = CQueue.top();
	CQueue.pop();
	bool WasInlined =
	Candidate.CalleeSamples->getContext().hasAttribute(ContextWasInlined);
	dbgs() << " " << Candidate.CalleeSamples->getNameWithContext()
	<< " (candidate size:" << Candidate.SizeCost
	<< ", call count: " << Candidate.CallsiteCount << ", previously "
	<< (WasInlined ? "inlined)\n" : "not inlined)\n");
	}
	});
	}

	void CSPreInliner::run() {
	if (!EnableCSPreInliner)
	return;

	#ifndef NDEBUG
	auto printProfileNames = [](StringMap<FunctionSamples> &Profiles,
	bool IsInput) {
	dbgs() << (IsInput ? "Input" : "Output") << " context-sensitive profiles ("
	<< Profiles.size() << " total):\n";
	for (auto &It : Profiles) {
	const FunctionSamples &Samples = It.second;
	dbgs() << " [" << Samples.getNameWithContext() << "] "
	<< Samples.getTotalSamples() << ":" << Samples.getHeadSamples()
	<< "\n";
	}
	};
	#endif

	LLVM_DEBUG(printProfileNames(ProfileMap, true));

	// Execute global pre-inliner to estimate a global top-down inline
	// decision and merge profiles accordingly. This helps with profile
	// merge for ThinLTO otherwise we won't be able to merge profiles back
	// to base profile across module/thin-backend boundaries.
	// It also helps better compress context profile to control profile
	// size, as we now only need context profile for functions going to
	// be inlined.
	for (StringRef FuncName : buildTopDownOrder()) {
	processFunction(FuncName);
	}

	// Not inlined context profiles are merged into its base, so we can
	// trim out such profiles from the output.
	std::vector<StringRef> ProfilesToBeRemoved;
	for (auto &It : ProfileMap) {
	SampleContext Context = It.second.getContext();
	if (!Context.isBaseContext() && !Context.hasState(InlinedContext)) {
	assert(Context.hasState(MergedContext) &&
	"Not inlined context profile should be merged already");
	ProfilesToBeRemoved.push_back(It.first());
	}
	}

	for (StringRef ContextName : ProfilesToBeRemoved) {
	ProfileMap.erase(ContextName);
	}

	// Make sure ProfileMap's key is consistent with FunctionSamples' name.
	SampleContextTrimmer(ProfileMap).canonicalizeContextProfiles();

	LLVM_DEBUG(printProfileNames(ProfileMap, false));
	}