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//===-- 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;
// 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() {
#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));
}
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