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//===- PGOCtxProfFlattening.cpp - Contextual Instr. Flattening ------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// Flattens the contextual profile and lowers it to MD_prof.
// This should happen after all IPO (which is assumed to have maintained the
// contextual profile) happened. Flattening consists of summing the values at
// the same index of the counters belonging to all the contexts of a function.
// The lowering consists of materializing the counter values to function
// entrypoint counts and branch probabilities.
//
// This pass also removes contextual instrumentation, which has been kept around
// to facilitate its functionality.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Instrumentation/PGOCtxProfFlattening.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/ScopeExit.h"
#include "llvm/Analysis/CFG.h"
#include "llvm/Analysis/CtxProfAnalysis.h"
#include "llvm/Analysis/ProfileSummaryInfo.h"
#include "llvm/IR/Analysis.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/PassManager.h"
#include "llvm/IR/ProfileSummary.h"
#include "llvm/ProfileData/ProfileCommon.h"
#include "llvm/Transforms/Instrumentation/PGOInstrumentation.h"
#include "llvm/Transforms/Scalar/DCE.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
using namespace llvm;
#define DEBUG_TYPE "ctx_prof_flatten"
namespace {
/// Assign branch weights and function entry count. Also update the PSI
/// builder.
void assignProfileData(Function &F, ArrayRef<uint64_t> RawCounters) {
assert(!RawCounters.empty());
ProfileAnnotator PA(F, RawCounters);
F.setEntryCount(RawCounters[0]);
SmallVector<uint64_t, 2> ProfileHolder;
for (auto &BB : F) {
for (auto &I : BB)
if (auto *SI = dyn_cast<SelectInst>(&I)) {
uint64_t TrueCount, FalseCount = 0;
if (!PA.getSelectInstrProfile(*SI, TrueCount, FalseCount))
continue;
setProfMetadata(SI, {TrueCount, FalseCount},
std::max(TrueCount, FalseCount));
}
if (succ_size(&BB) < 2)
continue;
uint64_t MaxCount = 0;
if (!PA.getOutgoingBranchWeights(BB, ProfileHolder, MaxCount))
continue;
assert(MaxCount > 0);
setProfMetadata(BB.getTerminator(), ProfileHolder, MaxCount);
}
}
[[maybe_unused]] bool areAllBBsReachable(const Function &F,
FunctionAnalysisManager &FAM) {
auto &DT = FAM.getResult<DominatorTreeAnalysis>(const_cast<Function &>(F));
return llvm::all_of(
F, [&](const BasicBlock &BB) { return DT.isReachableFromEntry(&BB); });
}
void clearColdFunctionProfile(Function &F) {
for (auto &BB : F)
BB.getTerminator()->setMetadata(LLVMContext::MD_prof, nullptr);
F.setEntryCount(0U);
}
void removeInstrumentation(Function &F) {
for (auto &BB : F)
for (auto &I : llvm::make_early_inc_range(BB))
if (isa<InstrProfCntrInstBase>(I))
I.eraseFromParent();
}
void annotateIndirectCall(
Module &M, CallBase &CB,
const DenseMap<uint32_t, FlatIndirectTargets> &FlatProf,
const InstrProfCallsite &Ins) {
auto Idx = Ins.getIndex()->getZExtValue();
auto FIt = FlatProf.find(Idx);
if (FIt == FlatProf.end())
return;
const auto &Targets = FIt->second;
SmallVector<InstrProfValueData, 2> Data;
uint64_t Sum = 0;
for (auto &[Guid, Count] : Targets) {
Data.push_back({/*.Value=*/Guid, /*.Count=*/Count});
Sum += Count;
}
llvm::sort(Data,
[](const InstrProfValueData &A, const InstrProfValueData &B) {
return A.Count > B.Count;
});
llvm::annotateValueSite(M, CB, Data, Sum,
InstrProfValueKind::IPVK_IndirectCallTarget,
Data.size());
LLVM_DEBUG(dbgs() << "[ctxprof] flat indirect call prof: " << CB
<< CB.getMetadata(LLVMContext::MD_prof) << "\n");
}
// We normally return a "Changed" bool, but the calling pass' run assumes
// something will change - some profile will be added - so this won't add much
// by returning false when applicable.
void annotateIndirectCalls(Module &M, const CtxProfAnalysis::Result &CtxProf) {
const auto FlatIndCalls = CtxProf.flattenVirtCalls();
for (auto &F : M) {
if (F.isDeclaration())
continue;
auto FlatProfIter = FlatIndCalls.find(AssignGUIDPass::getGUID(F));
if (FlatProfIter == FlatIndCalls.end())
continue;
const auto &FlatProf = FlatProfIter->second;
for (auto &BB : F) {
for (auto &I : BB) {
auto *CB = dyn_cast<CallBase>(&I);
if (!CB || !CB->isIndirectCall())
continue;
if (auto *Ins = CtxProfAnalysis::getCallsiteInstrumentation(*CB))
annotateIndirectCall(M, *CB, FlatProf, *Ins);
}
}
}
}
} // namespace
PreservedAnalyses PGOCtxProfFlatteningPass::run(Module &M,
ModuleAnalysisManager &MAM) {
// Ensure in all cases the instrumentation is removed: if this module had no
// roots, the contextual profile would evaluate to false, but there would
// still be instrumentation.
// Note: in such cases we leave as-is any other profile info (if present -
// e.g. synthetic weights, etc) because it wouldn't interfere with the
// contextual - based one (which would be in other modules)
auto OnExit = llvm::make_scope_exit([&]() {
if (IsPreThinlink)
return;
for (auto &F : M)
removeInstrumentation(F);
});
auto &CtxProf = MAM.getResult<CtxProfAnalysis>(M);
// post-thinlink, we only reprocess for the module(s) containing the
// contextual tree. For everything else, OnExit will just clean the
// instrumentation.
if (!IsPreThinlink && !CtxProf.isInSpecializedModule())
return PreservedAnalyses::none();
if (IsPreThinlink)
annotateIndirectCalls(M, CtxProf);
const auto FlattenedProfile = CtxProf.flatten();
for (auto &F : M) {
if (F.isDeclaration())
continue;
assert(areAllBBsReachable(
F, MAM.getResult<FunctionAnalysisManagerModuleProxy>(M)
.getManager()) &&
"Function has unreacheable basic blocks. The expectation was that "
"DCE was run before.");
auto It = FlattenedProfile.find(AssignGUIDPass::getGUID(F));
// If this function didn't appear in the contextual profile, it's cold.
if (It == FlattenedProfile.end())
clearColdFunctionProfile(F);
else
assignProfileData(F, It->second);
}
InstrProfSummaryBuilder PB(ProfileSummaryBuilder::DefaultCutoffs);
// use here the flat profiles just so the importer doesn't complain about
// how different the PSIs are between the module with the roots and the
// various modules it imports.
for (auto &C : FlattenedProfile) {
PB.addEntryCount(C.second[0]);
for (auto V : llvm::drop_begin(C.second))
PB.addInternalCount(V);
}
M.setProfileSummary(PB.getSummary()->getMD(M.getContext()),
ProfileSummary::Kind::PSK_Instr);
PreservedAnalyses PA;
PA.abandon<ProfileSummaryAnalysis>();
MAM.invalidate(M, PA);
auto &PSI = MAM.getResult<ProfileSummaryAnalysis>(M);
PSI.refresh(PB.getSummary());
return PreservedAnalyses::none();
}
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