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//===- PGOCtxProfWriter.h - Contextual Profile Writer -----------*- 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
//
//===----------------------------------------------------------------------===//
//
// This file declares a utility for writing a contextual profile to bitstream.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_PROFILEDATA_PGOCTXPROFWRITER_H_
#define LLVM_PROFILEDATA_PGOCTXPROFWRITER_H_
#include "llvm/Bitstream/BitCodeEnums.h"
#include "llvm/Bitstream/BitstreamWriter.h"
#include "llvm/ProfileData/CtxInstrContextNode.h"
namespace llvm {
enum PGOCtxProfileRecords { Invalid = 0, Version, Guid, CalleeIndex, Counters };
enum PGOCtxProfileBlockIDs {
ProfileMetadataBlockID = bitc::FIRST_APPLICATION_BLOCKID,
ContextNodeBlockID = ProfileMetadataBlockID + 1
};
/// Write one or more ContextNodes to the provided raw_fd_stream.
/// The caller must destroy the PGOCtxProfileWriter object before closing the
/// stream.
/// The design allows serializing a bunch of contexts embedded in some other
/// file. The overall format is:
///
/// [... other data written to the stream...]
/// SubBlock(ProfileMetadataBlockID)
/// Version
/// SubBlock(ContextNodeBlockID)
/// [RECORDS]
/// SubBlock(ContextNodeBlockID)
/// [RECORDS]
/// [... more SubBlocks]
/// EndBlock
/// EndBlock
///
/// The "RECORDS" are bitsream records. The IDs are in CtxProfileCodes (except)
/// for Version, which is just for metadata). All contexts will have Guid and
/// Counters, and all but the roots have CalleeIndex. The order in which the
/// records appear does not matter, but they must precede any subcontexts,
/// because that helps keep the reader code simpler.
///
/// Subblock containment captures the context->subcontext relationship. The
/// "next()" relationship in the raw profile, between call targets of indirect
/// calls, are just modeled as peer subblocks where the callee index is the
/// same.
///
/// Versioning: the writer may produce additional records not known by the
/// reader. The version number indicates a more structural change.
/// The current version, in particular, is set up to expect optional extensions
/// like value profiling - which would appear as additional records. For
/// example, value profiling would produce a new record with a new record ID,
/// containing the profiled values (much like the counters)
class PGOCtxProfileWriter final {
BitstreamWriter Writer;
void writeCounters(const ctx_profile::ContextNode &Node);
void writeImpl(std::optional<uint32_t> CallerIndex,
const ctx_profile::ContextNode &Node);
public:
PGOCtxProfileWriter(raw_ostream &Out,
std::optional<unsigned> VersionOverride = std::nullopt)
: Writer(Out, 0) {
Writer.EnterSubblock(PGOCtxProfileBlockIDs::ProfileMetadataBlockID,
CodeLen);
const auto Version = VersionOverride ? *VersionOverride : CurrentVersion;
Writer.EmitRecord(PGOCtxProfileRecords::Version,
SmallVector<unsigned, 1>({Version}));
}
~PGOCtxProfileWriter() { Writer.ExitBlock(); }
void write(const ctx_profile::ContextNode &);
// constants used in writing which a reader may find useful.
static constexpr unsigned CodeLen = 2;
static constexpr uint32_t CurrentVersion = 1;
static constexpr unsigned VBREncodingBits = 6;
};
} // namespace llvm
#endif
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