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//===---- MachineOutliner.h - Outliner data structures ------*- C++ -*-===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
/// \file
/// Contains all data structures shared between the outliner implemented in
/// MachineOutliner.cpp and target implementations of the outliner.
#include "llvm/CodeGen/LiveRegUnits.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/CodeGen/LivePhysRegs.h"
namespace llvm {
namespace outliner {
/// Represents how an instruction should be mapped by the outliner.
/// \p Legal instructions are those which are safe to outline.
/// \p LegalTerminator instructions are safe to outline, but only as the
/// last instruction in a sequence.
/// \p Illegal instructions are those which cannot be outlined.
/// \p Invisible instructions are instructions which can be outlined, but
/// shouldn't actually impact the outlining result.
enum InstrType { Legal, LegalTerminator, Illegal, Invisible };
/// An individual sequence of instructions to be replaced with a call to
/// an outlined function.
struct Candidate {
/// The start index of this \p Candidate in the instruction list.
unsigned StartIdx;
/// The number of instructions in this \p Candidate.
unsigned Len;
// The first instruction in this \p Candidate.
MachineBasicBlock::iterator FirstInst;
// The last instruction in this \p Candidate.
MachineBasicBlock::iterator LastInst;
// The basic block that contains this Candidate.
MachineBasicBlock *MBB;
/// Cost of calling an outlined function from this point as defined by the
/// target.
unsigned CallOverhead;
/// The index of this \p Candidate's \p OutlinedFunction in the list of
/// \p OutlinedFunctions.
unsigned FunctionIdx;
/// Identifier denoting the instructions to emit to call an outlined function
/// from this point. Defined by the target.
unsigned CallConstructionID;
/// Contains physical register liveness information for the MBB containing
/// this \p Candidate.
/// This is optionally used by the target to calculate more fine-grained
/// cost model information.
LiveRegUnits LRU;
/// Contains the accumulated register liveness information for the
/// instructions in this \p Candidate.
/// This is optionally used by the target to determine which registers have
/// been used across the sequence.
LiveRegUnits UsedInSequence;
/// Target-specific flags for this Candidate's MBB.
unsigned Flags = 0x0;
/// True if initLRU has been called on this Candidate.
bool LRUWasSet = false;
/// Return the number of instructions in this Candidate.
unsigned getLength() const { return Len; }
/// Return the start index of this candidate.
unsigned getStartIdx() const { return StartIdx; }
/// Return the end index of this candidate.
unsigned getEndIdx() const { return StartIdx + Len - 1; }
/// Set the CallConstructionID and CallOverhead of this candidate to CID and
/// CO respectively.
void setCallInfo(unsigned CID, unsigned CO) {
CallConstructionID = CID;
CallOverhead = CO;
/// Returns the call overhead of this candidate if it is in the list.
unsigned getCallOverhead() const { return CallOverhead; }
MachineBasicBlock::iterator &front() { return FirstInst; }
MachineBasicBlock::iterator &back() { return LastInst; }
MachineFunction *getMF() const { return MBB->getParent(); }
MachineBasicBlock *getMBB() const { return MBB; }
/// The number of instructions that would be saved by outlining every
/// candidate of this type.
/// This is a fixed value which is not updated during the candidate pruning
/// process. It is only used for deciding which candidate to keep if two
/// candidates overlap. The true benefit is stored in the OutlinedFunction
/// for some given candidate.
unsigned Benefit = 0;
Candidate(unsigned StartIdx, unsigned Len,
MachineBasicBlock::iterator &FirstInst,
MachineBasicBlock::iterator &LastInst, MachineBasicBlock *MBB,
unsigned FunctionIdx, unsigned Flags)
: StartIdx(StartIdx), Len(Len), FirstInst(FirstInst), LastInst(LastInst),
MBB(MBB), FunctionIdx(FunctionIdx), Flags(Flags) {}
Candidate() {}
/// Used to ensure that \p Candidates are outlined in an order that
/// preserves the start and end indices of other \p Candidates.
bool operator<(const Candidate &RHS) const {
return getStartIdx() > RHS.getStartIdx();
/// Compute the registers that are live across this Candidate.
/// Used by targets that need this information for cost model calculation.
/// If a target does not need this information, then this should not be
/// called.
void initLRU(const TargetRegisterInfo &TRI) {
assert(MBB->getParent()->getRegInfo().tracksLiveness() &&
"Candidate's Machine Function must track liveness");
// Only initialize once.
if (LRUWasSet)
LRUWasSet = true;
// Compute liveness from the end of the block up to the beginning of the
// outlining candidate.
std::for_each(MBB->rbegin(), (MachineBasicBlock::reverse_iterator)front(),
[this](MachineInstr &MI) { LRU.stepBackward(MI); });
// Walk over the sequence itself and figure out which registers were used
// in the sequence.
std::for_each(front(), std::next(back()),
[this](MachineInstr &MI) { UsedInSequence.accumulate(MI); });
/// The information necessary to create an outlined function for some
/// class of candidate.
struct OutlinedFunction {
std::vector<Candidate> Candidates;
/// The actual outlined function created.
/// This is initialized after we go through and create the actual function.
MachineFunction *MF = nullptr;
/// Represents the size of a sequence in bytes. (Some instructions vary
/// widely in size, so just counting the instructions isn't very useful.)
unsigned SequenceSize;
/// Target-defined overhead of constructing a frame for this function.
unsigned FrameOverhead;
/// Target-defined identifier for constructing a frame for this function.
unsigned FrameConstructionID;
/// Return the number of candidates for this \p OutlinedFunction.
unsigned getOccurrenceCount() const { return Candidates.size(); }
/// Return the number of bytes it would take to outline this
/// function.
unsigned getOutliningCost() const {
unsigned CallOverhead = 0;
for (const Candidate &C : Candidates)
CallOverhead += C.getCallOverhead();
return CallOverhead + SequenceSize + FrameOverhead;
/// Return the size in bytes of the unoutlined sequences.
unsigned getNotOutlinedCost() const {
return getOccurrenceCount() * SequenceSize;
/// Return the number of instructions that would be saved by outlining
/// this function.
unsigned getBenefit() const {
unsigned NotOutlinedCost = getNotOutlinedCost();
unsigned OutlinedCost = getOutliningCost();
return (NotOutlinedCost < OutlinedCost) ? 0
: NotOutlinedCost - OutlinedCost;
/// Return the number of instructions in this sequence.
unsigned getNumInstrs() const { return Candidates[0].getLength(); }
OutlinedFunction(std::vector<Candidate> &Candidates, unsigned SequenceSize,
unsigned FrameOverhead, unsigned FrameConstructionID)
: Candidates(Candidates), SequenceSize(SequenceSize),
FrameOverhead(FrameOverhead), FrameConstructionID(FrameConstructionID) {
const unsigned B = getBenefit();
for (Candidate &C : Candidates)
C.Benefit = B;
OutlinedFunction() {}
} // namespace outliner
} // namespace llvm