blob: 633a853b2c74824f6ac87408c3133bc714ae69e4 [file] [log] [blame]
//===- MacroFusion.cpp - Macro Fusion -------------------------------------===//
// The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
/// \file This file contains the implementation of the DAG scheduling mutation
/// to pair instructions back to back.
#include "llvm/CodeGen/MacroFusion.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineScheduler.h"
#include "llvm/CodeGen/ScheduleDAG.h"
#include "llvm/CodeGen/ScheduleDAGMutation.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetInstrInfo.h"
#define DEBUG_TYPE "machine-scheduler"
STATISTIC(NumFused, "Number of instr pairs fused");
using namespace llvm;
static cl::opt<bool> EnableMacroFusion("misched-fusion", cl::Hidden,
cl::desc("Enable scheduling for macro fusion."), cl::init(true));
static void fuseInstructionPair(ScheduleDAGMI &DAG, SUnit &FirstSU,
SUnit &SecondSU) {
// Create a single weak edge between the adjacent instrs. The only effect is
// to cause bottom-up scheduling to heavily prioritize the clustered instrs.
DAG.addEdge(&SecondSU, SDep(&FirstSU, SDep::Cluster));
// Adjust the latency between the anchor instr and its
// predecessors.
for (SDep &IDep : SecondSU.Preds)
if (IDep.getSUnit() == &FirstSU)
// Adjust the latency between the dependent instr and its
// predecessors.
for (SDep &IDep : FirstSU.Succs)
if (IDep.getSUnit() == &SecondSU)
DEBUG(dbgs() << DAG.MF.getName() << "(): Macro fuse ";
FirstSU.print(dbgs(), &DAG); dbgs() << " - ";
SecondSU.print(dbgs(), &DAG); dbgs() << " / ";
dbgs() << DAG.TII->getName(FirstSU.getInstr()->getOpcode()) << " - " <<
DAG.TII->getName(SecondSU.getInstr()->getOpcode()) << '\n'; );
if (&SecondSU != &DAG.ExitSU)
// Make instructions dependent on FirstSU also dependent on SecondSU to
// prevent them from being scheduled between FirstSU and and SecondSU.
for (const SDep &SI : FirstSU.Succs) {
if (SI.getSUnit() == &SecondSU)
DEBUG(dbgs() << " Copy Succ ";
SI.getSUnit()->print(dbgs(), &DAG); dbgs() << '\n';);
DAG.addEdge(SI.getSUnit(), SDep(&SecondSU, SDep::Artificial));
namespace {
/// \brief Post-process the DAG to create cluster edges between instrs that may
/// be fused by the processor into a single operation.
class MacroFusion : public ScheduleDAGMutation {
ShouldSchedulePredTy shouldScheduleAdjacent;
bool FuseBlock;
bool scheduleAdjacentImpl(ScheduleDAGMI &DAG, SUnit &AnchorSU);
MacroFusion(ShouldSchedulePredTy shouldScheduleAdjacent, bool FuseBlock)
: shouldScheduleAdjacent(shouldScheduleAdjacent), FuseBlock(FuseBlock) {}
void apply(ScheduleDAGInstrs *DAGInstrs) override;
} // end anonymous namespace
void MacroFusion::apply(ScheduleDAGInstrs *DAGInstrs) {
ScheduleDAGMI *DAG = static_cast<ScheduleDAGMI*>(DAGInstrs);
if (FuseBlock)
// For each of the SUnits in the scheduling block, try to fuse the instr in
// it with one in its predecessors.
for (SUnit &ISU : DAG->SUnits)
scheduleAdjacentImpl(*DAG, ISU);
if (DAG->ExitSU.getInstr())
// Try to fuse the instr in the ExitSU with one in its predecessors.
scheduleAdjacentImpl(*DAG, DAG->ExitSU);
/// \brief Implement the fusion of instr pairs in the scheduling DAG,
/// anchored at the instr in AnchorSU..
bool MacroFusion::scheduleAdjacentImpl(ScheduleDAGMI &DAG, SUnit &AnchorSU) {
const MachineInstr &AnchorMI = *AnchorSU.getInstr();
const TargetInstrInfo &TII = *DAG.TII;
const TargetSubtargetInfo &ST = DAG.MF.getSubtarget();
// Check if the anchor instr may be fused.
if (!shouldScheduleAdjacent(TII, ST, nullptr, AnchorMI))
return false;
// Explorer for fusion candidates among the dependencies of the anchor instr.
for (SDep &Dep : AnchorSU.Preds) {
// Ignore dependencies that don't enforce ordering.
if (Dep.getKind() == SDep::Anti || Dep.getKind() == SDep::Output ||
SUnit &DepSU = *Dep.getSUnit();
if (DepSU.isBoundaryNode())
const MachineInstr *DepMI = DepSU.getInstr();
if (!shouldScheduleAdjacent(TII, ST, DepMI, AnchorMI))
fuseInstructionPair(DAG, DepSU, AnchorSU);
return true;
return false;
ShouldSchedulePredTy shouldScheduleAdjacent) {
return llvm::make_unique<MacroFusion>(shouldScheduleAdjacent, true);
return nullptr;
ShouldSchedulePredTy shouldScheduleAdjacent) {
return llvm::make_unique<MacroFusion>(shouldScheduleAdjacent, false);
return nullptr;