llvm/llvm/lib/Target/Hexagon/HexagonNewValueJump.cpp

//===- HexagonNewValueJump.cpp - Hexagon Backend New Value Jump -----------===//
//
// 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 implements NewValueJump pass in Hexagon.
// Ideally, we should merge this as a Peephole pass prior to register
// allocation, but because we have a spill in between the feeder and new value
// jump instructions, we are forced to write after register allocation.
// Having said that, we should re-attempt to pull this earlier at some point
// in future.

// The basic approach looks for sequence of predicated jump, compare instruciton
// that genereates the predicate and, the feeder to the predicate. Once it finds
// all, it collapses compare and jump instruction into a new value jump
// intstructions.
//
//===----------------------------------------------------------------------===//

#include "llvm/InitializePasses.h"
#include "Hexagon.h"
#include "HexagonInstrInfo.h"
#include "HexagonRegisterInfo.h"
#include "HexagonSubtarget.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/TargetOpcodes.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/IR/DebugLoc.h"
#include "llvm/MC/MCInstrDesc.h"
#include "llvm/Pass.h"
#include "llvm/Support/BranchProbability.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
#include <cassert>
#include <cstdint>
#include <iterator>

usingnamespacellvm;

#define DEBUG_TYPE …

STATISTIC(NumNVJGenerated, "Number of New Value Jump Instructions created");

static cl::opt<int> DbgNVJCount("nvj-count", cl::init(-1), cl::Hidden,
    cl::desc("Maximum number of predicated jumps to be converted to "
    "New Value Jump"));

static cl::opt<bool> DisableNewValueJumps("disable-nvjump", cl::Hidden,
                                          cl::desc("Disable New Value Jumps"));

namespace llvm {

FunctionPass *createHexagonNewValueJump();
void initializeHexagonNewValueJumpPass(PassRegistry&);

} // end namespace llvm

namespace {

  struct HexagonNewValueJump : public MachineFunctionPass { … };

} // end anonymous namespace

char HexagonNewValueJump::ID = …;

INITIALIZE_PASS_BEGIN(HexagonNewValueJump, "hexagon-nvj",
                      "Hexagon NewValueJump", false, false)
INITIALIZE_PASS_DEPENDENCY(MachineBranchProbabilityInfoWrapperPass)
INITIALIZE_PASS_END(HexagonNewValueJump, "hexagon-nvj",
                    "Hexagon NewValueJump", false, false)

// We have identified this II could be feeder to NVJ,
// verify that it can be.
static bool canBeFeederToNewValueJump(const HexagonInstrInfo *QII,
                                      const TargetRegisterInfo *TRI,
                                      MachineBasicBlock::iterator II,
                                      MachineBasicBlock::iterator end,
                                      MachineBasicBlock::iterator skip,
                                      MachineFunction &MF) { … }

// These are the common checks that need to performed
// to determine if
// 1. compare instruction can be moved before jump.
// 2. feeder to the compare instruction can be moved before jump.
static bool commonChecksToProhibitNewValueJump(bool afterRA,
                          MachineBasicBlock::iterator MII) { … }

static bool canCompareBeNewValueJump(const HexagonInstrInfo *QII,
                                     const TargetRegisterInfo *TRI,
                                     MachineBasicBlock::iterator II,
                                     unsigned pReg,
                                     bool secondReg,
                                     bool optLocation,
                                     MachineBasicBlock::iterator end,
                                     MachineFunction &MF) { … }

// Given a compare operator, return a matching New Value Jump compare operator.
// Make sure that MI here is included in isNewValueJumpCandidate.
static unsigned getNewValueJumpOpcode(MachineInstr *MI, int reg,
                                      bool secondRegNewified,
                                      MachineBasicBlock *jmpTarget,
                                      const MachineBranchProbabilityInfo
                                      *MBPI) { … }

bool HexagonNewValueJump::isNewValueJumpCandidate(
    const MachineInstr &MI) const { … }

bool HexagonNewValueJump::runOnMachineFunction(MachineFunction &MF) { … }

FunctionPass *llvm::createHexagonNewValueJump() { … }