llvm/llvm/lib/Target/X86/X86FlagsCopyLowering.cpp

//====- X86FlagsCopyLowering.cpp - Lowers COPY nodes of EFLAGS ------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
/// \file
///
/// Lowers COPY nodes of EFLAGS by directly extracting and preserving individual
/// flag bits.
///
/// We have to do this by carefully analyzing and rewriting the usage of the
/// copied EFLAGS register because there is no general way to rematerialize the
/// entire EFLAGS register safely and efficiently. Using `popf` both forces
/// dynamic stack adjustment and can create correctness issues due to IF, TF,
/// and other non-status flags being overwritten. Using sequences involving
/// SAHF don't work on all x86 processors and are often quite slow compared to
/// directly testing a single status preserved in its own GPR.
///
//===----------------------------------------------------------------------===//

#include "X86.h"
#include "X86InstrBuilder.h"
#include "X86InstrInfo.h"
#include "X86Subtarget.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/ScopeExit.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineConstantPool.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/MachineSSAUpdater.h"
#include "llvm/CodeGen/TargetInstrInfo.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/CodeGen/TargetSchedule.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/IR/DebugLoc.h"
#include "llvm/MC/MCSchedule.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <cassert>
#include <iterator>
#include <utility>

usingnamespacellvm;

#define PASS_KEY …
#define DEBUG_TYPE …

STATISTIC(NumCopiesEliminated, "Number of copies of EFLAGS eliminated");
STATISTIC(NumSetCCsInserted, "Number of setCC instructions inserted");
STATISTIC(NumTestsInserted, "Number of test instructions inserted");
STATISTIC(NumAddsInserted, "Number of adds instructions inserted");
STATISTIC(NumNFsConvertedTo, "Number of NF instructions converted to");

namespace {

// Convenient array type for storing registers associated with each condition.
CondRegArray;

class X86FlagsCopyLoweringPass : public MachineFunctionPass { … };

} // end anonymous namespace

INITIALIZE_PASS_BEGIN(X86FlagsCopyLoweringPass, DEBUG_TYPE,
                      "X86 EFLAGS copy lowering", false, false)
INITIALIZE_PASS_END(X86FlagsCopyLoweringPass, DEBUG_TYPE,
                    "X86 EFLAGS copy lowering", false, false)

FunctionPass *llvm::createX86FlagsCopyLoweringPass() { … }

char X86FlagsCopyLoweringPass::ID = …;

void X86FlagsCopyLoweringPass::getAnalysisUsage(AnalysisUsage &AU) const { … }

static bool isArithmeticOp(unsigned Opc) { … }

static MachineBasicBlock &splitBlock(MachineBasicBlock &MBB,
                                     MachineInstr &SplitI,
                                     const X86InstrInfo &TII) { … }

enum EFLAGSClobber { … };

static EFLAGSClobber getClobberType(const MachineInstr &MI) { … }

bool X86FlagsCopyLoweringPass::runOnMachineFunction(MachineFunction &MF) { … }

/// Collect any conditions that have already been set in registers so that we
/// can re-use them rather than adding duplicates.
CondRegArray X86FlagsCopyLoweringPass::collectCondsInRegs(
    MachineBasicBlock &MBB, MachineBasicBlock::iterator TestPos) { … }

Register X86FlagsCopyLoweringPass::promoteCondToReg(
    MachineBasicBlock &TestMBB, MachineBasicBlock::iterator TestPos,
    const DebugLoc &TestLoc, X86::CondCode Cond) { … }

std::pair<unsigned, bool> X86FlagsCopyLoweringPass::getCondOrInverseInReg(
    MachineBasicBlock &TestMBB, MachineBasicBlock::iterator TestPos,
    const DebugLoc &TestLoc, X86::CondCode Cond, CondRegArray &CondRegs) { … }

void X86FlagsCopyLoweringPass::insertTest(MachineBasicBlock &MBB,
                                          MachineBasicBlock::iterator Pos,
                                          const DebugLoc &Loc, unsigned Reg) { … }

void X86FlagsCopyLoweringPass::rewriteSetCC(MachineBasicBlock &MBB,
                                            MachineBasicBlock::iterator Pos,
                                            const DebugLoc &Loc,
                                            MachineInstr &MI,
                                            CondRegArray &CondRegs) { … }

void X86FlagsCopyLoweringPass::rewriteArithmetic(
    MachineBasicBlock &MBB, MachineBasicBlock::iterator Pos,
    const DebugLoc &Loc, MachineInstr &MI, CondRegArray &CondRegs) { … }

static X86::CondCode getImplicitCondFromMI(unsigned Opc) { … }

static unsigned getOpcodeWithCC(unsigned Opc, X86::CondCode CC) { … }

void X86FlagsCopyLoweringPass::rewriteMI(MachineBasicBlock &MBB,
                                         MachineBasicBlock::iterator Pos,
                                         const DebugLoc &Loc, MachineInstr &MI,
                                         CondRegArray &CondRegs) { … }