llvm/llvm/lib/Target/X86/X86CallFrameOptimization.cpp

//===----- X86CallFrameOptimization.cpp - Optimize x86 call sequences -----===//
//
// 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 defines a pass that optimizes call sequences on x86.
// Currently, it converts movs of function parameters onto the stack into
// pushes. This is beneficial for two main reasons:
// 1) The push instruction encoding is much smaller than a stack-ptr-based mov.
// 2) It is possible to push memory arguments directly. So, if the
//    the transformation is performed pre-reg-alloc, it can help relieve
//    register pressure.
//
//===----------------------------------------------------------------------===//

#include "MCTargetDesc/X86BaseInfo.h"
#include "X86.h"
#include "X86FrameLowering.h"
#include "X86InstrInfo.h"
#include "X86MachineFunctionInfo.h"
#include "X86RegisterInfo.h"
#include "X86Subtarget.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineFrameInfo.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/TargetInstrInfo.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/IR/DebugLoc.h"
#include "llvm/IR/Function.h"
#include "llvm/MC/MCDwarf.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/MathExtras.h"
#include <cassert>
#include <cstddef>
#include <cstdint>
#include <iterator>

usingnamespacellvm;

#define DEBUG_TYPE …

static cl::opt<bool>
    NoX86CFOpt("no-x86-call-frame-opt",
               cl::desc("Avoid optimizing x86 call frames for size"),
               cl::init(false), cl::Hidden);

namespace {

class X86CallFrameOptimization : public MachineFunctionPass { … };

} // end anonymous namespace
char X86CallFrameOptimization::ID = …;
INITIALIZE_PASS(…)

// This checks whether the transformation is legal.
// Also returns false in cases where it's potentially legal, but
// we don't even want to try.
bool X86CallFrameOptimization::isLegal(MachineFunction &MF) { … }

// Check whether this transformation is profitable for a particular
// function - in terms of code size.
bool X86CallFrameOptimization::isProfitable(MachineFunction &MF,
                                            ContextVector &CallSeqVector) { … }

bool X86CallFrameOptimization::runOnMachineFunction(MachineFunction &MF) { … }

X86CallFrameOptimization::InstClassification
X86CallFrameOptimization::classifyInstruction(
    MachineBasicBlock &MBB, MachineBasicBlock::iterator MI,
    const X86RegisterInfo &RegInfo, DenseSet<unsigned int> &UsedRegs) { … }

void X86CallFrameOptimization::collectCallInfo(MachineFunction &MF,
                                               MachineBasicBlock &MBB,
                                               MachineBasicBlock::iterator I,
                                               CallContext &Context) { … }

void X86CallFrameOptimization::adjustCallSequence(MachineFunction &MF,
                                                  const CallContext &Context) { … }

MachineInstr *X86CallFrameOptimization::canFoldIntoRegPush(
    MachineBasicBlock::iterator FrameSetup, Register Reg) { … }

FunctionPass *llvm::createX86CallFrameOptimization() { … }