AArch64LowerHomogeneousPrologEpilog.cpp

//===- AArch64LowerHomogeneousPrologEpilog.cpp ----------------------------===//
//
// 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 contains a pass that lowers homogeneous prolog/epilog instructions.
//
//===----------------------------------------------------------------------===//

#include "AArch64InstrInfo.h"
#include "AArch64Subtarget.h"
#include "MCTargetDesc/AArch64InstPrinter.h"
#include "Utils/AArch64BaseInfo.h"
#include "llvm/CodeGen/MachineBasicBlock.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/TargetSubtargetInfo.h"
#include "llvm/IR/DebugLoc.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Module.h"
#include "llvm/Pass.h"
#include "llvm/Support/raw_ostream.h"
#include <optional>
#include <sstream>

usingnamespacellvm;

#define AARCH64_LOWER_HOMOGENEOUS_PROLOG_EPILOG_NAME …

cl::opt<int> FrameHelperSizeThreshold(
    "frame-helper-size-threshold", cl::init(2), cl::Hidden,
    cl::desc("The minimum number of instructions that are outlined in a frame "
             "helper (default = 2)"));

namespace {

class AArch64LowerHomogeneousPE { … };

class AArch64LowerHomogeneousPrologEpilog : public ModulePass { … };

} // end anonymous namespace

char AArch64LowerHomogeneousPrologEpilog::ID = …;

INITIALIZE_PASS(…)

bool AArch64LowerHomogeneousPrologEpilog::runOnModule(Module &M) { … }

bool AArch64LowerHomogeneousPE::run() { … }
enum FrameHelperType { … };

/// Return a frame helper name with the given CSRs and the helper type.
/// For instance, a prolog helper that saves x19 and x20 is named as
/// OUTLINED_FUNCTION_PROLOG_x19x20.
static std::string getFrameHelperName(SmallVectorImpl<unsigned> &Regs,
                                      FrameHelperType Type, unsigned FpOffset) { … }

/// Create a Function for the unique frame helper with the given name.
/// Return a newly created MachineFunction with an empty MachineBasicBlock.
static MachineFunction &createFrameHelperMachineFunction(Module *M,
                                                         MachineModuleInfo *MMI,
                                                         StringRef Name) { … }

/// Emit a store-pair instruction for frame-setup.
/// If Reg2 is AArch64::NoRegister, emit STR instead.
static void emitStore(MachineFunction &MF, MachineBasicBlock &MBB,
                      MachineBasicBlock::iterator Pos,
                      const TargetInstrInfo &TII, unsigned Reg1, unsigned Reg2,
                      int Offset, bool IsPreDec) { … }

/// Emit a load-pair instruction for frame-destroy.
/// If Reg2 is AArch64::NoRegister, emit LDR instead.
static void emitLoad(MachineFunction &MF, MachineBasicBlock &MBB,
                     MachineBasicBlock::iterator Pos,
                     const TargetInstrInfo &TII, unsigned Reg1, unsigned Reg2,
                     int Offset, bool IsPostDec) { … }

/// Return a unique function if a helper can be formed with the given Regs
/// and frame type.
/// 1) _OUTLINED_FUNCTION_PROLOG_x30x29x19x20x21x22:
///    stp x22, x21, [sp, #-32]!    ; x29/x30 has been stored at the caller
///    stp x20, x19, [sp, #16]
///    ret
///
/// 2) _OUTLINED_FUNCTION_PROLOG_FRAME32_x30x29x19x20x21x22:
///    stp x22, x21, [sp, #-32]!    ; x29/x30 has been stored at the caller
///    stp x20, x19, [sp, #16]
///    add fp, sp, #32
///    ret
///
/// 3) _OUTLINED_FUNCTION_EPILOG_x30x29x19x20x21x22:
///    mov x16, x30
///    ldp x29, x30, [sp, #32]
///    ldp x20, x19, [sp, #16]
///    ldp x22, x21, [sp], #48
///    ret x16
///
/// 4) _OUTLINED_FUNCTION_EPILOG_TAIL_x30x29x19x20x21x22:
///    ldp x29, x30, [sp, #32]
///    ldp x20, x19, [sp, #16]
///    ldp x22, x21, [sp], #48
///    ret
/// @param M module
/// @param MMI machine module info
/// @param Regs callee save regs that the helper will handle
/// @param Type frame helper type
/// @return a helper function
static Function *getOrCreateFrameHelper(Module *M, MachineModuleInfo *MMI,
                                        SmallVectorImpl<unsigned> &Regs,
                                        FrameHelperType Type,
                                        unsigned FpOffset = 0) { … }

/// This function checks if a frame helper should be used for
/// HOM_Prolog/HOM_Epilog pseudo instruction expansion.
/// @param MBB machine basic block
/// @param NextMBBI  next instruction following HOM_Prolog/HOM_Epilog
/// @param Regs callee save registers that are saved or restored.
/// @param Type frame helper type
/// @return True if a use of helper is qualified.
static bool shouldUseFrameHelper(MachineBasicBlock &MBB,
                                 MachineBasicBlock::iterator &NextMBBI,
                                 SmallVectorImpl<unsigned> &Regs,
                                 FrameHelperType Type) { … }

/// Lower a HOM_Epilog pseudo instruction into a helper call while
/// creating the helper on demand. Or emit a sequence of loads in place when not
/// using a helper call.
///
/// 1. With a helper including ret
///    HOM_Epilog x30, x29, x19, x20, x21, x22              ; MBBI
///    ret                                                  ; NextMBBI
///    =>
///    b _OUTLINED_FUNCTION_EPILOG_TAIL_x30x29x19x20x21x22
///    ...                                                  ; NextMBBI
///
/// 2. With a helper
///    HOM_Epilog x30, x29, x19, x20, x21, x22
///    =>
///    bl _OUTLINED_FUNCTION_EPILOG_x30x29x19x20x21x22
///
/// 3. Without a helper
///    HOM_Epilog x30, x29, x19, x20, x21, x22
///    =>
///    ldp x29, x30, [sp, #32]
///    ldp x20, x19, [sp, #16]
///    ldp x22, x21, [sp], #48
bool AArch64LowerHomogeneousPE::lowerEpilog(
    MachineBasicBlock &MBB, MachineBasicBlock::iterator MBBI,
    MachineBasicBlock::iterator &NextMBBI) { … }

/// Lower a HOM_Prolog pseudo instruction into a helper call while
/// creating the helper on demand. Or emit a sequence of stores in place when
/// not using a helper call.
///
/// 1. With a helper including frame-setup
///    HOM_Prolog x30, x29, x19, x20, x21, x22, 32
///    =>
///    stp x29, x30, [sp, #-16]!
///    bl _OUTLINED_FUNCTION_PROLOG_FRAME32_x30x29x19x20x21x22
///
/// 2. With a helper
///    HOM_Prolog x30, x29, x19, x20, x21, x22
///    =>
///    stp x29, x30, [sp, #-16]!
///    bl _OUTLINED_FUNCTION_PROLOG_x30x29x19x20x21x22
///
/// 3. Without a helper
///    HOM_Prolog x30, x29, x19, x20, x21, x22
///    =>
///    stp	x22, x21, [sp, #-48]!
///    stp	x20, x19, [sp, #16]
///    stp	x29, x30, [sp, #32]
bool AArch64LowerHomogeneousPE::lowerProlog(
    MachineBasicBlock &MBB, MachineBasicBlock::iterator MBBI,
    MachineBasicBlock::iterator &NextMBBI) { … }

/// Process each machine instruction
/// @param MBB machine basic block
/// @param MBBI current instruction iterator
/// @param NextMBBI next instruction iterator which can be updated
/// @return True when IR is changed.
bool AArch64LowerHomogeneousPE::runOnMI(MachineBasicBlock &MBB,
                                        MachineBasicBlock::iterator MBBI,
                                        MachineBasicBlock::iterator &NextMBBI) { … }

bool AArch64LowerHomogeneousPE::runOnMBB(MachineBasicBlock &MBB) { … }

bool AArch64LowerHomogeneousPE::runOnMachineFunction(MachineFunction &MF) { … }

ModulePass *llvm::createAArch64LowerHomogeneousPrologEpilogPass() { … }
llvm/llvm/lib/Target/AArch64/AArch64LowerHomogeneousPrologEpilog.cpp
