llvm/llvm/lib/Target/WebAssembly/WebAssemblyFrameLowering.cpp

//===-- WebAssemblyFrameLowering.cpp - WebAssembly Frame Lowering ----------==//
//
// 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
/// This file contains the WebAssembly implementation of
/// TargetFrameLowering class.
///
/// On WebAssembly, there aren't a lot of things to do here. There are no
/// callee-saved registers to save, and no spill slots.
///
/// The stack grows downward.
///
//===----------------------------------------------------------------------===//

#include "WebAssemblyFrameLowering.h"
#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
#include "Utils/WebAssemblyTypeUtilities.h"
#include "WebAssembly.h"
#include "WebAssemblyInstrInfo.h"
#include "WebAssemblyMachineFunctionInfo.h"
#include "WebAssemblySubtarget.h"
#include "WebAssemblyTargetMachine.h"
#include "llvm/CodeGen/Analysis.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineModuleInfoImpls.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/IR/Instructions.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/Support/Debug.h"
usingnamespacellvm;

#define DEBUG_TYPE …

// TODO: wasm64
// TODO: Emit TargetOpcode::CFI_INSTRUCTION instructions

// In an ideal world, when objects are added to the MachineFrameInfo by
// FunctionLoweringInfo::set, we could somehow hook into target-specific code to
// ensure they are assigned the right stack ID.  However there isn't a hook that
// runs between then and DAG building time, though, so instead we hoist stack
// objects lazily when they are first used, and comprehensively after the DAG is
// built via the PreprocessISelDAG hook, called by the
// SelectionDAGISel::runOnMachineFunction.  We have to do it in two places
// because we want to do it while building the selection DAG for uses of alloca,
// but not all alloca instructions are used so we have to follow up afterwards.
std::optional<unsigned>
WebAssemblyFrameLowering::getLocalForStackObject(MachineFunction &MF,
                                                 int FrameIndex) { … }

/// We need a base pointer in the case of having items on the stack that
/// require stricter alignment than the stack pointer itself.  Because we need
/// to shift the stack pointer by some unknown amount to force the alignment,
/// we need to record the value of the stack pointer on entry to the function.
bool WebAssemblyFrameLowering::hasBP(const MachineFunction &MF) const { … }

/// Return true if the specified function should have a dedicated frame pointer
/// register.
bool WebAssemblyFrameLowering::hasFP(const MachineFunction &MF) const { … }

/// Under normal circumstances, when a frame pointer is not required, we reserve
/// argument space for call sites in the function immediately on entry to the
/// current function. This eliminates the need for add/sub sp brackets around
/// call sites. Returns true if the call frame is included as part of the stack
/// frame.
bool WebAssemblyFrameLowering::hasReservedCallFrame(
    const MachineFunction &MF) const { … }

// Returns true if this function needs a local user-space stack pointer for its
// local frame (not for exception handling).
bool WebAssemblyFrameLowering::needsSPForLocalFrame(
    const MachineFunction &MF) const { … }

// In function with EH pads, we need to make a copy of the value of
// __stack_pointer global in SP32/64 register, in order to use it when
// restoring __stack_pointer after an exception is caught.
bool WebAssemblyFrameLowering::needsPrologForEH(
    const MachineFunction &MF) const { … }

/// Returns true if this function needs a local user-space stack pointer.
/// Unlike a machine stack pointer, the wasm user stack pointer is a global
/// variable, so it is loaded into a register in the prolog.
bool WebAssemblyFrameLowering::needsSP(const MachineFunction &MF) const { … }

/// Returns true if the local user-space stack pointer needs to be written back
/// to __stack_pointer global by this function (this is not meaningful if
/// needsSP is false). If false, the stack red zone can be used and only a local
/// SP is needed.
bool WebAssemblyFrameLowering::needsSPWriteback(
    const MachineFunction &MF) const { … }

unsigned WebAssemblyFrameLowering::getSPReg(const MachineFunction &MF) { … }

unsigned WebAssemblyFrameLowering::getFPReg(const MachineFunction &MF) { … }

unsigned
WebAssemblyFrameLowering::getOpcConst(const MachineFunction &MF) { … }

unsigned WebAssemblyFrameLowering::getOpcAdd(const MachineFunction &MF) { … }

unsigned WebAssemblyFrameLowering::getOpcSub(const MachineFunction &MF) { … }

unsigned WebAssemblyFrameLowering::getOpcAnd(const MachineFunction &MF) { … }

unsigned
WebAssemblyFrameLowering::getOpcGlobGet(const MachineFunction &MF) { … }

unsigned
WebAssemblyFrameLowering::getOpcGlobSet(const MachineFunction &MF) { … }

void WebAssemblyFrameLowering::writeSPToGlobal(
    unsigned SrcReg, MachineFunction &MF, MachineBasicBlock &MBB,
    MachineBasicBlock::iterator &InsertStore, const DebugLoc &DL) const { … }

MachineBasicBlock::iterator
WebAssemblyFrameLowering::eliminateCallFramePseudoInstr(
    MachineFunction &MF, MachineBasicBlock &MBB,
    MachineBasicBlock::iterator I) const { … }

void WebAssemblyFrameLowering::emitPrologue(MachineFunction &MF,
                                            MachineBasicBlock &MBB) const { … }

void WebAssemblyFrameLowering::emitEpilogue(MachineFunction &MF,
                                            MachineBasicBlock &MBB) const { … }

bool WebAssemblyFrameLowering::isSupportedStackID(
    TargetStackID::Value ID) const { … }

TargetFrameLowering::DwarfFrameBase
WebAssemblyFrameLowering::getDwarfFrameBase(const MachineFunction &MF) const { … }