llvm/lib/Target/WebAssembly/WebAssemblyFrameLowering.cpp - toolchain/llvm-project - Gitiles

 //===-- WebAssemblyFrameLowering.cpp - WebAssembly Frame Lowering ----------==//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
 /// \brief 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 "WebAssemblyInstrInfo.h"
 #include "WebAssemblyMachineFunctionInfo.h"
 #include "WebAssemblySubtarget.h"
 #include "WebAssemblyTargetMachine.h"
 #include "WebAssemblyUtilities.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/Support/Debug.h"
 using namespace llvm;

 #define DEBUG_TYPE "wasm-frame-info"

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

 /// 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 {
   const auto *RegInfo =
       MF.getSubtarget<WebAssemblySubtarget>().getRegisterInfo();
   return RegInfo->needsStackRealignment(MF);
 }

 /// Return true if the specified function should have a dedicated frame pointer
 /// register.
 bool WebAssemblyFrameLowering::hasFP(const MachineFunction &MF) const {
   const MachineFrameInfo &MFI = MF.getFrameInfo();

   // When we have var-sized objects, we move the stack pointer by an unknown
   // amount, and need to emit a frame pointer to restore the stack to where we
   // were on function entry.
   // If we already need a base pointer, we use that to fix up the stack pointer.
   // If there are no fixed-size objects, we would have no use of a frame
   // pointer, and thus should not emit one.
   bool HasFixedSizedObjects = MFI.getStackSize() > 0;
   bool NeedsFixedReference = !hasBP(MF) || HasFixedSizedObjects;

   return MFI.isFrameAddressTaken() ||
          (MFI.hasVarSizedObjects() && NeedsFixedReference) ||
          MFI.hasStackMap() || MFI.hasPatchPoint();
 }

 /// 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 {
   return !MF.getFrameInfo().hasVarSizedObjects();
 }


 /// 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 MachineFrameInfo &MFI) const {
   return MFI.getStackSize() || MFI.adjustsStack() || hasFP(MF);
 }

 /// Returns true if the local user-space stack pointer needs to be written back
 /// to memory 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 MachineFrameInfo &MFI) const {
   assert(needsSP(MF, MFI));
   return MFI.getStackSize() > RedZoneSize || MFI.hasCalls() ||
          MF.getFunction()->hasFnAttribute(Attribute::NoRedZone);
 }

 static void writeSPToMemory(unsigned SrcReg, MachineFunction &MF,
                             MachineBasicBlock &MBB,
                             MachineBasicBlock::iterator &InsertAddr,
                             MachineBasicBlock::iterator &InsertStore,
                             const DebugLoc &DL) {
   const auto *TII = MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();

   if (MF.getSubtarget<WebAssemblySubtarget>()
         .getTargetTriple().isOSBinFormatELF()) {
     const char *ES = "__stack_pointer";
     auto *SPSymbol = MF.createExternalSymbolName(ES);
     MachineRegisterInfo &MRI = MF.getRegInfo();
     const TargetRegisterClass *PtrRC =
         MRI.getTargetRegisterInfo()->getPointerRegClass(MF);
     unsigned Zero = MRI.createVirtualRegister(PtrRC);

     BuildMI(MBB, InsertAddr, DL, TII->get(WebAssembly::CONST_I32), Zero)
         .addImm(0);
     MachineMemOperand *MMO = MF.getMachineMemOperand(
         MachinePointerInfo(MF.getPSVManager().getExternalSymbolCallEntry(ES)),
         MachineMemOperand::MOStore, 4, 4);
     BuildMI(MBB, InsertStore, DL, TII->get(WebAssembly::STORE_I32))
         .addImm(2)  // p2align
         .addExternalSymbol(SPSymbol)
         .addReg(Zero)
         .addReg(SrcReg)
         .addMemOperand(MMO);
   } else {
     MachineModuleInfoWasm &MMIW =
         MF.getMMI().getObjFileInfo<MachineModuleInfoWasm>();
     BuildMI(MBB, InsertStore, DL, TII->get(WebAssembly::SET_GLOBAL_I32))
         .addImm(MMIW.getStackPointerGlobal())
         .addReg(SrcReg);
   }
 }

 MachineBasicBlock::iterator
 WebAssemblyFrameLowering::eliminateCallFramePseudoInstr(
     MachineFunction &MF, MachineBasicBlock &MBB,
     MachineBasicBlock::iterator I) const {
   assert(!I->getOperand(0).getImm() && (hasFP(MF) || hasBP(MF)) &&
          "Call frame pseudos should only be used for dynamic stack adjustment");
   const auto *TII = MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
   if (I->getOpcode() == TII->getCallFrameDestroyOpcode() &&
       needsSPWriteback(MF, MF.getFrameInfo())) {
     DebugLoc DL = I->getDebugLoc();
     writeSPToMemory(WebAssembly::SP32, MF, MBB, I, I, DL);
   }
   return MBB.erase(I);
 }

 void WebAssemblyFrameLowering::emitPrologue(MachineFunction &MF,
                                             MachineBasicBlock &MBB) const {
   // TODO: Do ".setMIFlag(MachineInstr::FrameSetup)" on emitted instructions
   auto &MFI = MF.getFrameInfo();
   assert(MFI.getCalleeSavedInfo().empty() &&
          "WebAssembly should not have callee-saved registers");

   if (!needsSP(MF, MFI)) return;
   uint64_t StackSize = MFI.getStackSize();

   const auto *TII = MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
   auto &MRI = MF.getRegInfo();

   auto InsertPt = MBB.begin();
   while (InsertPt != MBB.end() && WebAssembly::isArgument(*InsertPt))
     ++InsertPt;
   DebugLoc DL;

   const TargetRegisterClass *PtrRC =
       MRI.getTargetRegisterInfo()->getPointerRegClass(MF);
   unsigned SPReg = WebAssembly::SP32;
   if (StackSize)
     SPReg = MRI.createVirtualRegister(PtrRC);
   if (MF.getSubtarget<WebAssemblySubtarget>()
         .getTargetTriple().isOSBinFormatELF()) {
     const char *ES = "__stack_pointer";
     auto *SPSymbol = MF.createExternalSymbolName(ES);
     unsigned Zero = MRI.createVirtualRegister(PtrRC);

     BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::CONST_I32), Zero)
         .addImm(0);
     MachineMemOperand *LoadMMO = MF.getMachineMemOperand(
         MachinePointerInfo(MF.getPSVManager().getExternalSymbolCallEntry(ES)),
         MachineMemOperand::MOLoad, 4, 4);
     // Load the SP value.
     BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::LOAD_I32), SPReg)
         .addImm(2)       // p2align
         .addExternalSymbol(SPSymbol)
         .addReg(Zero)    // addr
         .addMemOperand(LoadMMO);
   } else {
     auto &MMIW = MF.getMMI().getObjFileInfo<MachineModuleInfoWasm>();
     if (!MMIW.hasStackPointerGlobal()) {
       MMIW.setStackPointerGlobal(MMIW.getGlobals().size());
       MMIW.addGlobal(MVT::i32);
     }
     BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::GET_GLOBAL_I32), SPReg)
         .addImm(MMIW.getStackPointerGlobal());
   }

   bool HasBP = hasBP(MF);
   if (HasBP) {
     auto FI = MF.getInfo<WebAssemblyFunctionInfo>();
     unsigned BasePtr = MRI.createVirtualRegister(PtrRC);
     FI->setBasePointerVreg(BasePtr);
     BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::COPY), BasePtr)
         .addReg(SPReg);
   }
   if (StackSize) {
     // Subtract the frame size
     unsigned OffsetReg = MRI.createVirtualRegister(PtrRC);
     BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::CONST_I32), OffsetReg)
         .addImm(StackSize);
     BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::SUB_I32),
             WebAssembly::SP32)
         .addReg(SPReg)
         .addReg(OffsetReg);
   }
   if (HasBP) {
     unsigned BitmaskReg = MRI.createVirtualRegister(PtrRC);
     unsigned Alignment = MFI.getMaxAlignment();
     assert((1u << countTrailingZeros(Alignment)) == Alignment &&
       "Alignment must be a power of 2");
     BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::CONST_I32), BitmaskReg)
         .addImm((int)~(Alignment - 1));
     BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::AND_I32),
             WebAssembly::SP32)
         .addReg(WebAssembly::SP32)
         .addReg(BitmaskReg);
   }
   if (hasFP(MF)) {
     // Unlike most conventional targets (where FP points to the saved FP),
     // FP points to the bottom of the fixed-size locals, so we can use positive
     // offsets in load/store instructions.
     BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::COPY),
             WebAssembly::FP32)
         .addReg(WebAssembly::SP32);
   }
   if (StackSize && needsSPWriteback(MF, MFI)) {
     writeSPToMemory(WebAssembly::SP32, MF, MBB, InsertPt, InsertPt, DL);
   }
 }

 void WebAssemblyFrameLowering::emitEpilogue(MachineFunction &MF,
                                             MachineBasicBlock &MBB) const {
   auto &MFI = MF.getFrameInfo();
   uint64_t StackSize = MFI.getStackSize();
   if (!needsSP(MF, MFI) || !needsSPWriteback(MF, MFI)) return;
   const auto *TII = MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
   auto &MRI = MF.getRegInfo();
   auto InsertPt = MBB.getFirstTerminator();
   DebugLoc DL;

   if (InsertPt != MBB.end())
     DL = InsertPt->getDebugLoc();

   // Restore the stack pointer. If we had fixed-size locals, add the offset
   // subtracted in the prolog.
   unsigned SPReg = 0;
   MachineBasicBlock::iterator InsertAddr = InsertPt;
   if (hasBP(MF)) {
     auto FI = MF.getInfo<WebAssemblyFunctionInfo>();
     SPReg = FI->getBasePointerVreg();
   } else if (StackSize) {
     const TargetRegisterClass *PtrRC =
         MRI.getTargetRegisterInfo()->getPointerRegClass(MF);
     unsigned OffsetReg = MRI.createVirtualRegister(PtrRC);
     InsertAddr =
         BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::CONST_I32), OffsetReg)
             .addImm(StackSize);
     // In the epilog we don't need to write the result back to the SP32 physreg
     // because it won't be used again. We can use a stackified register instead.
     SPReg = MRI.createVirtualRegister(PtrRC);
     BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::ADD_I32), SPReg)
         .addReg(hasFP(MF) ? WebAssembly::FP32 : WebAssembly::SP32)
         .addReg(OffsetReg);
   } else {
     SPReg = hasFP(MF) ? WebAssembly::FP32 : WebAssembly::SP32;
   }

   writeSPToMemory(SPReg, MF, MBB, InsertAddr, InsertPt, DL);
 }
	//===-- WebAssemblyFrameLowering.cpp - WebAssembly Frame Lowering ----------==//
	//
	// The LLVM Compiler Infrastructure
	//
	// This file is distributed under the University of Illinois Open Source
	// License. See LICENSE.TXT for details.
	//
	//===----------------------------------------------------------------------===//
	///
	/// \file
	/// \brief 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 "WebAssemblyInstrInfo.h"
	#include "WebAssemblyMachineFunctionInfo.h"
	#include "WebAssemblySubtarget.h"
	#include "WebAssemblyTargetMachine.h"
	#include "WebAssemblyUtilities.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/Support/Debug.h"
	using namespace llvm;

	#define DEBUG_TYPE "wasm-frame-info"

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

	/// 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 {
	const auto *RegInfo =
	MF.getSubtarget<WebAssemblySubtarget>().getRegisterInfo();
	return RegInfo->needsStackRealignment(MF);
	}

	/// Return true if the specified function should have a dedicated frame pointer
	/// register.
	bool WebAssemblyFrameLowering::hasFP(const MachineFunction &MF) const {
	const MachineFrameInfo &MFI = MF.getFrameInfo();

	// When we have var-sized objects, we move the stack pointer by an unknown
	// amount, and need to emit a frame pointer to restore the stack to where we
	// were on function entry.
	// If we already need a base pointer, we use that to fix up the stack pointer.
	// If there are no fixed-size objects, we would have no use of a frame
	// pointer, and thus should not emit one.
	bool HasFixedSizedObjects = MFI.getStackSize() > 0;
	bool NeedsFixedReference = !hasBP(MF) \|\| HasFixedSizedObjects;

	return MFI.isFrameAddressTaken() \|\|
	(MFI.hasVarSizedObjects() && NeedsFixedReference) \|\|
	MFI.hasStackMap() \|\| MFI.hasPatchPoint();
	}

	/// 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 {
	return !MF.getFrameInfo().hasVarSizedObjects();
	}


	/// 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 MachineFrameInfo &MFI) const {
	return MFI.getStackSize() \|\| MFI.adjustsStack() \|\| hasFP(MF);
	}

	/// Returns true if the local user-space stack pointer needs to be written back
	/// to memory 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 MachineFrameInfo &MFI) const {
	assert(needsSP(MF, MFI));
	return MFI.getStackSize() > RedZoneSize \|\| MFI.hasCalls() \|\|
	MF.getFunction()->hasFnAttribute(Attribute::NoRedZone);
	}

	static void writeSPToMemory(unsigned SrcReg, MachineFunction &MF,
	MachineBasicBlock &MBB,
	MachineBasicBlock::iterator &InsertAddr,
	MachineBasicBlock::iterator &InsertStore,
	const DebugLoc &DL) {
	const auto *TII = MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();

	if (MF.getSubtarget<WebAssemblySubtarget>()
	.getTargetTriple().isOSBinFormatELF()) {
	const char *ES = "__stack_pointer";
	auto *SPSymbol = MF.createExternalSymbolName(ES);
	MachineRegisterInfo &MRI = MF.getRegInfo();
	const TargetRegisterClass *PtrRC =
	MRI.getTargetRegisterInfo()->getPointerRegClass(MF);
	unsigned Zero = MRI.createVirtualRegister(PtrRC);

	BuildMI(MBB, InsertAddr, DL, TII->get(WebAssembly::CONST_I32), Zero)
	.addImm(0);
	MachineMemOperand *MMO = MF.getMachineMemOperand(
	MachinePointerInfo(MF.getPSVManager().getExternalSymbolCallEntry(ES)),
	MachineMemOperand::MOStore, 4, 4);
	BuildMI(MBB, InsertStore, DL, TII->get(WebAssembly::STORE_I32))
	.addImm(2) // p2align
	.addExternalSymbol(SPSymbol)
	.addReg(Zero)
	.addReg(SrcReg)
	.addMemOperand(MMO);
	} else {
	MachineModuleInfoWasm &MMIW =
	MF.getMMI().getObjFileInfo<MachineModuleInfoWasm>();
	BuildMI(MBB, InsertStore, DL, TII->get(WebAssembly::SET_GLOBAL_I32))
	.addImm(MMIW.getStackPointerGlobal())
	.addReg(SrcReg);
	}
	}

	MachineBasicBlock::iterator
	WebAssemblyFrameLowering::eliminateCallFramePseudoInstr(
	MachineFunction &MF, MachineBasicBlock &MBB,
	MachineBasicBlock::iterator I) const {
	assert(!I->getOperand(0).getImm() && (hasFP(MF) \|\| hasBP(MF)) &&
	"Call frame pseudos should only be used for dynamic stack adjustment");
	const auto *TII = MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
	if (I->getOpcode() == TII->getCallFrameDestroyOpcode() &&
	needsSPWriteback(MF, MF.getFrameInfo())) {
	DebugLoc DL = I->getDebugLoc();
	writeSPToMemory(WebAssembly::SP32, MF, MBB, I, I, DL);
	}
	return MBB.erase(I);
	}

	void WebAssemblyFrameLowering::emitPrologue(MachineFunction &MF,
	MachineBasicBlock &MBB) const {
	// TODO: Do ".setMIFlag(MachineInstr::FrameSetup)" on emitted instructions
	auto &MFI = MF.getFrameInfo();
	assert(MFI.getCalleeSavedInfo().empty() &&
	"WebAssembly should not have callee-saved registers");

	if (!needsSP(MF, MFI)) return;
	uint64_t StackSize = MFI.getStackSize();

	const auto *TII = MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
	auto &MRI = MF.getRegInfo();

	auto InsertPt = MBB.begin();
	while (InsertPt != MBB.end() && WebAssembly::isArgument(*InsertPt))
	++InsertPt;
	DebugLoc DL;

	const TargetRegisterClass *PtrRC =
	MRI.getTargetRegisterInfo()->getPointerRegClass(MF);
	unsigned SPReg = WebAssembly::SP32;
	if (StackSize)
	SPReg = MRI.createVirtualRegister(PtrRC);
	if (MF.getSubtarget<WebAssemblySubtarget>()
	.getTargetTriple().isOSBinFormatELF()) {
	const char *ES = "__stack_pointer";
	auto *SPSymbol = MF.createExternalSymbolName(ES);
	unsigned Zero = MRI.createVirtualRegister(PtrRC);

	BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::CONST_I32), Zero)
	.addImm(0);
	MachineMemOperand *LoadMMO = MF.getMachineMemOperand(
	MachinePointerInfo(MF.getPSVManager().getExternalSymbolCallEntry(ES)),
	MachineMemOperand::MOLoad, 4, 4);
	// Load the SP value.
	BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::LOAD_I32), SPReg)
	.addImm(2) // p2align
	.addExternalSymbol(SPSymbol)
	.addReg(Zero) // addr
	.addMemOperand(LoadMMO);
	} else {
	auto &MMIW = MF.getMMI().getObjFileInfo<MachineModuleInfoWasm>();
	if (!MMIW.hasStackPointerGlobal()) {
	MMIW.setStackPointerGlobal(MMIW.getGlobals().size());
	MMIW.addGlobal(MVT::i32);
	}
	BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::GET_GLOBAL_I32), SPReg)
	.addImm(MMIW.getStackPointerGlobal());
	}

	bool HasBP = hasBP(MF);
	if (HasBP) {
	auto FI = MF.getInfo<WebAssemblyFunctionInfo>();
	unsigned BasePtr = MRI.createVirtualRegister(PtrRC);
	FI->setBasePointerVreg(BasePtr);
	BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::COPY), BasePtr)
	.addReg(SPReg);
	}
	if (StackSize) {
	// Subtract the frame size
	unsigned OffsetReg = MRI.createVirtualRegister(PtrRC);
	BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::CONST_I32), OffsetReg)
	.addImm(StackSize);
	BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::SUB_I32),
	WebAssembly::SP32)
	.addReg(SPReg)
	.addReg(OffsetReg);
	}
	if (HasBP) {
	unsigned BitmaskReg = MRI.createVirtualRegister(PtrRC);
	unsigned Alignment = MFI.getMaxAlignment();
	assert((1u << countTrailingZeros(Alignment)) == Alignment &&
	"Alignment must be a power of 2");
	BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::CONST_I32), BitmaskReg)
	.addImm((int)~(Alignment - 1));
	BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::AND_I32),
	WebAssembly::SP32)
	.addReg(WebAssembly::SP32)
	.addReg(BitmaskReg);
	}
	if (hasFP(MF)) {
	// Unlike most conventional targets (where FP points to the saved FP),
	// FP points to the bottom of the fixed-size locals, so we can use positive
	// offsets in load/store instructions.
	BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::COPY),
	WebAssembly::FP32)
	.addReg(WebAssembly::SP32);
	}
	if (StackSize && needsSPWriteback(MF, MFI)) {
	writeSPToMemory(WebAssembly::SP32, MF, MBB, InsertPt, InsertPt, DL);
	}
	}

	void WebAssemblyFrameLowering::emitEpilogue(MachineFunction &MF,
	MachineBasicBlock &MBB) const {
	auto &MFI = MF.getFrameInfo();
	uint64_t StackSize = MFI.getStackSize();
	if (!needsSP(MF, MFI) \|\| !needsSPWriteback(MF, MFI)) return;
	const auto *TII = MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
	auto &MRI = MF.getRegInfo();
	auto InsertPt = MBB.getFirstTerminator();
	DebugLoc DL;

	if (InsertPt != MBB.end())
	DL = InsertPt->getDebugLoc();

	// Restore the stack pointer. If we had fixed-size locals, add the offset
	// subtracted in the prolog.
	unsigned SPReg = 0;
	MachineBasicBlock::iterator InsertAddr = InsertPt;
	if (hasBP(MF)) {
	auto FI = MF.getInfo<WebAssemblyFunctionInfo>();
	SPReg = FI->getBasePointerVreg();
	} else if (StackSize) {
	const TargetRegisterClass *PtrRC =
	MRI.getTargetRegisterInfo()->getPointerRegClass(MF);
	unsigned OffsetReg = MRI.createVirtualRegister(PtrRC);
	InsertAddr =
	BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::CONST_I32), OffsetReg)
	.addImm(StackSize);
	// In the epilog we don't need to write the result back to the SP32 physreg
	// because it won't be used again. We can use a stackified register instead.
	SPReg = MRI.createVirtualRegister(PtrRC);
	BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::ADD_I32), SPReg)
	.addReg(hasFP(MF) ? WebAssembly::FP32 : WebAssembly::SP32)
	.addReg(OffsetReg);
	} else {
	SPReg = hasFP(MF) ? WebAssembly::FP32 : WebAssembly::SP32;
	}

	writeSPToMemory(SPReg, MF, MBB, InsertAddr, InsertPt, DL);
	}