216 lines
8.6 KiB
C++
216 lines
8.6 KiB
C++
//===-- WebAssemblyFrameLowering.cpp - WebAssembly Frame Lowering ----------==//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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///
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/// \file
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/// \brief This file contains the WebAssembly implementation of
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/// TargetFrameLowering class.
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///
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/// On WebAssembly, there aren't a lot of things to do here. There are no
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/// callee-saved registers to save, and no spill slots.
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///
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/// The stack grows downward.
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///
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//===----------------------------------------------------------------------===//
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#include "WebAssemblyFrameLowering.h"
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#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
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#include "WebAssemblyInstrInfo.h"
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#include "WebAssemblyMachineFunctionInfo.h"
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#include "WebAssemblySubtarget.h"
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#include "WebAssemblyTargetMachine.h"
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#include "llvm/CodeGen/MachineFrameInfo.h"
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#include "llvm/CodeGen/MachineFunction.h"
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#include "llvm/CodeGen/MachineInstrBuilder.h"
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#include "llvm/CodeGen/MachineModuleInfo.h"
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#include "llvm/CodeGen/MachineRegisterInfo.h"
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#include "llvm/Support/Debug.h"
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using namespace llvm;
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#define DEBUG_TYPE "wasm-frame-info"
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// TODO: wasm64
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// TODO: Emit TargetOpcode::CFI_INSTRUCTION instructions
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/// Return true if the specified function should have a dedicated frame pointer
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/// register.
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bool WebAssemblyFrameLowering::hasFP(const MachineFunction &MF) const {
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const MachineFrameInfo &MFI = MF.getFrameInfo();
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const auto *RegInfo =
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MF.getSubtarget<WebAssemblySubtarget>().getRegisterInfo();
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return MFI.isFrameAddressTaken() || MFI.hasVarSizedObjects() ||
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MFI.hasStackMap() || MFI.hasPatchPoint() ||
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RegInfo->needsStackRealignment(MF);
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}
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/// Under normal circumstances, when a frame pointer is not required, we reserve
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/// argument space for call sites in the function immediately on entry to the
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/// current function. This eliminates the need for add/sub sp brackets around
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/// call sites. Returns true if the call frame is included as part of the stack
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/// frame.
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bool WebAssemblyFrameLowering::hasReservedCallFrame(
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const MachineFunction &MF) const {
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return !MF.getFrameInfo().hasVarSizedObjects();
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}
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/// Returns true if this function needs a local user-space stack pointer.
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/// Unlike a machine stack pointer, the wasm user stack pointer is a global
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/// variable, so it is loaded into a register in the prolog.
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bool WebAssemblyFrameLowering::needsSP(const MachineFunction &MF,
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const MachineFrameInfo &MFI) const {
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return MFI.getStackSize() || MFI.adjustsStack() || hasFP(MF);
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}
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/// Returns true if the local user-space stack pointer needs to be written back
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/// to memory by this function (this is not meaningful if needsSP is false). If
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/// false, the stack red zone can be used and only a local SP is needed.
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bool WebAssemblyFrameLowering::needsSPWriteback(
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const MachineFunction &MF, const MachineFrameInfo &MFI) const {
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assert(needsSP(MF, MFI));
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return MFI.getStackSize() > RedZoneSize || MFI.hasCalls() ||
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MF.getFunction()->hasFnAttribute(Attribute::NoRedZone);
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}
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static void writeSPToMemory(unsigned SrcReg, MachineFunction &MF,
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MachineBasicBlock &MBB,
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MachineBasicBlock::iterator &InsertAddr,
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MachineBasicBlock::iterator &InsertStore,
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const DebugLoc &DL) {
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const char *ES = "__stack_pointer";
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auto *SPSymbol = MF.createExternalSymbolName(ES);
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MachineRegisterInfo &MRI = MF.getRegInfo();
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const TargetRegisterClass *PtrRC =
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MRI.getTargetRegisterInfo()->getPointerRegClass(MF);
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unsigned Zero = MRI.createVirtualRegister(PtrRC);
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unsigned Drop = MRI.createVirtualRegister(PtrRC);
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const auto *TII = MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
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BuildMI(MBB, InsertAddr, DL, TII->get(WebAssembly::CONST_I32), Zero)
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.addImm(0);
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MachineMemOperand *MMO = MF.getMachineMemOperand(
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MachinePointerInfo(MF.getPSVManager().getExternalSymbolCallEntry(ES)),
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MachineMemOperand::MOStore, 4, 4);
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BuildMI(MBB, InsertStore, DL, TII->get(WebAssembly::STORE_I32), Drop)
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.addExternalSymbol(SPSymbol)
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.addReg(Zero)
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.addImm(2) // p2align
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.addReg(SrcReg)
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.addMemOperand(MMO);
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}
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MachineBasicBlock::iterator
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WebAssemblyFrameLowering::eliminateCallFramePseudoInstr(
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MachineFunction &MF, MachineBasicBlock &MBB,
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MachineBasicBlock::iterator I) const {
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assert(!I->getOperand(0).getImm() && hasFP(MF) &&
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"Call frame pseudos should only be used for dynamic stack adjustment");
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const auto *TII = MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
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if (I->getOpcode() == TII->getCallFrameDestroyOpcode() &&
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needsSPWriteback(MF, MF.getFrameInfo())) {
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DebugLoc DL = I->getDebugLoc();
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writeSPToMemory(WebAssembly::SP32, MF, MBB, I, I, DL);
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}
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return MBB.erase(I);
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}
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void WebAssemblyFrameLowering::emitPrologue(MachineFunction &MF,
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MachineBasicBlock &MBB) const {
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// TODO: Do ".setMIFlag(MachineInstr::FrameSetup)" on emitted instructions
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auto &MFI = MF.getFrameInfo();
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assert(MFI.getCalleeSavedInfo().empty() &&
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"WebAssembly should not have callee-saved registers");
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if (!needsSP(MF, MFI)) return;
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uint64_t StackSize = MFI.getStackSize();
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const auto *TII = MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
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auto &MRI = MF.getRegInfo();
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auto InsertPt = MBB.begin();
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DebugLoc DL;
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const TargetRegisterClass *PtrRC =
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MRI.getTargetRegisterInfo()->getPointerRegClass(MF);
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unsigned Zero = MRI.createVirtualRegister(PtrRC);
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unsigned SPReg = MRI.createVirtualRegister(PtrRC);
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const char *ES = "__stack_pointer";
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auto *SPSymbol = MF.createExternalSymbolName(ES);
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BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::CONST_I32), Zero)
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.addImm(0);
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MachineMemOperand *LoadMMO = MF.getMachineMemOperand(
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MachinePointerInfo(MF.getPSVManager().getExternalSymbolCallEntry(ES)),
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MachineMemOperand::MOLoad, 4, 4);
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// Load the SP value.
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BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::LOAD_I32),
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StackSize ? SPReg : (unsigned)WebAssembly::SP32)
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.addExternalSymbol(SPSymbol)
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.addReg(Zero) // addr
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.addImm(2) // p2align
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.addMemOperand(LoadMMO);
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if (StackSize) {
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// Subtract the frame size
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unsigned OffsetReg = MRI.createVirtualRegister(PtrRC);
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BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::CONST_I32), OffsetReg)
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.addImm(StackSize);
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BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::SUB_I32),
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WebAssembly::SP32)
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.addReg(SPReg)
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.addReg(OffsetReg);
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}
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if (hasFP(MF)) {
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// Unlike most conventional targets (where FP points to the saved FP),
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// FP points to the bottom of the fixed-size locals, so we can use positive
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// offsets in load/store instructions.
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BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::COPY),
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WebAssembly::FP32)
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.addReg(WebAssembly::SP32);
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}
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if (StackSize && needsSPWriteback(MF, MFI)) {
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writeSPToMemory(WebAssembly::SP32, MF, MBB, InsertPt, InsertPt, DL);
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}
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}
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void WebAssemblyFrameLowering::emitEpilogue(MachineFunction &MF,
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MachineBasicBlock &MBB) const {
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auto &MFI = MF.getFrameInfo();
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uint64_t StackSize = MFI.getStackSize();
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if (!needsSP(MF, MFI) || !needsSPWriteback(MF, MFI)) return;
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const auto *TII = MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
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auto &MRI = MF.getRegInfo();
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auto InsertPt = MBB.getFirstTerminator();
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DebugLoc DL;
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if (InsertPt != MBB.end())
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DL = InsertPt->getDebugLoc();
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// Restore the stack pointer. If we had fixed-size locals, add the offset
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// subtracted in the prolog.
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unsigned SPReg = 0;
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MachineBasicBlock::iterator InsertAddr = InsertPt;
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if (StackSize) {
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const TargetRegisterClass *PtrRC =
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MRI.getTargetRegisterInfo()->getPointerRegClass(MF);
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unsigned OffsetReg = MRI.createVirtualRegister(PtrRC);
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InsertAddr =
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BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::CONST_I32), OffsetReg)
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.addImm(StackSize);
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// In the epilog we don't need to write the result back to the SP32 physreg
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// because it won't be used again. We can use a stackified register instead.
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SPReg = MRI.createVirtualRegister(PtrRC);
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BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::ADD_I32), SPReg)
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.addReg(hasFP(MF) ? WebAssembly::FP32 : WebAssembly::SP32)
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.addReg(OffsetReg);
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} else {
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SPReg = hasFP(MF) ? WebAssembly::FP32 : WebAssembly::SP32;
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}
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writeSPToMemory(SPReg, MF, MBB, InsertAddr, InsertPt, DL);
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}
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