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//===-- RISCVFrameLowering.cpp - RISCV Frame Information ------------------===//
//
// 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 the RISCV implementation of TargetFrameLowering class.
//
//===----------------------------------------------------------------------===//
#include "RISCVFrameLowering.h"
#include "RISCVMachineFunctionInfo.h"
#include "RISCVSubtarget.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/RegisterScavenging.h"
#include "llvm/MC/MCDwarf.h"
using namespace llvm;
bool RISCVFrameLowering::hasFP(const MachineFunction &MF) const {
const TargetRegisterInfo *RegInfo = MF.getSubtarget().getRegisterInfo();
const MachineFrameInfo &MFI = MF.getFrameInfo();
return MF.getTarget().Options.DisableFramePointerElim(MF) ||
RegInfo->needsStackRealignment(MF) || MFI.hasVarSizedObjects() ||
MFI.isFrameAddressTaken();
}
// Determines the size of the frame and maximum call frame size.
void RISCVFrameLowering::determineFrameLayout(MachineFunction &MF) const {
MachineFrameInfo &MFI = MF.getFrameInfo();
const RISCVRegisterInfo *RI = STI.getRegisterInfo();
// Get the number of bytes to allocate from the FrameInfo.
uint64_t FrameSize = MFI.getStackSize();
// Get the alignment.
unsigned StackAlign = getStackAlignment();
if (RI->needsStackRealignment(MF)) {
unsigned MaxStackAlign = std::max(StackAlign, MFI.getMaxAlignment());
FrameSize += (MaxStackAlign - StackAlign);
StackAlign = MaxStackAlign;
}
// Set Max Call Frame Size
uint64_t MaxCallSize = alignTo(MFI.getMaxCallFrameSize(), StackAlign);
MFI.setMaxCallFrameSize(MaxCallSize);
// Make sure the frame is aligned.
FrameSize = alignTo(FrameSize, StackAlign);
// Update frame info.
MFI.setStackSize(FrameSize);
}
void RISCVFrameLowering::adjustReg(MachineBasicBlock &MBB,
MachineBasicBlock::iterator MBBI,
const DebugLoc &DL, unsigned DestReg,
unsigned SrcReg, int64_t Val,
MachineInstr::MIFlag Flag) const {
MachineRegisterInfo &MRI = MBB.getParent()->getRegInfo();
const RISCVInstrInfo *TII = STI.getInstrInfo();
if (DestReg == SrcReg && Val == 0)
return;
if (isInt<12>(Val)) {
BuildMI(MBB, MBBI, DL, TII->get(RISCV::ADDI), DestReg)
.addReg(SrcReg)
.addImm(Val)
.setMIFlag(Flag);
} else if (isInt<32>(Val)) {
unsigned Opc = RISCV::ADD;
bool isSub = Val < 0;
if (isSub) {
Val = -Val;
Opc = RISCV::SUB;
}
unsigned ScratchReg = MRI.createVirtualRegister(&RISCV::GPRRegClass);
TII->movImm32(MBB, MBBI, DL, ScratchReg, Val, Flag);
BuildMI(MBB, MBBI, DL, TII->get(Opc), DestReg)
.addReg(SrcReg)
.addReg(ScratchReg, RegState::Kill)
.setMIFlag(Flag);
} else {
report_fatal_error("adjustReg cannot yet handle adjustments >32 bits");
}
}
// Returns the register used to hold the frame pointer.
static unsigned getFPReg(const RISCVSubtarget &STI) { return RISCV::X8; }
// Returns the register used to hold the stack pointer.
static unsigned getSPReg(const RISCVSubtarget &STI) { return RISCV::X2; }
void RISCVFrameLowering::emitPrologue(MachineFunction &MF,
MachineBasicBlock &MBB) const {
assert(&MF.front() == &MBB && "Shrink-wrapping not yet supported");
MachineFrameInfo &MFI = MF.getFrameInfo();
auto *RVFI = MF.getInfo<RISCVMachineFunctionInfo>();
const RISCVRegisterInfo *RI = STI.getRegisterInfo();
const RISCVInstrInfo *TII = STI.getInstrInfo();
MachineBasicBlock::iterator MBBI = MBB.begin();
if (RI->needsStackRealignment(MF) && MFI.hasVarSizedObjects()) {
report_fatal_error(
"RISC-V backend can't currently handle functions that need stack "
"realignment and have variable sized objects");
}
unsigned FPReg = getFPReg(STI);
unsigned SPReg = getSPReg(STI);
// Debug location must be unknown since the first debug location is used
// to determine the end of the prologue.
DebugLoc DL;
// Determine the correct frame layout
determineFrameLayout(MF);
// FIXME (note copied from Lanai): This appears to be overallocating. Needs
// investigation. Get the number of bytes to allocate from the FrameInfo.
uint64_t StackSize = MFI.getStackSize();
// Early exit if there is no need to allocate on the stack
if (StackSize == 0 && !MFI.adjustsStack())
return;
// Allocate space on the stack if necessary.
adjustReg(MBB, MBBI, DL, SPReg, SPReg, -StackSize, MachineInstr::FrameSetup);
// Emit ".cfi_def_cfa_offset StackSize"
unsigned CFIIndex = MF.addFrameInst(
MCCFIInstruction::createDefCfaOffset(nullptr, -StackSize));
BuildMI(MBB, MBBI, DL, TII->get(TargetOpcode::CFI_INSTRUCTION))
.addCFIIndex(CFIIndex);
// The frame pointer is callee-saved, and code has been generated for us to
// save it to the stack. We need to skip over the storing of callee-saved
// registers as the frame pointer must be modified after it has been saved
// to the stack, not before.
// FIXME: assumes exactly one instruction is used to save each callee-saved
// register.
const std::vector<CalleeSavedInfo> &CSI = MFI.getCalleeSavedInfo();
std::advance(MBBI, CSI.size());
// Iterate over list of callee-saved registers and emit .cfi_offset
// directives.
for (const auto &Entry : CSI) {
int64_t Offset = MFI.getObjectOffset(Entry.getFrameIdx());
unsigned Reg = Entry.getReg();
unsigned CFIIndex = MF.addFrameInst(MCCFIInstruction::createOffset(
nullptr, RI->getDwarfRegNum(Reg, true), Offset));
BuildMI(MBB, MBBI, DL, TII->get(TargetOpcode::CFI_INSTRUCTION))
.addCFIIndex(CFIIndex);
}
// Generate new FP.
if (hasFP(MF)) {
adjustReg(MBB, MBBI, DL, FPReg, SPReg,
StackSize - RVFI->getVarArgsSaveSize(), MachineInstr::FrameSetup);
// Emit ".cfi_def_cfa $fp, 0"
unsigned CFIIndex = MF.addFrameInst(MCCFIInstruction::createDefCfa(
nullptr, RI->getDwarfRegNum(FPReg, true), 0));
BuildMI(MBB, MBBI, DL, TII->get(TargetOpcode::CFI_INSTRUCTION))
.addCFIIndex(CFIIndex);
// Realign Stack
const RISCVRegisterInfo *RI = STI.getRegisterInfo();
if (RI->needsStackRealignment(MF)) {
unsigned MaxAlignment = MFI.getMaxAlignment();
const RISCVInstrInfo *TII = STI.getInstrInfo();
if (isInt<12>(-(int)MaxAlignment)) {
BuildMI(MBB, MBBI, DL, TII->get(RISCV::ANDI), SPReg)
.addReg(SPReg)
.addImm(-(int)MaxAlignment);
} else {
unsigned ShiftAmount = countTrailingZeros(MaxAlignment);
unsigned VR =
MF.getRegInfo().createVirtualRegister(&RISCV::GPRRegClass);
BuildMI(MBB, MBBI, DL, TII->get(RISCV::SRLI), VR)
.addReg(SPReg)
.addImm(ShiftAmount);
BuildMI(MBB, MBBI, DL, TII->get(RISCV::SLLI), SPReg)
.addReg(VR)
.addImm(ShiftAmount);
}
}
}
}
void RISCVFrameLowering::emitEpilogue(MachineFunction &MF,
MachineBasicBlock &MBB) const {
MachineBasicBlock::iterator MBBI = MBB.getLastNonDebugInstr();
const RISCVRegisterInfo *RI = STI.getRegisterInfo();
MachineFrameInfo &MFI = MF.getFrameInfo();
auto *RVFI = MF.getInfo<RISCVMachineFunctionInfo>();
DebugLoc DL = MBBI->getDebugLoc();
unsigned FPReg = getFPReg(STI);
unsigned SPReg = getSPReg(STI);
// Skip to before the restores of callee-saved registers
// FIXME: assumes exactly one instruction is used to restore each
// callee-saved register.
auto LastFrameDestroy = std::prev(MBBI, MFI.getCalleeSavedInfo().size());
uint64_t StackSize = MFI.getStackSize();
uint64_t FPOffset = StackSize - RVFI->getVarArgsSaveSize();
// Restore the stack pointer using the value of the frame pointer. Only
// necessary if the stack pointer was modified, meaning the stack size is
// unknown.
if (RI->needsStackRealignment(MF) || MFI.hasVarSizedObjects()) {
assert(hasFP(MF) && "frame pointer should not have been eliminated");
adjustReg(MBB, LastFrameDestroy, DL, SPReg, FPReg, -FPOffset,
MachineInstr::FrameDestroy);
}
// Deallocate stack
adjustReg(MBB, MBBI, DL, SPReg, SPReg, StackSize, MachineInstr::FrameDestroy);
}
int RISCVFrameLowering::getFrameIndexReference(const MachineFunction &MF,
int FI,
unsigned &FrameReg) const {
const MachineFrameInfo &MFI = MF.getFrameInfo();
const TargetRegisterInfo *RI = MF.getSubtarget().getRegisterInfo();
const auto *RVFI = MF.getInfo<RISCVMachineFunctionInfo>();
// Callee-saved registers should be referenced relative to the stack
// pointer (positive offset), otherwise use the frame pointer (negative
// offset).
const std::vector<CalleeSavedInfo> &CSI = MFI.getCalleeSavedInfo();
int MinCSFI = 0;
int MaxCSFI = -1;
int Offset = MFI.getObjectOffset(FI) - getOffsetOfLocalArea() +
MFI.getOffsetAdjustment();
if (CSI.size()) {
MinCSFI = CSI[0].getFrameIdx();
MaxCSFI = CSI[CSI.size() - 1].getFrameIdx();
}
if (FI >= MinCSFI && FI <= MaxCSFI) {
FrameReg = RISCV::X2;
Offset += MF.getFrameInfo().getStackSize();
} else if (RI->needsStackRealignment(MF)) {
assert(!MFI.hasVarSizedObjects() &&
"Unexpected combination of stack realignment and varsized objects");
// If the stack was realigned, the frame pointer is set in order to allow
// SP to be restored, but we still access stack objects using SP.
FrameReg = RISCV::X2;
Offset += MF.getFrameInfo().getStackSize();
} else {
FrameReg = RI->getFrameRegister(MF);
if (hasFP(MF))
Offset += RVFI->getVarArgsSaveSize();
else
Offset += MF.getFrameInfo().getStackSize();
}
return Offset;
}
void RISCVFrameLowering::determineCalleeSaves(MachineFunction &MF,
BitVector &SavedRegs,
RegScavenger *RS) const {
TargetFrameLowering::determineCalleeSaves(MF, SavedRegs, RS);
// Unconditionally spill RA and FP only if the function uses a frame
// pointer.
if (hasFP(MF)) {
SavedRegs.set(RISCV::X1);
SavedRegs.set(RISCV::X8);
}
// If interrupt is enabled and there are calls in the handler,
// unconditionally save all Caller-saved registers and
// all FP registers, regardless whether they are used.
MachineFrameInfo &MFI = MF.getFrameInfo();
if (MF.getFunction().hasFnAttribute("interrupt") && MFI.hasCalls()) {
static const MCPhysReg CSRegs[] = { RISCV::X1, /* ra */
RISCV::X5, RISCV::X6, RISCV::X7, /* t0-t2 */
RISCV::X10, RISCV::X11, /* a0-a1, a2-a7 */
RISCV::X12, RISCV::X13, RISCV::X14, RISCV::X15, RISCV::X16, RISCV::X17,
RISCV::X28, RISCV::X29, RISCV::X30, RISCV::X31, 0 /* t3-t6 */
};
for (unsigned i = 0; CSRegs[i]; ++i)
SavedRegs.set(CSRegs[i]);
if (MF.getSubtarget<RISCVSubtarget>().hasStdExtD() ||
MF.getSubtarget<RISCVSubtarget>().hasStdExtF()) {
// If interrupt is enabled, this list contains all FP registers.
const MCPhysReg * Regs = MF.getRegInfo().getCalleeSavedRegs();
for (unsigned i = 0; Regs[i]; ++i)
if (RISCV::FPR32RegClass.contains(Regs[i]) ||
RISCV::FPR64RegClass.contains(Regs[i]))
SavedRegs.set(Regs[i]);
}
}
}
void RISCVFrameLowering::processFunctionBeforeFrameFinalized(
MachineFunction &MF, RegScavenger *RS) const {
const TargetRegisterInfo *RegInfo = MF.getSubtarget().getRegisterInfo();
MachineFrameInfo &MFI = MF.getFrameInfo();
const TargetRegisterClass *RC = &RISCV::GPRRegClass;
// estimateStackSize has been observed to under-estimate the final stack
// size, so give ourselves wiggle-room by checking for stack size
// representable an 11-bit signed field rather than 12-bits.
// FIXME: It may be possible to craft a function with a small stack that
// still needs an emergency spill slot for branch relaxation. This case
// would currently be missed.
if (!isInt<11>(MFI.estimateStackSize(MF))) {
int RegScavFI = MFI.CreateStackObject(
RegInfo->getSpillSize(*RC), RegInfo->getSpillAlignment(*RC), false);
RS->addScavengingFrameIndex(RegScavFI);
}
}
// Not preserve stack space within prologue for outgoing variables when the
// function contains variable size objects and let eliminateCallFramePseudoInstr
// preserve stack space for it.
bool RISCVFrameLowering::hasReservedCallFrame(const MachineFunction &MF) const {
return !MF.getFrameInfo().hasVarSizedObjects();
}
// Eliminate ADJCALLSTACKDOWN, ADJCALLSTACKUP pseudo instructions.
MachineBasicBlock::iterator RISCVFrameLowering::eliminateCallFramePseudoInstr(
MachineFunction &MF, MachineBasicBlock &MBB,
MachineBasicBlock::iterator MI) const {
unsigned SPReg = RISCV::X2;
DebugLoc DL = MI->getDebugLoc();
if (!hasReservedCallFrame(MF)) {
// If space has not been reserved for a call frame, ADJCALLSTACKDOWN and
// ADJCALLSTACKUP must be converted to instructions manipulating the stack
// pointer. This is necessary when there is a variable length stack
// allocation (e.g. alloca), which means it's not possible to allocate
// space for outgoing arguments from within the function prologue.
int64_t Amount = MI->getOperand(0).getImm();
if (Amount != 0) {
// Ensure the stack remains aligned after adjustment.
Amount = alignSPAdjust(Amount);
if (MI->getOpcode() == RISCV::ADJCALLSTACKDOWN)
Amount = -Amount;
adjustReg(MBB, MI, DL, SPReg, SPReg, Amount, MachineInstr::NoFlags);
}
}
return MBB.erase(MI);
}
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