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llvm-project/llvm/lib/Target/RISCV/RISCVFrameLowering.cpp

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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/IR/DiagnosticInfo.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();
}
bool RISCVFrameLowering::hasBP(const MachineFunction &MF) const {
const MachineFrameInfo &MFI = MF.getFrameInfo();
const TargetRegisterInfo *TRI = STI.getRegisterInfo();
return MFI.hasVarSizedObjects() && TRI->needsStackRealignment(MF);
}
// 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, Register DestReg,
Register 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 {
unsigned Opc = RISCV::ADD;
bool isSub = Val < 0;
if (isSub) {
Val = -Val;
Opc = RISCV::SUB;
}
Register ScratchReg = MRI.createVirtualRegister(&RISCV::GPRRegClass);
TII->movImm(MBB, MBBI, DL, ScratchReg, Val, Flag);
BuildMI(MBB, MBBI, DL, TII->get(Opc), DestReg)
.addReg(SrcReg)
.addReg(ScratchReg, RegState::Kill)
.setMIFlag(Flag);
}
}
// Returns the register used to hold the frame pointer.
static Register getFPReg(const RISCVSubtarget &STI) { return RISCV::X8; }
// Returns the register used to hold the stack pointer.
static Register 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();
Register FPReg = getFPReg(STI);
Register SPReg = getSPReg(STI);
Register BPReg = RISCVABI::getBPReg();
// 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;
// If the stack pointer has been marked as reserved, then produce an error if
// the frame requires stack allocation
if (STI.isRegisterReservedByUser(SPReg))
MF.getFunction().getContext().diagnose(DiagnosticInfoUnsupported{
MF.getFunction(), "Stack pointer required, but has been reserved."});
uint64_t FirstSPAdjustAmount = getFirstSPAdjustAmount(MF);
// Split the SP adjustment to reduce the offsets of callee saved spill.
if (FirstSPAdjustAmount)
StackSize = FirstSPAdjustAmount;
// 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());
Register 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)) {
if (STI.isRegisterReservedByUser(FPReg))
MF.getFunction().getContext().diagnose(DiagnosticInfoUnsupported{
MF.getFunction(), "Frame pointer required, but has been reserved."});
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);
}
// Emit the second SP adjustment after saving callee saved registers.
if (FirstSPAdjustAmount) {
uint64_t SecondSPAdjustAmount = MFI.getStackSize() - FirstSPAdjustAmount;
assert(SecondSPAdjustAmount > 0 &&
"SecondSPAdjustAmount should be greater than zero");
adjustReg(MBB, MBBI, DL, SPReg, SPReg, -SecondSPAdjustAmount,
MachineInstr::FrameSetup);
// If we are using a frame-pointer, and thus emitted ".cfi_def_cfa fp, 0",
// don't emit an sp-based .cfi_def_cfa_offset
if (!hasFP(MF)) {
// Emit ".cfi_def_cfa_offset StackSize"
unsigned CFIIndex = MF.addFrameInst(
MCCFIInstruction::createDefCfaOffset(nullptr, -MFI.getStackSize()));
BuildMI(MBB, MBBI, DL, TII->get(TargetOpcode::CFI_INSTRUCTION))
.addCFIIndex(CFIIndex);
}
}
if (hasFP(MF)) {
// 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);
Register 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);
}
// FP will be used to restore the frame in the epilogue, so we need
// another base register BP to record SP after re-alignment. SP will
// track the current stack after allocating variable sized objects.
if (hasBP(MF)) {
// move BP, SP
BuildMI(MBB, MBBI, DL, TII->get(RISCV::ADDI), BPReg)
.addReg(SPReg)
.addImm(0);
}
}
}
}
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();
Register FPReg = getFPReg(STI);
Register 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);
}
uint64_t FirstSPAdjustAmount = getFirstSPAdjustAmount(MF);
if (FirstSPAdjustAmount) {
uint64_t SecondSPAdjustAmount = MFI.getStackSize() - FirstSPAdjustAmount;
assert(SecondSPAdjustAmount > 0 &&
"SecondSPAdjustAmount should be greater than zero");
adjustReg(MBB, LastFrameDestroy, DL, SPReg, SPReg, SecondSPAdjustAmount,
MachineInstr::FrameDestroy);
}
if (FirstSPAdjustAmount)
StackSize = FirstSPAdjustAmount;
// 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();
uint64_t FirstSPAdjustAmount = getFirstSPAdjustAmount(MF);
if (CSI.size()) {
MinCSFI = CSI[0].getFrameIdx();
MaxCSFI = CSI[CSI.size() - 1].getFrameIdx();
}
if (FI >= MinCSFI && FI <= MaxCSFI) {
FrameReg = RISCV::X2;
if (FirstSPAdjustAmount)
Offset += FirstSPAdjustAmount;
else
Offset += MF.getFrameInfo().getStackSize();
} else if (RI->needsStackRealignment(MF) && !MFI.isFixedObjectIndex(FI)) {
// If the stack was realigned, the frame pointer is set in order to allow
// SP to be restored, so we need another base register to record the stack
// after realignment.
if (hasBP(MF))
FrameReg = RISCVABI::getBPReg();
else
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);
}
// Mark BP as used if function has dedicated base pointer.
if (hasBP(MF))
SavedRegs.set(RISCVABI::getBPReg());
// 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 {
Register 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);
}
// We would like to split the SP adjustment to reduce prologue/epilogue
// as following instructions. In this way, the offset of the callee saved
// register could fit in a single store.
// add sp,sp,-2032
// sw ra,2028(sp)
// sw s0,2024(sp)
// sw s1,2020(sp)
// sw s3,2012(sp)
// sw s4,2008(sp)
// add sp,sp,-64
uint64_t
RISCVFrameLowering::getFirstSPAdjustAmount(const MachineFunction &MF) const {
const MachineFrameInfo &MFI = MF.getFrameInfo();
const std::vector<CalleeSavedInfo> &CSI = MFI.getCalleeSavedInfo();
uint64_t StackSize = MFI.getStackSize();
uint64_t StackAlign = getStackAlignment();
// FIXME: Disable SplitSPAdjust if save-restore libcall enabled when the patch
// landing. The callee saved registers will be pushed by the
// save-restore libcalls, so we don't have to split the SP adjustment
// in this case.
//
// Return the FirstSPAdjustAmount if the StackSize can not fit in signed
// 12-bit and there exists a callee saved register need to be pushed.
if (!isInt<12>(StackSize) && (CSI.size() > 0)) {
// FirstSPAdjustAmount is choosed as (2048 - StackAlign)
// because 2048 will cause sp = sp + 2048 in epilogue split into
// multi-instructions. The offset smaller than 2048 can fit in signle
// load/store instruction and we have to stick with the stack alignment.
// 2048 is 16-byte alignment. The stack alignment for RV32 and RV64 is 16,
// for RV32E is 4. So (2048 - StackAlign) will satisfy the stack alignment.
return 2048 - StackAlign;
}
return 0;
}
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