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//===-- ARMSubtarget.cpp - ARM Subtarget Information ----------------------===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This file implements the ARM specific subclass of TargetSubtargetInfo.
#include "ARM.h"
#include "ARMCallLowering.h"
#include "ARMFrameLowering.h"
#include "ARMInstrInfo.h"
#include "ARMLegalizerInfo.h"
#include "ARMRegisterBankInfo.h"
#include "ARMSubtarget.h"
#include "ARMTargetMachine.h"
#include "MCTargetDesc/ARMMCTargetDesc.h"
#include "Thumb1FrameLowering.h"
#include "Thumb1InstrInfo.h"
#include "Thumb2InstrInfo.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/Twine.h"
#include "llvm/CodeGen/GlobalISel/InstructionSelect.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/GlobalValue.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/MC/MCTargetOptions.h"
#include "llvm/Support/CodeGen.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Target/TargetOptions.h"
#include "llvm/TargetParser/ARMTargetParser.h"
#include "llvm/TargetParser/Triple.h"
using namespace llvm;
#define DEBUG_TYPE "arm-subtarget"
#include ""
static cl::opt<bool>
cl::init(true), cl::Hidden);
enum ITMode {
static cl::opt<ITMode>
IT(cl::desc("IT block support"), cl::Hidden, cl::init(DefaultIT),
cl::values(clEnumValN(DefaultIT, "arm-default-it",
"Generate any type of IT block"),
clEnumValN(RestrictedIT, "arm-restrict-it",
"Disallow complex IT blocks")));
/// ForceFastISel - Use the fast-isel, even for subtargets where it is not
/// currently supported (for testing only).
static cl::opt<bool>
cl::init(false), cl::Hidden);
static cl::opt<bool> EnableSubRegLiveness("arm-enable-subreg-liveness",
cl::init(false), cl::Hidden);
/// initializeSubtargetDependencies - Initializes using a CPU and feature string
/// so that we can use initializer lists for subtarget initialization.
ARMSubtarget &ARMSubtarget::initializeSubtargetDependencies(StringRef CPU,
StringRef FS) {
initSubtargetFeatures(CPU, FS);
return *this;
ARMFrameLowering *ARMSubtarget::initializeFrameLowering(StringRef CPU,
StringRef FS) {
ARMSubtarget &STI = initializeSubtargetDependencies(CPU, FS);
if (STI.isThumb1Only())
return (ARMFrameLowering *)new Thumb1FrameLowering(STI);
return new ARMFrameLowering(STI);
ARMSubtarget::ARMSubtarget(const Triple &TT, const std::string &CPU,
const std::string &FS,
const ARMBaseTargetMachine &TM, bool IsLittle,
bool MinSize)
: ARMGenSubtargetInfo(TT, CPU, /*TuneCPU*/ CPU, FS),
UseMulOps(UseFusedMulOps), CPUString(CPU), OptMinSize(MinSize),
IsLittle(IsLittle), TargetTriple(TT), Options(TM.Options), TM(TM),
FrameLowering(initializeFrameLowering(CPU, FS)),
// At this point initializeSubtargetDependencies has been called so
// we can query directly.
? (ARMBaseInstrInfo *)new Thumb1InstrInfo(*this)
: !isThumb()
? (ARMBaseInstrInfo *)new ARMInstrInfo(*this)
: (ARMBaseInstrInfo *)new Thumb2InstrInfo(*this)),
TLInfo(TM, *this) {
CallLoweringInfo.reset(new ARMCallLowering(*getTargetLowering()));
Legalizer.reset(new ARMLegalizerInfo(*this));
auto *RBI = new ARMRegisterBankInfo(*getRegisterInfo());
// FIXME: At this point, we can't rely on Subtarget having RBI.
// It's awkward to mix passing RBI and the Subtarget; should we pass
// TII/TRI as well?
*static_cast<const ARMBaseTargetMachine *>(&TM), *this, *RBI));
const CallLowering *ARMSubtarget::getCallLowering() const {
return CallLoweringInfo.get();
InstructionSelector *ARMSubtarget::getInstructionSelector() const {
return InstSelector.get();
const LegalizerInfo *ARMSubtarget::getLegalizerInfo() const {
return Legalizer.get();
const RegisterBankInfo *ARMSubtarget::getRegBankInfo() const {
return RegBankInfo.get();
bool ARMSubtarget::isXRaySupported() const {
// We don't currently suppport Thumb, but Windows requires Thumb.
return hasV6Ops() && hasARMOps() && !isTargetWindows();
void ARMSubtarget::initializeEnvironment() {
// MCAsmInfo isn't always present (e.g. in opt) so we can't initialize this
// directly from it, but we can try to make sure they're consistent when both
// available.
UseSjLjEH = (isTargetDarwin() && !isTargetWatchABI() &&
Options.ExceptionModel == ExceptionHandling::None) ||
Options.ExceptionModel == ExceptionHandling::SjLj;
assert((!TM.getMCAsmInfo() ||
(TM.getMCAsmInfo()->getExceptionHandlingType() ==
ExceptionHandling::SjLj) == UseSjLjEH) &&
"inconsistent sjlj choice between CodeGen and MC");
void ARMSubtarget::initSubtargetFeatures(StringRef CPU, StringRef FS) {
if (CPUString.empty()) {
CPUString = "generic";
if (isTargetDarwin()) {
StringRef ArchName = TargetTriple.getArchName();
ARM::ArchKind AK = ARM::parseArch(ArchName);
if (AK == ARM::ArchKind::ARMV7S)
// Default to the Swift CPU when targeting armv7s/thumbv7s.
CPUString = "swift";
else if (AK == ARM::ArchKind::ARMV7K)
// Default to the Cortex-a7 CPU when targeting armv7k/thumbv7k.
// ARMv7k does not use SjLj exception handling.
CPUString = "cortex-a7";
// Insert the architecture feature derived from the target triple into the
// feature string. This is important for setting features that are implied
// based on the architecture version.
std::string ArchFS = ARM_MC::ParseARMTriple(TargetTriple, CPUString);
if (!FS.empty()) {
if (!ArchFS.empty())
ArchFS = (Twine(ArchFS) + "," + FS).str();
ArchFS = std::string(FS);
ParseSubtargetFeatures(CPUString, /*TuneCPU*/ CPUString, ArchFS);
// FIXME: This used enable V6T2 support implicitly for Thumb2 mode.
// Assert this for now to make the change obvious.
assert(hasV6T2Ops() || !hasThumb2());
if (genExecuteOnly()) {
// Execute only support for >= v8-M Baseline requires movt support
if (hasV8MBaselineOps())
NoMovt = false;
if (!hasV6MOps())
report_fatal_error("Cannot generate execute-only code for this target");
// Keep a pointer to static instruction cost data for the specified CPU.
SchedModel = getSchedModelForCPU(CPUString);
// Initialize scheduling itinerary for the specified CPU.
InstrItins = getInstrItineraryForCPU(CPUString);
// FIXME: this is invalid for WindowsCE
if (isTargetWindows())
NoARM = true;
if (isAAPCS_ABI())
stackAlignment = Align(8);
if (isTargetNaCl() || isAAPCS16_ABI())
stackAlignment = Align(16);
// FIXME: Completely disable sibcall for Thumb1 since ThumbRegisterInfo::
// emitEpilogue is not ready for them. Thumb tail calls also use t2B, as
// the Thumb1 16-bit unconditional branch doesn't have sufficient relocation
// support in the assembler and linker to be used. This would need to be
// fixed to fully support tail calls in Thumb1.
// For ARMv8-M, we /do/ implement tail calls. Doing this is tricky for v8-M
// baseline, since the LDM/POP instruction on Thumb doesn't take LR. This
// means if we need to reload LR, it takes extra instructions, which outweighs
// the value of the tail call; but here we don't know yet whether LR is going
// to be used. We take the optimistic approach of generating the tail call and
// perhaps taking a hit if we need to restore the LR.
// Thumb1 PIC calls to external symbols use BX, so they can be tail calls,
// but we need to make sure there are enough registers; the only valid
// registers are the 4 used for parameters. We don't currently do this
// case.
SupportsTailCall = !isThumb1Only() || hasV8MBaselineOps();
if (isTargetMachO() && isTargetIOS() && getTargetTriple().isOSVersionLT(5, 0))
SupportsTailCall = false;
switch (IT) {
case DefaultIT:
RestrictIT = false;
case RestrictedIT:
RestrictIT = true;
// NEON f32 ops are non-IEEE 754 compliant. Darwin is ok with it by default.
const FeatureBitset &Bits = getFeatureBits();
if ((Bits[ARM::ProcA5] || Bits[ARM::ProcA8]) && // Where this matters
(Options.UnsafeFPMath || isTargetDarwin()))
HasNEONForFP = true;
if (isRWPI())
ReserveR9 = true;
// If MVEVectorCostFactor is still 0 (has not been set to anything else), default it to 2
if (MVEVectorCostFactor == 0)
MVEVectorCostFactor = 2;
// FIXME: Teach TableGen to deal with these instead of doing it manually here.
switch (ARMProcFamily) {
case Others:
case CortexA5:
case CortexA7:
LdStMultipleTiming = DoubleIssue;
case CortexA8:
LdStMultipleTiming = DoubleIssue;
case CortexA9:
LdStMultipleTiming = DoubleIssueCheckUnalignedAccess;
PreISelOperandLatencyAdjustment = 1;
case CortexA12:
case CortexA15:
MaxInterleaveFactor = 2;
PreISelOperandLatencyAdjustment = 1;
PartialUpdateClearance = 12;
case CortexA17:
case CortexA32:
case CortexA35:
case CortexA53:
case CortexA55:
case CortexA57:
case CortexA72:
case CortexA73:
case CortexA75:
case CortexA76:
case CortexA77:
case CortexA78:
case CortexA78C:
case CortexA710:
case CortexR4:
case CortexR4F:
case CortexR5:
case CortexR7:
case CortexM3:
case CortexM7:
case CortexR52:
case CortexX1:
case CortexX1C:
case Exynos:
LdStMultipleTiming = SingleIssuePlusExtras;
MaxInterleaveFactor = 4;
if (!isThumb())
PrefLoopLogAlignment = 3;
case Kryo:
case Krait:
PreISelOperandLatencyAdjustment = 1;
case NeoverseN1:
case NeoverseN2:
case NeoverseV1:
case Swift:
MaxInterleaveFactor = 2;
LdStMultipleTiming = SingleIssuePlusExtras;
PreISelOperandLatencyAdjustment = 1;
PartialUpdateClearance = 12;
bool ARMSubtarget::isTargetHardFloat() const { return TM.isTargetHardFloat(); }
bool ARMSubtarget::isAPCS_ABI() const {
assert(TM.TargetABI != ARMBaseTargetMachine::ARM_ABI_UNKNOWN);
return TM.TargetABI == ARMBaseTargetMachine::ARM_ABI_APCS;
bool ARMSubtarget::isAAPCS_ABI() const {
assert(TM.TargetABI != ARMBaseTargetMachine::ARM_ABI_UNKNOWN);
return TM.TargetABI == ARMBaseTargetMachine::ARM_ABI_AAPCS ||
TM.TargetABI == ARMBaseTargetMachine::ARM_ABI_AAPCS16;
bool ARMSubtarget::isAAPCS16_ABI() const {
assert(TM.TargetABI != ARMBaseTargetMachine::ARM_ABI_UNKNOWN);
return TM.TargetABI == ARMBaseTargetMachine::ARM_ABI_AAPCS16;
bool ARMSubtarget::isROPI() const {
return TM.getRelocationModel() == Reloc::ROPI ||
TM.getRelocationModel() == Reloc::ROPI_RWPI;
bool ARMSubtarget::isRWPI() const {
return TM.getRelocationModel() == Reloc::RWPI ||
TM.getRelocationModel() == Reloc::ROPI_RWPI;
bool ARMSubtarget::isGVIndirectSymbol(const GlobalValue *GV) const {
if (!TM.shouldAssumeDSOLocal(*GV->getParent(), GV))
return true;
// 32 bit macho has no relocation for a-b if a is undefined, even if b is in
// the section that is being relocated. This means we have to use o load even
// for GVs that are known to be local to the dso.
if (isTargetMachO() && TM.isPositionIndependent() &&
(GV->isDeclarationForLinker() || GV->hasCommonLinkage()))
return true;
return false;
bool ARMSubtarget::isGVInGOT(const GlobalValue *GV) const {
return isTargetELF() && TM.isPositionIndependent() &&
!TM.shouldAssumeDSOLocal(*GV->getParent(), GV);
unsigned ARMSubtarget::getMispredictionPenalty() const {
return SchedModel.MispredictPenalty;
bool ARMSubtarget::enableMachineScheduler() const {
// The MachineScheduler can increase register usage, so we use more high
// registers and end up with more T2 instructions that cannot be converted to
// T1 instructions. At least until we do better at converting to thumb1
// instructions, on cortex-m at Oz where we are size-paranoid, don't use the
// Machine scheduler, relying on the DAG register pressure scheduler instead.
if (isMClass() && hasMinSize())
return false;
// Enable the MachineScheduler before register allocation for subtargets
// with the use-misched feature.
return useMachineScheduler();
bool ARMSubtarget::enableSubRegLiveness() const {
if (EnableSubRegLiveness.getNumOccurrences())
return EnableSubRegLiveness;
// Enable SubRegLiveness for MVE to better optimize s subregs for mqpr regs
// and q subregs for qqqqpr regs.
return hasMVEIntegerOps();
bool ARMSubtarget::enableMachinePipeliner() const {
// Enable the MachinePipeliner before register allocation for subtargets
// with the use-mipipeliner feature.
return getSchedModel().hasInstrSchedModel() && useMachinePipeliner();
bool ARMSubtarget::useDFAforSMS() const { return false; }
// This overrides the PostRAScheduler bit in the SchedModel for any CPU.
bool ARMSubtarget::enablePostRAScheduler() const {
if (enableMachineScheduler())
return false;
if (disablePostRAScheduler())
return false;
// Thumb1 cores will generally not benefit from post-ra scheduling
return !isThumb1Only();
bool ARMSubtarget::enablePostRAMachineScheduler() const {
if (!enableMachineScheduler())
return false;
if (disablePostRAScheduler())
return false;
return !isThumb1Only();
bool ARMSubtarget::useStride4VFPs() const {
// For general targets, the prologue can grow when VFPs are allocated with
// stride 4 (more vpush instructions). But WatchOS uses a compact unwind
// format which it's more important to get right.
return isTargetWatchABI() ||
(useWideStrideVFP() && !OptMinSize);
bool ARMSubtarget::useMovt() const {
// NOTE Windows on ARM needs to use mov.w/mov.t pairs to materialise 32-bit
// immediates as it is inherently position independent, and may be out of
// range otherwise.
return !NoMovt && hasV8MBaselineOps() &&
(isTargetWindows() || !OptMinSize || genExecuteOnly());
bool ARMSubtarget::useFastISel() const {
// Enable fast-isel for any target, for testing only.
if (ForceFastISel)
return true;
// Limit fast-isel to the targets that are or have been tested.
if (!hasV6Ops())
return false;
// Thumb2 support on iOS; ARM support on iOS, Linux and NaCl.
return TM.Options.EnableFastISel &&
((isTargetMachO() && !isThumb1Only()) ||
(isTargetLinux() && !isThumb()) || (isTargetNaCl() && !isThumb()));
unsigned ARMSubtarget::getGPRAllocationOrder(const MachineFunction &MF) const {
// The GPR register class has multiple possible allocation orders, with
// tradeoffs preferred by different sub-architectures and optimisation goals.
// The allocation orders are:
// 0: (the default tablegen order, not used)
// 1: r14, r0-r13
// 2: r0-r7
// 3: r0-r7, r12, lr, r8-r11
// Note that the register allocator will change this order so that
// callee-saved registers are used later, as they require extra work in the
// prologue/epilogue (though we sometimes override that).
// For thumb1-only targets, only the low registers are allocatable.
if (isThumb1Only())
return 2;
// Allocate low registers first, so we can select more 16-bit instructions.
// We also (in ignoreCSRForAllocationOrder) override the default behaviour
// with regards to callee-saved registers, because pushing extra registers is
// much cheaper (in terms of code size) than using high registers. After
// that, we allocate r12 (doesn't need to be saved), lr (saving it means we
// can return with the pop, don't need an extra "bx lr") and then the rest of
// the high registers.
if (isThumb2() && MF.getFunction().hasMinSize())
return 3;
// Otherwise, allocate in the default order, using LR first because saving it
// allows a shorter epilogue sequence.
return 1;
bool ARMSubtarget::ignoreCSRForAllocationOrder(const MachineFunction &MF,
unsigned PhysReg) const {
// To minimize code size in Thumb2, we prefer the usage of low regs (lower
// cost per use) so we can use narrow encoding. By default, caller-saved
// registers (e.g. lr, r12) are always allocated first, regardless of
// their cost per use. When optForMinSize, we prefer the low regs even if
// they are CSR because usually push/pop can be folded into existing ones.
return isThumb2() && MF.getFunction().hasMinSize() &&
bool ARMSubtarget::splitFramePointerPush(const MachineFunction &MF) const {
const Function &F = MF.getFunction();
if (!MF.getTarget().getMCAsmInfo()->usesWindowsCFI() ||
return false;
const MachineFrameInfo &MFI = MF.getFrameInfo();
return MFI.hasVarSizedObjects() || getRegisterInfo()->hasStackRealignment(MF);