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//===-- X86Subtarget.cpp - X86 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 X86 specific subclass of TargetSubtargetInfo.
#include "X86.h"
#include "X86CallLowering.h"
#include "X86LegalizerInfo.h"
#include "X86RegisterBankInfo.h"
#include "X86Subtarget.h"
#include "MCTargetDesc/X86BaseInfo.h"
#include "X86TargetMachine.h"
#include "llvm/ADT/Triple.h"
#include "llvm/CodeGen/GlobalISel/CallLowering.h"
#include "llvm/CodeGen/GlobalISel/InstructionSelect.h"
#include "llvm/IR/Attributes.h"
#include "llvm/IR/ConstantRange.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/GlobalValue.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/CodeGen.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetMachine.h"
#if defined(_MSC_VER)
#include <intrin.h>
using namespace llvm;
#define DEBUG_TYPE "subtarget"
#include ""
// Temporary option to control early if-conversion for x86 while adding machine
// models.
static cl::opt<bool>
X86EarlyIfConv("x86-early-ifcvt", cl::Hidden,
cl::desc("Enable early if-conversion on X86"));
/// Classify a blockaddress reference for the current subtarget according to how
/// we should reference it in a non-pcrel context.
unsigned char X86Subtarget::classifyBlockAddressReference() const {
return classifyLocalReference(nullptr);
/// Classify a global variable reference for the current subtarget according to
/// how we should reference it in a non-pcrel context.
unsigned char
X86Subtarget::classifyGlobalReference(const GlobalValue *GV) const {
return classifyGlobalReference(GV, *GV->getParent());
unsigned char
X86Subtarget::classifyLocalReference(const GlobalValue *GV) const {
// If we're not PIC, it's not very interesting.
if (!isPositionIndependent())
return X86II::MO_NO_FLAG;
if (is64Bit()) {
// 64-bit ELF PIC local references may use GOTOFF relocations.
if (isTargetELF()) {
switch (TM.getCodeModel()) {
// 64-bit small code model is simple: All rip-relative.
case CodeModel::Tiny:
llvm_unreachable("Tiny codesize model not supported on X86");
case CodeModel::Small:
case CodeModel::Kernel:
return X86II::MO_NO_FLAG;
// The large PIC code model uses GOTOFF.
case CodeModel::Large:
return X86II::MO_GOTOFF;
// Medium is a hybrid: RIP-rel for code, GOTOFF for DSO local data.
case CodeModel::Medium:
if (isa<Function>(GV))
return X86II::MO_NO_FLAG; // All code is RIP-relative
return X86II::MO_GOTOFF; // Local symbols use GOTOFF.
llvm_unreachable("invalid code model");
// Otherwise, this is either a RIP-relative reference or a 64-bit movabsq,
// both of which use MO_NO_FLAG.
return X86II::MO_NO_FLAG;
// The COFF dynamic linker just patches the executable sections.
if (isTargetCOFF())
return X86II::MO_NO_FLAG;
if (isTargetDarwin()) {
// 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 (GV && (GV->isDeclarationForLinker() || GV->hasCommonLinkage()))
return X86II::MO_GOTOFF;
unsigned char X86Subtarget::classifyGlobalReference(const GlobalValue *GV,
const Module &M) const {
// The static large model never uses stubs.
if (TM.getCodeModel() == CodeModel::Large && !isPositionIndependent())
return X86II::MO_NO_FLAG;
// Absolute symbols can be referenced directly.
if (GV) {
if (Optional<ConstantRange> CR = GV->getAbsoluteSymbolRange()) {
// See if we can use the 8-bit immediate form. Note that some instructions
// will sign extend the immediate operand, so to be conservative we only
// accept the range [0,128).
if (CR->getUnsignedMax().ult(128))
return X86II::MO_ABS8;
return X86II::MO_NO_FLAG;
if (TM.shouldAssumeDSOLocal(M, GV))
return classifyLocalReference(GV);
if (isTargetCOFF()) {
if (GV->hasDLLImportStorageClass())
return X86II::MO_COFFSTUB;
if (is64Bit()) {
// ELF supports a large, truly PIC code model with non-PC relative GOT
// references. Other object file formats do not. Use the no-flag, 64-bit
// reference for them.
if (TM.getCodeModel() == CodeModel::Large)
return isTargetELF() ? X86II::MO_GOT : X86II::MO_NO_FLAG;
return X86II::MO_GOTPCREL;
if (isTargetDarwin()) {
if (!isPositionIndependent())
return X86II::MO_GOT;
unsigned char
X86Subtarget::classifyGlobalFunctionReference(const GlobalValue *GV) const {
return classifyGlobalFunctionReference(GV, *GV->getParent());
unsigned char
X86Subtarget::classifyGlobalFunctionReference(const GlobalValue *GV,
const Module &M) const {
if (TM.shouldAssumeDSOLocal(M, GV))
return X86II::MO_NO_FLAG;
if (isTargetCOFF()) {
assert(GV->hasDLLImportStorageClass() &&
"shouldAssumeDSOLocal gave inconsistent answer");
const Function *F = dyn_cast_or_null<Function>(GV);
if (isTargetELF()) {
if (is64Bit() && F && (CallingConv::X86_RegCall == F->getCallingConv()))
// According to psABI, PLT stub clobbers XMM8-XMM15.
// In Regcall calling convention those registers are used for passing
// parameters. Thus we need to prevent lazy binding in Regcall.
return X86II::MO_GOTPCREL;
// If PLT must be avoided then the call should be via GOTPCREL.
if (((F && F->hasFnAttribute(Attribute::NonLazyBind)) ||
(!F && M.getRtLibUseGOT())) &&
return X86II::MO_GOTPCREL;
return X86II::MO_PLT;
if (is64Bit()) {
if (F && F->hasFnAttribute(Attribute::NonLazyBind))
// If the function is marked as non-lazy, generate an indirect call
// which loads from the GOT directly. This avoids runtime overhead
// at the cost of eager binding (and one extra byte of encoding).
return X86II::MO_GOTPCREL;
return X86II::MO_NO_FLAG;
return X86II::MO_NO_FLAG;
/// Return true if the subtarget allows calls to immediate address.
bool X86Subtarget::isLegalToCallImmediateAddr() const {
// FIXME: I386 PE/COFF supports PC relative calls using IMAGE_REL_I386_REL32
// but WinCOFFObjectWriter::RecordRelocation cannot emit them. Once it does,
// the following check for Win32 should be removed.
if (In64BitMode || isTargetWin32())
return false;
return isTargetELF() || TM.getRelocationModel() == Reloc::Static;
void X86Subtarget::initSubtargetFeatures(StringRef CPU, StringRef FS) {
std::string CPUName = CPU;
if (CPUName.empty())
CPUName = "generic";
std::string FullFS = FS;
if (In64BitMode) {
// SSE2 should default to enabled in 64-bit mode, but can be turned off
// explicitly.
if (!FullFS.empty())
FullFS = "+sse2," + FullFS;
FullFS = "+sse2";
// If no CPU was specified, enable 64bit feature to satisy later check.
if (CPUName == "generic") {
if (!FullFS.empty())
FullFS = "+64bit," + FullFS;
FullFS = "+64bit";
// LAHF/SAHF are always supported in non-64-bit mode.
if (!In64BitMode) {
if (!FullFS.empty())
FullFS = "+sahf," + FullFS;
FullFS = "+sahf";
// Parse features string and set the CPU.
ParseSubtargetFeatures(CPUName, FullFS);
// All CPUs that implement SSE4.2 or SSE4A support unaligned accesses of
// 16-bytes and under that are reasonably fast. These features were
// introduced with Intel's Nehalem/Silvermont and AMD's Family10h
// micro-architectures respectively.
if (hasSSE42() || hasSSE4A())
IsUAMem16Slow = false;
// It's important to keep the MCSubtargetInfo feature bits in sync with
// target data structure which is shared with MC code emitter, etc.
if (In64BitMode)
else if (In32BitMode)
else if (In16BitMode)
llvm_unreachable("Not 16-bit, 32-bit or 64-bit mode!");
LLVM_DEBUG(dbgs() << "Subtarget features: SSELevel " << X86SSELevel
<< ", 3DNowLevel " << X863DNowLevel << ", 64bit "
<< HasX86_64 << "\n");
if (In64BitMode && !HasX86_64)
report_fatal_error("64-bit code requested on a subtarget that doesn't "
"support it!");
// Stack alignment is 16 bytes on Darwin, Linux, kFreeBSD and Solaris (both
// 32 and 64 bit) and for all 64-bit targets.
if (StackAlignOverride)
stackAlignment = StackAlignOverride;
else if (isTargetDarwin() || isTargetLinux() || isTargetSolaris() ||
isTargetKFreeBSD() || In64BitMode)
stackAlignment = 16;
// Some CPUs have more overhead for gather. The specified overhead is relative
// to the Load operation. "2" is the number provided by Intel architects. This
// parameter is used for cost estimation of Gather Op and comparison with
// other alternatives.
// TODO: Remove the explicit hasAVX512()?, That would mean we would only
// enable gather with a -march.
if (hasAVX512() || (hasAVX2() && hasFastGather()))
GatherOverhead = 2;
if (hasAVX512())
ScatterOverhead = 2;
// Consume the vector width attribute or apply any target specific limit.
if (PreferVectorWidthOverride)
PreferVectorWidth = PreferVectorWidthOverride;
else if (Prefer256Bit)
PreferVectorWidth = 256;
X86Subtarget &X86Subtarget::initializeSubtargetDependencies(StringRef CPU,
StringRef FS) {
initSubtargetFeatures(CPU, FS);
return *this;
X86Subtarget::X86Subtarget(const Triple &TT, StringRef CPU, StringRef FS,
const X86TargetMachine &TM,
unsigned StackAlignOverride,
unsigned PreferVectorWidthOverride,
unsigned RequiredVectorWidth)
: X86GenSubtargetInfo(TT, CPU, FS),
PICStyle(PICStyles::None), TM(TM), TargetTriple(TT),
In64BitMode(TargetTriple.getArch() == Triple::x86_64),
In32BitMode(TargetTriple.getArch() == Triple::x86 &&
TargetTriple.getEnvironment() != Triple::CODE16),
In16BitMode(TargetTriple.getArch() == Triple::x86 &&
TargetTriple.getEnvironment() == Triple::CODE16),
InstrInfo(initializeSubtargetDependencies(CPU, FS)), TLInfo(TM, *this),
FrameLowering(*this, getStackAlignment()) {
// Determine the PICStyle based on the target selected.
if (!isPositionIndependent())
else if (is64Bit())
else if (isTargetCOFF())
else if (isTargetDarwin())
else if (isTargetELF())
CallLoweringInfo.reset(new X86CallLowering(*getTargetLowering()));
Legalizer.reset(new X86LegalizerInfo(*this, TM));
auto *RBI = new X86RegisterBankInfo(*getRegisterInfo());
InstSelector.reset(createX86InstructionSelector(TM, *this, *RBI));
const CallLowering *X86Subtarget::getCallLowering() const {
return CallLoweringInfo.get();
const InstructionSelector *X86Subtarget::getInstructionSelector() const {
return InstSelector.get();
const LegalizerInfo *X86Subtarget::getLegalizerInfo() const {
return Legalizer.get();
const RegisterBankInfo *X86Subtarget::getRegBankInfo() const {
return RegBankInfo.get();
bool X86Subtarget::enableEarlyIfConversion() const {
return hasCMov() && X86EarlyIfConv;