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llvm-project/llvm/lib/Target/Hexagon/HexagonTargetObjectFile.cpp

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//===-- HexagonTargetObjectFile.cpp ---------------------------------------===//
//
// 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 declarations of the HexagonTargetAsmInfo properties.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "hexagon-sdata"
#include "HexagonTargetObjectFile.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/Twine.h"
#include "llvm/BinaryFormat/ELF.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/GlobalObject.h"
#include "llvm/IR/GlobalValue.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Type.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/SectionKind.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetMachine.h"
using namespace llvm;
static cl::opt<unsigned> SmallDataThreshold("hexagon-small-data-threshold",
cl::init(8), cl::Hidden,
cl::desc("The maximum size of an object in the sdata section"));
static cl::opt<bool> NoSmallDataSorting("mno-sort-sda", cl::init(false),
cl::Hidden, cl::desc("Disable small data sections sorting"));
static cl::opt<bool> StaticsInSData("hexagon-statics-in-small-data",
cl::init(false), cl::Hidden, cl::ZeroOrMore,
cl::desc("Allow static variables in .sdata"));
static cl::opt<bool> TraceGVPlacement("trace-gv-placement",
cl::Hidden, cl::init(false),
cl::desc("Trace global value placement"));
static cl::opt<bool>
EmitJtInText("hexagon-emit-jt-text", cl::Hidden, cl::init(false),
cl::desc("Emit hexagon jump tables in function section"));
static cl::opt<bool>
EmitLutInText("hexagon-emit-lut-text", cl::Hidden, cl::init(false),
cl::desc("Emit hexagon lookup tables in function section"));
// TraceGVPlacement controls messages for all builds. For builds with assertions
// (debug or release), messages are also controlled by the usual debug flags
// (e.g. -debug and -debug-only=globallayout)
#define TRACE_TO(s, X) s << X
#ifdef NDEBUG
#define TRACE(X) \
do { \
if (TraceGVPlacement) { \
TRACE_TO(errs(), X); \
} \
} while (false)
#else
#define TRACE(X) \
do { \
if (TraceGVPlacement) { \
TRACE_TO(errs(), X); \
} else { \
LLVM_DEBUG(TRACE_TO(dbgs(), X)); \
} \
} while (false)
#endif
// Returns true if the section name is such that the symbol will be put
// in a small data section.
// For instance, global variables with section attributes such as ".sdata"
// ".sdata.*", ".sbss", and ".sbss.*" will go into small data.
static bool isSmallDataSection(StringRef Sec) {
// sectionName is either ".sdata" or ".sbss". Looking for an exact match
// obviates the need for checks for section names such as ".sdatafoo".
if (Sec.equals(".sdata") || Sec.equals(".sbss") || Sec.equals(".scommon"))
return true;
// If either ".sdata." or ".sbss." is a substring of the section name
// then put the symbol in small data.
return Sec.find(".sdata.") != StringRef::npos ||
Sec.find(".sbss.") != StringRef::npos ||
Sec.find(".scommon.") != StringRef::npos;
}
static const char *getSectionSuffixForSize(unsigned Size) {
switch (Size) {
default:
return "";
case 1:
return ".1";
case 2:
return ".2";
case 4:
return ".4";
case 8:
return ".8";
}
}
void HexagonTargetObjectFile::Initialize(MCContext &Ctx,
const TargetMachine &TM) {
TargetLoweringObjectFileELF::Initialize(Ctx, TM);
SmallDataSection =
getContext().getELFSection(".sdata", ELF::SHT_PROGBITS,
ELF::SHF_WRITE | ELF::SHF_ALLOC |
ELF::SHF_HEX_GPREL);
SmallBSSSection =
getContext().getELFSection(".sbss", ELF::SHT_NOBITS,
ELF::SHF_WRITE | ELF::SHF_ALLOC |
ELF::SHF_HEX_GPREL);
}
MCSection *HexagonTargetObjectFile::SelectSectionForGlobal(
const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
TRACE("[SelectSectionForGlobal] GO(" << GO->getName() << ") ");
TRACE("input section(" << GO->getSection() << ") ");
TRACE((GO->hasPrivateLinkage() ? "private_linkage " : "")
<< (GO->hasLocalLinkage() ? "local_linkage " : "")
<< (GO->hasInternalLinkage() ? "internal " : "")
<< (GO->hasExternalLinkage() ? "external " : "")
<< (GO->hasCommonLinkage() ? "common_linkage " : "")
<< (GO->hasCommonLinkage() ? "common " : "" )
<< (Kind.isCommon() ? "kind_common " : "" )
<< (Kind.isBSS() ? "kind_bss " : "" )
<< (Kind.isBSSLocal() ? "kind_bss_local " : "" ));
// If the lookup table is used by more than one function, do not place
// it in text section.
if (EmitLutInText && GO->getName().startswith("switch.table")) {
if (const Function *Fn = getLutUsedFunction(GO))
return selectSectionForLookupTable(GO, TM, Fn);
}
if (isGlobalInSmallSection(GO, TM))
return selectSmallSectionForGlobal(GO, Kind, TM);
if (Kind.isCommon()) {
// This is purely for LTO+Linker Script because commons don't really have a
// section. However, the BitcodeSectionWriter pass will query for the
// sections of commons (and the linker expects us to know their section) so
// we'll return one here.
return BSSSection;
}
TRACE("default_ELF_section\n");
// Otherwise, we work the same as ELF.
return TargetLoweringObjectFileELF::SelectSectionForGlobal(GO, Kind, TM);
}
MCSection *HexagonTargetObjectFile::getExplicitSectionGlobal(
const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
TRACE("[getExplicitSectionGlobal] GO(" << GO->getName() << ") from("
<< GO->getSection() << ") ");
TRACE((GO->hasPrivateLinkage() ? "private_linkage " : "")
<< (GO->hasLocalLinkage() ? "local_linkage " : "")
<< (GO->hasInternalLinkage() ? "internal " : "")
<< (GO->hasExternalLinkage() ? "external " : "")
<< (GO->hasCommonLinkage() ? "common_linkage " : "")
<< (GO->hasCommonLinkage() ? "common " : "" )
<< (Kind.isCommon() ? "kind_common " : "" )
<< (Kind.isBSS() ? "kind_bss " : "" )
<< (Kind.isBSSLocal() ? "kind_bss_local " : "" ));
if (GO->hasSection()) {
StringRef Section = GO->getSection();
if (Section.find(".access.text.group") != StringRef::npos)
return getContext().getELFSection(GO->getSection(), ELF::SHT_PROGBITS,
ELF::SHF_ALLOC | ELF::SHF_EXECINSTR);
if (Section.find(".access.data.group") != StringRef::npos)
return getContext().getELFSection(GO->getSection(), ELF::SHT_PROGBITS,
ELF::SHF_WRITE | ELF::SHF_ALLOC);
}
if (isGlobalInSmallSection(GO, TM))
return selectSmallSectionForGlobal(GO, Kind, TM);
// Otherwise, we work the same as ELF.
TRACE("default_ELF_section\n");
return TargetLoweringObjectFileELF::getExplicitSectionGlobal(GO, Kind, TM);
}
/// Return true if this global value should be placed into small data/bss
/// section.
bool HexagonTargetObjectFile::isGlobalInSmallSection(const GlobalObject *GO,
const TargetMachine &TM) const {
bool HaveSData = isSmallDataEnabled(TM);
if (!HaveSData)
LLVM_DEBUG(dbgs() << "Small-data allocation is disabled, but symbols "
"may have explicit section assignments...\n");
// Only global variables, not functions.
LLVM_DEBUG(dbgs() << "Checking if value is in small-data, -G"
<< SmallDataThreshold << ": \"" << GO->getName() << "\": ");
const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GO);
if (!GVar) {
LLVM_DEBUG(dbgs() << "no, not a global variable\n");
return false;
}
// Globals with external linkage that have an original section set must be
// emitted to that section, regardless of whether we would put them into
// small data or not. This is how we can support mixing -G0/-G8 in LTO.
if (GVar->hasSection()) {
bool IsSmall = isSmallDataSection(GVar->getSection());
LLVM_DEBUG(dbgs() << (IsSmall ? "yes" : "no")
<< ", has section: " << GVar->getSection() << '\n');
return IsSmall;
}
// If sdata is disabled, stop the checks here.
if (!HaveSData) {
LLVM_DEBUG(dbgs() << "no, small-data allocation is disabled\n");
return false;
}
if (GVar->isConstant()) {
LLVM_DEBUG(dbgs() << "no, is a constant\n");
return false;
}
bool IsLocal = GVar->hasLocalLinkage();
if (!StaticsInSData && IsLocal) {
LLVM_DEBUG(dbgs() << "no, is static\n");
return false;
}
Type *GType = GVar->getValueType();
if (isa<ArrayType>(GType)) {
LLVM_DEBUG(dbgs() << "no, is an array\n");
return false;
}
// If the type is a struct with no body provided, treat is conservatively.
// There cannot be actual definitions of object of such a type in this CU
// (only references), so assuming that they are not in sdata is safe. If
// these objects end up in the sdata, the references will still be valid.
if (StructType *ST = dyn_cast<StructType>(GType)) {
if (ST->isOpaque()) {
LLVM_DEBUG(dbgs() << "no, has opaque type\n");
return false;
}
}
unsigned Size = GVar->getParent()->getDataLayout().getTypeAllocSize(GType);
if (Size == 0) {
LLVM_DEBUG(dbgs() << "no, has size 0\n");
return false;
}
if (Size > SmallDataThreshold) {
LLVM_DEBUG(dbgs() << "no, size exceeds sdata threshold: " << Size << '\n');
return false;
}
LLVM_DEBUG(dbgs() << "yes\n");
return true;
}
bool HexagonTargetObjectFile::isSmallDataEnabled(const TargetMachine &TM)
const {
return SmallDataThreshold > 0 && !TM.isPositionIndependent();
}
unsigned HexagonTargetObjectFile::getSmallDataSize() const {
return SmallDataThreshold;
}
bool HexagonTargetObjectFile::shouldPutJumpTableInFunctionSection(
bool UsesLabelDifference, const Function &F) const {
return EmitJtInText;
}
/// Descends any type down to "elementary" components,
/// discovering the smallest addressable one.
/// If zero is returned, declaration will not be modified.
unsigned HexagonTargetObjectFile::getSmallestAddressableSize(const Type *Ty,
const GlobalValue *GV, const TargetMachine &TM) const {
// Assign the smallest element access size to the highest
// value which assembler can handle.
unsigned SmallestElement = 8;
if (!Ty)
return 0;
switch (Ty->getTypeID()) {
case Type::StructTyID: {
const StructType *STy = cast<const StructType>(Ty);
for (auto &E : STy->elements()) {
unsigned AtomicSize = getSmallestAddressableSize(E, GV, TM);
if (AtomicSize < SmallestElement)
SmallestElement = AtomicSize;
}
return (STy->getNumElements() == 0) ? 0 : SmallestElement;
}
case Type::ArrayTyID: {
const ArrayType *ATy = cast<const ArrayType>(Ty);
return getSmallestAddressableSize(ATy->getElementType(), GV, TM);
}
case Type::FixedVectorTyID:
case Type::ScalableVectorTyID: {
const VectorType *PTy = cast<const VectorType>(Ty);
return getSmallestAddressableSize(PTy->getElementType(), GV, TM);
}
case Type::PointerTyID:
case Type::HalfTyID:
case Type::FloatTyID:
case Type::DoubleTyID:
case Type::IntegerTyID: {
const DataLayout &DL = GV->getParent()->getDataLayout();
// It is unfortunate that DL's function take non-const Type*.
return DL.getTypeAllocSize(const_cast<Type*>(Ty));
}
case Type::FunctionTyID:
case Type::VoidTyID:
case Type::BFloatTyID:
case Type::X86_FP80TyID:
case Type::FP128TyID:
case Type::PPC_FP128TyID:
case Type::LabelTyID:
case Type::MetadataTyID:
case Type::X86_MMXTyID:
case Type::TokenTyID:
return 0;
}
return 0;
}
MCSection *HexagonTargetObjectFile::selectSmallSectionForGlobal(
const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
const Type *GTy = GO->getValueType();
unsigned Size = getSmallestAddressableSize(GTy, GO, TM);
// If we have -ffunction-section or -fdata-section then we should emit the
// global value to a unique section specifically for it... even for sdata.
bool EmitUniquedSection = TM.getDataSections();
TRACE("Small data. Size(" << Size << ")");
// Handle Small Section classification here.
if (Kind.isBSS() || Kind.isBSSLocal()) {
// If -mno-sort-sda is not set, find out smallest accessible entity in
// declaration and add it to the section name string.
// Note. It does not track the actual usage of the value, only its de-
// claration. Also, compiler adds explicit pad fields to some struct
// declarations - they are currently counted towards smallest addres-
// sable entity.
if (NoSmallDataSorting) {
TRACE(" default sbss\n");
return SmallBSSSection;
}
StringRef Prefix(".sbss");
SmallString<128> Name(Prefix);
Name.append(getSectionSuffixForSize(Size));
if (EmitUniquedSection) {
Name.append(".");
Name.append(GO->getName());
}
TRACE(" unique sbss(" << Name << ")\n");
return getContext().getELFSection(Name.str(), ELF::SHT_NOBITS,
ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_HEX_GPREL);
}
if (Kind.isCommon()) {
// This is purely for LTO+Linker Script because commons don't really have a
// section. However, the BitcodeSectionWriter pass will query for the
// sections of commons (and the linker expects us to know their section) so
// we'll return one here.
if (NoSmallDataSorting)
return BSSSection;
Twine Name = Twine(".scommon") + getSectionSuffixForSize(Size);
TRACE(" small COMMON (" << Name << ")\n");
return getContext().getELFSection(Name.str(), ELF::SHT_NOBITS,
ELF::SHF_WRITE | ELF::SHF_ALLOC |
ELF::SHF_HEX_GPREL);
}
// We could have changed sdata object to a constant... in this
// case the Kind could be wrong for it.
if (Kind.isMergeableConst()) {
TRACE(" const_object_as_data ");
const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GO);
if (GVar->hasSection() && isSmallDataSection(GVar->getSection()))
Kind = SectionKind::getData();
}
if (Kind.isData()) {
if (NoSmallDataSorting) {
TRACE(" default sdata\n");
return SmallDataSection;
}
StringRef Prefix(".sdata");
SmallString<128> Name(Prefix);
Name.append(getSectionSuffixForSize(Size));
if (EmitUniquedSection) {
Name.append(".");
Name.append(GO->getName());
}
TRACE(" unique sdata(" << Name << ")\n");
return getContext().getELFSection(Name.str(), ELF::SHT_PROGBITS,
ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_HEX_GPREL);
}
TRACE("default ELF section\n");
// Otherwise, we work the same as ELF.
return TargetLoweringObjectFileELF::SelectSectionForGlobal(GO, Kind, TM);
}
// Return the function that uses the lookup table. If there are more
// than one live function that uses this look table, bail out and place
// the lookup table in default section.
const Function *
HexagonTargetObjectFile::getLutUsedFunction(const GlobalObject *GO) const {
const Function *ReturnFn = nullptr;
for (auto U : GO->users()) {
// validate each instance of user to be a live function.
auto *I = dyn_cast<Instruction>(U);
if (!I)
continue;
auto *Bb = I->getParent();
if (!Bb)
continue;
auto *UserFn = Bb->getParent();
if (!ReturnFn)
ReturnFn = UserFn;
else if (ReturnFn != UserFn)
return nullptr;
}
return ReturnFn;
}
MCSection *HexagonTargetObjectFile::selectSectionForLookupTable(
const GlobalObject *GO, const TargetMachine &TM, const Function *Fn) const {
SectionKind Kind = SectionKind::getText();
// If the function has explicit section, place the lookup table in this
// explicit section.
if (Fn->hasSection())
return getExplicitSectionGlobal(Fn, Kind, TM);
const auto *FuncObj = dyn_cast<GlobalObject>(Fn);
return SelectSectionForGlobal(FuncObj, Kind, TM);
}
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