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Extend BasicBlock sections to allow specifying clusters of basic blocks
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in the same section.

This allows specifying BasicBlock clusters like the following example:
!foo
!!0 1 2
!!4
This places basic blocks 0, 1, and 2 in one section in this order, and
places basic block rust-lang#4 in a single section of its own.
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@rlavaee
rlavaee committed Apr 13, 2020
1 parent ec228d7 commit 0d4ec16
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Showing 22 changed files with 492 additions and 409 deletions.
4 changes: 4 additions & 0 deletions llvm/include/llvm/CodeGen/AsmPrinter.h
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Original file line number Diff line number Diff line change
Expand Up @@ -141,6 +141,10 @@ class AsmPrinter : public MachineFunctionPass {
MCSymbol *CurrentFnEnd = nullptr;
MCSymbol *CurExceptionSym = nullptr;

// The symbol used to represent the start of the current BB section of the
// function. This is used to calculate the size of the BB section.
MCSymbol *CurrentSectionBeginSym = nullptr;

// The garbage collection metadata printer table.
void *GCMetadataPrinters = nullptr; // Really a DenseMap.

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79 changes: 50 additions & 29 deletions llvm/include/llvm/CodeGen/MachineBasicBlock.h
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Expand Up @@ -46,17 +46,35 @@ class raw_ostream;
class TargetRegisterClass;
class TargetRegisterInfo;

enum MachineBasicBlockSection : unsigned {
/// This is also the order of sections in a function. Basic blocks that are
/// part of the original function section (entry block) come first, followed
/// by exception handling basic blocks, cold basic blocks and finally basic
// blocks that need unique sections.
MBBS_Entry,
MBBS_Exception,
MBBS_Cold,
MBBS_Unique,
/// None implies no sections for any basic block, the default.
MBBS_None,
// This structure uniquely identifies a basic block section.
// Possible values are
// {Type: Default, Number: (unsigned)} (These are regular section IDs)
// {Type: Exception, Number: 0} (ExceptionSectionID)
// {Type: Cold, Number: 0} (ColdSectionID)
struct MBBSectionID {
enum SectionType {
Default = 0, // Regular section (these sections are distinguished by the
// Number field).
Exception, // Special section type for exception handling blocks
Cold, // Special section type for cold blocks
} Type;
unsigned Number;

MBBSectionID(unsigned N) : Type(Default), Number(N) {}

// Special unique sections for cold and exception blocks.
const static MBBSectionID ColdSectionID;
const static MBBSectionID ExceptionSectionID;

bool operator==(const MBBSectionID &Other) const {
return Type == Other.Type && Number == Other.Number;
}

bool operator!=(const MBBSectionID &Other) const { return !(*this == Other); }

private:
// This is only used to construct the special cold and exception sections.
MBBSectionID(SectionType T) : Type(T), Number(0) {}
};

template <> struct ilist_traits<MachineInstr> {
Expand Down Expand Up @@ -143,8 +161,14 @@ class MachineBasicBlock
/// Indicate that this basic block is the entry block of a cleanup funclet.
bool IsCleanupFuncletEntry = false;

/// Stores the Section type of the basic block with basic block sections.
MachineBasicBlockSection SectionType = MBBS_None;
/// With basic block sections, this stores the Section ID of the basic block.
MBBSectionID SectionID{0};

// Indicate that this basic block begins a section.
bool IsBeginSection = false;

// Indicate that this basic block ends a section.
bool IsEndSection = false;

/// Default target of the callbr of a basic block.
bool InlineAsmBrDefaultTarget = false;
Expand Down Expand Up @@ -435,16 +459,20 @@ class MachineBasicBlock
void setIsCleanupFuncletEntry(bool V = true) { IsCleanupFuncletEntry = V; }

/// Returns true if this block begins any section.
bool isBeginSection() const;
bool isBeginSection() const { return IsBeginSection; }

/// Returns true if this block ends any section.
bool isEndSection() const;
bool isEndSection() const { return IsEndSection; }

/// Returns the type of section this basic block belongs to.
MachineBasicBlockSection getSectionType() const { return SectionType; }
void setIsBeginSection(bool V = true) { IsBeginSection = V; }

/// Indicate that the basic block belongs to a Section Type.
void setSectionType(MachineBasicBlockSection V) { SectionType = V; }
void setIsEndSection(bool V = true) { IsEndSection = V; }

/// Returns the section ID of this basic block.
MBBSectionID getSectionID() const { return SectionID; }

/// Sets the section ID for this basic block.
void setSectionID(MBBSectionID V) { SectionID = V; }

/// Returns true if this is the indirect dest of an INLINEASM_BR.
bool isInlineAsmBrIndirectTarget(const MachineBasicBlock *Tgt) const {
Expand Down Expand Up @@ -485,10 +513,9 @@ class MachineBasicBlock
void moveAfter(MachineBasicBlock *NewBefore);

/// Returns true if this and MBB belong to the same section.
bool sameSection(const MachineBasicBlock *MBB) const;

/// Returns the basic block that ends the section which contains this one.
const MachineBasicBlock *getSectionEndMBB() const;
bool sameSection(const MachineBasicBlock *MBB) const {
return getSectionID() == MBB->getSectionID();
}

/// Update the terminator instructions in block to account for changes to the
/// layout. If the block previously used a fallthrough, it may now need a
Expand Down Expand Up @@ -876,12 +903,6 @@ class MachineBasicBlock
/// Return the MCSymbol for this basic block.
MCSymbol *getSymbol() const;

/// Sets the MCSymbol corresponding to the end of this basic block.
void setEndMCSymbol(MCSymbol *Sym) { EndMCSymbol = Sym; }

/// Returns the MCSymbol corresponding to the end of this basic block.
MCSymbol *getEndMCSymbol() const { return EndMCSymbol; }

Optional<uint64_t> getIrrLoopHeaderWeight() const {
return IrrLoopHeaderWeight;
}
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22 changes: 4 additions & 18 deletions llvm/include/llvm/CodeGen/MachineFunction.h
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Original file line number Diff line number Diff line change
Expand Up @@ -346,11 +346,6 @@ class MachineFunction {
/// Section Type for basic blocks, only relevant with basic block sections.
BasicBlockSection BBSectionsType = BasicBlockSection::None;

/// With Basic Block Sections, this stores the bb ranges of cold and
/// exception sections.
std::pair<int, int> ColdSectionRange = {-1, -1};
std::pair<int, int> ExceptionSectionRange = {-1, -1};

/// List of C++ TypeInfo used.
std::vector<const GlobalValue *> TypeInfos;

Expand Down Expand Up @@ -508,22 +503,13 @@ class MachineFunction {

void setBBSectionsType(BasicBlockSection V) { BBSectionsType = V; }

void setSectionRange();

/// Returns true if this basic block number starts a cold or exception
/// section.
bool isSectionStartMBB(int N) const {
return (N == ColdSectionRange.first || N == ExceptionSectionRange.first);
}

/// Returns true if this basic block ends a cold or exception section.
bool isSectionEndMBB(int N) const {
return (N == ColdSectionRange.second || N == ExceptionSectionRange.second);
}

/// Creates basic block Labels for this function.
void createBBLabels();

/// Assign IsBeginSection IsEndSection fields for basic blocks in this
/// function.
void assignBeginEndSections();

/// getTarget - Return the target machine this machine code is compiled with
const LLVMTargetMachine &getTarget() const { return Target; }

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4 changes: 0 additions & 4 deletions llvm/include/llvm/CodeGen/TargetLoweringObjectFileImpl.h
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Expand Up @@ -69,10 +69,6 @@ class TargetLoweringObjectFileELF : public TargetLoweringObjectFile {
const MachineBasicBlock &MBB,
const TargetMachine &TM) const override;

MCSection *getNamedSectionForMachineBasicBlock(
const Function &F, const MachineBasicBlock &MBB, const TargetMachine &TM,
const char *Suffix) const override;

bool shouldPutJumpTableInFunctionSection(bool UsesLabelDifference,
const Function &F) const override;

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4 changes: 0 additions & 4 deletions llvm/include/llvm/Target/TargetLoweringObjectFile.h
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Original file line number Diff line number Diff line change
Expand Up @@ -92,10 +92,6 @@ class TargetLoweringObjectFile : public MCObjectFileInfo {
const MachineBasicBlock &MBB,
const TargetMachine &TM) const;

virtual MCSection *getNamedSectionForMachineBasicBlock(
const Function &F, const MachineBasicBlock &MBB, const TargetMachine &TM,
const char *Suffix) const;

/// Classify the specified global variable into a set of target independent
/// categories embodied in SectionKind.
static SectionKind getKindForGlobal(const GlobalObject *GO,
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91 changes: 45 additions & 46 deletions llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1097,14 +1097,6 @@ void AsmPrinter::emitFunctionBody() {
// Print out code for the function.
bool HasAnyRealCode = false;
int NumInstsInFunction = 0;
bool emitBBSections = MF->hasBBSections();
MachineBasicBlock *EndOfRegularSectionMBB = nullptr;
if (emitBBSections) {
EndOfRegularSectionMBB =
const_cast<MachineBasicBlock *>(MF->front().getSectionEndMBB());
assert(EndOfRegularSectionMBB->isEndSection() &&
"The MBB at the end of the regular section must end a section");
}

for (auto &MBB : *MF) {
// Print a label for the basic block.
Expand Down Expand Up @@ -1185,17 +1177,41 @@ void AsmPrinter::emitFunctionBody() {
}
}
}
if (&MBB != EndOfRegularSectionMBB &&
(MF->hasBBLabels() || MBB.isEndSection())) {
// Emit size directive for the size of this basic block. Create a symbol
// for the end of the basic block.
MCSymbol *CurrentBBEnd = OutContext.createTempSymbol();

// We need a temporary symbol for the end of this basic block, if either we
// have BBLabels enabled and we want to emit size directive for the BBs, or
// if this basic blocks marks the end of a section (except the section
// containing the entry basic block as the end symbol for that section is
// CurrentFnEnd).
MCSymbol *CurrentBBEnd = nullptr;
if ((MAI->hasDotTypeDotSizeDirective() && MF->hasBBLabels()) ||
(MBB.isEndSection() && !MBB.sameSection(&MF->front()))) {
CurrentBBEnd = OutContext.createTempSymbol();
OutStreamer->emitLabel(CurrentBBEnd);
}

// Helper for emitting the size directive associated with a basic block
// symbol.
auto emitELFSizeDirective = [&](MCSymbol *SymForSize) {
assert(CurrentBBEnd && "Basicblock end symbol not set!");
const MCExpr *SizeExp = MCBinaryExpr::createSub(
MCSymbolRefExpr::create(CurrentBBEnd, OutContext),
MCSymbolRefExpr::create(MBB.getSymbol(), OutContext), OutContext);
OutStreamer->emitLabel(CurrentBBEnd);
MBB.setEndMCSymbol(CurrentBBEnd);
OutStreamer->emitELFSize(MBB.getSymbol(), SizeExp);
MCSymbolRefExpr::create(SymForSize, OutContext), OutContext);
OutStreamer->emitELFSize(SymForSize, SizeExp);
};

// Emit size directive for the size of each basic block, if BBLabels is
// enabled.
if (MAI->hasDotTypeDotSizeDirective() && MF->hasBBLabels())
emitELFSizeDirective(MBB.getSymbol());

// Emit size directive for the size of each basic block section once we
// get to the end of that section.
if (MBB.isEndSection()) {
if (!MBB.sameSection(&MF->front())) {
if (MAI->hasDotTypeDotSizeDirective())
emitELFSizeDirective(CurrentSectionBeginSym);
}
}
emitBasicBlockEnd(MBB);
}
Expand Down Expand Up @@ -1230,9 +1246,8 @@ void AsmPrinter::emitFunctionBody() {
}
}

// Switch to the original section if basic block sections was used.
if (emitBBSections)
OutStreamer->SwitchSection(MF->getSection());
// Switch to the original section in case basic block sections was used.
OutStreamer->SwitchSection(MF->getSection());

const Function &F = MF->getFunction();
for (const auto &BB : F) {
Expand All @@ -1249,7 +1264,7 @@ void AsmPrinter::emitFunctionBody() {
emitFunctionBodyEnd();

if (needFuncLabelsForEHOrDebugInfo(*MF, MMI) ||
MAI->hasDotTypeDotSizeDirective() || emitBBSections) {
MAI->hasDotTypeDotSizeDirective()) {
// Create a symbol for the end of function.
CurrentFnEnd = createTempSymbol("func_end");
OutStreamer->emitLabel(CurrentFnEnd);
Expand All @@ -1272,8 +1287,6 @@ void AsmPrinter::emitFunctionBody() {
HI.Handler->markFunctionEnd();
}

if (emitBBSections)
EndOfRegularSectionMBB->setEndMCSymbol(CurrentFnEnd);

// Print out jump tables referenced by the function.
emitJumpTableInfo();
Expand Down Expand Up @@ -1753,6 +1766,7 @@ void AsmPrinter::SetupMachineFunction(MachineFunction &MF) {

CurrentFnSymForSize = CurrentFnSym;
CurrentFnBegin = nullptr;
CurrentSectionBeginSym = nullptr;
CurExceptionSym = nullptr;
bool NeedsLocalForSize = MAI->needsLocalForSize();
if (F.hasFnAttribute("patchable-function-entry") ||
Expand Down Expand Up @@ -2981,7 +2995,6 @@ static void emitBasicBlockLoopComments(const MachineBasicBlock &MBB,
/// MachineBasicBlock, an alignment (if present) and a comment describing
/// it if appropriate.
void AsmPrinter::emitBasicBlockStart(const MachineBasicBlock &MBB) {
bool BBSections = MF->hasBBSections();
// End the previous funclet and start a new one.
if (MBB.isEHFuncletEntry()) {
for (const HandlerInfo &HI : Handlers) {
Expand All @@ -2991,11 +3004,9 @@ void AsmPrinter::emitBasicBlockStart(const MachineBasicBlock &MBB) {
}

// Emit an alignment directive for this block, if needed.
if (MBB.pred_empty() || !BBSections) {
const Align Alignment = MBB.getAlignment();
if (Alignment != Align(1))
emitAlignment(Alignment);
}
const Align Alignment = MBB.getAlignment();
if (Alignment != Align(1))
emitAlignment(Alignment);

// If the block has its address taken, emit any labels that were used to
// reference the block. It is possible that there is more than one label
Expand Down Expand Up @@ -3027,9 +3038,8 @@ void AsmPrinter::emitBasicBlockStart(const MachineBasicBlock &MBB) {
emitBasicBlockLoopComments(MBB, MLI, *this);
}

bool emitBBLabels = BBSections || MF->hasBBLabels();
if (MBB.pred_empty() ||
(!emitBBLabels && isBlockOnlyReachableByFallthrough(&MBB) &&
(!MF->hasBBLabels() && isBlockOnlyReachableByFallthrough(&MBB) &&
!MBB.isEHFuncletEntry() && !MBB.hasLabelMustBeEmitted())) {
if (isVerbose()) {
// NOTE: Want this comment at start of line, don't emit with AddComment.
Expand All @@ -3040,23 +3050,12 @@ void AsmPrinter::emitBasicBlockStart(const MachineBasicBlock &MBB) {
if (isVerbose() && MBB.hasLabelMustBeEmitted()) {
OutStreamer->AddComment("Label of block must be emitted");
}
// With -fbasicblock-sections, a basic block can start a new section.
if (MBB.getSectionType() == MachineBasicBlockSection::MBBS_Exception) {
// Create the exception section for this function.
OutStreamer->SwitchSection(
getObjFileLowering().getNamedSectionForMachineBasicBlock(
MF->getFunction(), MBB, TM, ".eh"));
} else if (MBB.getSectionType() == MachineBasicBlockSection::MBBS_Cold) {
// Create the cold section here.
OutStreamer->SwitchSection(
getObjFileLowering().getNamedSectionForMachineBasicBlock(
MF->getFunction(), MBB, TM, ".unlikely"));
} else if (MBB.isBeginSection() && MBB.isEndSection()) {
// Switch to a new section if this basic block must begin a section.
if (MBB.isBeginSection()) {
OutStreamer->SwitchSection(
getObjFileLowering().getSectionForMachineBasicBlock(MF->getFunction(),
MBB, TM));
} else if (BBSections) {
OutStreamer->SwitchSection(MF->getSection());
CurrentSectionBeginSym = MBB.getSymbol();
}
OutStreamer->emitLabel(MBB.getSymbol());
}
Expand Down Expand Up @@ -3090,7 +3089,7 @@ void AsmPrinter::emitVisibility(MCSymbol *Sym, unsigned Visibility,
/// the predecessor and this block is a fall-through.
bool AsmPrinter::
isBlockOnlyReachableByFallthrough(const MachineBasicBlock *MBB) const {
// With BasicBlock Sections, no block is a fall through.
// With BasicBlock Sections, beginning of the section is not a fallthrough.
if (MBB->isBeginSection())
return false;

Expand Down
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