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[llvm] Reduce memory footprint of Debug metadata nodes (#71227)
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Using a combination of reordering fields and using empty SubclassData32
/ SubclassData1, it's possible to improve the size of data structures
used to store debug info in the IR:

Before:

DILexicalBlock: 24
DILexicalBlockFile: 24
DIModule: 24
DITemplateParameter: 24
DICommonBlock: 24
DIMacro: 24
DICompileUnit: 56
DIType: 48
DINamespace: 24
DIVariable: 24
DIGlobalVariable: 32
DILocalVariable: 32
DILabel: 24

After:

DILexicalBlock: 24
DILexicalBlockFile: 16
DIModule: 16
DITemplateParameter: 16
DICommonBlock: 16
DIMacro: 16
DICompileUnit: 48
DIType: 40
DINamespace: 16
DIVariable: 24
DIGlobalVariable: 24
DILocalVariable: 32
DILabel: 16
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@serge-sans-paille
serge-sans-paille committed Nov 16, 2023
1 parent ae623d1 commit 102f7fc
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Showing 2 changed files with 90 additions and 58 deletions.
115 changes: 70 additions & 45 deletions llvm/include/llvm/IR/DebugInfoMetadata.h
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Expand Up @@ -128,6 +128,8 @@ class DITypeRefArray {
/// A metadata node with a DWARF tag (i.e., a constant named \c DW_TAG_*,
/// defined in llvm/BinaryFormat/Dwarf.h). Called \a DINode because it's
/// potentially used for non-DWARF output.
///
/// Uses the SubclassData16 Metadata slot.
class DINode : public MDNode {
friend class LLVMContextImpl;
friend class MDNode;
Expand Down Expand Up @@ -227,6 +229,8 @@ class DINode : public MDNode {
/// (possibly empty) null-separated \a MDString header that contains arbitrary
/// fields. The remaining operands are \a dwarf_operands(), and are pointers
/// to other metadata.
///
/// Uses the SubclassData32 Metadata slot.
class GenericDINode : public DINode {
friend class LLVMContextImpl;
friend class MDNode;
Expand Down Expand Up @@ -695,12 +699,13 @@ std::optional<StringRef> DIScope::getSource() const {
/// TODO: Remove the hardcoded name and context, since many types don't use
/// them.
/// TODO: Split up flags.
///
/// Uses the SubclassData32 Metadata slot.
class DIType : public DIScope {
unsigned Line;
DIFlags Flags;
uint64_t SizeInBits;
uint64_t OffsetInBits;
uint32_t AlignInBits;

protected:
DIType(LLVMContext &C, unsigned ID, StorageType Storage, unsigned Tag,
Expand All @@ -716,7 +721,7 @@ class DIType : public DIScope {
this->Line = Line;
this->Flags = Flags;
this->SizeInBits = SizeInBits;
this->AlignInBits = AlignInBits;
this->SubclassData32 = AlignInBits;
this->OffsetInBits = OffsetInBits;
}

Expand All @@ -735,7 +740,7 @@ class DIType : public DIScope {

unsigned getLine() const { return Line; }
uint64_t getSizeInBits() const { return SizeInBits; }
uint32_t getAlignInBits() const { return AlignInBits; }
uint32_t getAlignInBits() const { return SubclassData32; }
uint32_t getAlignInBytes() const { return getAlignInBits() / CHAR_BIT; }
uint64_t getOffsetInBits() const { return OffsetInBits; }
DIFlags getFlags() const { return Flags; }
Expand Down Expand Up @@ -1389,13 +1394,13 @@ class DICompileUnit : public DIScope {

private:
unsigned SourceLanguage;
bool IsOptimized;
unsigned RuntimeVersion;
unsigned EmissionKind;
uint64_t DWOId;
unsigned EmissionKind;
unsigned NameTableKind;
bool IsOptimized;
bool SplitDebugInlining;
bool DebugInfoForProfiling;
unsigned NameTableKind;
bool RangesBaseAddress;

DICompileUnit(LLVMContext &C, StorageType Storage, unsigned SourceLanguage,
Expand Down Expand Up @@ -1876,6 +1881,10 @@ class DISubprogram : public DILocalScope {
/// Debug location.
///
/// A debug location in source code, used for debug info and otherwise.
///
/// Uses the SubclassData1, SubclassData16 and SubclassData32
/// Metadata slots.

class DILocation : public MDNode {
friend class LLVMContextImpl;
friend class MDNode;
Expand Down Expand Up @@ -2161,17 +2170,20 @@ class DILexicalBlockBase : public DILocalScope {
}
};

/// Debug lexical block.
///
/// Uses the SubclassData32 Metadata slot.
class DILexicalBlock : public DILexicalBlockBase {
friend class LLVMContextImpl;
friend class MDNode;

unsigned Line;
uint16_t Column;

DILexicalBlock(LLVMContext &C, StorageType Storage, unsigned Line,
unsigned Column, ArrayRef<Metadata *> Ops)
: DILexicalBlockBase(C, DILexicalBlockKind, Storage, Ops), Line(Line),
: DILexicalBlockBase(C, DILexicalBlockKind, Storage, Ops),
Column(Column) {
SubclassData32 = Line;
assert(Column < (1u << 16) && "Expected 16-bit column");
}
~DILexicalBlock() = default;
Expand Down Expand Up @@ -2206,7 +2218,7 @@ class DILexicalBlock : public DILexicalBlockBase {

TempDILexicalBlock clone() const { return cloneImpl(); }

unsigned getLine() const { return Line; }
unsigned getLine() const { return SubclassData32; }
unsigned getColumn() const { return Column; }

static bool classof(const Metadata *MD) {
Expand All @@ -2218,12 +2230,11 @@ class DILexicalBlockFile : public DILexicalBlockBase {
friend class LLVMContextImpl;
friend class MDNode;

unsigned Discriminator;

DILexicalBlockFile(LLVMContext &C, StorageType Storage,
unsigned Discriminator, ArrayRef<Metadata *> Ops)
: DILexicalBlockBase(C, DILexicalBlockFileKind, Storage, Ops),
Discriminator(Discriminator) {}
: DILexicalBlockBase(C, DILexicalBlockFileKind, Storage, Ops) {
SubclassData32 = Discriminator;
}
~DILexicalBlockFile() = default;

static DILexicalBlockFile *getImpl(LLVMContext &Context, DILocalScope *Scope,
Expand Down Expand Up @@ -2255,7 +2266,7 @@ class DILexicalBlockFile : public DILexicalBlockBase {
(Scope, File, Discriminator))

TempDILexicalBlockFile clone() const { return cloneImpl(); }
unsigned getDiscriminator() const { return Discriminator; }
unsigned getDiscriminator() const { return SubclassData32; }

static bool classof(const Metadata *MD) {
return MD->getMetadataID() == DILexicalBlockFileKind;
Expand Down Expand Up @@ -2338,12 +2349,13 @@ DILocation::cloneByMultiplyingDuplicationFactor(unsigned DF) const {
return std::nullopt;
}

/// Debug lexical block.
///
/// Uses the SubclassData1 Metadata slot.
class DINamespace : public DIScope {
friend class LLVMContextImpl;
friend class MDNode;

unsigned ExportSymbols : 1;

DINamespace(LLVMContext &Context, StorageType Storage, bool ExportSymbols,
ArrayRef<Metadata *> Ops);
~DINamespace() = default;
Expand Down Expand Up @@ -2373,7 +2385,7 @@ class DINamespace : public DIScope {

TempDINamespace clone() const { return cloneImpl(); }

bool getExportSymbols() const { return ExportSymbols; }
bool getExportSymbols() const { return SubclassData1; }
DIScope *getScope() const { return cast_or_null<DIScope>(getRawScope()); }
StringRef getName() const { return getStringOperand(2); }

Expand All @@ -2387,11 +2399,11 @@ class DINamespace : public DIScope {

/// Represents a module in the programming language, for example, a Clang
/// module, or a Fortran module.
///
/// Uses the SubclassData1 and SubclassData32 Metadata slots.
class DIModule : public DIScope {
friend class LLVMContextImpl;
friend class MDNode;
unsigned LineNo;
bool IsDecl;

DIModule(LLVMContext &Context, StorageType Storage, unsigned LineNo,
bool IsDecl, ArrayRef<Metadata *> Ops);
Expand Down Expand Up @@ -2443,8 +2455,8 @@ class DIModule : public DIScope {
StringRef getConfigurationMacros() const { return getStringOperand(3); }
StringRef getIncludePath() const { return getStringOperand(4); }
StringRef getAPINotesFile() const { return getStringOperand(5); }
unsigned getLineNo() const { return LineNo; }
bool getIsDecl() const { return IsDecl; }
unsigned getLineNo() const { return SubclassData32; }
bool getIsDecl() const { return SubclassData1; }

Metadata *getRawScope() const { return getOperand(1); }
MDString *getRawName() const { return getOperandAs<MDString>(2); }
Expand All @@ -2460,13 +2472,15 @@ class DIModule : public DIScope {
};

/// Base class for template parameters.
///
/// Uses the SubclassData1 Metadata slot.
class DITemplateParameter : public DINode {
protected:
bool IsDefault;

DITemplateParameter(LLVMContext &Context, unsigned ID, StorageType Storage,
unsigned Tag, bool IsDefault, ArrayRef<Metadata *> Ops)
: DINode(Context, ID, Storage, Tag, Ops), IsDefault(IsDefault) {}
: DINode(Context, ID, Storage, Tag, Ops) {
SubclassData1 = IsDefault;
}
~DITemplateParameter() = default;

public:
Expand All @@ -2475,7 +2489,7 @@ class DITemplateParameter : public DINode {

MDString *getRawName() const { return getOperandAs<MDString>(0); }
Metadata *getRawType() const { return getOperand(1); }
bool isDefault() const { return IsDefault; }
bool isDefault() const { return SubclassData1; }

static bool classof(const Metadata *MD) {
return MD->getMetadataID() == DITemplateTypeParameterKind ||
Expand Down Expand Up @@ -2572,9 +2586,10 @@ class DITemplateValueParameter : public DITemplateParameter {
};

/// Base class for variables.
///
/// Uses the SubclassData32 Metadata slot.
class DIVariable : public DINode {
unsigned Line;
uint32_t AlignInBits;

protected:
DIVariable(LLVMContext &C, unsigned ID, StorageType Storage, signed Line,
Expand All @@ -2587,7 +2602,7 @@ class DIVariable : public DINode {
StringRef getName() const { return getStringOperand(1); }
DIFile *getFile() const { return cast_or_null<DIFile>(getRawFile()); }
DIType *getType() const { return cast_or_null<DIType>(getRawType()); }
uint32_t getAlignInBits() const { return AlignInBits; }
uint32_t getAlignInBits() const { return SubclassData32; }
uint32_t getAlignInBytes() const { return getAlignInBits() / CHAR_BIT; }
/// Determines the size of the variable's type.
std::optional<uint64_t> getSizeInBits() const;
Expand Down Expand Up @@ -3161,9 +3176,10 @@ class DIGlobalVariable : public DIVariable {
}
};

/// Debug common block.
///
/// Uses the SubclassData32 Metadata slot.
class DICommonBlock : public DIScope {
unsigned LineNo;

friend class LLVMContextImpl;
friend class MDNode;

Expand Down Expand Up @@ -3205,7 +3221,7 @@ class DICommonBlock : public DIScope {
}
StringRef getName() const { return getStringOperand(2); }
DIFile *getFile() const { return cast_or_null<DIFile>(getRawFile()); }
unsigned getLineNo() const { return LineNo; }
unsigned getLineNo() const { return SubclassData32; }

Metadata *getRawScope() const { return getOperand(0); }
Metadata *getRawDecl() const { return getOperand(1); }
Expand Down Expand Up @@ -3310,12 +3326,11 @@ class DILocalVariable : public DIVariable {

/// Label.
///
/// Uses the SubclassData32 Metadata slot.
class DILabel : public DINode {
friend class LLVMContextImpl;
friend class MDNode;

unsigned Line;

DILabel(LLVMContext &C, StorageType Storage, unsigned Line,
ArrayRef<Metadata *> Ops);
~DILabel() = default;
Expand Down Expand Up @@ -3353,7 +3368,7 @@ class DILabel : public DINode {
DILocalScope *getScope() const {
return cast_or_null<DILocalScope>(getRawScope());
}
unsigned getLine() const { return Line; }
unsigned getLine() const { return SubclassData32; }
StringRef getName() const { return getStringOperand(1); }
DIFile *getFile() const { return cast_or_null<DIFile>(getRawFile()); }

Expand Down Expand Up @@ -3455,15 +3470,17 @@ class DIObjCProperty : public DINode {
};

/// An imported module (C++ using directive or similar).
///
/// Uses the SubclassData32 Metadata slot.
class DIImportedEntity : public DINode {
friend class LLVMContextImpl;
friend class MDNode;

unsigned Line;

DIImportedEntity(LLVMContext &C, StorageType Storage, unsigned Tag,
unsigned Line, ArrayRef<Metadata *> Ops)
: DINode(C, DIImportedEntityKind, Storage, Tag, Ops), Line(Line) {}
: DINode(C, DIImportedEntityKind, Storage, Tag, Ops) {
SubclassData32 = Line;
}
~DIImportedEntity() = default;

static DIImportedEntity *getImpl(LLVMContext &Context, unsigned Tag,
Expand Down Expand Up @@ -3499,7 +3516,7 @@ class DIImportedEntity : public DINode {

TempDIImportedEntity clone() const { return cloneImpl(); }

unsigned getLine() const { return Line; }
unsigned getLine() const { return SubclassData32; }
DIScope *getScope() const { return cast_or_null<DIScope>(getRawScope()); }
DINode *getEntity() const { return cast_or_null<DINode>(getRawEntity()); }
StringRef getName() const { return getStringOperand(2); }
Expand Down Expand Up @@ -3567,6 +3584,8 @@ class DIGlobalVariableExpression : public MDNode {
/// \c DW_MACINFO_*, defined in llvm/BinaryFormat/Dwarf.h). Called \a
/// DIMacroNode
/// because it's potentially used for non-DWARF output.
///
/// Uses the SubclassData16 Metadata slot.
class DIMacroNode : public MDNode {
friend class LLVMContextImpl;
friend class MDNode;
Expand Down Expand Up @@ -3611,15 +3630,18 @@ class DIMacroNode : public MDNode {
}
};

/// Macro
///
/// Uses the SubclassData32 Metadata slot.
class DIMacro : public DIMacroNode {
friend class LLVMContextImpl;
friend class MDNode;

unsigned Line;

DIMacro(LLVMContext &C, StorageType Storage, unsigned MIType, unsigned Line,
ArrayRef<Metadata *> Ops)
: DIMacroNode(C, DIMacroKind, Storage, MIType, Ops), Line(Line) {}
: DIMacroNode(C, DIMacroKind, Storage, MIType, Ops) {
SubclassData32 = Line;
}
~DIMacro() = default;

static DIMacro *getImpl(LLVMContext &Context, unsigned MIType, unsigned Line,
Expand Down Expand Up @@ -3649,7 +3671,7 @@ class DIMacro : public DIMacroNode {

TempDIMacro clone() const { return cloneImpl(); }

unsigned getLine() const { return Line; }
unsigned getLine() const { return SubclassData32; }

StringRef getName() const { return getStringOperand(0); }
StringRef getValue() const { return getStringOperand(1); }
Expand All @@ -3662,15 +3684,18 @@ class DIMacro : public DIMacroNode {
}
};

/// Macro file
///
/// Uses the SubclassData32 Metadata slot.
class DIMacroFile : public DIMacroNode {
friend class LLVMContextImpl;
friend class MDNode;

unsigned Line;

DIMacroFile(LLVMContext &C, StorageType Storage, unsigned MIType,
unsigned Line, ArrayRef<Metadata *> Ops)
: DIMacroNode(C, DIMacroFileKind, Storage, MIType, Ops), Line(Line) {}
: DIMacroNode(C, DIMacroFileKind, Storage, MIType, Ops) {
SubclassData32 = Line;
}
~DIMacroFile() = default;

static DIMacroFile *getImpl(LLVMContext &Context, unsigned MIType,
Expand Down Expand Up @@ -3711,7 +3736,7 @@ class DIMacroFile : public DIMacroNode {
replaceOperandWith(1, Elements.get());
}

unsigned getLine() const { return Line; }
unsigned getLine() const { return SubclassData32; }
DIFile *getFile() const { return cast_or_null<DIFile>(getRawFile()); }

DIMacroNodeArray getElements() const {
Expand Down

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