[MC] Add MCFragment allocation helpers

`allocFragment` might be changed to a placement new when the allocation
strategy changes.

`allocInitialFragment` is to deduplicate the following pattern
```
  auto *F = new MCDataFragment();
  Result->addFragment(*F);
  F->setParent(Result);
```

Pull Request: #95197

Author: MaskRay

llvm/include/llvm/MC/MCCodeView.h

@@ -143,7 +143,7 @@ struct MCCVFunctionInfo {
 /// Holds state from .cv_file and .cv_loc directives for later emission.
 class CodeViewContext {
 public:
-  CodeViewContext();
+  CodeViewContext(MCContext *MCCtx) : MCCtx(MCCtx) {}
   ~CodeViewContext();
 
   CodeViewContext &operator=(const CodeViewContext &other) = delete;
@@ -223,6 +223,8 @@ class CodeViewContext {
   std::pair<StringRef, unsigned> addToStringTable(StringRef S);
 
 private:
+  MCContext *MCCtx;
+
   /// Map from string to string table offset.
   StringMap<unsigned> StringTable;
 

llvm/include/llvm/MC/MCContext.h

@@ -44,6 +44,7 @@ namespace llvm {
 
 class CodeViewContext;
 class MCAsmInfo;
+class MCDataFragment;
 class MCInst;
 class MCLabel;
 class MCObjectFileInfo;
@@ -345,6 +346,8 @@ class MCContext {
   void reportCommon(SMLoc Loc,
                     std::function<void(SMDiagnostic &, const SourceMgr *)>);
 
+  MCDataFragment *allocInitialFragment(MCSection &Sec);
+
   MCSymbol *createSymbolImpl(const StringMapEntry<bool> *Name,
                              bool IsTemporary);
   MCSymbol *createSymbol(StringRef Name, bool AlwaysAddSuffix,
@@ -437,6 +440,10 @@ class MCContext {
   /// Create and return a new MC instruction.
   MCInst *createMCInst();
 
+  template <typename F, typename... Args> F *allocFragment(Args &&...args) {
+    return new F(std::forward<Args>(args)...);
+  }
+
   /// \name Symbol Management
   /// @{
 

llvm/lib/MC/MCAssembler.cpp

@@ -820,8 +820,11 @@ void MCAssembler::layout(MCAsmLayout &Layout) {
   for (MCSection &Sec : *this) {
     // Create dummy fragments to eliminate any empty sections, this simplifies
     // layout.
-    if (Sec.empty())
-      new MCDataFragment(&Sec);
+    if (Sec.empty()) {
+      auto *F = getContext().allocFragment<MCDataFragment>();
+      F->setParent(&Sec);
+      Sec.addFragment(*F);
+    }
 
     Sec.setOrdinal(SectionIndex++);
   }

llvm/lib/MC/MCCodeView.cpp

@@ -26,8 +26,6 @@
 using namespace llvm;
 using namespace llvm::codeview;
 
-CodeViewContext::CodeViewContext() = default;
-
 CodeViewContext::~CodeViewContext() {
   // If someone inserted strings into the string table but never actually
   // emitted them somewhere, clean up the fragment.
@@ -138,7 +136,7 @@ void CodeViewContext::recordCVLoc(MCContext &Ctx, const MCSymbol *Label,
 
 MCDataFragment *CodeViewContext::getStringTableFragment() {
   if (!StrTabFragment) {
-    StrTabFragment = new MCDataFragment();
+    StrTabFragment = MCCtx->allocFragment<MCDataFragment>();
     // Start a new string table out with a null byte.
     StrTabFragment->getContents().push_back('\0');
   }
@@ -450,9 +448,9 @@ void CodeViewContext::emitInlineLineTableForFunction(MCObjectStreamer &OS,
                                                      const MCSymbol *FnEndSym) {
   // Create and insert a fragment into the current section that will be encoded
   // later.
-  new MCCVInlineLineTableFragment(PrimaryFunctionId, SourceFileId,
-                                  SourceLineNum, FnStartSym, FnEndSym,
-                                  OS.getCurrentSectionOnly());
+  auto *F = MCCtx->allocFragment<MCCVInlineLineTableFragment>(
+      PrimaryFunctionId, SourceFileId, SourceLineNum, FnStartSym, FnEndSym);
+  OS.insert(F);
 }
 
 MCFragment *CodeViewContext::emitDefRange(
@@ -461,8 +459,10 @@ MCFragment *CodeViewContext::emitDefRange(
     StringRef FixedSizePortion) {
   // Create and insert a fragment into the current section that will be encoded
   // later.
-  return new MCCVDefRangeFragment(Ranges, FixedSizePortion,
-                           OS.getCurrentSectionOnly());
+  auto *F =
+      MCCtx->allocFragment<MCCVDefRangeFragment>(Ranges, FixedSizePortion);
+  OS.insert(F);
+  return F;
 }
 
 static unsigned computeLabelDiff(MCAsmLayout &Layout, const MCSymbol *Begin,

llvm/lib/MC/MCContext.cpp

@@ -195,6 +195,15 @@ MCInst *MCContext::createMCInst() {
   return new (MCInstAllocator.Allocate()) MCInst;
 }
 
+// Allocate the initial MCDataFragment for the begin symbol.
+MCDataFragment *MCContext::allocInitialFragment(MCSection &Sec) {
+  assert(!Sec.curFragList()->Head);
+  auto *F = allocFragment<MCDataFragment>();
+  F->setParent(&Sec);
+  Sec.addFragment(*F);
+  return F;
+}
+
 //===----------------------------------------------------------------------===//
 // Symbol Manipulation
 //===----------------------------------------------------------------------===//
@@ -497,11 +506,8 @@ MCSectionELF *MCContext::createELFSectionImpl(StringRef Section, unsigned Type,
       MCSectionELF(Section, Type, Flags, K, EntrySize, Group, Comdat, UniqueID,
                    R, LinkedToSym);
 
-  auto *F = new MCDataFragment();
-  Ret->addFragment(*F);
-  F->setParent(Ret);
+  auto *F = allocInitialFragment(*Ret);
   R->setFragment(F);
-
   return Ret;
 }
 
@@ -797,11 +803,8 @@ MCSectionWasm *MCContext::getWasmSection(const Twine &Section, SectionKind Kind,
       MCSectionWasm(CachedName, Kind, Flags, GroupSym, UniqueID, Begin);
   Entry.second = Result;
 
-  auto *F = new MCDataFragment();
-  Result->addFragment(*F);
-  F->setParent(Result);
+  auto *F = allocInitialFragment(*Result);
   Begin->setFragment(F);
-
   return Result;
 }
 
@@ -863,10 +866,7 @@ MCSectionXCOFF *MCContext::getXCOFFSection(
 
   Entry.second = Result;
 
-  auto *F = new MCDataFragment();
-  Result->addFragment(*F);
-  F->setParent(Result);
-
+  auto *F = allocInitialFragment(*Result);
   if (Begin)
     Begin->setFragment(F);
 
@@ -886,10 +886,7 @@ MCSectionSPIRV *MCContext::getSPIRVSection() {
   MCSectionSPIRV *Result = new (SPIRVAllocator.Allocate())
       MCSectionSPIRV(SectionKind::getText(), Begin);
 
-  auto *F = new MCDataFragment();
-  Result->addFragment(*F);
-  F->setParent(Result);
-
+  allocInitialFragment(*Result);
   return Result;
 }
 
@@ -909,10 +906,7 @@ MCSectionDXContainer *MCContext::getDXContainerSection(StringRef Section,
       new (DXCAllocator.Allocate()) MCSectionDXContainer(Name, K, nullptr);
 
   // The first fragment will store the header
-  auto *F = new MCDataFragment();
-  MapIt->second->addFragment(*F);
-  F->setParent(MapIt->second);
-
+  allocInitialFragment(*MapIt->second);
   return MapIt->second;
 }
 
@@ -1043,7 +1037,7 @@ void MCContext::finalizeDwarfSections(MCStreamer &MCOS) {
 
 CodeViewContext &MCContext::getCVContext() {
   if (!CVContext)
-    CVContext.reset(new CodeViewContext);
+    CVContext.reset(new CodeViewContext(this));
   return *CVContext;
 }
 

llvm/lib/MC/MCELFStreamer.cpp

@@ -585,7 +585,7 @@ void MCELFStreamer::emitInstToData(const MCInst &Inst,
       // When not in a bundle-locked group and the -mc-relax-all flag is used,
       // we create a new temporary fragment which will be later merged into
       // the current fragment.
-      DF = new MCDataFragment();
+      DF = getContext().allocFragment<MCDataFragment>();
     else if (isBundleLocked() && !Sec.isBundleGroupBeforeFirstInst()) {
       // If we are bundle-locked, we re-use the current fragment.
       // The bundle-locking directive ensures this is a new data fragment.
@@ -596,13 +596,14 @@ void MCELFStreamer::emitInstToData(const MCInst &Inst,
       // Optimize memory usage by emitting the instruction to a
       // MCCompactEncodedInstFragment when not in a bundle-locked group and
       // there are no fixups registered.
-      MCCompactEncodedInstFragment *CEIF = new MCCompactEncodedInstFragment();
+      MCCompactEncodedInstFragment *CEIF =
+          getContext().allocFragment<MCCompactEncodedInstFragment>();
       insert(CEIF);
       CEIF->getContents().append(Code.begin(), Code.end());
       CEIF->setHasInstructions(STI);
       return;
     } else {
-      DF = new MCDataFragment();
+      DF = getContext().allocFragment<MCDataFragment>();
       insert(DF);
     }
     if (Sec.getBundleLockState() == MCSection::BundleLockedAlignToEnd) {
@@ -661,7 +662,7 @@ void MCELFStreamer::emitBundleLock(bool AlignToEnd) {
 
   if (getAssembler().getRelaxAll() && !isBundleLocked()) {
     // TODO: drop the lock state and set directly in the fragment
-    MCDataFragment *DF = new MCDataFragment();
+    MCDataFragment *DF = getContext().allocFragment<MCDataFragment>();
     BundleGroups.push_back(DF);
   }
 

llvm/lib/MC/MCMachOStreamer.cpp

@@ -199,7 +199,7 @@ void MCMachOStreamer::emitLabel(MCSymbol *Symbol, SMLoc Loc) {
   // We have to create a new fragment if this is an atom defining symbol,
   // fragments cannot span atoms.
   if (getAssembler().isSymbolLinkerVisible(*Symbol))
-    insert(new MCDataFragment());
+    insert(getContext().allocFragment<MCDataFragment>());
 
   MCObjectStreamer::emitLabel(Symbol, Loc);
 
@@ -555,7 +555,9 @@ void MCMachOStreamer::finalizeCGProfile() {
   MCSection *CGProfileSection = Asm.getContext().getMachOSection(
       "__LLVM", "__cg_profile", 0, SectionKind::getMetadata());
   Asm.registerSection(*CGProfileSection);
-  auto *Frag = new MCDataFragment(CGProfileSection);
+  auto *Frag = getContext().allocFragment<MCDataFragment>();
+  Frag->setParent(CGProfileSection);
+  CGProfileSection->addFragment(*Frag);
   // For each entry, reserve space for 2 32-bit indices and a 64-bit count.
   size_t SectionBytes =
       Asm.CGProfile.size() * (2 * sizeof(uint32_t) + sizeof(uint64_t));
@@ -595,7 +597,9 @@ void MCMachOStreamer::createAddrSigSection() {
   MCSection *AddrSigSection =
       Asm.getContext().getObjectFileInfo()->getAddrSigSection();
   Asm.registerSection(*AddrSigSection);
-  auto *Frag = new MCDataFragment(AddrSigSection);
+  auto *Frag = getContext().allocFragment<MCDataFragment>();
+  Frag->setParent(AddrSigSection);
+  AddrSigSection->addFragment(*Frag);
   // We will generate a series of pointer-sized symbol relocations at offset
   // 0x0. Set the section size to be large enough to contain a single pointer
   // (instead of emitting a zero-sized section) so these relocations are

llvm/lib/MC/MCObjectStreamer.cpp

@@ -225,7 +225,7 @@ MCDataFragment *
 MCObjectStreamer::getOrCreateDataFragment(const MCSubtargetInfo *STI) {
   MCDataFragment *F = dyn_cast_or_null<MCDataFragment>(getCurrentFragment());
   if (!F || !canReuseDataFragment(*F, *Assembler, STI)) {
-    F = new MCDataFragment();
+    F = getContext().allocFragment<MCDataFragment>();
     insert(F);
   }
   return F;
@@ -343,7 +343,7 @@ void MCObjectStreamer::emitULEB128Value(const MCExpr *Value) {
     emitULEB128IntValue(IntValue);
     return;
   }
-  insert(new MCLEBFragment(*Value, false));
+  insert(getContext().allocFragment<MCLEBFragment>(*Value, false));
 }
 
 void MCObjectStreamer::emitSLEB128Value(const MCExpr *Value) {
@@ -352,7 +352,7 @@ void MCObjectStreamer::emitSLEB128Value(const MCExpr *Value) {
     emitSLEB128IntValue(IntValue);
     return;
   }
-  insert(new MCLEBFragment(*Value, true));
+  insert(getContext().allocFragment<MCLEBFragment>(*Value, true));
 }
 
 void MCObjectStreamer::emitWeakReference(MCSymbol *Alias,
@@ -470,7 +470,8 @@ void MCObjectStreamer::emitInstToFragment(const MCInst &Inst,
 
   // Always create a new, separate fragment here, because its size can change
   // during relaxation.
-  MCRelaxableFragment *IF = new MCRelaxableFragment(Inst, STI);
+  MCRelaxableFragment *IF =
+      getContext().allocFragment<MCRelaxableFragment>(Inst, STI);
   insert(IF);
 
   SmallString<128> Code;
@@ -544,7 +545,8 @@ void MCObjectStreamer::emitDwarfAdvanceLineAddr(int64_t LineDelta,
     return;
   }
   const MCExpr *AddrDelta = buildSymbolDiff(*this, Label, LastLabel, SMLoc());
-  insert(new MCDwarfLineAddrFragment(LineDelta, *AddrDelta));
+  insert(getContext().allocFragment<MCDwarfLineAddrFragment>(LineDelta,
+                                                             *AddrDelta));
 }
 
 void MCObjectStreamer::emitDwarfLineEndEntry(MCSection *Section,
@@ -569,7 +571,8 @@ void MCObjectStreamer::emitDwarfAdvanceFrameAddr(const MCSymbol *LastLabel,
                                                  const MCSymbol *Label,
                                                  SMLoc Loc) {
   const MCExpr *AddrDelta = buildSymbolDiff(*this, Label, LastLabel, Loc);
-  insert(new MCDwarfCallFrameFragment(*AddrDelta, nullptr));
+  insert(getContext().allocFragment<MCDwarfCallFrameFragment>(*AddrDelta,
+                                                              nullptr));
 }
 
 void MCObjectStreamer::emitCVLocDirective(unsigned FunctionId, unsigned FileNo,
@@ -640,7 +643,8 @@ void MCObjectStreamer::emitValueToAlignment(Align Alignment, int64_t Value,
                                             unsigned MaxBytesToEmit) {
   if (MaxBytesToEmit == 0)
     MaxBytesToEmit = Alignment.value();
-  insert(new MCAlignFragment(Alignment, Value, ValueSize, MaxBytesToEmit));
+  insert(getContext().allocFragment<MCAlignFragment>(
+      Alignment, Value, ValueSize, MaxBytesToEmit));
 
   // Update the maximum alignment on the current section if necessary.
   MCSection *CurSec = getCurrentSectionOnly();
@@ -657,7 +661,7 @@ void MCObjectStreamer::emitCodeAlignment(Align Alignment,
 void MCObjectStreamer::emitValueToOffset(const MCExpr *Offset,
                                          unsigned char Value,
                                          SMLoc Loc) {
-  insert(new MCOrgFragment(*Offset, Value, Loc));
+  insert(getContext().allocFragment<MCOrgFragment>(*Offset, Value, Loc));
 }
 
 // Associate DTPRel32 fixup with data and resize data area
@@ -844,7 +848,8 @@ void MCObjectStreamer::emitFill(const MCExpr &NumBytes, uint64_t FillValue,
   flushPendingLabels(DF, DF->getContents().size());
 
   assert(getCurrentSectionOnly() && "need a section");
-  insert(new MCFillFragment(FillValue, 1, NumBytes, Loc));
+  insert(
+      getContext().allocFragment<MCFillFragment>(FillValue, 1, NumBytes, Loc));
 }
 
 void MCObjectStreamer::emitFill(const MCExpr &NumValues, int64_t Size,
@@ -874,7 +879,8 @@ void MCObjectStreamer::emitFill(const MCExpr &NumValues, int64_t Size,
   flushPendingLabels(DF, DF->getContents().size());
 
   assert(getCurrentSectionOnly() && "need a section");
-  insert(new MCFillFragment(Expr, Size, NumValues, Loc));
+  insert(
+      getContext().allocFragment<MCFillFragment>(Expr, Size, NumValues, Loc));
 }
 
 void MCObjectStreamer::emitNops(int64_t NumBytes, int64_t ControlledNopLength,
@@ -885,7 +891,8 @@ void MCObjectStreamer::emitNops(int64_t NumBytes, int64_t ControlledNopLength,
 
   assert(getCurrentSectionOnly() && "need a section");
 
-  insert(new MCNopsFragment(NumBytes, ControlledNopLength, Loc, STI));
+  insert(getContext().allocFragment<MCNopsFragment>(
+      NumBytes, ControlledNopLength, Loc, STI));
 }
 
 void MCObjectStreamer::emitFileDirective(StringRef Filename) {

llvm/lib/MC/MCPseudoProbe.cpp

@@ -80,7 +80,8 @@ void MCPseudoProbe::emit(MCObjectStreamer *MCOS,
     if (AddrDelta->evaluateAsAbsolute(Delta, MCOS->getAssemblerPtr())) {
       MCOS->emitSLEB128IntValue(Delta);
     } else {
-      MCOS->insert(new MCPseudoProbeAddrFragment(AddrDelta));
+      MCOS->insert(MCOS->getContext().allocFragment<MCPseudoProbeAddrFragment>(
+          AddrDelta));
     }
   } else {
     // Emit the GUID of the split function that the sentinel probe represents.

llvm/lib/MC/MCWinCOFFStreamer.cpp

@@ -196,7 +196,7 @@ void MCWinCOFFStreamer::emitCOFFSafeSEH(MCSymbol const *Symbol) {
   getAssembler().registerSection(*SXData);
   SXData->ensureMinAlignment(Align(4));
 
-  new MCSymbolIdFragment(Symbol, SXData);
+  getContext().allocFragment<MCSymbolIdFragment>(Symbol, SXData);
 
   getAssembler().registerSymbol(*Symbol);
   CSymbol->setIsSafeSEH();
@@ -212,7 +212,8 @@ void MCWinCOFFStreamer::emitCOFFSymbolIndex(MCSymbol const *Symbol) {
   getAssembler().registerSection(*Sec);
   Sec->ensureMinAlignment(Align(4));
 
-  new MCSymbolIdFragment(Symbol, getCurrentSectionOnly());
+  getContext().allocFragment<MCSymbolIdFragment>(Symbol,
+                                                 getCurrentSectionOnly());
 
   getAssembler().registerSymbol(*Symbol);
 }