Move FragmentAllocator from MCContext to MCObjectStreamer

In MCContext::reset, delete a stale comment as MCCodeView no longer
owns or deallocates MCFragment.

Author: MaskRay

llvm/include/llvm/MC/MCCodeView.h

@@ -203,7 +203,7 @@ class CodeViewContext {
   void encodeInlineLineTable(const MCAssembler &Asm,
                              MCCVInlineLineTableFragment &F);
 
-  MCFragment *
+  void
   emitDefRange(MCObjectStreamer &OS,
                ArrayRef<std::pair<const MCSymbol *, const MCSymbol *>> Ranges,
                StringRef FixedSizePortion);

llvm/include/llvm/MC/MCContext.h

@@ -434,11 +434,6 @@ class MCContext {
   /// Create and return a new MC instruction.
   LLVM_ABI MCInst *createMCInst();
 
-  template <typename F, typename... Args> F *allocFragment(Args &&...args) {
-    return new (FragmentAllocator.Allocate(sizeof(F), alignof(F)))
-        F(std::forward<Args>(args)...);
-  }
-
   /// \name Symbol Management
   /// @{
 

llvm/include/llvm/MC/MCObjectStreamer.h

@@ -55,7 +55,11 @@ class MCObjectStreamer : public MCStreamer {
   SmallVector<std::unique_ptr<uint8_t[]>, 0> FragStorage;
   // Available bytes in the current block for trailing data or new fragments.
   size_t FragSpace = 0;
+  // Used to allocate special fragments that do not use MCFragment's fixed-size
+  // part.
+  BumpPtrAllocator SpecialFragAllocator;
 
+  void addSpecialFragment(MCFragment *F);
   void emitInstToData(const MCInst &Inst, const MCSubtargetInfo &);
   void emitCFIStartProcImpl(MCDwarfFrameInfo &Frame) override;
   void emitCFIEndProcImpl(MCDwarfFrameInfo &Frame) override;
@@ -85,16 +89,23 @@ class MCObjectStreamer : public MCStreamer {
   /// \name MCStreamer Interface
   /// @{
 
-  // Add a fragment with a variable-size tail and start a new empty fragment.
-  void insert(MCFragment *F);
-
   uint8_t *getCurFragEnd() const {
     return reinterpret_cast<uint8_t *>(CurFrag + 1) + CurFrag->getFixedSize();
   }
   MCFragment *allocFragSpace(size_t Headroom);
   // Add a new fragment to the current section without a variable-size tail.
   void newFragment();
 
+  // Add a new special fragment to the current section and start a new empty
+  // fragment.
+  template <typename FT, typename... Args>
+  FT *newSpecialFragment(Args &&...args) {
+    auto *F = new (SpecialFragAllocator.Allocate(sizeof(FT), alignof(FT)))
+        FT(std::forward<Args>(args)...);
+    addSpecialFragment(F);
+    return F;
+  }
+
   void ensureHeadroom(size_t Headroom);
   void appendContents(ArrayRef<char> Contents);
   void appendContents(size_t Num, uint8_t Elt);

llvm/lib/MC/MCCodeView.cpp

@@ -436,12 +436,11 @@ void CodeViewContext::emitInlineLineTableForFunction(MCObjectStreamer &OS,
                                                      const MCSymbol *FnEndSym) {
   // Create and insert a fragment into the current section that will be encoded
   // later.
-  auto *F = MCCtx->allocFragment<MCCVInlineLineTableFragment>(
+  OS.newSpecialFragment<MCCVInlineLineTableFragment>(
       PrimaryFunctionId, SourceFileId, SourceLineNum, FnStartSym, FnEndSym);
-  OS.insert(F);
 }
 
-MCFragment *CodeViewContext::emitDefRange(
+void CodeViewContext::emitDefRange(
     MCObjectStreamer &OS,
     ArrayRef<std::pair<const MCSymbol *, const MCSymbol *>> Ranges,
     StringRef FixedSizePortion) {
@@ -451,9 +450,7 @@ MCFragment *CodeViewContext::emitDefRange(
   auto &Saved = DefRangeStorage.emplace_back(Ranges.begin(), Ranges.end());
   // Create and insert a fragment into the current section that will be encoded
   // later.
-  auto *F = MCCtx->allocFragment<MCCVDefRangeFragment>(Saved, FixedSizePortion);
-  OS.insert(F);
-  return F;
+  OS.newSpecialFragment<MCCVDefRangeFragment>(Saved, FixedSizePortion);
 }
 
 static unsigned computeLabelDiff(const MCAssembler &Asm, const MCSymbol *Begin,

llvm/lib/MC/MCContext.cpp

@@ -153,15 +153,12 @@ void MCContext::reset() {
   SPIRVAllocator.DestroyAll();
   WasmSignatureAllocator.DestroyAll();
 
-  // ~CodeViewContext may destroy a MCFragment outside of sections and need to
-  // be reset before FragmentAllocator.
   CVContext.reset();
 
   MCSubtargetAllocator.DestroyAll();
   InlineAsmUsedLabelNames.clear();
   Symbols.clear();
   Allocator.Reset();
-  FragmentAllocator.Reset();
   Instances.clear();
   CompilationDir.clear();
   MainFileName.clear();

llvm/lib/MC/MCObjectStreamer.cpp

@@ -84,7 +84,7 @@ void MCObjectStreamer::ensureHeadroom(size_t Headroom) {
   addFragment(F);
 }
 
-void MCObjectStreamer::insert(MCFragment *Frag) {
+void MCObjectStreamer::addSpecialFragment(MCFragment *Frag) {
   assert(Frag->getKind() != MCFragment::FT_Data &&
          "F should have a variable-size tail");
   // Frag is not connected to FragSpace. Before modifying CurFrag with
@@ -173,6 +173,7 @@ void MCObjectStreamer::reset() {
   EmitDebugFrame = false;
   FragStorage.clear();
   FragSpace = 0;
+  SpecialFragAllocator.Reset();
   MCStreamer::reset();
 }
 
@@ -649,7 +650,7 @@ void MCObjectStreamer::emitCodeAlignment(Align Alignment,
 void MCObjectStreamer::emitValueToOffset(const MCExpr *Offset,
                                          unsigned char Value,
                                          SMLoc Loc) {
-  insert(getContext().allocFragment<MCOrgFragment>(*Offset, Value, Loc));
+  newSpecialFragment<MCOrgFragment>(*Offset, Value, Loc);
 }
 
 void MCObjectStreamer::emitRelocDirective(const MCExpr &Offset, StringRef Name,
@@ -681,8 +682,7 @@ void MCObjectStreamer::emitRelocDirective(const MCExpr &Offset, StringRef Name,
 void MCObjectStreamer::emitFill(const MCExpr &NumBytes, uint64_t FillValue,
                                 SMLoc Loc) {
   assert(getCurrentSectionOnly() && "need a section");
-  insert(
-      getContext().allocFragment<MCFillFragment>(FillValue, 1, NumBytes, Loc));
+  newSpecialFragment<MCFillFragment>(FillValue, 1, NumBytes, Loc);
 }
 
 void MCObjectStreamer::emitFill(const MCExpr &NumValues, int64_t Size,
@@ -709,15 +709,13 @@ void MCObjectStreamer::emitFill(const MCExpr &NumValues, int64_t Size,
 
   // Otherwise emit as fragment.
   assert(getCurrentSectionOnly() && "need a section");
-  insert(
-      getContext().allocFragment<MCFillFragment>(Expr, Size, NumValues, Loc));
+  newSpecialFragment<MCFillFragment>(Expr, Size, NumValues, Loc);
 }
 
 void MCObjectStreamer::emitNops(int64_t NumBytes, int64_t ControlledNopLength,
                                 SMLoc Loc, const MCSubtargetInfo &STI) {
   assert(getCurrentSectionOnly() && "need a section");
-  insert(getContext().allocFragment<MCNopsFragment>(
-      NumBytes, ControlledNopLength, Loc, STI));
+  newSpecialFragment<MCNopsFragment>(NumBytes, ControlledNopLength, Loc, STI);
 }
 
 void MCObjectStreamer::emitFileDirective(StringRef Filename) {

llvm/lib/MC/MCWinCOFFStreamer.cpp

@@ -258,7 +258,7 @@ void MCWinCOFFStreamer::emitCOFFSafeSEH(MCSymbol const *Symbol) {
   switchSection(SXData);
   SXData->ensureMinAlignment(Align(4));
 
-  insert(getContext().allocFragment<MCSymbolIdFragment>(Symbol));
+  newSpecialFragment<MCSymbolIdFragment>(Symbol);
   getAssembler().registerSymbol(*Symbol);
   CSymbol->setIsSafeSEH();
 
@@ -273,7 +273,7 @@ void MCWinCOFFStreamer::emitCOFFSymbolIndex(MCSymbol const *Symbol) {
   MCSection *Sec = getCurrentSectionOnly();
   Sec->ensureMinAlignment(Align(4));
 
-  insert(getContext().allocFragment<MCSymbolIdFragment>(Symbol));
+  newSpecialFragment<MCSymbolIdFragment>(Symbol);
   getAssembler().registerSymbol(*Symbol);
 }
 

llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp

@@ -511,9 +511,8 @@ void X86AsmBackend::emitInstructionBegin(MCObjectStreamer &OS,
                           isFirstMacroFusibleInst(Inst, *MCII))) {
     // If we meet a unfused branch or the first instuction in a fusiable pair,
     // insert a BoundaryAlign fragment.
-    PendingBA = OS.getContext().allocFragment<MCBoundaryAlignFragment>(
-        AlignBoundary, STI);
-    OS.insert(PendingBA);
+    PendingBA =
+        OS.newSpecialFragment<MCBoundaryAlignFragment>(AlignBoundary, STI);
   }
 }