MC: Remove bundle alignment mode

The being-removed PNaCl has a Software Fault Isolation mechanism, which
requires that certain instructions and groups of instructions do not
cross a bundle boundary. When `.bundle_align_mode` is in effect, each
instruction is placed in its own fragment, allowing flexible NOP
padding.

This feature has significantly complicated our refactoring of MCStreamer
and MCFragment, leading to considerable effort spent untangling
it (including flushPendingLabels (7500646),
MCAssembler iteration improvement, and recent MCFragment refactoring).

* Make MCObjectStreamer::emitInstToData non-virtual and delete
  MCELFStreamer::emitInstTodata
* Delete MCELFStreamer::emitValueImpl and emitValueToAlignment

Minor instructions:u decrease for both -O0 -g and -O3 builds
https://llvm-compile-time-tracker.com/compare.php?from=c06d3a7b728293cbc53ff91239d6cd87c0982ffb&to=9b078c7f228bc5b6cdbfe839f751c9407f8aec3e&stat=instructions:u

Pull Request: llvm#148781

Author: MaskRay

llvm/include/llvm/MC/MCAssembler.h

@@ -85,11 +85,6 @@ class MCAssembler {
   // refactoring too.
   mutable SmallPtrSet<const MCSymbol *, 32> ThumbFuncs;
 
-  /// The bundle alignment size currently set in the assembler.
-  ///
-  /// By default it's 0, which means bundling is disabled.
-  unsigned BundleAlignSize = 0;
-
   /// Evaluate a fixup to a relocatable expression and the value which should be
   /// placed into the fixup.
   ///
@@ -143,8 +138,6 @@ class MCAssembler {
   /// Compute the effective fragment size.
   LLVM_ABI uint64_t computeFragmentSize(const MCFragment &F) const;
 
-  LLVM_ABI void layoutBundle(MCFragment *Prev, MCFragment *F) const;
-
   // Get the offset of the given fragment inside its containing section.
   uint64_t getFragmentOffset(const MCFragment &F) const { return F.Offset; }
 
@@ -203,16 +196,6 @@ class MCAssembler {
   bool getRelaxAll() const { return RelaxAll; }
   void setRelaxAll(bool Value) { RelaxAll = Value; }
 
-  bool isBundlingEnabled() const { return BundleAlignSize != 0; }
-
-  unsigned getBundleAlignSize() const { return BundleAlignSize; }
-
-  void setBundleAlignSize(unsigned Size) {
-    assert((Size == 0 || !(Size & (Size - 1))) &&
-           "Expect a power-of-two bundle align size");
-    BundleAlignSize = Size;
-  }
-
   const_iterator begin() const { return Sections.begin(); }
   const_iterator end() const { return Sections.end(); }
 
@@ -226,12 +209,6 @@ class MCAssembler {
   LLVM_ABI bool registerSection(MCSection &Section);
   LLVM_ABI bool registerSymbol(const MCSymbol &Symbol);
 
-  /// Write the necessary bundle padding to \p OS.
-  /// Expects a fragment \p F containing instructions and its size \p FSize.
-  LLVM_ABI void writeFragmentPadding(raw_ostream &OS,
-                                     const MCEncodedFragment &F,
-                                     uint64_t FSize) const;
-
   LLVM_ABI void reportError(SMLoc L, const Twine &Msg) const;
   // Record pending errors during layout iteration, as they may go away once the
   // layout is finalized.

llvm/include/llvm/MC/MCELFStreamer.h

@@ -65,24 +65,15 @@ class MCELFStreamer : public MCObjectStreamer {
   void emitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
                              Align ByteAlignment) override;
 
-  void emitValueImpl(const MCExpr *Value, unsigned Size,
-                     SMLoc Loc = SMLoc()) override;
-
   void emitIdent(StringRef IdentString) override;
 
-  void emitValueToAlignment(Align, int64_t, uint8_t, unsigned) override;
-
   void emitCGProfileEntry(const MCSymbolRefExpr *From,
                           const MCSymbolRefExpr *To, uint64_t Count) override;
 
   // This is final. Override MCTargetStreamer::finish instead for
   // target-specific code.
   void finishImpl() final;
 
-  void emitBundleAlignMode(Align Alignment) override;
-  void emitBundleLock(bool AlignToEnd) override;
-  void emitBundleUnlock() override;
-
   /// ELF object attributes section emission support
   struct AttributeItem {
     // This structure holds all attributes, accounting for their string /
@@ -151,9 +142,6 @@ class MCELFStreamer : public MCObjectStreamer {
   }
 
 private:
-  bool isBundleLocked() const;
-  void emitInstToData(const MCInst &Inst, const MCSubtargetInfo &) override;
-
   void finalizeCGProfileEntry(const MCSymbolRefExpr *&S, uint64_t Offset);
   void finalizeCGProfile();
 

llvm/include/llvm/MC/MCObjectStreamer.h

@@ -59,7 +59,7 @@ class MCObjectStreamer : public MCStreamer {
   DenseMap<const MCSymbol *, SmallVector<PendingAssignment, 1>>
       pendingAssignments;
 
-  virtual void emitInstToData(const MCInst &Inst, const MCSubtargetInfo &);
+  void emitInstToData(const MCInst &Inst, const MCSubtargetInfo &);
   void emitCFIStartProcImpl(MCDwarfFrameInfo &Frame) override;
   void emitCFIEndProcImpl(MCDwarfFrameInfo &Frame) override;
   void emitInstructionImpl(const MCInst &Inst, const MCSubtargetInfo &STI);
@@ -127,9 +127,6 @@ class MCObjectStreamer : public MCStreamer {
   /// can change its size during relaxation.
   void emitInstToFragment(const MCInst &Inst, const MCSubtargetInfo &);
 
-  void emitBundleAlignMode(Align Alignment) override;
-  void emitBundleLock(bool AlignToEnd) override;
-  void emitBundleUnlock() override;
   void emitBytes(StringRef Data) override;
   void emitValueToAlignment(Align Alignment, int64_t Fill = 0,
                             uint8_t FillLen = 1,

llvm/include/llvm/MC/MCSection.h

@@ -61,13 +61,6 @@ class LLVM_ABI MCSection {
     SV_DXContainer,
   };
 
-  /// Express the state of bundle locked groups while emitting code.
-  enum BundleLockStateType {
-    NotBundleLocked,
-    BundleLocked,
-    BundleLockedAlignToEnd
-  };
-
   struct iterator {
     MCFragment *F = nullptr;
     iterator() = default;
@@ -94,16 +87,6 @@ class LLVM_ABI MCSection {
   /// The section index in the assemblers section list.
   unsigned Ordinal = 0;
 
-  /// Keeping track of bundle-locked state.
-  BundleLockStateType BundleLockState = NotBundleLocked;
-
-  /// Current nesting depth of bundle_lock directives.
-  unsigned BundleLockNestingDepth = 0;
-
-  /// We've seen a bundle_lock directive but not its first instruction
-  /// yet.
-  bool BundleGroupBeforeFirstInst : 1;
-
   /// Whether this section has had instructions emitted into it.
   bool HasInstructions : 1;
 
@@ -169,17 +152,6 @@ class LLVM_ABI MCSection {
   unsigned getOrdinal() const { return Ordinal; }
   void setOrdinal(unsigned Value) { Ordinal = Value; }
 
-  BundleLockStateType getBundleLockState() const { return BundleLockState; }
-  void setBundleLockState(BundleLockStateType NewState);
-  bool isBundleLocked() const { return BundleLockState != NotBundleLocked; }
-
-  bool isBundleGroupBeforeFirstInst() const {
-    return BundleGroupBeforeFirstInst;
-  }
-  void setBundleGroupBeforeFirstInst(bool IsFirst) {
-    BundleGroupBeforeFirstInst = IsFirst;
-  }
-
   bool hasInstructions() const { return HasInstructions; }
   void setHasInstructions(bool Value) { HasInstructions = Value; }
 
@@ -259,7 +231,6 @@ class MCFragment {
   ///
   /// MCEncodedFragment
   bool HasInstructions : 1;
-  bool AlignToBundleEnd : 1;
   /// MCDataFragment
   bool LinkerRelaxable : 1;
   /// MCRelaxableFragment: x86-specific
@@ -297,7 +268,6 @@ class MCFragment {
 /// Interface implemented by fragments that contain encoded instructions and/or
 /// data.
 class MCEncodedFragment : public MCFragment {
-  uint8_t BundlePadding = 0;
   uint32_t ContentStart = 0;
   uint32_t ContentEnd = 0;
   uint32_t FixupStart = 0;
@@ -329,21 +299,6 @@ class MCEncodedFragment : public MCFragment {
     }
   }
 
-  /// Should this fragment be placed at the end of an aligned bundle?
-  bool alignToBundleEnd() const { return AlignToBundleEnd; }
-  void setAlignToBundleEnd(bool V) { AlignToBundleEnd = V; }
-
-  /// Get the padding size that must be inserted before this fragment.
-  /// Used for bundling. By default, no padding is inserted.
-  /// Note that padding size is restricted to 8 bits. This is an optimization
-  /// to reduce the amount of space used for each fragment. In practice, larger
-  /// padding should never be required.
-  uint8_t getBundlePadding() const { return BundlePadding; }
-
-  /// Set the padding size for this fragment. By default it's a no-op,
-  /// and only some fragments have a meaningful implementation.
-  void setBundlePadding(uint8_t N) { BundlePadding = N; }
-
   /// Retrieve the MCSubTargetInfo in effect when the instruction was encoded.
   /// Guaranteed to be non-null if hasInstructions() == true
   const MCSubtargetInfo *getSubtargetInfo() const { return STI; }

llvm/include/llvm/MC/MCStreamer.h

@@ -1068,19 +1068,6 @@ class LLVM_ABI MCStreamer {
                                const MCPseudoProbeInlineStack &InlineStack,
                                MCSymbol *FnSym);
 
-  /// Set the bundle alignment mode from now on in the section.
-  /// The value 1 means turn the bundle alignment off.
-  virtual void emitBundleAlignMode(Align Alignment);
-
-  /// The following instructions are a bundle-locked group.
-  ///
-  /// \param AlignToEnd - If true, the bundle-locked group will be aligned to
-  ///                     the end of a bundle.
-  virtual void emitBundleLock(bool AlignToEnd);
-
-  /// Ends a bundle-locked group.
-  virtual void emitBundleUnlock();
-
   /// If this file is backed by a assembly streamer, this dumps the
   /// specified string in the output .s file.  This capability is indicated by
   /// the hasRawTextSupport() predicate.  By default this aborts.

llvm/lib/MC/MCAsmStreamer.cpp

@@ -407,10 +407,6 @@ class MCAsmStreamer final : public MCStreamer {
                        const MCPseudoProbeInlineStack &InlineStack,
                        MCSymbol *FnSym) override;
 
-  void emitBundleAlignMode(Align Alignment) override;
-  void emitBundleLock(bool AlignToEnd) override;
-  void emitBundleUnlock() override;
-
   std::optional<std::pair<bool, std::string>>
   emitRelocDirective(const MCExpr &Offset, StringRef Name, const MCExpr *Expr,
                      SMLoc Loc, const MCSubtargetInfo &STI) override;
@@ -2472,23 +2468,6 @@ void MCAsmStreamer::emitPseudoProbe(uint64_t Guid, uint64_t Index,
   EmitEOL();
 }
 
-void MCAsmStreamer::emitBundleAlignMode(Align Alignment) {
-  OS << "\t.bundle_align_mode " << Log2(Alignment);
-  EmitEOL();
-}
-
-void MCAsmStreamer::emitBundleLock(bool AlignToEnd) {
-  OS << "\t.bundle_lock";
-  if (AlignToEnd)
-    OS << " align_to_end";
-  EmitEOL();
-}
-
-void MCAsmStreamer::emitBundleUnlock() {
-  OS << "\t.bundle_unlock";
-  EmitEOL();
-}
-
 std::optional<std::pair<bool, std::string>>
 MCAsmStreamer::emitRelocDirective(const MCExpr &Offset, StringRef Name,
                                   const MCExpr *Expr, SMLoc,