The fragment implies the section, don't store both.

This reduces MCSymbol from 64 to 56 bytes on x86_64.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@238747 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/MC/MCAssembler.h

@@ -23,7 +23,6 @@
 #include "llvm/MC/MCLinkerOptimizationHint.h"
 #include "llvm/MC/MCSection.h"
 #include "llvm/MC/MCSubtargetInfo.h"
-#include "llvm/MC/MCSymbol.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/DataTypes.h"
 #include <algorithm>
@@ -910,15 +909,7 @@ public:
     return true;
   }
 
-  void registerSymbol(const MCSymbol &Symbol, bool *Created = nullptr) {
-    bool New = !Symbol.isRegistered();
-    if (Created)
-      *Created = New;
-    if (New) {
-      Symbol.setIsRegistered(true);
-      Symbols.push_back(&Symbol);
-    }
-  }
+  void registerSymbol(const MCSymbol &Symbol, bool *Created = nullptr);
 
   ArrayRef<std::string> getFileNames() { return FileNames; }
 

include/llvm/MC/MCSymbol.h

@@ -14,8 +14,8 @@
 #ifndef LLVM_MC_MCSYMBOL_H
 #define LLVM_MC_MCSYMBOL_H
 
-#include "llvm/ADT/PointerIntPair.h"
 #include "llvm/ADT/StringMap.h"
+#include "llvm/MC/MCAssembler.h"
 #include "llvm/MC/MCExpr.h"
 #include "llvm/Support/Compiler.h"
 
@@ -44,10 +44,20 @@ class MCSymbol {
   /// held by the StringMap that lives in MCContext.
   const StringMapEntry<bool> *Name;
 
-  /// The section the symbol is defined in. This is null for undefined symbols,
-  /// and the special AbsolutePseudoSection value for absolute symbols. If this
-  /// is a variable symbol, this caches the variable value's section.
-  mutable MCSection *Section;
+  /// If a symbol has a Fragment, the section is implied, so we only need
+  /// one pointer.
+  /// FIXME: We might be able to simplify this by having the asm streamer create
+  /// dummy fragments.
+  union {
+    /// The section the symbol is defined in. This is null for undefined
+    /// symbols, and the special AbsolutePseudoSection value for absolute
+    /// symbols. If this is a variable symbol, this caches the variable value's
+    /// section.
+    mutable MCSection *Section;
+
+    /// The fragment this symbol's value is relative to, if any.
+    mutable MCFragment *Fragment;
+  };
 
   /// Value - If non-null, the value for a variable symbol.
   const MCExpr *Value;
@@ -65,6 +75,14 @@ class MCSymbol {
 
   mutable bool IsRegistered : 1;
 
+  /// This symbol is visible outside this translation unit.
+  mutable unsigned IsExternal : 1;
+
+  /// This symbol is private extern.
+  mutable unsigned IsPrivateExtern : 1;
+
+  mutable unsigned HasFragment : 1;
+
   /// Index field, for use by the object file implementation.
   mutable uint32_t Index = 0;
 
@@ -89,23 +107,22 @@ class MCSymbol {
   /// additional per symbol information which is not easily classified.
   mutable uint32_t Flags = 0;
 
-  /// The fragment this symbol's value is relative to, if any. Also stores if
-  /// this symbol is visible outside this translation unit (bit 0) or if it is
-  /// private extern (bit 1).
-  mutable PointerIntPair<MCFragment *, 2> Fragment;
-
 private: // MCContext creates and uniques these.
   friend class MCExpr;
   friend class MCContext;
   MCSymbol(const StringMapEntry<bool> *Name, bool isTemporary)
       : Name(Name), Section(nullptr), Value(nullptr), IsTemporary(isTemporary),
-        IsRedefinable(false), IsUsed(false), IsRegistered(false) {
+        IsRedefinable(false), IsUsed(false), IsRegistered(false),
+        IsExternal(false), IsPrivateExtern(false), HasFragment(false) {
     Offset = 0;
   }
 
   MCSymbol(const MCSymbol &) = delete;
   void operator=(const MCSymbol &) = delete;
   MCSection *getSectionPtr() const {
+    if (MCFragment *F = getFragment())
+      return F->getParent();
+    assert(!HasFragment);
     if (Section || !Value)
       return Section;
     return Section = Value->findAssociatedSection();
@@ -137,6 +154,7 @@ public:
     if (IsRedefinable) {
       Value = nullptr;
       Section = nullptr;
+      HasFragment = false;
       IsRedefinable = false;
     }
   }
@@ -169,11 +187,15 @@ public:
   /// Mark the symbol as defined in the section \p S.
   void setSection(MCSection &S) {
     assert(!isVariable() && "Cannot set section of variable");
+    assert(!HasFragment);
     Section = &S;
   }
 
-  /// setUndefined - Mark the symbol as undefined.
-  void setUndefined() { Section = nullptr; }
+  /// Mark the symbol as undefined.
+  void setUndefined() {
+    HasFragment = false;
+    Section = nullptr;
+  }
 
   /// @}
   /// \name Variable Symbols
@@ -252,18 +274,21 @@ public:
     Flags = (Flags & ~Mask) | Value;
   }
 
-  MCFragment *getFragment() const { return Fragment.getPointer(); }
-  void setFragment(MCFragment *Value) const { Fragment.setPointer(Value); }
-
-  bool isExternal() const { return Fragment.getInt() & 1; }
-  void setExternal(bool Value) const {
-    Fragment.setInt((Fragment.getInt() & ~1) | unsigned(Value));
+  MCFragment *getFragment() const {
+    if (!HasFragment)
+      return nullptr;
+    return Fragment;
+  }
+  void setFragment(MCFragment *Value) const {
+    HasFragment = true;
+    Fragment = Value;
   }
 
-  bool isPrivateExtern() const { return Fragment.getInt() & 2; }
-  void setPrivateExtern(bool Value) {
-    Fragment.setInt((Fragment.getInt() & ~2) | (unsigned(Value) << 1));
-  }
+  bool isExternal() const { return IsExternal; }
+  void setExternal(bool Value) const { IsExternal = Value; }
+
+  bool isPrivateExtern() const { return IsPrivateExtern; }
+  void setPrivateExtern(bool Value) { IsPrivateExtern = Value; }
 
   /// print - Print the value to the stream \p OS.
   void print(raw_ostream &OS) const;

lib/MC/MCAssembler.cpp

@@ -579,6 +579,16 @@ static void writeFragmentContents(const MCFragment &F, MCObjectWriter *OW) {
   OW->WriteBytes(EF.getContents());
 }
 
+void MCAssembler::registerSymbol(const MCSymbol &Symbol, bool *Created) {
+  bool New = !Symbol.isRegistered();
+  if (Created)
+    *Created = New;
+  if (New) {
+    Symbol.setIsRegistered(true);
+    Symbols.push_back(&Symbol);
+  }
+}
+
 void MCAssembler::writeFragmentPadding(const MCFragment &F, uint64_t FSize,
                                        MCObjectWriter *OW) const {
   // Should NOP padding be written out before this fragment?

lib/MC/MCELF.cpp

@@ -13,6 +13,7 @@
 
 #include "llvm/MC/MCELF.h"
 #include "llvm/MC/MCAssembler.h"
+#include "llvm/MC/MCSymbol.h"
 #include "llvm/MC/MCELFSymbolFlags.h"
 #include "llvm/MC/MCFixupKindInfo.h"
 #include "llvm/Support/ELF.h"

lib/MC/MCMachOStreamer.cpp

@@ -419,11 +419,11 @@ void MCMachOStreamer::EmitZerofill(MCSection *Section, MCSymbol *Symbol,
   if (ByteAlignment != 1)
     new MCAlignFragment(ByteAlignment, 0, 0, ByteAlignment, Section);
 
+  AssignSection(Symbol, Section);
+
   MCFragment *F = new MCFillFragment(0, 0, Size, Section);
   Symbol->setFragment(F);
 
-  AssignSection(Symbol, Section);
-
   // Update the maximum alignment on the zero fill section if necessary.
   if (ByteAlignment > Section->getAlignment())
     Section->setAlignment(ByteAlignment);

lib/MC/MCSymbol.cpp

@@ -42,7 +42,8 @@ void MCSymbol::setVariableValue(const MCExpr *Value) {
   assert(!IsUsed && "Cannot set a variable that has already been used.");
   assert(Value && "Invalid variable value!");
   this->Value = Value;
-  this->Section = nullptr;
+  Section = nullptr;
+  HasFragment = false;
 }
 
 void MCSymbol::print(raw_ostream &OS) const {