[AST] Pack bitfields in TypeRepr (#5981)

Author: rintaro

include/swift/AST/TypeRepr.h

@@ -45,37 +45,60 @@ class alignas(8) TypeRepr {
   TypeRepr(const TypeRepr&) = delete;
   void operator=(const TypeRepr&) = delete;
 
-  /// \brief The subclass of TypeRepr that this is.
-  unsigned Kind : 6;
+  class TypeReprBitfields {
+    friend class TypeRepr;
+    /// The subclass of TypeRepr that this is.
+    unsigned Kind : 6;
+
+    /// Whether this type representation is known to contain an invalid
+    /// type.
+    unsigned Invalid : 1;
+
+    /// Whether this type representation had a warning emitted related to it.
+    /// This is a hack related to how we resolve type exprs multiple times in
+    /// generic contexts.
+    unsigned Warned : 1;
+  };
+  enum { NumTypeReprBits = 8 };
+  class TupleTypeReprBitfields {
+    friend class TupleTypeRepr;
+    unsigned : NumTypeReprBits;
+    // HasNames, HasLabels?
+    unsigned NameStatus : 2;
+    // Whether this tuple has '...' and its position.
+    unsigned HasEllipsis : 1;
+  };
 
-  /// Whether this type representation is known to contain an invalid
-  /// type.
-  unsigned Invalid : 1;
+protected:
+  union {
+    TypeReprBitfields TypeReprBits;
+    TupleTypeReprBitfields TupleTypeReprBits;
+  };
 
-  /// Whether this type representation had a warning emitted related to it.
-  /// This is a hack related to how we resolve type exprs multiple times in
-  /// generic contexts.
-  unsigned Warned : 1;
+  TypeRepr(TypeReprKind K) {
+    TypeReprBits.Kind = static_cast<unsigned>(K);
+    TypeReprBits.Invalid = false;
+    TypeReprBits.Warned = false;
+  }
 
+private:
   SourceLoc getLocImpl() const { return getStartLoc(); }
 
-protected:
-  TypeRepr(TypeReprKind K)
-    : Kind(static_cast<unsigned>(K)), Invalid(false), Warned(false) {}
-
 public:
-  TypeReprKind getKind() const { return static_cast<TypeReprKind>(Kind); }
+  TypeReprKind getKind() const {
+    return static_cast<TypeReprKind>(TypeReprBits.Kind);
+  }
 
   /// Is this type representation known to be invalid?
-  bool isInvalid() const { return Invalid; }
+  bool isInvalid() const { return TypeReprBits.Invalid; }
 
   /// Note that this type representation describes an invalid type.
-  void setInvalid() { Invalid = true; }
+  void setInvalid() { TypeReprBits.Invalid = true; }
 
   /// If a warning is produced about this type repr, keep track of that so we
   /// don't emit another one upon further reanalysis.
-  bool isWarnedAbout() const { return Warned; }
-  void setWarned() { Warned = true; }
+  bool isWarnedAbout() const { return TypeReprBits.Warned; }
+  void setWarned() { TypeReprBits.Warned = true; }
 
   /// Get the representative location for pointing at this type.
   SourceLoc getLoc() const;
@@ -556,21 +579,21 @@ class TupleTypeRepr final : public TypeRepr,
     NotNamed = 0,
     HasNames = 1,
     HasLabels = 2
-  } NameStatus : 2;
-  bool HasEllipsis : 1;
+  };
 
   size_t numTrailingObjects(OverloadToken<TypeRepr *>) const {
     return NumElements;
   }
   size_t numTrailingObjects(OverloadToken<Identifier>) const {
-    return NameStatus >= HasNames ? NumElements : 0;
+    return TupleTypeReprBits.NameStatus >= HasNames ? NumElements : 0;
   }
   size_t numTrailingObjects(OverloadToken<SourceLoc>) const {
-    switch (NameStatus) {
+    switch (TupleTypeReprBits.NameStatus) {
     case NotNamed: return 0;
     case HasNames: return NumElements;
     case HasLabels: return NumElements + NumElements;
     }
+    llvm_unreachable("all cases should have been handled");
   }
 
   TupleTypeRepr(ArrayRef<TypeRepr *> Elements, SourceRange Parens,
@@ -581,8 +604,12 @@ class TupleTypeRepr final : public TypeRepr,
 public:
 
   unsigned getNumElements() const { return NumElements; }
-  bool hasElementNames() const { return NameStatus >= HasNames; }
-  bool hasUnderscoreLocs() const { return NameStatus == HasLabels; }
+  bool hasElementNames() const {
+    return TupleTypeReprBits.NameStatus >= HasNames;
+  }
+  bool hasUnderscoreLocs() const {
+    return TupleTypeReprBits.NameStatus == HasLabels;
+  }
 
   ArrayRef<TypeRepr *> getElements() const {
     return { getTrailingObjects<TypeRepr *>(), NumElements };
@@ -622,19 +649,19 @@ class TupleTypeRepr final : public TypeRepr,
   }
 
   SourceRange getParens() const { return Parens; }
+
+  bool hasEllipsis() const { return TupleTypeReprBits.HasEllipsis; }
   SourceLoc getEllipsisLoc() const {
-    return HasEllipsis ?
+    return hasEllipsis() ?
       getTrailingObjects<SourceLocAndIdx>()[0].first : SourceLoc();
   }
   unsigned getEllipsisIndex() const {
-    return HasEllipsis ?
+    return hasEllipsis() ?
       getTrailingObjects<SourceLocAndIdx>()[0].second : NumElements;
   }
-  bool hasEllipsis() const { return HasEllipsis; }
-
   void removeEllipsis() {
-    if (HasEllipsis) {
-      HasEllipsis = false;
+    if (hasEllipsis()) {
+      TupleTypeReprBits.HasEllipsis = false;
       getTrailingObjects<SourceLocAndIdx>()[0] = {SourceLoc(), NumElements};
     }
   }

lib/AST/TypeRepr.cpp

@@ -394,10 +394,11 @@ TupleTypeRepr::TupleTypeRepr(ArrayRef<TypeRepr *> Elements, SourceRange Parens,
                              ArrayRef<SourceLoc> underscoreLocs,
                              SourceLoc Ellipsis, unsigned EllipsisIdx)
     : TypeRepr(TypeReprKind::Tuple), NumElements(Elements.size()),
-      Parens(Parens), HasEllipsis(Ellipsis.isValid()) {
+      Parens(Parens) {
 
-  NameStatus = ElementNames.empty() ? NotNamed
-             : underscoreLocs.empty() ? HasNames : HasLabels;
+  TupleTypeReprBits.NameStatus = ElementNames.empty() ? NotNamed
+                               : underscoreLocs.empty() ? HasNames : HasLabels;
+  TupleTypeReprBits.HasEllipsis = Ellipsis.isValid();
 
   // Copy elements.
   std::uninitialized_copy(Elements.begin(), Elements.end(),