Reduce duplication in MCSymbol Name handling. NFC>

Based on feedback to r239428 by David Blaikie, use const_cast to reduce
duplication of the const and non-const versions of getNameEntryPtr.

Also have that method return the pointer to the name directly instead
of users having to then get the name from the union.

Finally, add a FIXME that we should use a static_assert once available in
the new operator.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239429 91177308-0d34-0410-b5e6-96231b3b80d8

Author: cooperp

include/llvm/MC/MCSymbol.h

@@ -136,7 +136,7 @@ class MCSymbol {
         Kind(Kind) {
     Offset = 0;
     if (Name)
-      getNameEntryPtr().NameEntry = Name;
+      getNameEntryPtr() = Name;
   }
 
   // Provide custom new/delete as we will only allocate space for a name
@@ -169,15 +169,13 @@ class MCSymbol {
   }
 
   /// \brief Get a reference to the name field.  Requires that we have a name
-  NameEntryStorageTy &getNameEntryPtr() {
+  const StringMapEntry<bool> *&getNameEntryPtr() {
     assert(HasName && "Name is required");
     NameEntryStorageTy *Name = reinterpret_cast<NameEntryStorageTy *>(this);
-    return *(Name - 1);
+    return (*(Name - 1)).NameEntry;
   }
-  const NameEntryStorageTy &getNameEntryPtr() const {
-    assert(HasName && "Name is required");
-    const auto *Name = reinterpret_cast<const NameEntryStorageTy *>(this);
-    return *(Name - 1);
+  const StringMapEntry<bool> *&getNameEntryPtr() const {
+    return const_cast<MCSymbol*>(this)->getNameEntryPtr();
   }
 
 public:
@@ -186,7 +184,7 @@ class MCSymbol {
     if (!HasName)
       return StringRef();
 
-    return getNameEntryPtr().NameEntry->first();
+    return getNameEntryPtr()->first();
   }
 
   bool isRegistered() const { return IsRegistered; }

lib/MC/MCSymbol.cpp

@@ -28,6 +28,7 @@ void *MCSymbol::operator new(size_t s, const StringMapEntry<bool> *Name,
   // For safety, ensure that the alignment of a pointer is enough for an
   // MCSymbol.  This also ensures we don't need padding between the name and
   // symbol.
+  // FIXME: Use static_assert when constexpr is supported.
   assert(alignOf<MCSymbol>() <= alignOf<NameEntryStorageTy>() &&
          "Bad alignment of MCSymbol");
   void *Storage = Ctx.allocate(Size, alignOf<NameEntryStorageTy>());