- fixed FMemArena to always return 16 byte aligned pointers.

Unfortunately this turned out harder than expected because of FSharedStringArena making some strong assumptions about the underlying implementation.

(cherry picked from commit 2f6dc46f14)

src/memarena.cpp

@@ -48,6 +48,7 @@ struct FMemArena::Block
 	Block *NextBlock;
 	void *Limit;			// End of this block
 	void *Avail;			// Start of free space in this block
+	void *alignme;			// align to 16 bytes.
 
 	void Reset();
 	void *Alloc(size_t size);
@@ -96,7 +97,7 @@ FMemArena::~FMemArena()
 //
 //==========================================================================
 
-void *FMemArena::Alloc(size_t size)
+void *FMemArena::iAlloc(size_t size)
 {
 	Block *block;
 
@@ -112,6 +113,11 @@ void *FMemArena::Alloc(size_t size)
 	return block->Alloc(size);
 }
 
+void *FMemArena::Alloc(size_t size)
+{
+	return iAlloc((size + 15) & ~15);
+}
+
 //==========================================================================
 //
 // FMemArena :: FreeAll
@@ -318,7 +324,7 @@ FString *FSharedStringArena::Alloc(const FString &source)
 	strnode = FindString(source, source.Len(), hash);
 	if (strnode == NULL)
 	{
-		strnode = (Node *)FMemArena::Alloc(sizeof(Node));
+		strnode = (Node *)iAlloc(sizeof(Node));
 		::new(&strnode->String) FString(source);
 		strnode->Hash = hash;
 		hash %= countof(Buckets);
@@ -353,7 +359,7 @@ FString *FSharedStringArena::Alloc(const char *source, size_t strlen)
 	strnode = FindString(source, strlen, hash);
 	if (strnode == NULL)
 	{
-		strnode = (Node *)FMemArena::Alloc(sizeof(Node));
+		strnode = (Node *)iAlloc(sizeof(Node));
 		::new(&strnode->String) FString(source, strlen);
 		strnode->Hash = hash;
 		hash %= countof(Buckets);

src/memarena.h

@@ -54,6 +54,7 @@ protected:
 
 	Block *AddBlock(size_t size);
 	void FreeBlockChain(Block *&top);
+	void *iAlloc(size_t size);
 
 	Block *TopBlock;
 	Block *FreeBlocks;