From acebbf58eb9d09e8763b485623607bed62a733d2 Mon Sep 17 00:00:00 2001
From: Nik Bougalis <nikb@bougalis.net>
Date: Wed, 18 May 2016 17:26:23 -0700
Subject: [PATCH] Use only requested amount of aligned_storage

---
 src/ripple/protocol/impl/STVar.cpp | 45 +++++++++++++++++-------------
 src/ripple/protocol/impl/STVar.h   | 17 +++++------
 2 files changed, 34 insertions(+), 28 deletions(-)

diff --git a/src/ripple/protocol/impl/STVar.cpp b/src/ripple/protocol/impl/STVar.cpp
index 7609a76fb..dbf27130d 100644
--- a/src/ripple/protocol/impl/STVar.cpp
+++ b/src/ripple/protocol/impl/STVar.cpp
@@ -45,11 +45,9 @@ STVar::~STVar()
 }
 
 STVar::STVar (STVar const& other)
-    : p_(nullptr)
 {
     if (other.p_ != nullptr)
-        p_ = other.p_->copy(
-            sizeof(d_), &d_);
+        p_ = other.p_->copy(max_size, &d_);
 }
 
 STVar::STVar (STVar&& other)
@@ -61,37 +59,42 @@ STVar::STVar (STVar&& other)
     }
     else
     {
-        p_ = other.p_->move(
-            sizeof(d_), &d_);
+        p_ = other.p_->move(max_size, &d_);
     }
 }
 
 STVar&
 STVar::operator= (STVar const& rhs)
 {
-    destroy();
-    p_ = nullptr;
-    if (rhs.p_)
-        p_ = rhs.p_->copy(
-            sizeof(d_), &d_);
+    if (&rhs != this)
+    {
+        destroy();
+        if (rhs.p_)
+            p_ = rhs.p_->copy(max_size, &d_);
+        else
+            p_ = nullptr;
+    }
+
     return *this;
 }
 
 STVar&
 STVar::operator= (STVar&& rhs)
 {
-    destroy();
-    if (rhs.on_heap())
+    if (&rhs != this)
     {
-        p_ = rhs.p_;
-        rhs.p_ = nullptr;
-    }
-    else
-    {
-        p_ = nullptr;
-        p_ = rhs.p_->move(
-            sizeof(d_), &d_);
+        destroy();
+        if (rhs.on_heap())
+        {
+            p_ = rhs.p_;
+            rhs.p_ = nullptr;
+        }
+        else
+        {
+            p_ = rhs.p_->move(max_size, &d_);
+        }
     }
+
     return *this;
 }
 
@@ -161,6 +164,8 @@ STVar::destroy()
         delete p_;
     else
         p_->~STBase();
+
+    p_ = nullptr;
 }
 
 } // detail
diff --git a/src/ripple/protocol/impl/STVar.h b/src/ripple/protocol/impl/STVar.h
index 8722f24d7..d8e221bee 100644
--- a/src/ripple/protocol/impl/STVar.h
+++ b/src/ripple/protocol/impl/STVar.h
@@ -42,7 +42,10 @@ extern nonPresentObject_t nonPresentObject;
 class STVar
 {
 private:
-    std::aligned_storage<72>::type d_;
+    // The largest "small object" we can accomodate
+    static std::size_t constexpr max_size = 72;
+
+    std::aligned_storage<max_size>::type d_;
     STBase* p_ = nullptr;
 
 public:
@@ -54,12 +57,12 @@ public:
 
     STVar (STBase&& t)
     {
-        p_ = t.move(sizeof(d_), &d_);
+        p_ = t.move(max_size, &d_);
     }
 
     STVar (STBase const& t)
     {
-        p_ = t.copy(sizeof(d_), &d_);
+        p_ = t.copy(max_size, &d_);
     }
 
     STVar (defaultObject_t, SField const& name);
@@ -89,12 +92,10 @@ private:
     void
     construct(Args&&... args)
     {
-        if(sizeof(T) > sizeof(d_))
-            p_ = new T(
-                std::forward<Args>(args)...);
+        if(sizeof(T) > max_size)
+            p_ = new T(std::forward<Args>(args)...);
         else
-            p_ = new(&d_) T(
-                std::forward<Args>(args)...);
+            p_ = new(&d_) T(std::forward<Args>(args)...);
     }
 
     bool