From: John McCall <rjmccall@apple.com>
Date: Wed, 2 May 2012 05:39:15 +0000 (+0000)
Subject: Update SmallVector to support move semantics if the host does.
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=38dbb606755232e229f11994fc2bbf10e8c5788b;p=oota-llvm.git

Update SmallVector to support move semantics if the host does.
Note that support for rvalue references does not imply support
for the full set of move-related STL operations.

I've preserved support for an odd little thing in insert() where
we're trying to support inserting a new element from an existing
one.  If we actually want to support that, there's a lot more we
need to do:  insert can call either grow or push_back, neither of
which is safe against this particular use pattern.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@155979 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/include/llvm/ADT/SmallVector.h b/include/llvm/ADT/SmallVector.h
index 8b75ff56a3c..973e0284ab0 100644
--- a/include/llvm/ADT/SmallVector.h
+++ b/include/llvm/ADT/SmallVector.h
@@ -14,6 +14,7 @@
 #ifndef LLVM_ADT_SMALLVECTOR_H
 #define LLVM_ADT_SMALLVECTOR_H
 
+#include "llvm/Support/Compiler.h"
 #include "llvm/Support/type_traits.h"
 #include <algorithm>
 #include <cassert>
@@ -54,6 +55,11 @@ protected:
     return BeginX == static_cast<const void*>(&FirstEl);
   }
 
+  /// resetToSmall - Put this vector in a state of being small.
+  void resetToSmall() {
+    BeginX = EndX = CapacityX = &FirstEl;
+  }
+
   /// grow_pod - This is an implementation of the grow() method which only works
   /// on POD-like data types and is out of line to reduce code duplication.
   void grow_pod(size_t MinSizeInBytes, size_t TSize);
@@ -160,28 +166,84 @@ protected:
     }
   }
 
-  /// uninitialized_copy - Copy the range [I, E) onto the uninitialized memory
-  /// starting with "Dest", constructing elements into it as needed.
+  /// move - Use move-assignment to move the range [I, E) onto the
+  /// objects starting with "Dest".  This is just <memory>'s
+  /// std::move, but not all stdlibs actually provide that.
+  template<typename It1, typename It2>
+  static It2 move(It1 I, It1 E, It2 Dest) {
+#if LLVM_USE_RVALUE_REFERENCES
+    for (; I != E; ++I, ++Dest)
+      *Dest = ::std::move(*I);
+    return Dest;
+#else
+    return ::std::copy(I, E, Dest);
+#endif
+  }
+
+  /// move_backward - Use move-assignment to move the range
+  /// [I, E) onto the objects ending at "Dest", moving objects
+  /// in reverse order.  This is just <algorithm>'s
+  /// std::move_backward, but not all stdlibs actually provide that.
+  template<typename It1, typename It2>
+  static It2 move_backward(It1 I, It1 E, It2 Dest) {
+#if LLVM_USE_RVALUE_REFERENCES
+    while (I != E)
+      *--Dest = ::std::move(*--E);
+    return Dest;
+#else
+    return ::std::copy_backward(I, E, Dest);
+#endif
+  }
+
+  /// uninitialized_move - Move the range [I, E) into the uninitialized
+  /// memory starting with "Dest", constructing elements as needed.
+  template<typename It1, typename It2>
+  static void uninitialized_move(It1 I, It1 E, It2 Dest) {
+#if LLVM_USE_RVALUE_REFERENCES
+    for (; I != E; ++I, ++Dest)
+      ::new ((void*) &*Dest) T(::std::move(*I));
+#else
+    ::std::uninitialized_copy(I, E, Dest);
+#endif
+  }
+
+  /// uninitialized_copy - Copy the range [I, E) onto the uninitialized
+  /// memory starting with "Dest", constructing elements as needed.
   template<typename It1, typename It2>
   static void uninitialized_copy(It1 I, It1 E, It2 Dest) {
     std::uninitialized_copy(I, E, Dest);
   }
 
-  /// grow - double the size of the allocated memory, guaranteeing space for at
-  /// least one more element or MinSize if specified.
+  /// grow - Grow the allocated memory (without initializing new
+  /// elements), doubling the size of the allocated memory.
+  /// Guarantees space for at least one more element, or MinSize more
+  /// elements if specified.
   void grow(size_t MinSize = 0);
   
 public:
   void push_back(const T &Elt) {
     if (this->EndX < this->CapacityX) {
     Retry:
-      new (this->end()) T(Elt);
+      ::new ((void*) this->end()) T(Elt);
+      this->setEnd(this->end()+1);
+      return;
+    }
+    this->grow();
+    goto Retry;
+  }
+
+#if LLVM_USE_RVALUE_REFERENCES
+  void push_back(T &&Elt) {
+    if (this->EndX < this->CapacityX) {
+    Retry:
+      ::new ((void*) this->end()) T(::std::move(Elt));
       this->setEnd(this->end()+1);
       return;
     }
     this->grow();
     goto Retry;
   }
+#endif
   
   void pop_back() {
     this->setEnd(this->end()-1);
@@ -199,8 +261,8 @@ void SmallVectorTemplateBase<T, isPodLike>::grow(size_t MinSize) {
     NewCapacity = MinSize;
   T *NewElts = static_cast<T*>(malloc(NewCapacity*sizeof(T)));
 
-  // Copy the elements over.
-  this->uninitialized_copy(this->begin(), this->end(), NewElts);
+  // Move the elements over.
+  this->uninitialized_move(this->begin(), this->end(), NewElts);
 
   // Destroy the original elements.
   destroy_range(this->begin(), this->end());
@@ -225,6 +287,29 @@ protected:
   // No need to do a destroy loop for POD's.
   static void destroy_range(T *, T *) {}
 
+  /// move - Use move-assignment to move the range [I, E) onto the
+  /// objects starting with "Dest".  For PODs, this is just memcpy.
+  template<typename It1, typename It2>
+  static It2 move(It1 I, It1 E, It2 Dest) {
+    return ::std::copy(I, E, Dest);
+  }
+
+  /// move_backward - Use move-assignment to move the range
+  /// [I, E) onto the objects ending at "Dest", moving objects
+  /// in reverse order.
+  template<typename It1, typename It2>
+  static It2 move_backward(It1 I, It1 E, It2 Dest) {
+    return ::std::copy_backward(I, E, Dest);
+  }
+
+  /// uninitialized_move - Move the range [I, E) onto the uninitialized memory
+  /// starting with "Dest", constructing elements into it as needed.
+  template<typename It1, typename It2>
+  static void uninitialized_move(It1 I, It1 E, It2 Dest) {
+    // Just do a copy.
+    uninitialized_copy(I, E, Dest);
+  }
+
   /// uninitialized_copy - Copy the range [I, E) onto the uninitialized memory
   /// starting with "Dest", constructing elements into it as needed.
   template<typename It1, typename It2>
@@ -330,7 +415,11 @@ public:
   }
 
   T pop_back_val() {
+#if LLVM_USE_RVALUE_REFERENCES
+    T Result = ::std::move(this->back());
+#else
     T Result = this->back();
+#endif
     this->pop_back();
     return Result;
   }
@@ -392,6 +481,36 @@ public:
     return(N);
   }
 
+#if LLVM_USE_RVALUE_REFERENCES
+  iterator insert(iterator I, T &&Elt) {
+    if (I == this->end()) {  // Important special case for empty vector.
+      this->push_back(::std::move(Elt));
+      return this->end()-1;
+    }
+
+    if (this->EndX < this->CapacityX) {
+    Retry:
+      ::new ((void*) this->end()) T(::std::move(this->back()));
+      this->setEnd(this->end()+1);
+      // Push everything else over.
+      this->move_backward(I, this->end()-1, this->end());
+
+      // If we just moved the element we're inserting, be sure to update
+      // the reference.
+      T *EltPtr = &Elt;
+      if (I <= EltPtr && EltPtr < this->EndX)
+        ++EltPtr;
+
+      *I = ::std::move(*EltPtr);
+      return I;
+    }
+    size_t EltNo = I-this->begin();
+    this->grow();
+    I = this->begin()+EltNo;
+    goto Retry;
+  }
+#endif
+
   iterator insert(iterator I, const T &Elt) {
     if (I == this->end()) {  // Important special case for empty vector.
       this->push_back(Elt);
@@ -400,10 +519,10 @@ public:
 
     if (this->EndX < this->CapacityX) {
     Retry:
-      new (this->end()) T(this->back());
+      ::new ((void*) this->end()) T(this->back());
       this->setEnd(this->end()+1);
       // Push everything else over.
-      std::copy_backward(I, this->end()-1, this->end());
+      this->move_backward(I, this->end()-1, this->end());
 
       // If we just moved the element we're inserting, be sure to update
       // the reference.
@@ -444,7 +563,7 @@ public:
       append(this->end()-NumToInsert, this->end());
 
       // Copy the existing elements that get replaced.
-      std::copy_backward(I, OldEnd-NumToInsert, OldEnd);
+      this->move_backward(I, OldEnd-NumToInsert, OldEnd);
 
       std::fill_n(I, NumToInsert, Elt);
       return I;
@@ -493,7 +612,7 @@ public:
       append(this->end()-NumToInsert, this->end());
 
       // Copy the existing elements that get replaced.
-      std::copy_backward(I, OldEnd-NumToInsert, OldEnd);
+      this->move_backward(I, OldEnd-NumToInsert, OldEnd);
 
       std::copy(From, To, I);
       return I;
@@ -519,8 +638,11 @@ public:
     return I;
   }
 
-  const SmallVectorImpl
-  &operator=(const SmallVectorImpl &RHS);
+  SmallVectorImpl &operator=(const SmallVectorImpl &RHS);
+
+#if LLVM_USE_RVALUE_REFERENCES
+  SmallVectorImpl &operator=(SmallVectorImpl &&RHS);
+#endif
 
   bool operator==(const SmallVectorImpl &RHS) const {
     if (this->size() != RHS.size()) return false;
@@ -590,7 +712,7 @@ void SmallVectorImpl<T>::swap(SmallVectorImpl<T> &RHS) {
 }
 
 template <typename T>
-const SmallVectorImpl<T> &SmallVectorImpl<T>::
+SmallVectorImpl<T> &SmallVectorImpl<T>::
   operator=(const SmallVectorImpl<T> &RHS) {
   // Avoid self-assignment.
   if (this == &RHS) return *this;
@@ -617,6 +739,7 @@ const SmallVectorImpl<T> &SmallVectorImpl<T>::
 
   // If we have to grow to have enough elements, destroy the current elements.
   // This allows us to avoid copying them during the grow.
+  // FIXME: don't do this if they're efficiently moveable.
   if (this->capacity() < RHSSize) {
     // Destroy current elements.
     this->destroy_range(this->begin(), this->end());
@@ -637,6 +760,69 @@ const SmallVectorImpl<T> &SmallVectorImpl<T>::
   return *this;
 }
 
+#if LLVM_USE_RVALUE_REFERENCES
+template <typename T>
+SmallVectorImpl<T> &SmallVectorImpl<T>::operator=(SmallVectorImpl<T> &&RHS) {
+  // Avoid self-assignment.
+  if (this == &RHS) return *this;
+
+  // If the RHS isn't small, clear this vector and then steal its buffer.
+  if (!RHS.isSmall()) {
+    this->destroy_range(this->begin(), this->end());
+    if (!this->isSmall()) free(this->begin());
+    this->BeginX = RHS.BeginX;
+    this->EndX = RHS.EndX;
+    this->CapacityX = RHS.CapacityX;
+    RHS.resetToSmall();
+    return *this;
+  }
+
+  // If we already have sufficient space, assign the common elements, then
+  // destroy any excess.
+  size_t RHSSize = RHS.size();
+  size_t CurSize = this->size();
+  if (CurSize >= RHSSize) {
+    // Assign common elements.
+    iterator NewEnd = this->begin();
+    if (RHSSize)
+      NewEnd = this->move(RHS.begin(), RHS.end(), NewEnd);
+
+    // Destroy excess elements and trim the bounds.
+    this->destroy_range(NewEnd, this->end());
+    this->setEnd(NewEnd);
+
+    // Clear the RHS.
+    RHS.clear();
+
+    return *this;
+  }
+
+  // If we have to grow to have enough elements, destroy the current elements.
+  // This allows us to avoid copying them during the grow.
+  // FIXME: this may not actually make any sense if we can efficiently move
+  // elements.
+  if (this->capacity() < RHSSize) {
+    // Destroy current elements.
+    this->destroy_range(this->begin(), this->end());
+    this->setEnd(this->begin());
+    CurSize = 0;
+    this->grow(RHSSize);
+  } else if (CurSize) {
+    // Otherwise, use assignment for the already-constructed elements.
+    this->move(RHS.begin(), RHS.end(), this->begin());
+  }
+
+  // Move-construct the new elements in place.
+  this->uninitialized_move(RHS.begin()+CurSize, RHS.end(),
+                           this->begin()+CurSize);
+
+  // Set end.
+  this->setEnd(this->begin()+RHSSize);
+
+  RHS.clear();
+  return *this;
+}
+#endif
 
 /// SmallVector - This is a 'vector' (really, a variable-sized array), optimized
 /// for the case when the array is small.  It contains some number of elements
@@ -692,6 +878,18 @@ public:
     return *this;
   }
 
+#if LLVM_USE_RVALUE_REFERENCES
+  SmallVector(SmallVector &&RHS) : SmallVectorImpl<T>(NumTsAvailable) {
+    if (!RHS.empty())
+      SmallVectorImpl<T>::operator=(::std::move(RHS));
+  }
+
+  const SmallVector &operator=(SmallVector &&RHS) {
+    SmallVectorImpl<T>::operator=(::std::move(RHS));
+    return *this;
+  }
+#endif
+
 };
 
 /// Specialize SmallVector at N=0.  This specialization guarantees
diff --git a/include/llvm/Support/Compiler.h b/include/llvm/Support/Compiler.h
index d0b186ea7c2..0ae02e85c57 100644
--- a/include/llvm/Support/Compiler.h
+++ b/include/llvm/Support/Compiler.h
@@ -19,6 +19,25 @@
 # define __has_feature(x) 0
 #endif
 
+/// LLVM_HAS_RVALUE_REFERENCES - Does the compiler provide r-value references?
+/// This implies that <utility> provides the one-argument std::move;  it
+/// does not imply the existence of any other C++ library features.
+#if (__has_feature(cxx_rvalue_references)   \
+     || defined(__GXX_EXPERIMENTAL_CXX0X__) \
+     || _MSC_VER >= 1600)
+#define LLVM_USE_RVALUE_REFERENCES 1
+#else
+#define LLVM_USE_RVALUE_REFERENCES 0
+#endif
+
+/// llvm_move - Expands to ::std::move if the compiler supports
+/// r-value references; otherwise, expands to the argument.
+#if LLVM_USE_RVALUE_REFERENCES
+#define llvm_move(value) (::std::move(arg))
+#else
+#define llvm_move(value) (value)
+#endif
+
 /// LLVM_LIBRARY_VISIBILITY - If a class marked with this attribute is linked
 /// into a shared library, then the class should be private to the library and
 /// not accessible from outside it.  Can also be used to mark variables and