From 2a9a2dba4c02e7eea3aeba2be5dc1fc377d5aa5c Mon Sep 17 00:00:00 2001
From: John McCall <rjmccall@apple.com>
Date: Thu, 2 Sep 2010 21:55:03 +0000
Subject: [PATCH] After some discussion with djg, teach SmallVector to grow
 from a zero capacity and remove the workaround in SmallVector<T,0>.  There
 are some theoretical benefits to a N->2N+1 growth policy anyway.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@112870 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/ADT/SmallVector.h | 23 ++++++-----------------
 lib/Support/SmallVector.cpp    |  2 +-
 2 files changed, 7 insertions(+), 18 deletions(-)

diff --git a/include/llvm/ADT/SmallVector.h b/include/llvm/ADT/SmallVector.h
index a76e9c77f16..1d6181a95da 100644
--- a/include/llvm/ADT/SmallVector.h
+++ b/include/llvm/ADT/SmallVector.h
@@ -206,7 +206,7 @@ template <typename T, bool isPodLike>
 void SmallVectorTemplateBase<T, isPodLike>::grow(size_t MinSize) {
   size_t CurCapacity = this->capacity();
   size_t CurSize = this->size();
-  size_t NewCapacity = 2*CurCapacity;
+  size_t NewCapacity = 2*CurCapacity + 1; // Always grow, even from zero.
   if (NewCapacity < MinSize)
     NewCapacity = MinSize;
   T *NewElts = static_cast<T*>(malloc(NewCapacity*sizeof(T)));
@@ -712,38 +712,27 @@ public:
 /// members are required.
 template <typename T>
 class SmallVector<T,0> : public SmallVectorImpl<T> {
-  // SmallVector doesn't like growing from zero capacity.  As a
-  // temporary workaround, avoid changing the growth algorithm by
-  // forcing capacity to be at least 1 in the constructors.
-
 public:
-  SmallVector() : SmallVectorImpl<T>(0) {
-    this->reserve(1); // workaround
-  }
+  SmallVector() : SmallVectorImpl<T>(0) {}
 
   explicit SmallVector(unsigned Size, const T &Value = T())
     : SmallVectorImpl<T>(0) {
-    this->reserve(Size ? Size : 1); // workaround
+    this->reserve(Size);
     while (Size--)
       this->push_back(Value);
   }
 
   template<typename ItTy>
   SmallVector(ItTy S, ItTy E) : SmallVectorImpl<T>(0) {
-    if (S == E) this->reserve(1); // workaround
     this->append(S, E);
   }
 
   SmallVector(const SmallVector &RHS) : SmallVectorImpl<T>(0) {
-    if (!RHS.empty())
-      SmallVectorImpl<T>::operator=(RHS);
-    else
-      this->reserve(1); // workaround
+    SmallVectorImpl<T>::operator=(RHS);
   }
 
-  const SmallVector &operator=(const SmallVector &RHS) {
-    SmallVectorImpl<T>::operator=(RHS);
-    return *this;
+  SmallVector &operator=(const SmallVectorImpl<T> &RHS) {
+    return SmallVectorImpl<T>::operator=(RHS);
   }
 
 };
diff --git a/lib/Support/SmallVector.cpp b/lib/Support/SmallVector.cpp
index 2e17af86415..a89f1495763 100644
--- a/lib/Support/SmallVector.cpp
+++ b/lib/Support/SmallVector.cpp
@@ -18,7 +18,7 @@ using namespace llvm;
 /// on POD-like datatypes and is out of line to reduce code duplication.
 void SmallVectorBase::grow_pod(size_t MinSizeInBytes, size_t TSize) {
   size_t CurSizeBytes = size_in_bytes();
-  size_t NewCapacityInBytes = 2 * capacity_in_bytes();
+  size_t NewCapacityInBytes = 2 * capacity_in_bytes() + TSize; // Always grow.
   if (NewCapacityInBytes < MinSizeInBytes)
     NewCapacityInBytes = MinSizeInBytes;