From 5e6a705985f960b8d8a6df969930a51b5136bdfa Mon Sep 17 00:00:00 2001
From: Benjamin Kramer <benny.kra@googlemail.com>
Date: Tue, 13 Apr 2010 14:41:51 +0000
Subject: [PATCH] Let BumpPtrAllocator lazily allocate the first slab.

We have some code in llvm and clang where a BumpPtrAllocator is declared in a
class but never used in the common case. Stop wasting memory there.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@101130 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Support/Allocator.cpp | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/lib/Support/Allocator.cpp b/lib/Support/Allocator.cpp
index 31b45c8d4aa..ef40e47d985 100644
--- a/lib/Support/Allocator.cpp
+++ b/lib/Support/Allocator.cpp
@@ -23,9 +23,7 @@ namespace llvm {
 BumpPtrAllocator::BumpPtrAllocator(size_t size, size_t threshold,
                                    SlabAllocator &allocator)
     : SlabSize(size), SizeThreshold(threshold), Allocator(allocator),
-      CurSlab(0), BytesAllocated(0) {
-  StartNewSlab();
-}
+      CurSlab(0), BytesAllocated(0) { }
 
 BumpPtrAllocator::~BumpPtrAllocator() {
   DeallocateSlabs(CurSlab);
@@ -72,6 +70,8 @@ void BumpPtrAllocator::DeallocateSlabs(MemSlab *Slab) {
 /// Reset - Deallocate all but the current slab and reset the current pointer
 /// to the beginning of it, freeing all memory allocated so far.
 void BumpPtrAllocator::Reset() {
+  if (!CurSlab) // Start a new slab if we didn't allocate one already.
+    StartNewSlab();
   DeallocateSlabs(CurSlab->NextPtr);
   CurSlab->NextPtr = 0;
   CurPtr = (char*)(CurSlab + 1);
@@ -81,6 +81,9 @@ void BumpPtrAllocator::Reset() {
 /// Allocate - Allocate space at the specified alignment.
 ///
 void *BumpPtrAllocator::Allocate(size_t Size, size_t Alignment) {
+  if (!CurSlab) // Start a new slab if we haven't allocated one already.
+    StartNewSlab();
+
   // Keep track of how many bytes we've allocated.
   BytesAllocated += Size;