[Allocator] Switch the BumpPtrAllocator to use a vector of pointers to

slabs rather than embedding a singly linked list in the slabs
themselves. This has a few advantages:

- Better utilization of the slab's memory by not wasting 16-bytes at the
  front.
- Simpler allocation strategy by not having a struct packed at the
  front.
- Avoids paging every allocated slab in just to traverse them for
  deallocating or dumping stats.

The latter is the really nice part. Folks have complained from time to
time bitterly that tearing down a BumpPtrAllocator, even if it doesn't
run any destructors, pages in all of the memory allocated. Now it won't.
=]

Also resolves a FIXME with the scaling of the slab sizes. The scaling
now disregards specially sized slabs for allocations larger than the
threshold.

llvm-svn: 206147

1 files changed, 6 insertions, 9 deletions

diff --git a/llvm/lib/ExecutionEngine/JIT/JITMemoryManager.cpp b/llvm/lib/ExecutionEngine/JIT/JITMemoryManager.cpp
index 0d1ea0263c7..e5a41eb0536 100644
--- a/llvm/lib/ExecutionEngine/JIT/JITMemoryManager.cpp
+++ b/llvm/lib/ExecutionEngine/JIT/JITMemoryManager.cpp
@@ -274,8 +274,8 @@ namespace {
   public:
     JITSlabAllocator(DefaultJITMemoryManager &jmm) : JMM(jmm) { }
     virtual ~JITSlabAllocator() { }
-    MemSlab *Allocate(size_t Size) override;
-    void Deallocate(MemSlab *Slab) override;
+    void *Allocate(size_t Size) override;
+    void Deallocate(void *Slab, size_t Size) override;
   };
 
   /// DefaultJITMemoryManager - Manage memory for the JIT code generation.
@@ -568,16 +568,13 @@ namespace {
   };
 }
 
-MemSlab *JITSlabAllocator::Allocate(size_t Size) {
+void *JITSlabAllocator::Allocate(size_t Size) {
   sys::MemoryBlock B = JMM.allocateNewSlab(Size);
-  MemSlab *Slab = (MemSlab*)B.base();
-  Slab->Size = B.size();
-  Slab->NextPtr = 0;
-  return Slab;
+  return B.base();
 }
 
-void JITSlabAllocator::Deallocate(MemSlab *Slab) {
-  sys::MemoryBlock B(Slab, Slab->Size);
+void JITSlabAllocator::Deallocate(void *Slab, size_t Size) {
+  sys::MemoryBlock B(Slab, Size);
   sys::Memory::ReleaseRWX(B);
 }