BumpPtrAllocator: Make sure threshold cannot be initialized with a value smaller than the slab size.

This replaces r151834 with a simpler fix.

llvm-svn: 151842

lib/Support/Allocator.cpp

@@ -22,8 +22,8 @@ namespace llvm {
 
 BumpPtrAllocator::BumpPtrAllocator(size_t size, size_t threshold,
                                    SlabAllocator &allocator)
-    : SlabSize(size), SizeThreshold(threshold), Allocator(allocator),
-      CurSlab(0), BytesAllocated(0) { }
+    : SlabSize(size), SizeThreshold(std::min(size, threshold)),
+      Allocator(allocator), CurSlab(0), BytesAllocated(0) { }
 
 BumpPtrAllocator::~BumpPtrAllocator() {
   DeallocateSlabs(CurSlab);
@@ -87,21 +87,15 @@ void BumpPtrAllocator::Reset() {
 /// Allocate - Allocate space at the specified alignment.
 ///
 void *BumpPtrAllocator::Allocate(size_t Size, size_t Alignment) {
-  // 0-byte alignment means 1-byte alignment.
-  if (Alignment == 0) Alignment = 1;
-
-  size_t PaddedSize = Size + sizeof(MemSlab) + Alignment - 1;
-
-  // If requested size exceeds slab size, increase slab size.
-  while (PaddedSize > SlabSize)
-    SlabSize *= 2;
-
   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;
 
+  // 0-byte alignment means 1-byte alignment.
+  if (Alignment == 0) Alignment = 1;
+
   // Allocate the aligned space, going forwards from CurPtr.
   char *Ptr = AlignPtr(CurPtr, Alignment);
 
@@ -112,6 +106,7 @@ void *BumpPtrAllocator::Allocate(size_t Size, size_t Alignment) {
   }
 
   // If Size is really big, allocate a separate slab for it.
+  size_t PaddedSize = Size + sizeof(MemSlab) + Alignment - 1;
   if (PaddedSize > SizeThreshold) {
     MemSlab *NewSlab = Allocator.Allocate(PaddedSize);
 

unittests/Support/AllocatorTest.cpp

@@ -98,7 +98,7 @@ TEST(AllocatorTest, TestSmallSlabSize) {
   BumpPtrAllocator Alloc(128);
 
   Alloc.Allocate(200, 0);
-  EXPECT_EQ(1U, Alloc.GetNumSlabs());
+  EXPECT_EQ(2U, Alloc.GetNumSlabs());
 }
 
 // Mock slab allocator that returns slabs aligned on 4096 bytes.  There is no