Fix llvm::BumpPtrAllocatorImpl::Reset()

BumpPtrAllocator's Reset wouldn't clear CustomSizedSlabs if Slabs.size() == 0.

Patch by Kal <b17c0de@gmail.com>!

llvm-svn: 237588

llvm/include/llvm/Support/Allocator.h

@@ -187,6 +187,9 @@ public:
   /// \brief Deallocate all but the current slab and reset the current pointer
   /// to the beginning of it, freeing all memory allocated so far.
   void Reset() {
+    DeallocateCustomSizedSlabs();
+    CustomSizedSlabs.clear();
+
     if (Slabs.empty())
       return;
 
@@ -198,8 +201,6 @@ public:
     // Deallocate all but the first slab, and deallocate all custom-sized slabs.
     DeallocateSlabs(std::next(Slabs.begin()), Slabs.end());
     Slabs.erase(std::next(Slabs.begin()), Slabs.end());
-    DeallocateCustomSizedSlabs();
-    CustomSizedSlabs.clear();
   }
 
   /// \brief Allocate space at the specified alignment.

llvm/unittests/Support/AllocatorTest.cpp

@@ -61,6 +61,13 @@ TEST(AllocatorTest, ThreeSlabs) {
 // again.
 TEST(AllocatorTest, TestReset) {
   BumpPtrAllocator Alloc;
+
+  // Allocate something larger than the SizeThreshold=4096.
+  (void)Alloc.Allocate(5000, 1);
+  Alloc.Reset();
+  // Calling Reset should free all CustomSizedSlabs.
+  EXPECT_EQ(0u, Alloc.GetNumSlabs());
+
   Alloc.Allocate(3000, 1);
   EXPECT_EQ(1U, Alloc.GetNumSlabs());
   Alloc.Allocate(3000, 1);