These changes are suspects in the recent bot flakiness.

runtime/vm/heap.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/heap.h"
 
 #include "platform/assert.h"
 #include "platform/utils.h"
 #include "vm/flags.h"
 #include "vm/isolate.h"
@@ skipping 39 matching lines @@
 Heap::~Heap() {
   delete barrier_;
   delete barrier_done_;
 
   for (int sel = 0; sel < kNumWeakSelectors; sel++) {
     delete new_weak_tables_[sel];
     delete old_weak_tables_[sel];
   }
 }
 
-void Heap::AbandonRemainingTLAB(Thread* thread) {
-  uword start = thread->top();
-  uword end = thread->end();
-  ASSERT(end >= start);
-  intptr_t size = end - start;
-  if (end == new_space_.end()) {
-    size = 0;
-  }
-  ASSERT(Utils::IsAligned(size, kObjectAlignment));
-  if (size >= kObjectAlignment) {
-    FreeListElement::AsElement(start, size);
-    ASSERT(RawObject::FromAddr(start)->Size() == size);
-    ASSERT((start + size) == new_space_.top());
-  }
-  thread->set_top(0);
-  thread->set_end(0);
-}
-
-intptr_t Heap::CalculateTLABSize() {
-  intptr_t size = new_space_.end() - new_space_.top();
-  return Utils::RoundDown(size, kObjectAlignment);
-}
-
 uword Heap::AllocateNew(intptr_t size) {
   ASSERT(Thread::Current()->no_safepoint_scope_depth() == 0);
   // Currently, only the Dart thread may allocate in new space.
   isolate()->AssertCurrentThreadIsMutator();
   Thread* thread = Thread::Current();
   uword addr = new_space_.TryAllocateInTLAB(thread, size);
-  if (addr != 0) {
-    return addr;
-  }
-
-  intptr_t tlab_size = CalculateTLABSize();
-  if ((tlab_size > 0) && (size > tlab_size)) {
-    return AllocateOld(size, HeapPage::kData);
-  }
-
-  AbandonRemainingTLAB(thread);
-  if (tlab_size > 0) {
-    uword tlab_top = new_space_.TryAllocateNewTLAB(thread, tlab_size);
-    if (tlab_top != 0) {
-      addr = new_space_.TryAllocateInTLAB(thread, size);
-      ASSERT(addr != 0);
-      return addr;
+  if (addr == 0) {
+    // This call to CollectGarbage might end up "reusing" a collection spawned
+    // from a different thread and will be racing to allocate the requested
+    // memory with other threads being released after the collection.
+    CollectGarbage(kNew);
+    addr = new_space_.TryAllocateInTLAB(thread, size);
+    if (addr == 0) {
+      return AllocateOld(size, HeapPage::kData);
     }
   }
-
-  ASSERT(!thread->HasActiveTLAB());
-
-  // This call to CollectGarbage might end up "reusing" a collection spawned
-  // from a different thread and will be racing to allocate the requested
-  // memory with other threads being released after the collection.
-  CollectGarbage(kNew);
-  tlab_size = CalculateTLABSize();
-  uword tlab_top = new_space_.TryAllocateNewTLAB(thread, tlab_size);
-  if (tlab_top != 0) {
-    addr = new_space_.TryAllocateInTLAB(thread, size);
-    // It is possible a GC doesn't clear enough space.
-    // In that case, we must fall through and allocate into old space.
-    if (addr != 0) {
-      return addr;
-    }
-  }
-  return AllocateOld(size, HeapPage::kData);
+  return addr;
 }
 
 uword Heap::AllocateOld(intptr_t size, HeapPage::PageType type) {
   ASSERT(Thread::Current()->no_safepoint_scope_depth() == 0);
   uword addr = old_space_.TryAllocate(size, type);
   if (addr != 0) {
     return addr;
   }
   // If we are in the process of running a sweep, wait for the sweeper to free
   // memory.
@@ skipping 461 matching lines @@
 
 bool Heap::Verify(MarkExpectation mark_expectation) const {
   HeapIterationScope heap_iteration_scope;
   return VerifyGC(mark_expectation);
 }
 
 bool Heap::VerifyGC(MarkExpectation mark_expectation) const {
   StackZone stack_zone(Thread::Current());
 
   // Change the new space's top_ with the more up-to-date thread's view of top_
-  uword saved_top = new_space_.FlushTLS();
+  new_space_.FlushTLS();
 
   ObjectSet* allocated_set =
       CreateAllocatedObjectSet(stack_zone.GetZone(), mark_expectation);
   VerifyPointersVisitor visitor(isolate(), allocated_set);
   VisitObjectPointers(&visitor);
 
-  new_space_.UnflushTLS(saved_top);
   // Only returning a value so that Heap::Validate can be called from an ASSERT.
   return true;
 }
 
 void Heap::PrintSizes() const {
   OS::PrintErr(
       "New space (%" Pd64 "k of %" Pd64
       "k) "
       "Old space (%" Pd64 "k of %" Pd64 "k)\n",
       (UsedInWords(kNew) / KBInWords), (CapacityInWords(kNew) / KBInWords),
@@ skipping 254 matching lines @@
     : StackResource(thread) {
   Dart::vm_isolate()->heap()->WriteProtect(false);
 }
 
 WritableVMIsolateScope::~WritableVMIsolateScope() {
   ASSERT(Dart::vm_isolate()->heap()->UsedInWords(Heap::kNew) == 0);
   Dart::vm_isolate()->heap()->WriteProtect(true);
 }
 
 }  // namespace dart