[heap] make inline-allocation-observers precise

Now that we no longer require AllocationInfo::limit to be aligned [1], we can do
more accurate inline-allocation-observation. This lets us get notified when the
next allocation that crosses the step-size boundary is allocated.

Fixed the test-cases. They make significantly more sense now given the step
sizes and the number of times we get notifications. For example, with a step
size of 512, an allocation of 16kb results in 32 notifications instead of 30
now.

[1] https://codereview.chromium.org/1444883003

R=hpayer@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1448913003

Cr-Commit-Position: refs/heads/master@{#32091}

src/heap/spaces.cc

@@ -1516,7 +1516,7 @@ void NewSpace::UpdateInlineAllocationLimit(int size_in_bytes) {
     // Lower limit during incremental marking.
     Address high = to_space_.page_high();
     Address new_top = allocation_info_.top() + size_in_bytes;
-    Address new_limit = new_top + GetNextInlineAllocationStepSize();
+    Address new_limit = new_top + GetNextInlineAllocationStepSize() - 1;
     allocation_info_.set_limit(Min(new_limit, high));
   }
   DCHECK_SEMISPACE_ALLOCATION_INFO(allocation_info_, to_space_);

src/heap/spaces.h

@@ -1493,9 +1493,6 @@ class AllocationInfo {
   }
 
   INLINE(Address limit()) const {
-    SLOW_DCHECK(limit_ == NULL ||
-                (reinterpret_cast<intptr_t>(limit_) & kHeapObjectTagMask) ==
-                    0);
     return limit_;
   }
 
@@ -2513,7 +2510,7 @@ class InlineAllocationObserver {
  public:
   explicit InlineAllocationObserver(intptr_t step_size)
       : step_size_(step_size), bytes_to_next_step_(step_size) {
-    DCHECK(step_size >= kPointerSize && (step_size & kHeapObjectTagMask) == 0);
+    DCHECK(step_size >= kPointerSize);
   }
   virtual ~InlineAllocationObserver() {}
 
@@ -2521,15 +2518,13 @@ class InlineAllocationObserver {
   intptr_t step_size() const { return step_size_; }
   intptr_t bytes_to_next_step() const { return bytes_to_next_step_; }
 
-  // Pure virtual method provided by the subclasses that gets called when more
-  // than step_size byte have been allocated.
+  // Pure virtual method provided by the subclasses that gets called when at
+  // least step_size bytes have been allocated.
   virtual void Step(int bytes_allocated) = 0;
 
   // Called each time the new space does an inline allocation step. This may be
   // more frequently than the step_size we are monitoring (e.g. when there are
-  // multiple observers, or when page or space boundary is encountered.) The
-  // Step method is only called once more than step_size bytes have been
-  // allocated.
+  // multiple observers, or when page or space boundary is encountered.)
   void InlineAllocationStep(int bytes_allocated) {
     bytes_to_next_step_ -= bytes_allocated;
     if (bytes_to_next_step_ <= 0) {

test/cctest/test-spaces.cc

@@ -834,13 +834,8 @@ UNINITIALIZED_TEST(InlineAllocationObserver) {
     AllocateUnaligned(new_space, 64);
     CHECK_EQ(observer1.count(), 0);
 
-    // The observer should not get called even when we have allocated exactly
-    // 128 bytes.
+    // The observer should get called when we have allocated exactly 128 bytes.
     AllocateUnaligned(new_space, 64);
-    CHECK_EQ(observer1.count(), 0);
-
-    // The next allocation gets the notification.
-    AllocateUnaligned(new_space, 8);
     CHECK_EQ(observer1.count(), 1);
 
     // Another >128 bytes should get another notification.
@@ -851,35 +846,35 @@ UNINITIALIZED_TEST(InlineAllocationObserver) {
     AllocateUnaligned(new_space, 1024);
     CHECK_EQ(observer1.count(), 3);
 
-    // Allocating another 2048 bytes in small objects should get 12
+    // Allocating another 2048 bytes in small objects should get 16
     // notifications.
     for (int i = 0; i < 64; ++i) {
       AllocateUnaligned(new_space, 32);
     }
-    CHECK_EQ(observer1.count(), 15);
+    CHECK_EQ(observer1.count(), 19);
 
     // Multiple observers should work.
     Observer observer2(96);
     new_space->AddInlineAllocationObserver(&observer2);
 
     AllocateUnaligned(new_space, 2048);
-    CHECK_EQ(observer1.count(), 16);
+    CHECK_EQ(observer1.count(), 20);
     CHECK_EQ(observer2.count(), 1);
 
     AllocateUnaligned(new_space, 104);
-    CHECK_EQ(observer1.count(), 16);
+    CHECK_EQ(observer1.count(), 20);
     CHECK_EQ(observer2.count(), 2);
 
     // Callback should stop getting called after an observer is removed.
     new_space->RemoveInlineAllocationObserver(&observer1);
 
     AllocateUnaligned(new_space, 384);
-    CHECK_EQ(observer1.count(), 16);  // no more notifications.
+    CHECK_EQ(observer1.count(), 20);  // no more notifications.
     CHECK_EQ(observer2.count(), 3);   // this one is still active.
 
     new_space->RemoveInlineAllocationObserver(&observer2);
     AllocateUnaligned(new_space, 384);
-    CHECK_EQ(observer1.count(), 16);
+    CHECK_EQ(observer1.count(), 20);
     CHECK_EQ(observer2.count(), 3);
   }
   isolate->Dispose();
@@ -911,8 +906,8 @@ UNINITIALIZED_TEST(InlineAllocationObserverCadence) {
     new_space->RemoveInlineAllocationObserver(&observer1);
     new_space->RemoveInlineAllocationObserver(&observer2);
 
-    CHECK_EQ(observer1.count(), 30);
-    CHECK_EQ(observer2.count(), 26);
+    CHECK_EQ(observer1.count(), 32);
+    CHECK_EQ(observer2.count(), 28);
   }
   isolate->Dispose();
 }