The --optimize-for-size flag should imply a small semi-space

test/cctest/test-heap.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
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 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 4342 matching lines @@
   i::FLAG_expose_gc = true;
   i::FLAG_max_semi_space_size = 2;
   CcTest::InitializeVM();
   v8::HandleScope scope(CcTest::isolate());
   Isolate* isolate = CcTest::i_isolate();
   Heap* heap = isolate->heap();
   NewSpace* new_space = heap->new_space();
 
   // In this test we will try to overwrite the promotion queue which is at the
   // end of to-space. To actually make that possible, we need at least two
-  // semi-space pages and take advantage of fragementation.
+  // semi-space pages and take advantage of fragmentation.
   // (1) Grow semi-space to two pages.
   // (2) Create a few small long living objects and call the scavenger to
   // move them to the other semi-space.
   // (3) Create a huge object, i.e., remainder of first semi-space page and
   // create another huge object which should be of maximum allocatable memory
   // size of the second semi-space page.
   // (4) Call the scavenger again.
   // What will happen is: the scavenger will promote the objects created in (2)
   // and will create promotion queue entries at the end of the second
   // semi-space page during the next scavenge when it promotes the objects to
   // the old generation. The first allocation of (3) will fill up the first
   // semi-space page. The second allocation in (3) will not fit into the first
   // semi-space page, but it will overwrite the promotion queue which are in
   // the second semi-space page. If the right guards are in place, the promotion
   // queue will be evacuated in that case.
 
   // Grow the semi-space to two pages to make semi-space copy overwrite the
   // promotion queue, which will be at the end of the second page.
   intptr_t old_capacity = new_space->Capacity();
+
+  // If we are in a low memory config, we can't grow to two pages and we can't
+  // run this test. This also means the issue we are testing cannot arise, as
+  // there is no fragmentation.
+  if (new_space->IsAtMaximumCapacity()) return;
+
   new_space->Grow();
   CHECK(new_space->IsAtMaximumCapacity());
   CHECK(2 * old_capacity == new_space->Capacity());
 
   // Call the scavenger two times to get an empty new space
   heap->CollectGarbage(NEW_SPACE);
   heap->CollectGarbage(NEW_SPACE);
 
   // First create a few objects which will survive a scavenge, and will get
   // promoted to the old generation later on. These objects will create
@@ skipping 86 matching lines @@
 #ifdef DEBUG
 TEST(PathTracer) {
   CcTest::InitializeVM();
   v8::HandleScope scope(CcTest::isolate());
 
   v8::Local<v8::Value> result = CompileRun("'abc'");
   Handle<Object> o = v8::Utils::OpenHandle(*result);
   CcTest::i_isolate()->heap()->TracePathToObject(*o);
 }
 #endif  // DEBUG