[heap] Report proper OOM failure if semi-space copy fails.

src/heap/mark-compact.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/heap/mark-compact.h"
 
 #include "src/base/atomicops.h"
 #include "src/base/bits.h"
 #include "src/base/sys-info.h"
 #include "src/code-stubs.h"
@@ skipping 1701 matching lines @@
           TryPromoteObject(object, size)) {
         continue;
       }
 
       AllocationAlignment alignment = object->RequiredAlignment();
       AllocationResult allocation = new_space->AllocateRaw(size, alignment);
       if (allocation.IsRetry()) {
         if (!new_space->AddFreshPage()) {
           // Shouldn't happen. We are sweeping linearly, and to-space
           // has the same number of pages as from-space, so there is
-          // always room.
-          UNREACHABLE();
+          // always room unless we are in an OOM situation.
+          FatalProcessOutOfMemory("MarkCompactCollector: semi-space copy\n");
         }
         allocation = new_space->AllocateRaw(size, alignment);
         DCHECK(!allocation.IsRetry());
       }
       Object* target = allocation.ToObjectChecked();
 
       MigrateObject(HeapObject::cast(target), object, size, NEW_SPACE, nullptr);
       if (V8_UNLIKELY(target->IsJSArrayBuffer())) {
         heap()->array_buffer_tracker()->MarkLive(JSArrayBuffer::cast(target));
       }
@@ skipping 2905 matching lines @@
     MarkBit mark_bit = Marking::MarkBitFrom(host);
     if (Marking::IsBlack(mark_bit)) {
       RelocInfo rinfo(pc, RelocInfo::CODE_TARGET, 0, host);
       RecordRelocSlot(&rinfo, target);
     }
   }
 }
 
 }  // namespace internal
 }  // namespace v8