Added allocation folding support for old space allocations.

src/hydrogen-instructions.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // 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 3288 matching lines @@
   // have so far but not Tagged, use that representation instead.
   Representation input_rep = value()->representation();
   if (!input_rep.IsTagged()) rep = rep.generalize(input_rep);
   return rep;
 }
 
 
 void HAllocate::HandleSideEffectDominator(GVNFlag side_effect,
                                           HValue* dominator) {
   ASSERT(side_effect == kChangesNewSpacePromotion);
+  Zone* zone = block()->zone();
   if (!FLAG_use_allocation_folding) return;
 
   // Try to fold allocations together with their dominating allocations.
   if (!dominator->IsAllocate()) {
     if (FLAG_trace_allocation_folding) {
       PrintF("#%d (%s) cannot fold into #%d (%s)\n",
           id(), Mnemonic(), dominator->id(), dominator->Mnemonic());
     }
     return;
   }
 
-  HAllocate* dominator_allocate_instr = HAllocate::cast(dominator);
-  HValue* dominator_size = dominator_allocate_instr->size();
+  HAllocate* dominator_allocate = HAllocate::cast(dominator);
+  HValue* dominator_size = dominator_allocate->size();
   HValue* current_size = size();
-  // We can just fold allocations that are guaranteed in new space.
+
   // TODO(hpayer): Add support for non-constant allocation in dominator.
-  if (!IsNewSpaceAllocation() || !current_size->IsInteger32Constant() ||
-      !dominator_allocate_instr->IsNewSpaceAllocation() ||
+  if (!current_size->IsInteger32Constant() ||
       !dominator_size->IsInteger32Constant()) {
     if (FLAG_trace_allocation_folding) {
-      PrintF("#%d (%s) cannot fold into #%d (%s)\n",
+      PrintF("#%d (%s) cannot fold into #%d (%s), dynamic allocation size\n",
           id(), Mnemonic(), dominator->id(), dominator->Mnemonic());
     }
     return;
   }
 
+  dominator_allocate = GetFoldableDominator(dominator_allocate);
+  if (dominator_allocate == NULL) {
+    return;
+  }
+
+  ASSERT((IsNewSpaceAllocation() &&
+         dominator_allocate->IsNewSpaceAllocation()) ||
+         (IsOldDataSpaceAllocation() &&
+         dominator_allocate->IsOldDataSpaceAllocation()) ||
+         (IsOldPointerSpaceAllocation() &&
+         dominator_allocate->IsOldPointerSpaceAllocation()));
+
   // First update the size of the dominator allocate instruction.
+  dominator_size = dominator_allocate->size();
   int32_t dominator_size_constant =
       HConstant::cast(dominator_size)->GetInteger32Constant();
   int32_t current_size_constant =
       HConstant::cast(current_size)->GetInteger32Constant();
   int32_t new_dominator_size = dominator_size_constant + current_size_constant;
 
   if (MustAllocateDoubleAligned()) {
-    if (!dominator_allocate_instr->MustAllocateDoubleAligned()) {
-      dominator_allocate_instr->MakeDoubleAligned();
+    if (!dominator_allocate->MustAllocateDoubleAligned()) {
+      dominator_allocate->MakeDoubleAligned();
     }
     if ((dominator_size_constant & kDoubleAlignmentMask) != 0) {
       dominator_size_constant += kDoubleSize / 2;
       new_dominator_size += kDoubleSize / 2;
     }
   }
 
   if (new_dominator_size > Page::kMaxNonCodeHeapObjectSize) {
     if (FLAG_trace_allocation_folding) {
       PrintF("#%d (%s) cannot fold into #%d (%s) due to size: %d\n",
-          id(), Mnemonic(), dominator->id(), dominator->Mnemonic(),
-          new_dominator_size);
+          id(), Mnemonic(), dominator_allocate->id(),
+          dominator_allocate->Mnemonic(), new_dominator_size);
     }
     return;
   }
-  HBasicBlock* block = dominator->block();
-  Zone* zone = block->zone();
-  HInstruction* new_dominator_size_constant =
-      HConstant::New(zone, context(), new_dominator_size);
-  new_dominator_size_constant->InsertBefore(dominator_allocate_instr);
-  dominator_allocate_instr->UpdateSize(new_dominator_size_constant);
+
+  HInstruction* new_dominator_size_constant = HConstant::CreateAndInsert(
+      zone, context(), new_dominator_size, dominator_allocate, true);
+  dominator_allocate->UpdateSize(new_dominator_size_constant);
 
 #ifdef VERIFY_HEAP
-  if (FLAG_verify_heap) {
-    dominator_allocate_instr->MakePrefillWithFiller();
+  if (FLAG_verify_heap && dominator_allocate->IsNewSpaceAllocation()) {
+    dominator_allocate->MakePrefillWithFiller();
   }
 #endif
 
   // After that replace the dominated allocate instruction.
   HInstruction* dominated_allocate_instr =
       HInnerAllocatedObject::New(zone,
                                  context(),
-                                 dominator_allocate_instr,
+                                 dominator_allocate,
                                  dominator_size_constant,
                                  type());
   dominated_allocate_instr->InsertBefore(this);
   DeleteAndReplaceWith(dominated_allocate_instr);
   if (FLAG_trace_allocation_folding) {
     PrintF("#%d (%s) folded into #%d (%s)\n",
-        id(), Mnemonic(), dominator->id(), dominator->Mnemonic());
+        id(), Mnemonic(), dominator_allocate->id(),
+        dominator_allocate->Mnemonic());
   }
 }
 
 
+HAllocate* HAllocate::GetFoldableDominator(HAllocate* dominator) {
+  if (!IsFoldable(dominator)) {
+    // We cannot hoist old space allocations over new space allocations.
+    if (IsNewSpaceAllocation() || dominator->IsNewSpaceAllocation()) {
+      if (FLAG_trace_allocation_folding) {
+        PrintF("#%d (%s) cannot fold into #%d (%s), new space hoisting\n",
+            id(), Mnemonic(), dominator->id(), dominator->Mnemonic());
+      }
+      return NULL;
+    }
+
+    // We can hoist old data space allocations over an old pointer space
+    // allocation and vice versa. For that we have to check the dominator
+    // of the dominator allocate instruction.
+    HAllocate* previous_dominator = dominator->dominating_allocate();
+    if (previous_dominator == NULL) {
+      set_dominating_allocate(dominator);
+      if (FLAG_trace_allocation_folding) {
+        PrintF("#%d (%s) cannot fold into #%d (%s), different spaces\n",
+            id(), Mnemonic(), dominator->id(), dominator->Mnemonic());
+      }
+      return NULL;
+    }
+
+    // If we stored a dominator in our actual dominator, then it must be in
+    // the space of the dominated allocation operation. We can hoist the old
+    // space allocation over the actual dominator.
+    dominator = previous_dominator;
+
+    // We can just fold old space allocations that are in the same basic block,
+    // since it is not guaranteed that we fill up the whole allocated old
+    // space memory.
+    // TODO(hpayer): Remove this limitation and add filler maps for each each
+    // allocation as soon as we have store elimination.
+    if (block()->block_id() != dominator->block()->block_id()) {
+      if (FLAG_trace_allocation_folding) {
+        PrintF("#%d (%s) cannot fold into #%d (%s), different basic blocks\n",
+            id(), Mnemonic(), dominator->id(), dominator->Mnemonic());
+      }
+      return NULL;
+    }
+
+    ASSERT((IsOldDataSpaceAllocation() &&
+           dominator->IsOldDataSpaceAllocation()) ||
+           (IsOldPointerSpaceAllocation() &&
+           dominator->IsOldPointerSpaceAllocation()));
+
+    int32_t current_size = HConstant::cast(size())->GetInteger32Constant();
+    HConstant* dominator_free_space_size = dominator->filler_free_space_size();
+    if (dominator_free_space_size != NULL) {
+      // We already hoisted one old space allocation, i.e., we already installed
+      // a filler map. Hence, we just have to update the free space size.
+      UpdateFreeSpaceFiller(dominator_free_space_size,
+          dominator_free_space_size->GetInteger32Constant() + current_size);
+    } else {
+      // This is the first old space allocation that gets hoisted. We have to
+      // install a filler map since the follwing allocation may cause a GC.
+      int32_t dominator_size =
+          HConstant::cast(dominator->size())->GetInteger32Constant();
+      CreateFreeSpaceFiller(dominator, dominator_size, current_size);
+    }
+  }
+  return dominator;
+}
+
+
+void HAllocate::UpdateFreeSpaceFiller(HConstant* old_filler_size,
+                                      int32_t filler_size) {
+  Zone* zone = block()->zone();
+  HConstant* new_free_space_size = HConstant::CreateAndInsert(
+      zone, context(), filler_size, old_filler_size, true);
+  old_filler_size->DeleteAndReplaceWith(new_free_space_size);
+}
+
+
+void HAllocate::CreateFreeSpaceFiller(HAllocate* dominator,
+                                      int32_t dominator_size,
+                                      int32_t filler_size) {
+  Zone* zone = block()->zone();
+  HInstruction* free_space_instr =
+      HInnerAllocatedObject::New(zone, context(), dominator, dominator_size,
+          type());
+  free_space_instr->InsertAfter(dominator);
+  HConstant* filler_map = HConstant::New(

[titzer, 2013/08/07 11:53:44]

You can use CreateAndInsert() here.

[Hannes Payer (out of office), 2013/08/07 12:47:55]

No, I cannot - different HConstant. Actually I am not convinced that
CreateAndInsert improves the code significantly. It is tailored for the int32_t
case.

+      zone,
+      context(),
+      isolate()->factory()->free_space_map(),
+      UniqueValueId(isolate()->heap()->free_space_map()));
+  filler_map->InsertAfter(free_space_instr);
+  HInstruction* store_map = HStoreNamedField::New(zone, context(),
+      free_space_instr, HObjectAccess::ForMap(), filler_map);
+  store_map->SetFlag(HValue::kHasNoObservableSideEffects);
+  store_map->InsertAfter(filler_map);
+
+  HConstant* free_space_size = HConstant::CreateAndInsert(
+      zone, context(), filler_size, store_map, false);

[titzer, 2013/08/07 11:53:44]

Is there any way to make this an InsertBefore() as well? This boolean
before/after parameter is cryptic.

[Hannes Payer (out of office), 2013/08/07 12:47:55]

No, it would just get to complicated. I prefer keeping the logical chain of
operations here. I added two static functions CreateAndInsertBefore and
CreateAndInsertAfter.

+  dominator->set_filler_free_space_size(free_space_size);
+  HObjectAccess access =
+      HObjectAccess::ForJSObjectOffset(FreeSpace::kSizeOffset);
+  HInstruction* store_size = HStoreNamedField::New(zone, context(),
+      free_space_instr, access, free_space_size);
+  store_size->SetFlag(HValue::kHasNoObservableSideEffects);
+  store_size->InsertAfter(free_space_size);
+}
+
+
 void HAllocate::PrintDataTo(StringStream* stream) {
   size()->PrintNameTo(stream);
   stream->Add(" (");
   if (IsNewSpaceAllocation()) stream->Add("N");
   if (IsOldPointerSpaceAllocation()) stream->Add("P");
   if (IsOldDataSpaceAllocation()) stream->Add("D");
   if (MustAllocateDoubleAligned()) stream->Add("A");
   if (MustPrefillWithFiller()) stream->Add("F");
   stream->Add(")");
 }
@@ skipping 721 matching lines @@
       break;
     case kExternalMemory:
       stream->Add("[external-memory]");
       break;
   }
 
   stream->Add("@%d", offset());
 }
 
 } }  // namespace v8::internal