[stubs] Optimize LoadGlobalViaContextStub and StoreGlobalViaContextStub.

src/x64/code-stubs-x64.cc

 // Copyright 2013 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/v8.h"
 
 #if V8_TARGET_ARCH_X64
 
 #include "src/bootstrapper.h"
 #include "src/code-stubs.h"
@@ skipping 5019 matching lines @@
   Label fast_elements_case;
   __ cmpl(rcx, Immediate(FAST_ELEMENTS));
   __ j(equal, &fast_elements_case);
   GenerateCase(masm, FAST_HOLEY_ELEMENTS);
 
   __ bind(&fast_elements_case);
   GenerateCase(masm, FAST_ELEMENTS);
 }
 
 
+void LoadGlobalViaContextStub::Generate(MacroAssembler* masm) {
+  Register context_reg = rsi;

[Igor Sheludko, 2015/07/18 20:52:44]

What about using LoadGlobalViaContextDescriptor::SlotRegister() and friends
here?

[Benedikt Meurer, 2015/07/24 05:18:29]

I explicitly changed it to not use those functions because that would make the
register allocation less readable. Now everything is explicit by just reading
the function.

+  Register slot_reg = rbx;
+  Register name_reg = rcx;
+  Register result_reg = rax;
+  Label slow_case;
+
+  // Go up context chain to the script context.
+  for (int i = 0; i < depth(); ++i) {
+    __ movp(rdi, ContextOperand(context_reg, Context::PREVIOUS_INDEX));
+    context_reg = rdi;

[Igor Sheludko, 2015/07/18 20:52:44]

Nice!

[Benedikt Meurer, 2015/07/24 05:18:29]

Acknowledged.

+  }
+
+  // Load the PropertyCell value at the specified slot.
+  __ movp(result_reg, ContextOperand(context_reg, slot_reg));
+  __ movp(result_reg, FieldOperand(result_reg, PropertyCell::kValueOffset));
+
+  // Check that value is not the_hole.
+  __ CompareRoot(result_reg, Heap::kTheHoleValueRootIndex);
+  __ j(equal, &slow_case, Label::kNear);
+  __ Ret();
+
+  // Fallback to the runtime.
+  __ bind(&slow_case);
+  __ Integer32ToSmi(slot_reg, slot_reg);
+  __ PopReturnAddressTo(kScratchRegister);
+  __ Push(slot_reg);
+  __ Push(name_reg);
+  __ Push(kScratchRegister);
+  __ TailCallRuntime(Runtime::kLoadGlobalViaContext, 2, 1);
+}
+
+
+void StoreGlobalViaContextStub::Generate(MacroAssembler* masm) {
+  Register context_reg = rsi;

[Igor Sheludko, 2015/07/18 20:52:44]

Same here.

[Benedikt Meurer, 2015/07/24 05:18:29]

See above.

+  Register slot_reg = rbx;
+  Register name_reg = rcx;
+  Register value_reg = rax;
+  Register cell_reg = r8;
+  Register cell_details_reg = rdx;
+  Register cell_value_reg = r9;
+  Label fast_case, slow_case;
+
+  if (FLAG_debug_code) {
+    __ CompareRoot(value_reg, Heap::kTheHoleValueRootIndex);
+    __ Check(not_equal, kUnexpectedValue);
+    __ AssertName(name_reg);
+  }
+
+  // Go up context chain to the script context.
+  for (int i = 0; i < depth(); ++i) {
+    __ movp(rdi, ContextOperand(context_reg, Context::PREVIOUS_INDEX));
+    context_reg = rdi;
+  }
+
+  // Load the PropertyCell at the specified slot.
+  __ movp(cell_reg, ContextOperand(context_reg, slot_reg));
+
+  // Load PropertyDetails for the cell (actually only the cell_type and kind).
+  __ SmiToInteger32(cell_details_reg,
+                    FieldOperand(cell_reg, PropertyCell::kDetailsOffset));
+  __ andl(cell_details_reg,
+          Immediate(PropertyDetails::PropertyCellTypeField::kMask |
+                    PropertyDetails::KindField::kMask));
+
+
+  // Check if PropertyCell holds mutable data.
+  Label not_mutable_data;
+  __ cmpl(cell_details_reg,
+          Immediate(PropertyDetails::PropertyCellTypeField::encode(
+                        PropertyCellType::kMutable) |
+                    PropertyDetails::KindField::encode(kData)));
+  __ j(not_equal, &not_mutable_data);
+  __ bind(&fast_case);
+  __ movp(FieldOperand(cell_reg, PropertyCell::kValueOffset), value_reg);
+  __ RecordWriteField(cell_reg, PropertyCell::kValueOffset, value_reg,
+                      cell_value_reg, kDontSaveFPRegs);
+  // RecordWriteField clobbers the value register, so we need to reload.
+  __ movp(value_reg, FieldOperand(cell_reg, PropertyCell::kValueOffset));
+  __ Ret();
+  __ bind(&not_mutable_data);
+
+  // Check if PropertyCell value matches the new value (relevant for Constant
+  // and ConstantType cells).
+  Label not_same_value;
+  __ movp(cell_value_reg, FieldOperand(cell_reg, PropertyCell::kValueOffset));
+  __ cmpp(cell_value_reg, value_reg);
+  __ j(not_equal, &not_same_value,
+       FLAG_debug_code ? Label::kFar : Label::kNear);
+  if (FLAG_debug_code) {
+    Label done;
+    // This can only be true for Constant and ConstantType cells, because we

[Igor Sheludko, 2015/07/18 20:52:44]

We could probably get here for PropertyCellType::kUndefined if we store an
undefined value. I think it's ok just to check that KindField part is kData.

[Benedikt Meurer, 2015/07/24 05:18:29]

Acknowledged.

+    // never store the_hole via this stub.
+    __ cmpl(cell_details_reg,
+            Immediate(PropertyDetails::PropertyCellTypeField::encode(
+                          PropertyCellType::kConstant) |
+                      PropertyDetails::KindField::encode(kData)));
+    __ j(equal, &done);
+    __ cmpl(cell_details_reg,
+            Immediate(PropertyDetails::PropertyCellTypeField::encode(
+                          PropertyCellType::kConstantType) |
+                      PropertyDetails::KindField::encode(kData)));
+    __ Check(equal, kUnexpectedValue);
+    __ bind(&done);
+  }
+  __ Ret();
+  __ bind(&not_same_value);
+
+  // Check if PropertyCell contains data with constant type.
+  __ cmpl(cell_details_reg,
+          Immediate(PropertyDetails::PropertyCellTypeField::encode(
+                        PropertyCellType::kConstantType) |
+                    PropertyDetails::KindField::encode(kData)));
+  __ j(not_equal, &slow_case, Label::kNear);
+
+  // Now either both old and new values must be SMIs or both must be heap
+  // objects with same map.
+  Label value_is_heap_object;
+  __ JumpIfNotSmi(value_reg, &value_is_heap_object, Label::kNear);
+  __ JumpIfNotSmi(cell_value_reg, &slow_case, Label::kNear);
+  // Old and new values are SMIs, no need for a write barrier here.
+  __ movp(FieldOperand(cell_reg, PropertyCell::kValueOffset), value_reg);
+  __ Ret();
+  __ bind(&value_is_heap_object);
+  __ JumpIfSmi(cell_value_reg, &slow_case, Label::kNear);
+  Register cell_value_map_reg = cell_value_reg;
+  __ movp(cell_value_map_reg,
+          FieldOperand(cell_value_reg, HeapObject::kMapOffset));
+  __ cmpp(cell_value_map_reg, FieldOperand(value_reg, HeapObject::kMapOffset));
+  __ j(equal, &fast_case);

[Igor Sheludko, 2015/07/19 20:29:29]

I think it is better to write field and RecordWriteField(..., OMIT_SMI_CHECK)
here instead of jumping to fast case that does a smi check in RecordWriteField()
again.

[Igor Sheludko, 2015/07/20 09:01:16]

Even better idea: we could add an explicit smi check before the above
RecordWriteField(), which we can then call as RecordWriteField(...,
OMIT_SMI_CHECK) and jump there from here after storing to the cell.

[Benedikt Meurer, 2015/07/24 05:18:29]

Acknowledged.

[Benedikt Meurer, 2015/07/24 05:18:29]

Done.

+
+  // Fallback to the runtime.
+  __ bind(&slow_case);
+  __ Integer32ToSmi(slot_reg, slot_reg);
+  __ PopReturnAddressTo(kScratchRegister);
+  __ Push(slot_reg);
+  __ Push(name_reg);
+  __ Push(value_reg);
+  __ Push(kScratchRegister);
+  __ TailCallRuntime(is_strict(language_mode())
+                         ? Runtime::kStoreGlobalViaContext_Strict
+                         : Runtime::kStoreGlobalViaContext_Sloppy,
+                     3, 1);
+}
+
+
 static int Offset(ExternalReference ref0, ExternalReference ref1) {
   int64_t offset = (ref0.address() - ref1.address());
   // Check that fits into int.
   DCHECK(static_cast<int>(offset) == offset);
   return static_cast<int>(offset);
 }
 
 
 // Prepares stack to put arguments (aligns and so on).  WIN64 calling
 // convention requires to put the pointer to the return value slot into
@@ skipping 382 matching lines @@
                            kStackSpace, nullptr, return_value_operand, NULL);
 }
 
 
 #undef __
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_X64