Avoid jumping to the runtime for ForInFilter

src/full-codegen/x64/full-codegen-x64.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.
 
 #if V8_TARGET_ARCH_X64
 
 #include "src/ast/scopes.h"
 #include "src/code-factory.h"
 #include "src/code-stubs.h"
 #include "src/codegen.h"
@@ skipping 965 matching lines @@
   // The enum cache is valid.  Load the map of the object being
   // iterated over and use the cache for the iteration.
   Label use_cache;
   __ movp(rax, FieldOperand(rax, HeapObject::kMapOffset));
   __ jmp(&use_cache, Label::kNear);
 
   // Get the set of properties to enumerate.
   __ bind(&call_runtime);
   __ Push(rax);  // Duplicate the enumerable object on the stack.
   __ CallRuntime(Runtime::kForInEnumerate);
+

[Igor Sheludko, 2016/07/20 11:06:51]

Spurious change?

   PrepareForBailoutForId(stmt->EnumId(), BailoutState::TOS_REGISTER);
 
   // If we got a map from the runtime call, we can do a fast
   // modification check. Otherwise, we got a fixed array, and we have
   // to do a slow check.
   Label fixed_array;
   __ CompareRoot(FieldOperand(rax, HeapObject::kMapOffset),
                  Heap::kMetaMapRootIndex);
   __ j(not_equal, &fixed_array);
 
@@ skipping 33 matching lines @@
   __ Push(Smi::FromInt(0));  // Initial index.
 
   // Generate code for doing the condition check.
   __ bind(&loop);
   SetExpressionAsStatementPosition(stmt->each());
 
   __ movp(rax, Operand(rsp, 0 * kPointerSize));  // Get the current index.
   __ cmpp(rax, Operand(rsp, 1 * kPointerSize));  // Compare to the array length.
   __ j(above_equal, loop_statement.break_label());
 
-  // Get the current entry of the array into register rbx.
+  // Get the current entry of the array into register rax.
   __ movp(rbx, Operand(rsp, 2 * kPointerSize));
   SmiIndex index = masm()->SmiToIndex(rax, rax, kPointerSizeLog2);
-  __ movp(rbx, FieldOperand(rbx,
-                            index.reg,
-                            index.scale,
-                            FixedArray::kHeaderSize));
+  __ movp(rax,
+          FieldOperand(rbx, index.reg, index.scale, FixedArray::kHeaderSize));
 
   // Get the expected map from the stack or a smi in the
   // permanent slow case into register rdx.
   __ movp(rdx, Operand(rsp, 3 * kPointerSize));
 
   // Check if the expected map still matches that of the enumerable.
   // If not, we may have to filter the key.
   Label update_each;
-  __ movp(rcx, Operand(rsp, 4 * kPointerSize));
-  __ cmpp(rdx, FieldOperand(rcx, HeapObject::kMapOffset));
+  __ movp(rbx, Operand(rsp, 4 * kPointerSize));
+  __ cmpp(rdx, FieldOperand(rbx, HeapObject::kMapOffset));
   __ j(equal, &update_each, Label::kNear);
 
   // We need to filter the key, record slow-path here.
   int const vector_index = SmiFromSlot(slot)->value();
   __ EmitLoadTypeFeedbackVector(rdx);
   __ Move(FieldOperand(rdx, FixedArray::OffsetOfElementAt(vector_index)),
           TypeFeedbackVector::MegamorphicSentinel(isolate()));
 
-  // Convert the entry to a string or null if it isn't a property
-  // anymore. If the property has been removed while iterating, we
-  // just skip it.
-  __ Push(rcx);  // Enumerable.
-  __ Push(rbx);  // Current entry.
-  __ CallRuntime(Runtime::kForInFilter);
+  // rax contains the key.  The receiver in rbx is the second argument to the
+  // ForInFilterStub.  ForInFilter returns undefined if the receiver doesn't
+  // have the key or returns the name-converted key.
+  ForInFilterStub has_stub(isolate());
+  __ CallStub(&has_stub);
   PrepareForBailoutForId(stmt->FilterId(), BailoutState::TOS_REGISTER);
-  __ CompareRoot(rax, Heap::kUndefinedValueRootIndex);
+  __ CompareRoot(result_register(), Heap::kUndefinedValueRootIndex);
+  RestoreContext();

[Igor Sheludko, 2016/07/20 11:06:51]

I would prefer to see the RestoreContext() call right after the CallStub (here
and in other ports). I guess if we bailout here then the context will already be
correct. Right?

[Camillo Bruni, 2016/07/20 12:42:42]

right, changed.

   __ j(equal, loop_statement.continue_label());
-  __ movp(rbx, rax);
 
   // Update the 'each' property or variable from the possibly filtered
-  // entry in register rbx.
+  // entry in register rax.
   __ bind(&update_each);
-  __ movp(result_register(), rbx);
   // Perform the assignment as if via '='.
   { EffectContext context(this);
     EmitAssignment(stmt->each(), stmt->EachFeedbackSlot());
     PrepareForBailoutForId(stmt->AssignmentId(), BailoutState::NO_REGISTERS);
   }
 
   // Both Crankshaft and Turbofan expect BodyId to be right before stmt->body().
   PrepareForBailoutForId(stmt->BodyId(), BailoutState::NO_REGISTERS);
   // Generate code for the body of the loop.
   Visit(stmt->body());
@@ skipping 2577 matching lines @@
   DCHECK_EQ(
       isolate->builtins()->OnStackReplacement()->entry(),
       Assembler::target_address_at(call_target_address, unoptimized_code));
   return ON_STACK_REPLACEMENT;
 }
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_X64