Avoid creating weak cells for literal arrays that are empty of literals.

src/x64/builtins-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/code-factory.h"
 #include "src/codegen.h"
 #include "src/deoptimizer.h"
 #include "src/full-codegen/full-codegen.h"
@@ skipping 944 matching lines @@
   __ movp(temp, FieldOperand(temp, WeakCell::kValueOffset));
   __ cmpp(temp, native_context);
   __ j(not_equal, &loop_bottom);
   // OSR id set to none?
   __ movp(temp, FieldOperand(map, index, times_pointer_size,
                              SharedFunctionInfo::kOffsetToPreviousOsrAstId));
   __ SmiToInteger32(temp, temp);
   const int bailout_id = BailoutId::None().ToInt();
   __ cmpl(temp, Immediate(bailout_id));
   __ j(not_equal, &loop_bottom);
+
   // Literals available?
+  Label got_literals, maybe_cleared_weakcell;
   __ movp(temp, FieldOperand(map, index, times_pointer_size,
                              SharedFunctionInfo::kOffsetToPreviousLiterals));
+  // temp contains either a WeakCell pointing to the literals array or the
+  // literals array directly.
+  STATIC_ASSERT(WeakCell::kValueOffset == FixedArray::kLengthOffset);
+  __ movp(r15, FieldOperand(temp, WeakCell::kValueOffset));
+  __ JumpIfSmi(r15, &maybe_cleared_weakcell);
+  // r15 is a pointer, therefore temp is a WeakCell pointing to a literals
+  // array.
   __ movp(temp, FieldOperand(temp, WeakCell::kValueOffset));
-  __ JumpIfSmi(temp, &gotta_call_runtime);
+  __ jmp(&got_literals);
+
+  // r15 is a smi. If it's 0, then we are looking at a cleared WeakCell
+  // around the literals array, and we should visit the runtime. If it's > 0,
+  // then temp already contains the literals array.
+  __ bind(&maybe_cleared_weakcell);
+  __ cmpp(r15, Immediate(0));
+  __ j(equal, &gotta_call_runtime);
 
   // Save the literals in the closure.
+  __ bind(&got_literals);
   __ movp(FieldOperand(closure, JSFunction::kLiteralsOffset), temp);
   __ movp(r15, index);
   __ RecordWriteField(closure, JSFunction::kLiteralsOffset, temp, r15,
                       kDontSaveFPRegs, EMIT_REMEMBERED_SET, OMIT_SMI_CHECK);
 
   // Code available?
   Register entry = rcx;
   __ movp(entry, FieldOperand(map, index, times_pointer_size,
                               SharedFunctionInfo::kOffsetToPreviousCachedCode));
   __ movp(entry, FieldOperand(entry, WeakCell::kValueOffset));
@@ skipping 1962 matching lines @@
   __ ret(0);
 }
 
 
 #undef __
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_X64