X87: Avoid creating weak cells for literal arrays that are empty of literals.

  port 3cfcc7e1 (r36786)

  original commit message:
  It may be that we have a feedback vector, but no literals. In this case
  we can store into the OptimizedCodeMap directly instead of using a WeakCell,
  because all data in the feedback vector is already held weakly.

  The use of a WeakCell in the OptimizedCodeMap is only required when
  there are literals which may hold maps strongly.

  This is to address a performance regression caused by the creation of
  a large number of WeakCells.

BUG=

Review-Url: https://codereview.chromium.org/2081663004
Cr-Commit-Position: refs/heads/master@{#37123}

src/x87/builtins-x87.cc

@@ -898,13 +898,30 @@ void Builtins::Generate_CompileLazy(MacroAssembler* masm) {
   const int bailout_id = BailoutId::None().ToInt();
   __ cmp(temp, Immediate(Smi::FromInt(bailout_id)));
   __ j(not_equal, &loop_bottom);
+
   // Literals available?
+  Label got_literals, maybe_cleared_weakcell;
   __ mov(temp, FieldOperand(map, index, times_half_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);
+  __ JumpIfSmi(FieldOperand(temp, WeakCell::kValueOffset),
+               &maybe_cleared_weakcell);
+  // The WeakCell value is a pointer, therefore it's a valid literals array.
   __ mov(temp, FieldOperand(temp, WeakCell::kValueOffset));
-  __ JumpIfSmi(temp, &gotta_call_runtime);
+  __ jmp(&got_literals);
+
+  // We have 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);
+  __ cmp(FieldOperand(temp, WeakCell::kValueOffset), Immediate(0));
+  __ j(equal, &gotta_call_runtime);
 
   // Save the literals in the closure.
+  __ bind(&got_literals);
   __ mov(ecx, Operand(esp, 0));
   __ mov(FieldOperand(ecx, JSFunction::kLiteralsOffset), temp);
   __ push(index);