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

src/mips/builtins-mips.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_MIPS
 
 #include "src/codegen.h"
 #include "src/debug/debug.h"
 #include "src/deoptimizer.h"
 #include "src/full-codegen/full-codegen.h"
@@ skipping 1276 matching lines @@
   __ Addu(array_pointer, map, Operand(at));
   __ lw(temp, FieldMemOperand(array_pointer,
                               SharedFunctionInfo::kOffsetToPreviousContext));
   __ lw(temp, FieldMemOperand(temp, WeakCell::kValueOffset));
   __ Branch(&loop_bottom, ne, temp, Operand(native_context));
   // OSR id set to none?
   __ lw(temp, FieldMemOperand(array_pointer,
                               SharedFunctionInfo::kOffsetToPreviousOsrAstId));
   const int bailout_id = BailoutId::None().ToInt();
   __ Branch(&loop_bottom, ne, temp, Operand(Smi::FromInt(bailout_id)));
+
   // Literals available?
+  Label got_literals, maybe_cleared_weakcell;
   __ lw(temp, FieldMemOperand(array_pointer,
                               SharedFunctionInfo::kOffsetToPreviousLiterals));
+  // temp contains either a WeakCell pointing to the literals array or the
+  // literals array directly.
+  STATIC_ASSERT(WeakCell::kValueOffset == FixedArray::kLengthOffset);
+  __ lw(t0, FieldMemOperand(temp, WeakCell::kValueOffset));
+  __ JumpIfSmi(t0, &maybe_cleared_weakcell);
+  // t0 is a pointer, therefore temp is a WeakCell pointing to a literals array.
   __ lw(temp, FieldMemOperand(temp, WeakCell::kValueOffset));
-  __ JumpIfSmi(temp, &gotta_call_runtime);
+  __ jmp(&got_literals);
+
+  // t0 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);
+  __ Branch(&gotta_call_runtime, eq, t0, Operand(Smi::FromInt(0)));
 
   // Save the literals in the closure.
+  __ bind(&got_literals);
   __ lw(t0, MemOperand(sp, 0));
   __ sw(temp, FieldMemOperand(t0, JSFunction::kLiteralsOffset));
   __ push(index);
   __ RecordWriteField(t0, JSFunction::kLiteralsOffset, temp, index,
                       kRAHasNotBeenSaved, kDontSaveFPRegs, EMIT_REMEMBERED_SET,
                       OMIT_SMI_CHECK);
   __ pop(index);
 
   // Code available?
   Register entry = t0;
@@ skipping 1567 matching lines @@
   }
 }
 
 
 #undef __
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_MIPS