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

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=chromium:615831

Review-Url: https://codereview.chromium.org/2031123003
Cr-Commit-Position: refs/heads/master@{#36786}

src/arm/builtins-arm.cc

@@ -1297,13 +1297,29 @@ void Builtins::Generate_CompileLazy(MacroAssembler* masm) {
   const int bailout_id = BailoutId::None().ToInt();
   __ cmp(temp, Operand(Smi::FromInt(bailout_id)));
   __ b(ne, &loop_bottom);
+
   // Literals available?
+  Label got_literals, maybe_cleared_weakcell;
   __ ldr(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);
+  __ ldr(r4, FieldMemOperand(temp, WeakCell::kValueOffset));
+  __ JumpIfSmi(r4, &maybe_cleared_weakcell);
+  // r4 is a pointer, therefore temp is a WeakCell pointing to a literals array.
   __ ldr(temp, FieldMemOperand(temp, WeakCell::kValueOffset));
-  __ JumpIfSmi(temp, &gotta_call_runtime);
+  __ jmp(&got_literals);
+
+  // r4 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);
+  __ cmp(r4, Operand(Smi::FromInt(0)));
+  __ b(eq, &gotta_call_runtime);
 
   // Save the literals in the closure.
+  __ bind(&got_literals);
   __ ldr(r4, MemOperand(sp, 0));
   __ str(temp, FieldMemOperand(r4, JSFunction::kLiteralsOffset));
   __ push(index);

src/arm64/builtins-arm64.cc

@@ -1308,13 +1308,31 @@ void Builtins::Generate_CompileLazy(MacroAssembler* masm) {
   const int bailout_id = BailoutId::None().ToInt();
   __ Cmp(temp, Operand(Smi::FromInt(bailout_id)));
   __ B(ne, &loop_bottom);
+
   // Literals available?
+  Label got_literals, maybe_cleared_weakcell;
+  Register temp2 = x7;
   __ Ldr(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);
+  __ Ldr(temp2, FieldMemOperand(temp, WeakCell::kValueOffset));
+  __ JumpIfSmi(temp2, &maybe_cleared_weakcell);
+  // temp2 is a pointer, therefore temp is a WeakCell pointing to a literals
+  // array.
   __ Ldr(temp, FieldMemOperand(temp, WeakCell::kValueOffset));
-  __ JumpIfSmi(temp, &gotta_call_runtime);
+  __ jmp(&got_literals);
+
+  // r4 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);
+  __ Cmp(temp2, Operand(Smi::FromInt(0)));
+  __ B(eq, &gotta_call_runtime);
 
   // Save the literals in the closure.
+  __ bind(&got_literals);
   __ Str(temp, FieldMemOperand(closure, JSFunction::kLiteralsOffset));
   __ RecordWriteField(closure, JSFunction::kLiteralsOffset, temp, x7,
                       kLRHasNotBeenSaved, kDontSaveFPRegs, EMIT_REMEMBERED_SET,

src/ia32/builtins-ia32.cc

@@ -896,13 +896,30 @@ 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);

src/mips/builtins-mips.cc

@@ -1294,13 +1294,28 @@ void Builtins::Generate_CompileLazy(MacroAssembler* masm) {
                               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);

src/mips64/builtins-mips64.cc

@@ -1280,13 +1280,27 @@ void Builtins::Generate_CompileLazy(MacroAssembler* masm) {
                               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;
   __ ld(temp, FieldMemOperand(array_pointer,
                               SharedFunctionInfo::kOffsetToPreviousLiterals));
+  // temp contains either a WeakCell pointing to the literals array or the
+  // literals array directly.
+  __ ld(a4, FieldMemOperand(temp, WeakCell::kValueOffset));
+  __ JumpIfSmi(a4, &maybe_cleared_weakcell);
+  // a4 is a pointer, therefore temp is a WeakCell pointing to a literals array.
   __ ld(temp, FieldMemOperand(temp, WeakCell::kValueOffset));
-  __ JumpIfSmi(temp, &gotta_call_runtime);
+  __ jmp(&got_literals);
+
+  // a4 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, a4, Operand(Smi::FromInt(0)));
 
   // Save the literals in the closure.
+  __ bind(&got_literals);
   __ ld(a4, MemOperand(sp, 0));
   __ sd(temp, FieldMemOperand(a4, JSFunction::kLiteralsOffset));
   __ push(index);

src/objects.cc

@@ -11610,9 +11610,13 @@ void SharedFunctionInfo::AddToOptimizedCodeMap(
             isolate->factory()->NewWeakCell(code.ToHandleChecked());
         old_code_map->set(entry + kCachedCodeOffset, *code_cell);
       }
-      Handle<WeakCell> literals_cell =
+      if (literals->literals_count() == 0) {
-          isolate->factory()->NewWeakCell(literals);
+        old_code_map->set(entry + kLiteralsOffset, *literals);
-      old_code_map->set(entry + kLiteralsOffset, *literals_cell);
+      } else {
+        Handle<WeakCell> literals_cell =
+            isolate->factory()->NewWeakCell(literals);
+        old_code_map->set(entry + kLiteralsOffset, *literals_cell);
+      }
       return;
     }
 
@@ -11643,12 +11647,18 @@ void SharedFunctionInfo::AddToOptimizedCodeMap(
   Handle<WeakCell> code_cell =
       code.is_null() ? isolate->factory()->empty_weak_cell()
                      : isolate->factory()->NewWeakCell(code.ToHandleChecked());
-  Handle<WeakCell> literals_cell = isolate->factory()->NewWeakCell(literals);
   WeakCell* context_cell = native_context->self_weak_cell();
 
   new_code_map->set(entry + kContextOffset, context_cell);
   new_code_map->set(entry + kCachedCodeOffset, *code_cell);
-  new_code_map->set(entry + kLiteralsOffset, *literals_cell);
+
+  if (literals->literals_count() == 0) {
+    new_code_map->set(entry + kLiteralsOffset, *literals);
+  } else {
+    Handle<WeakCell> literals_cell = isolate->factory()->NewWeakCell(literals);
+    new_code_map->set(entry + kLiteralsOffset, *literals_cell);
+  }
+
   new_code_map->set(entry + kOsrAstIdOffset, Smi::FromInt(osr_ast_id.ToInt()));
 
 #ifdef DEBUG
@@ -11659,8 +11669,16 @@ void SharedFunctionInfo::AddToOptimizedCodeMap(
     DCHECK(cell->cleared() ||
            (cell->value()->IsCode() &&
             Code::cast(cell->value())->kind() == Code::OPTIMIZED_FUNCTION));
-    cell = WeakCell::cast(new_code_map->get(i + kLiteralsOffset));
+    Object* lits = new_code_map->get(i + kLiteralsOffset);
-    DCHECK(cell->cleared() || cell->value()->IsFixedArray());
+    if (lits->IsWeakCell()) {
+      cell = WeakCell::cast(lits);
+      DCHECK(cell->cleared() ||
+             (cell->value()->IsLiteralsArray() &&
+              LiteralsArray::cast(cell->value())->literals_count() > 0));
+    } else {
+      DCHECK(lits->IsLiteralsArray() &&
+             LiteralsArray::cast(lits)->literals_count() == 0);
+    }
     DCHECK(new_code_map->get(i + kOsrAstIdOffset)->IsSmi());
   }
 #endif
@@ -13278,13 +13296,18 @@ CodeAndLiterals SharedFunctionInfo::SearchOptimizedCodeMap(
     } else {
       DCHECK_LE(entry + kEntryLength, code_map->length());
       WeakCell* cell = WeakCell::cast(code_map->get(entry + kCachedCodeOffset));
-      WeakCell* literals_cell =
+      Object* lits = code_map->get(entry + kLiteralsOffset);
-          WeakCell::cast(code_map->get(entry + kLiteralsOffset));
+      LiteralsArray* literals = nullptr;
-
+      if (lits->IsWeakCell()) {
+        WeakCell* literal_cell = WeakCell::cast(lits);
+        if (!literal_cell->cleared()) {
+          literals = LiteralsArray::cast(literal_cell->value());
+        }
+      } else {
+        literals = LiteralsArray::cast(lits);
+      }
       result = {cell->cleared() ? nullptr : Code::cast(cell->value()),
-                literals_cell->cleared()
+                literals};
-                    ? nullptr
-                    : LiteralsArray::cast(literals_cell->value())};
     }
   }
   return result;

src/type-feedback-vector.cc

@@ -284,11 +284,19 @@ void TypeFeedbackVector::ClearAllKeyedStoreICs(Isolate* isolate) {
       int length = optimized_code_map->length();
       for (int i = SharedFunctionInfo::kEntriesStart; i < length;
            i += SharedFunctionInfo::kEntryLength) {
-        WeakCell* cell = WeakCell::cast(
+        Object* lits =
-            optimized_code_map->get(i + SharedFunctionInfo::kLiteralsOffset));
+            optimized_code_map->get(i + SharedFunctionInfo::kLiteralsOffset);
-        if (cell->value()->IsLiteralsArray()) {
+        TypeFeedbackVector* vector = nullptr;
-          TypeFeedbackVector* vector =
+        if (lits->IsWeakCell()) {
-              LiteralsArray::cast(cell->value())->feedback_vector();
+          WeakCell* cell = WeakCell::cast(lits);
+          if (cell->value()->IsLiteralsArray()) {
+            vector = LiteralsArray::cast(cell->value())->feedback_vector();
+          }
+        } else {
+          DCHECK(lits->IsLiteralsArray());
+          vector = LiteralsArray::cast(lits)->feedback_vector();
+        }
+        if (vector != nullptr) {
           vector->ClearKeyedStoreICs(shared);
         }
       }

src/x64/builtins-x64.cc

@@ -962,13 +962,30 @@ void Builtins::Generate_CompileLazy(MacroAssembler* masm) {
   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,