Support array literals with FAST_DOUBLE_ELEMENTS ElementsKind.

src/arm/full-codegen-arm.cc

Index: src/arm/full-codegen-arm.cc
diff --git a/src/arm/full-codegen-arm.cc b/src/arm/full-codegen-arm.cc
index b6cb7ad55fbc5df21827d4e5be6c061f5ee2a000..f579a40663f9e5b20e233992bd906022b795a1a9 100644
--- a/src/arm/full-codegen-arm.cc
+++ b/src/arm/full-codegen-arm.cc
@@ -1467,13 +1467,19 @@ void FullCodeGenerator::VisitArrayLiteral(ArrayLiteral* expr) {
 
   ZoneList<Expression*>* subexprs = expr->values();
   int length = subexprs->length();
+  Handle<FixedArray> constant_elements = expr->constant_elements();
+  ASSERT_EQ(2, constant_elements->length());
+  ElementsKind constant_elements_kind =
+      static_cast<ElementsKind>(Smi::cast(constant_elements->get(0))->value());
+  Handle<FixedArrayBase> constant_elements_values(
+      FixedArrayBase::cast(constant_elements->get(1)));
 
   __ ldr(r3, MemOperand(fp, JavaScriptFrameConstants::kFunctionOffset));
   __ ldr(r3, FieldMemOperand(r3, JSFunction::kLiteralsOffset));
   __ mov(r2, Operand(Smi::FromInt(expr->literal_index())));
-  __ mov(r1, Operand(expr->constant_elements()));
+  __ mov(r1, Operand(constant_elements));
   __ Push(r3, r2, r1);
-  if (expr->constant_elements()->map() ==
+  if (constant_elements_values->map() ==
       isolate()->heap()->fixed_cow_array_map()) {
     FastCloneShallowArrayStub stub(
         FastCloneShallowArrayStub::COPY_ON_WRITE_ELEMENTS, length);
@@ -1485,8 +1491,14 @@ void FullCodeGenerator::VisitArrayLiteral(ArrayLiteral* expr) {
   } else if (length > FastCloneShallowArrayStub::kMaximumClonedLength) {
     __ CallRuntime(Runtime::kCreateArrayLiteralShallow, 3);
   } else {
-    FastCloneShallowArrayStub stub(
-        FastCloneShallowArrayStub::CLONE_ELEMENTS, length);
+    ASSERT(constant_elements_kind == FAST_ELEMENTS ||
+           constant_elements_kind == FAST_SMI_ONLY_ELEMENTS ||
+           FLAG_smi_only_arrays);
+    FastCloneShallowArrayStub::Mode mode =
+        constant_elements_kind == FAST_DOUBLE_ELEMENTS
+        ? FastCloneShallowArrayStub::CLONE_DOUBLE_ELEMENTS
+        : FastCloneShallowArrayStub::CLONE_ELEMENTS;
+    FastCloneShallowArrayStub stub(mode, length);
     __ CallStub(&stub);
   }
 
@@ -1509,24 +1521,65 @@ void FullCodeGenerator::VisitArrayLiteral(ArrayLiteral* expr) {
     }
     VisitForAccumulatorValue(subexpr);
 
-    // Store the subexpression value in the array's elements.
     __ ldr(r6, MemOperand(sp));  // Copy of array literal.
     __ ldr(r1, FieldMemOperand(r6, JSObject::kElementsOffset));
+    __ ldr(r2, FieldMemOperand(r6, JSObject::kMapOffset));
     int offset = FixedArray::kHeaderSize + (i * kPointerSize);
-    __ str(result_register(), FieldMemOperand(r1, offset));
 
-    Label no_map_change;
-    __ JumpIfSmi(result_register(), &no_map_change);
-    // Update the write barrier for the array store with r0 as the scratch
-    // register.
+    Label element_done;
+    Label double_elements;
+    Label smi_element;
+    Label slow_elements;
+    Label fast_elements;
+    __ CheckFastElements(r2, r3, &double_elements);

[Kevin Millikin (Chromium), 2011/10/19 08:10:45]

This code checks the element kind for every stored computed value.  A small
improvement to this code is to check up front, save the kind (tagged in the
stack?) as a state, and update it when a transition is taken.

[danno, 2011/10/19 11:36:40]

Agreed. I will factor this stuff out into a shared stub that also tracks the
ElementsKind without reloading in another CL.
On 2011/10/19 08:10:45, Kevin Millikin wrote:

+
+    // FAST_SMI_ONLY_ELEMENTS or FAST_ELEMENTS
+    __ JumpIfSmi(result_register(), &smi_element);
+    __ CheckFastSmiOnlyElements(r2, r3, &fast_elements);

[Kevin Millikin (Chromium), 2011/10/19 08:10:45]

It's a bit confusing (to me) that the label is for *not* fast smi only elements.
 That's because it seems more natural, given the function name, to interpret it
as something like "branch on fast smi only elements".

[danno, 2011/10/19 11:36:40]

I modelled this after CheckMap, which also has a similar semantic. All of these
should probably be renamed to VerifyHasXXXX. Another CL, if you don't mind?
On 2011/10/19 08:10:45, Kevin Millikin wrote:

+
+    // Store into the array literal requires a elements transition. Call into
+    // the runtime.
+    __ bind(&slow_elements);
+    __ push(r6);  // Copy of array literal.
+    __ mov(r1, Operand(Smi::FromInt(i)));
+    __ mov(r2, Operand(Smi::FromInt(NONE)));  // PropertyAttributes
+    __ mov(r3, Operand(Smi::FromInt(strict_mode_flag())));  // Strict mode.
+    __ Push(r1, result_register(), r2, r3);
+
+    // Do tail-call to runtime routine.
+    __ CallRuntime(Runtime::kSetProperty, 5);

[Kevin Millikin (Chromium), 2011/10/19 08:10:45]

Save this for a future CL, but I think that it would be better to have a custom
function for exactly setting an element as part of initializing an array
literal.

The general SetProperty has a lot of stuff that we know we don't need (checking
attributes, strict vs. non-strict differences, proxies, etc.).

[danno, 2011/10/19 11:36:40]

Agreed. Next CL.
On 2011/10/19 08:10:45, Kevin Millikin wrote:

+    __ b(&element_done);
+
+      // Array literal has ElementsKind of FAST_DOUBLE_ELEMENTS
+    __ bind(&double_elements);
+    __ mov(r3, Operand(Smi::FromInt(i)));
+    __ StoreNumberToDoubleElements(result_register(),

[Kevin Millikin (Chromium), 2011/10/19 08:10:45]

My biggest concern is that this is a lot of generated code (for the double store
particularly, but also the write barrier and all the rest) per-computed value.

It might be better to pass the value, array, index, and current element kind to
a stub (and get back a new element kind or update it in place), where the stub
is a little interpreter for array stores implemented in assembly.

What do you think?

[danno, 2011/10/19 11:36:40]

I'll refactor this stuff into a separate stub in a follow-on CL.
On 2011/10/19 08:10:45, Kevin Millikin wrote:

+                                   r3,
+                                   r6,
+                                   r1,
+                                   r4,
+                                   r5,
+                                   r9,
+                                   r7,
+                                   &slow_elements);
+    __ b(&element_done);
+
+    // Array literal has ElementsKind of FAST_ELEMENTS and value is an object.
+    __ bind(&fast_elements);
+    __ str(result_register(), FieldMemOperand(r1, offset));
+    // Update the write barrier for the array store.
     __ RecordWriteField(
         r1, offset, result_register(), r2, kLRHasBeenSaved, kDontSaveFPRegs,
         EMIT_REMEMBERED_SET, OMIT_SMI_CHECK);
-    __ ldr(r3, FieldMemOperand(r1, HeapObject::kMapOffset));
-    __ CheckFastSmiOnlyElements(r3, r2, &no_map_change);
-    __ push(r6);  // Copy of array literal.
-    __ CallRuntime(Runtime::kNonSmiElementStored, 1);
-    __ bind(&no_map_change);
+    __ b(&element_done);
+
+    // Array literal has ElementsKind of FAST_SMI_ONLY_ELEMENTS or
+    // FAST_ELEMENTS, and value is Smi.
+    __ bind(&smi_element);
+    __ str(result_register(), FieldMemOperand(r1, offset));
+    // Fall through
+
+    __ bind(&element_done);
 
     PrepareForBailoutForId(expr->GetIdForElement(i), NO_REGISTERS);
   }