[turbofan] inline %StringIteratorPrototype%.next in JSBuiltinReducer.

src/compiler/js-builtin-reducer.cc

Index: src/compiler/js-builtin-reducer.cc
diff --git a/src/compiler/js-builtin-reducer.cc b/src/compiler/js-builtin-reducer.cc
index 762020438878fdbc5566ba07848fd601c870b6ca..991c35ee98a0027f52ff898ce1ca838a65343992 100644
--- a/src/compiler/js-builtin-reducer.cc
+++ b/src/compiler/js-builtin-reducer.cc
@@ -9,11 +9,11 @@
 #include "src/compiler/js-graph.h"
 #include "src/compiler/node-matchers.h"
 #include "src/compiler/node-properties.h"
+#include "src/compiler/operator-properties.h"
 #include "src/compiler/simplified-operator.h"
 #include "src/compiler/type-cache.h"
 #include "src/compiler/types.h"
 #include "src/objects-inl.h"
-
 namespace v8 {
 namespace internal {
 namespace compiler {
@@ -1026,6 +1026,156 @@ Reduction JSBuiltinReducer::ReduceStringCharCodeAt(Node* node) {
   return NoChange();
 }
 
+Reduction JSBuiltinReducer::ReduceStringIteratorPrototypeNext(Node* node) {
+  Node* receiver = NodeProperties::GetValueInput(node, 1);
+  Node* effect = NodeProperties::GetEffectInput(node);
+  Node* control = NodeProperties::GetControlInput(node);
+  Node* context = NodeProperties::GetContextInput(node);
+  if (HasInstanceTypeWitness(receiver, effect, JS_STRING_ITERATOR_TYPE)) {
+    Node* string = effect = graph()->NewNode(
+        simplified()->LoadField(AccessBuilder::ForJSStringIteratorString()),
+        receiver, effect, control);
+    Node* index = effect = graph()->NewNode(
+        simplified()->LoadField(AccessBuilder::ForJSStringIteratorIndex()),
+        receiver, effect, control);
+    Node* length = effect = graph()->NewNode(
+        simplified()->LoadField(AccessBuilder::ForStringLength()), string,
+        effect, control);
+
+    // branch0: if (index < length)
+    Node* check0 =
+        graph()->NewNode(simplified()->NumberLessThan(), index, length);
+    Node* branch0 =
+        graph()->NewNode(common()->Branch(BranchHint::kTrue), check0, control);
+
+    Node* etrue0 = effect;

[Benedikt Meurer, 2016/09/29 13:04:27]

You don't need the etrue0.

+    Node* vtrue0;
+    Node* if_true0 = graph()->NewNode(common()->IfTrue(), branch0);
+    Node* done_true;

[Benedikt Meurer, 2016/09/29 13:04:27]

Can you indent the branches below and add { } for readability? I have a hard
time following the control flow.

+    {
+      done_true = jsgraph()->FalseConstant();
+      Node* uint32_index =

[Benedikt Meurer, 2016/09/29 13:04:27]

You don't need this NumberToUint32. The type of the index field should be
Type::UnsignedSmall() and thus make the verifier and everyone happy. :-)

[caitp, 2016/09/29 17:21:44]

Ah, makes sense. Thanks!

+          graph()->NewNode(simplified()->NumberToUint32(), index);
+      Node* lead = graph()->NewNode(simplified()->StringCharCodeAt(), string,
+                                    uint32_index, if_true0);
+      Node* codepoint;
+      Node* control;
+      Node* check1 = graph()->NewNode(simplified()->NumberLessThan(), lead,
+                                      jsgraph()->Int32Constant(0xD800));
+      Node* branch1 = graph()->NewNode(common()->Branch(BranchHint::kTrue),
+                                       check1, if_true0);
+
+      Node* if_false1 = graph()->NewNode(common()->IfFalse(), branch1);
+      Node* check2 = graph()->NewNode(simplified()->NumberLessThanOrEqual(),
+                                      lead, jsgraph()->Int32Constant(0xDC00));
+      Node* branch2 = graph()->NewNode(common()->Branch(BranchHint::kTrue),
+                                       check2, if_false1);
+
+      Node* if_true2 = graph()->NewNode(common()->IfTrue(), branch2);
+      Node* next_index = graph()->NewNode(simplified()->NumberAdd(), index,
+                                          jsgraph()->OneConstant());
+      Node* check3 =
+          graph()->NewNode(simplified()->NumberLessThan(), next_index, length);
+      Node* branch3 = graph()->NewNode(common()->Branch(BranchHint::kTrue),
+                                       check3, if_true2);
+
+      Node* if_true3 = graph()->NewNode(common()->IfTrue(), branch3);
+      Node* uint32_next_index =
+          graph()->NewNode(simplified()->NumberToUint32(), next_index);

[Benedikt Meurer, 2016/09/29 13:04:27]

Same here, you don't need it if you have the types right.

+      Node* trail = graph()->NewNode(simplified()->StringCharCodeAt(), string,
+                                     uint32_next_index, if_true3);
+      Node* check4 = graph()->NewNode(simplified()->NumberLessThanOrEqual(),
+                                      jsgraph()->Int32Constant(0xDC00), trail);
+      Node* branch4 = graph()->NewNode(common()->Branch(BranchHint::kTrue),
+                                       check4, if_true3);
+
+      Node* if_true4 = graph()->NewNode(common()->IfTrue(), branch4);
+      Node* check5 = graph()->NewNode(simplified()->NumberLessThanOrEqual(),
+                                      trail, jsgraph()->Int32Constant(0xDFFF));
+      Node* branch5 = graph()->NewNode(common()->Branch(BranchHint::kTrue),
+                                       check5, if_true4);
+
+      Node* if_true5 = graph()->NewNode(common()->IfTrue(), branch5);
+      codepoint = graph()->NewNode(
+          simplified()->NumberBitwiseOr(),
+          graph()->NewNode(simplified()->NumberShiftLeft(), trail,
+                           jsgraph()->Int32Constant(16)),
+          lead);
+
+      Node* if_false5 = graph()->NewNode(common()->IfFalse(), branch5);
+      control = graph()->NewNode(common()->Merge(2), if_true5, if_false5);
+      codepoint =
+          graph()->NewNode(common()->Phi(MachineRepresentation::kWord32, 2),
+                           codepoint, lead, control);
+
+      Node* if_false4 = graph()->NewNode(common()->IfFalse(), branch4);
+      control = graph()->NewNode(common()->Merge(2), if_true4, if_false4);
+      codepoint =
+          graph()->NewNode(common()->Phi(MachineRepresentation::kWord32, 2),
+                           codepoint, lead, control);
+      Node* if_false3 = graph()->NewNode(common()->IfFalse(), branch3);
+      control = graph()->NewNode(common()->Merge(2), if_true3, if_false3);
+      codepoint =
+          graph()->NewNode(common()->Phi(MachineRepresentation::kWord32, 2),
+                           codepoint, lead, control);
+      Node* if_false2 = graph()->NewNode(common()->IfFalse(), branch2);
+      control = graph()->NewNode(common()->Merge(2), if_true2, if_false2);
+      codepoint =
+          graph()->NewNode(common()->Phi(MachineRepresentation::kWord32, 2),
+                           codepoint, lead, control);
+      Node* if_true1 = graph()->NewNode(common()->IfTrue(), branch1);
+      control = graph()->NewNode(common()->Merge(2), if_true1, if_false1);
+      codepoint =
+          graph()->NewNode(common()->Phi(MachineRepresentation::kWord32, 2),
+                           codepoint, lead, control);
+
+      vtrue0 = etrue0 = graph()->NewNode(

[Benedikt Meurer, 2016/09/29 13:04:27]

StringFromCodePoint doesn't produce an effect.

+          simplified()->StringFromCodePoint(UnicodeEncoding::UTF16), codepoint);
+    }
+
+    Node* if_false0 = graph()->NewNode(common()->IfFalse(), branch0);
+    Node* vfalse0;
+    Node* done_false;
+    {
+      done_false = jsgraph()->TrueConstant();
+      vfalse0 = jsgraph()->UndefinedConstant();
+    }
+
+    control = graph()->NewNode(common()->Merge(2), if_true0, if_false0);
+    Node* value_phi =
+        graph()->NewNode(common()->Phi(MachineRepresentation::kTagged, 2),
+                         vtrue0, vfalse0, control);
+    Node* done_phi =
+        graph()->NewNode(common()->Phi(MachineRepresentation::kTagged, 2),
+                         done_true, done_false, control);
+
+    Node* native_context = effect =
+        graph()->NewNode(jsgraph()->javascript()->LoadContext(
+                             0, Context::NATIVE_CONTEXT_INDEX, true),
+                         context, context, effect);
+    Node* map = effect =
+        graph()->NewNode(jsgraph()->javascript()->LoadContext(
+                             0, Context::ITERATOR_RESULT_MAP_INDEX, true),
+                         context, native_context, effect);
+
+    Node* value = effect = graph()->NewNode(
+        simplified()->Allocate(NOT_TENURED),
+        jsgraph()->Int32Constant(JSIteratorResult::kSize), effect, control);
+    effect = graph()->NewNode(simplified()->StoreField(AccessBuilder::ForMap()),
+                              value, map, effect, control);

[Benedikt Meurer, 2016/09/29 13:04:27]

You need to initialize properties and elements here as well (to the empty fixed
array).

+    effect = graph()->NewNode(
+        simplified()->StoreField(AccessBuilder::ForJSIteratorResultDone()),
+        value, done_phi, effect, control);
+    effect = graph()->NewNode(
+        simplified()->StoreField(AccessBuilder::ForJSIteratorResultValue()),
+        value, value_phi, effect, control);
+
+    ReplaceWithValue(node, value, effect, control);
+    return Replace(value);
+  }
+  return NoChange();
+}
+
 Reduction JSBuiltinReducer::ReduceArrayBufferViewAccessor(
     Node* node, InstanceType instance_type, FieldAccess const& access) {
   Node* receiver = NodeProperties::GetValueInput(node, 1);
@@ -1195,6 +1345,8 @@ Reduction JSBuiltinReducer::Reduce(Node* node) {
       return ReduceStringCharAt(node);
     case kStringCharCodeAt:
       return ReduceStringCharCodeAt(node);
+    case kStringIteratorPrototypeNext:
+      return ReduceStringIteratorPrototypeNext(node);
     case kDataViewByteLength:
       return ReduceArrayBufferViewAccessor(
           node, JS_DATA_VIEW_TYPE,