[for-in] Further refactorings and unification around for-in.

src/compiler/typer.cc

Index: src/compiler/typer.cc
diff --git a/src/compiler/typer.cc b/src/compiler/typer.cc
index 1024f0a25dbafb0e7a3a5d5f8a3dfae2cf934a08..0f1183c7b9a8f4282a97b9760df82f6e06cc2631 100644
--- a/src/compiler/typer.cc
+++ b/src/compiler/typer.cc
@@ -650,12 +650,12 @@ Type* Typer::Visitor::TypeCall(Node* node) { return Type::Any(); }
 
 
 Type* Typer::Visitor::TypeProjection(Node* node) {
-  // TODO(bmeurer): Make this beautiful! Use tuple type here.
-  if (node->InputAt(0)->opcode() == IrOpcode::kJSForInPrepare &&
-      ProjectionIndexOf(node->op()) == 2) {
-    return typer_->cache_.kSmi;
+  Type* const type = Operand(node, 0);
+  if (type->Is(Type::None())) return Type::None();
+  int const index = static_cast<int>(ProjectionIndexOf(node->op()));
+  if (type->IsTuple() && index < type->AsTuple()->Arity()) {
+    return type->AsTuple()->Element(index);
   }
-  // TODO(titzer): use the output type of the input to determine the bounds.
   return Type::Any();
 }
 
@@ -1618,8 +1618,13 @@ Type* Typer::Visitor::TypeJSForInNext(Node* node) {
 
 
 Type* Typer::Visitor::TypeJSForInPrepare(Node* node) {
-  // TODO(bmeurer): Return a tuple type here.
-  return Type::Any();
+  STATIC_ASSERT(Map::EnumLengthBits::kMax <= FixedArray::kMaxLength);
+  Factory* const f = isolate()->factory();
+  Type* const cache_type = Type::Union(
+      typer_->cache_.kSmi, Type::Class(f->meta_map(), zone()), zone());
+  Type* const cache_array = Type::Class(f->fixed_array_map(), zone());
+  Type* const cache_length = typer_->cache_.kFixedArrayLengthType;
+  return Type::Tuple(cache_type, cache_array, cache_length, zone());
 }