[turbofan] Add support for String.prototype.charCodeAt/charAt.

src/compiler/simplified-lowering.cc

 // Copyright 2014 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.
 
 #include "src/compiler/simplified-lowering.h"
 
 #include <limits>
 
 #include "src/address-map.h"
 #include "src/base/bits.h"
@@ skipping 804 matching lines @@
     // Compute the representation.
     Type* type = TypeOf(node);
     if (type->Is(Type::None())) {
       return MachineRepresentation::kNone;
     } else if (type->Is(Type::Signed32()) || type->Is(Type::Unsigned32())) {
       return MachineRepresentation::kWord32;
     } else if (use.IsUsedAsWord32()) {
       return MachineRepresentation::kWord32;
     } else if (type->Is(Type::Boolean())) {
       return MachineRepresentation::kBit;
+    } else if (use.IsUsedAsFloat64()) {
+      return MachineRepresentation::kFloat64;
+    } else if (type->Is(
+                   Type::Union(Type::SignedSmall(), Type::NaN(), zone()))) {
+      // TODO(turbofan): For Phis that return either NaN or some Smi, it's
+      // beneficial to not go all the way to double, unless the uses are
+      // double uses. For tagging that just means some potentially expensive
+      // allocation code; we might want to do the same for -0 as well?
+      return MachineRepresentation::kTagged;
     } else if (type->Is(Type::Number())) {
       return MachineRepresentation::kFloat64;
-    } else if (use.IsUsedAsFloat64()) {
-      return MachineRepresentation::kFloat64;
     } else if (type->Is(Type::Internal())) {
       // We mark (u)int64 as Type::Internal.
       // TODO(jarin) This is a workaround for our lack of (u)int64
       // types. This can be removed once we can represent (u)int64
       // unambiguously. (At the moment internal objects, such as the hole,
       // are also Type::Internal()).
       bool is_word64 = GetInfo(node->InputAt(0))->representation() ==
                        MachineRepresentation::kWord64;
 #ifdef DEBUG
       // Check that all the inputs agree on being Word64.
@@ skipping 1090 matching lines @@
               jsgraph_->isolate(), jsgraph_->zone(), callable.descriptor(), 0,
               flags, properties);
           node->InsertInput(jsgraph_->zone(), 0,
                             jsgraph_->HeapConstant(callable.code()));
           node->AppendInput(jsgraph_->zone(), jsgraph_->NoContextConstant());
           node->AppendInput(jsgraph_->zone(), jsgraph_->graph()->start());
           NodeProperties::ChangeOp(node, jsgraph_->common()->Call(desc));
         }
         return;
       }
+      case IrOpcode::kStringCharCodeAt: {
+        VisitBinop(node, UseInfo::AnyTagged(), UseInfo::TruncatingWord32(),
+                   MachineRepresentation::kWord32);
+        return;
+      }
       case IrOpcode::kStringFromCharCode: {
         VisitUnop(node, UseInfo::TruncatingWord32(),
                   MachineRepresentation::kTagged);
         return;
       }
 
       case IrOpcode::kCheckBounds: {
         if (TypeOf(node->InputAt(0))->Is(Type::Unsigned32())) {
           VisitBinop(node, UseInfo::TruncatingWord32(),
                      MachineRepresentation::kWord32);
@@ skipping 1552 matching lines @@
         isolate(), graph()->zone(), callable.descriptor(), 0, flags,
         Operator::kNoProperties);
     to_number_operator_.set(common()->Call(desc));
   }
   return to_number_operator_.get();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8