[turbofan] Introduce a dedicated StringCharAt operator.

src/compiler/effect-control-linearizer.cc

 // Copyright 2015 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/effect-control-linearizer.h"
 
 #include "src/code-factory.h"
 #include "src/compiler/access-builder.h"
 #include "src/compiler/compiler-source-position-table.h"
 #include "src/compiler/js-graph.h"
@@ skipping 727 matching lines @@
       break;
     case IrOpcode::kArrayBufferWasNeutered:
       state = LowerArrayBufferWasNeutered(node, *effect, *control);
       break;
     case IrOpcode::kStringFromCharCode:
       state = LowerStringFromCharCode(node, *effect, *control);
       break;
     case IrOpcode::kStringFromCodePoint:
       state = LowerStringFromCodePoint(node, *effect, *control);
       break;
+    case IrOpcode::kStringCharAt:
+      state = LowerStringCharAt(node, *effect, *control);
+      break;
     case IrOpcode::kStringCharCodeAt:
       state = LowerStringCharCodeAt(node, *effect, *control);
       break;
     case IrOpcode::kStringEqual:
       state = LowerStringEqual(node, *effect, *control);
       break;
     case IrOpcode::kStringLessThan:
       state = LowerStringLessThan(node, *effect, *control);
       break;
     case IrOpcode::kStringLessThanOrEqual:
@@ skipping 1461 matching lines @@
                        graph()->NewNode(machine()->Word32And(), value_bit_field,
                                         jsgraph()->Int32Constant(
                                             JSArrayBuffer::WasNeutered::kMask)),
                        jsgraph()->Int32Constant(0)),
       jsgraph()->Int32Constant(0));
 
   return ValueEffectControl(value, effect, control);
 }
 
 EffectControlLinearizer::ValueEffectControl
+EffectControlLinearizer::LowerStringCharAt(Node* node, Node* effect,
+                                           Node* control) {
+  Callable const callable = CodeFactory::StringCharAt(isolate());
+  Operator::Properties properties = Operator::kNoThrow | Operator::kNoWrite;
+  CallDescriptor::Flags flags = CallDescriptor::kNoFlags;
+  CallDescriptor* desc = Linkage::GetStubCallDescriptor(
+      isolate(), graph()->zone(), callable.descriptor(), 0, flags, properties);
+  node->InsertInput(graph()->zone(), 0,
+                    jsgraph()->HeapConstant(callable.code()));
+  node->InsertInput(graph()->zone(), 3, jsgraph()->NoContextConstant());
+  node->InsertInput(graph()->zone(), 4, effect);
+  NodeProperties::ChangeOp(node, common()->Call(desc));
+  return ValueEffectControl(node, node, control);
+}
+
+EffectControlLinearizer::ValueEffectControl
 EffectControlLinearizer::LowerStringCharCodeAt(Node* node, Node* effect,
                                                Node* control) {
   Node* subject = node->InputAt(0);
   Node* index = node->InputAt(1);
 
   // We may need to loop several times for ConsString/SlicedString {subject}s.
   Node* loop =
       graph()->NewNode(common()->Loop(4), control, control, control, control);
   Node* lsubject =
       graph()->NewNode(common()->Phi(MachineRepresentation::kTagged, 4),
@@ skipping 1577 matching lines @@
         isolate(), graph()->zone(), callable.descriptor(), 0, flags,
         Operator::kEliminatable);
     to_number_operator_.set(common()->Call(desc));
   }
   return to_number_operator_.get();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8