[turbofan] Teach escape analysis about StringCharAt

src/compiler/escape-analysis.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/escape-analysis.h"
 
 #include <limits>
 
 #include "src/base/flags.h"
 #include "src/bootstrapper.h"
@@ skipping 800 matching lines @@
       // TODO(mstarzinger): The following list of operators will eventually be
       // handled by the EscapeAnalysisReducer (similar to ObjectIsSmi).
       case IrOpcode::kConvertTaggedHoleToUndefined:
       case IrOpcode::kStringEqual:
       case IrOpcode::kStringLessThan:
       case IrOpcode::kStringLessThanOrEqual:
       case IrOpcode::kTypeGuard:
       case IrOpcode::kPlainPrimitiveToNumber:
       case IrOpcode::kPlainPrimitiveToWord32:
       case IrOpcode::kPlainPrimitiveToFloat64:
+      case IrOpcode::kStringCharAt:
       case IrOpcode::kStringCharCodeAt:
       case IrOpcode::kObjectIsCallable:
       case IrOpcode::kObjectIsNumber:
       case IrOpcode::kObjectIsReceiver:
       case IrOpcode::kObjectIsString:
       case IrOpcode::kObjectIsUndetectable:
         if (SetEscaped(rep)) {
           TRACE("Setting #%d (%s) to escaped because of use by #%d (%s)\n",
                 rep->id(), rep->op()->mnemonic(), use->id(),
                 use->op()->mnemonic());
@@ skipping 881 matching lines @@
     }
   }
   return false;
 }
 
 Graph* EscapeAnalysis::graph() const { return status_analysis_->graph(); }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8