[turbofan] Improve JSON output

src/hydrogen.cc

 // Copyright 2013 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/hydrogen.h"
 
 #include <sstream>
 
 #include "src/v8.h"
 
@@ skipping 3493 matching lines @@
     inlined_functions_.Add(InlinedFunctionInfo(shared), zone());
 
     if (!shared->script()->IsUndefined()) {
       Handle<Script> script(Script::cast(shared->script()));
       if (!script->source()->IsUndefined()) {
         CodeTracer::Scope tracing_scopex(isolate()->GetCodeTracer());
         OFStream os(tracing_scopex.file());
         os << "--- FUNCTION SOURCE (" << shared->DebugName()->ToCString().get()
            << ") id{" << info()->optimization_id() << "," << id << "} ---\n";
         {
-          StringCharacterStream stream(String::cast(script->source()),
-                                       shared->start_position());
-          // fun->end_position() points to the last character in the stream. We
-          // need to compensate by adding one to calculate the length.
-          int source_len =
-              shared->end_position() - shared->start_position() + 1;
-          for (int i = 0; i < source_len; i++) {
-            if (stream.HasMore()) {
-              os << AsReversiblyEscapedUC16(stream.GetNext());
-            }
+          DisallowHeapAllocation no_allocation;
+          int start = shared->start_position();
+          int len = shared->end_position() - start + 1;
+          String::SubStringRange source(String::cast(script->source()), start,
+                                        len);
+          for (const auto& c : source) {
+            os << AsReversiblyEscapedUC16(c);
           }
         }
 
         os << "\n--- END ---\n";
       }
     }
   }
 
   int inline_id = inlining_id_to_function_id_.length();
   inlining_id_to_function_id_.Add(id, zone());
@@ skipping 9948 matching lines @@
   if (ShouldProduceTraceOutput()) {
     isolate()->GetHTracer()->TraceHydrogen(name(), graph_);
   }
 
 #ifdef DEBUG
   graph_->Verify(false);  // No full verify.
 #endif
 }
 
 } }  // namespace v8::internal