Move some isolate state setup from C++ code to JumpToExceptionHandler stub

runtime/vm/stub_code_arm64.cc

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"
 #if defined(TARGET_ARCH_ARM64)
 
 #include "vm/assembler.h"
 #include "vm/code_generator.h"
 #include "vm/compiler.h"
@@ skipping 1801 matching lines @@
 }
 
 
 // Jump to the exception or error handler.
 // LR: return address.
 // R0: program_counter.
 // R1: stack_pointer.
 // R2: frame_pointer.
 // R3: error object.
 // R4: address of stacktrace object.
+// R5: isolate.
 // Does not return.
 void StubCode::GenerateJumpToExceptionHandlerStub(Assembler* assembler) {
   ASSERT(kExceptionObjectReg == R0);
   ASSERT(kStackTraceObjectReg == R1);
   __ mov(LR, R0);  // Program counter.
   __ mov(SP, R1);  // Stack pointer.
   __ mov(FP, R2);  // Frame_pointer.
   __ mov(R0, R3);  // Exception object.
   __ mov(R1, R4);  // StackTrace object.
+  // Set the tag.
+  __ LoadImmediate(R2, VMTag::kScriptTagId, kNoPP);
+  __ StoreToOffset(R2, R5, Isolate::vm_tag_offset(), kNoPP);
+  // Clear top exit frame.
+  __ StoreToOffset(ZR, R5, Isolate::top_exit_frame_info_offset(), kNoPP);
   __ ret();  // Jump to the exception handler code.
 }
 
 
 // Calls to the runtime to optimize the given function.
 // R6: function to be re-optimized.
 // R4: argument descriptor (preserved).
 void StubCode::GenerateOptimizeFunctionStub(Assembler* assembler) {
   __ EnterStubFrame();
   __ Push(R4);
@@ skipping 120 matching lines @@
   const Register right = R0;
   __ LoadFromOffset(left, SP, 1 * kWordSize, kNoPP);
   __ LoadFromOffset(right, SP, 0 * kWordSize, kNoPP);
   GenerateIdenticalWithNumberCheckStub(assembler, left, right, temp);
   __ ret();
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM64