Revert "Remove unnecessary check in RegExpExecStub."

src/arm64/code-stubs-arm64.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/v8.h"
 
 #if V8_TARGET_ARCH_ARM64
 
 #include "src/bootstrapper.h"
 #include "src/code-stubs.h"
@@ skipping 2837 matching lines @@
 
   // Return last match info.
   __ Peek(x0, kLastMatchInfoOffset);
   __ PopCPURegList(used_callee_saved_registers);
   // Drop the 4 arguments of the stub from the stack.
   __ Drop(4);
   __ Ret();
 
   __ Bind(&exception);
   Register exception_value = x0;
-  // Result must now be exception.
+  // A stack overflow (on the backtrack stack) may have occured
+  // in the RegExp code but no exception has been created yet.
+  // If there is no pending exception, handle that in the runtime system.
   __ Mov(x10, Operand(isolate()->factory()->the_hole_value()));
   __ Mov(x11,
          Operand(ExternalReference(Isolate::kPendingExceptionAddress,
                                    isolate())));
   __ Ldr(exception_value, MemOperand(x11));
+  __ Cmp(x10, exception_value);
+  __ B(eq, &runtime);
+
   __ Str(x10, MemOperand(x11));  // Clear pending exception.
 
   // Check if the exception is a termination. If so, throw as uncatchable.
   Label termination_exception;
   __ JumpIfRoot(exception_value,
                 Heap::kTerminationExceptionRootIndex,
                 &termination_exception);
 
   __ Throw(exception_value, x10, x11, x12, x13);
 
@@ skipping 2549 matching lines @@
                               MemOperand(fp, 6 * kPointerSize),
                               NULL);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM64