[arm64] Don't try convert binary operation to shifted form when both operands are the same.

src/arm64/lithium-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 <sstream>
 
 #include "src/arm64/lithium-codegen-arm64.h"
 #include "src/hydrogen-osr.h"
 #include "src/lithium-inl.h"
 
@@ skipping 2114 matching lines @@
                                                                 HValue** left) {
   if (!val->representation().IsInteger32()) return NULL;
   if (!(val->IsBitwise() || val->IsAdd() || val->IsSub())) return NULL;
 
   HBinaryOperation* hinstr = HBinaryOperation::cast(val);
   HValue* hleft = hinstr->left();
   HValue* hright = hinstr->right();
   DCHECK(hleft->representation().Equals(hinstr->representation()));
   DCHECK(hright->representation().Equals(hinstr->representation()));
 
+  if (hleft == hright) return NULL;
+
   if ((hright->IsConstant() &&
        LikelyFitsImmField(hinstr, HConstant::cast(hright)->Integer32Value())) ||
       (hinstr->IsCommutative() && hleft->IsConstant() &&
        LikelyFitsImmField(hinstr, HConstant::cast(hleft)->Integer32Value()))) {
     // The constant operand will likely fit in the immediate field. We are
     // better off with
     //     lsl x8, x9, #imm
     //     add x0, x8, #imm2
     // than with
     //     mov x16, #imm2
@@ skipping 646 matching lines @@
   LOperand* context = UseFixed(instr->context(), cp);
   LOperand* function = UseRegisterAtStart(instr->function());
   LAllocateBlockContext* result =
       new(zone()) LAllocateBlockContext(context, function);
   return MarkAsCall(DefineFixed(result, cp), instr);
 }
 
 
 }  // namespace internal
 }  // namespace v8